Merge branch 'atlas_fixes'

docs/CHANGELOG.txt

@@ -72,6 +72,11 @@ Other Changes:
   Missing calls to End(), past the assert, should not lead to crashes or to the fallback Debug window appearing on screen.
   Those changes makes it easier to integrate dear imgui with a scripting language allowing, given asserts are redirected
   into e.g. an error log and stopping the script execution.
+- ImFontAtlas: Stb and FreeType: Atlas width is now properly based on total surface rather than glyph count (unless overridden with TexDesiredWidth).
+- ImFontAtlas: Stb and FreeType: Fixed atlas builder so missing glyphs won't influence the atlas texture width. (#2233)
+- ImFontAtlas: Stb and FreeType: Fixed atlas builder so duplicate glyphs (when merging fonts) won't be included in the rasterized atlas.
+- ImFontAtlas: FreeType: Fixed abnormally high atlas height.
+- ImFontAtlas: FreeType: Fixed support for any values of TexGlyphPadding (not just only 1).
 - ImDrawList: Optimized some of the functions for performance of debug builds where non-inline function call cost are non-negligible.
   (Our test UI scene on VS2015 Debug Win64 with /RTC1 went ~5.9 ms -> ~4.9 ms. In Release same scene stays at ~0.3 ms.)
 - IO: Added BackendPlatformUserData, BackendRendererUserData, BackendLanguageUserData void* for storage use by back-ends.

docs/TODO.txt

@@ -235,9 +235,7 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - pie menus patterns (#434)
  - markup: simple markup language for color change? (#902)
 
-!- font: need handling of missing glyphs by not packing/rasterizing glyph 0 of a given font.
- - font: MergeMode: flags to select overwriting or not.
- - font: MergeMode: duplicate glyphs are stored in the atlas texture which is suboptimal.
+ - font: MergeMode: flags to select overwriting or not (this is now very easy with refactored ImFontAtlasBuildWithStbTruetype)
  - font: free the Alpha buffer if user only requested RGBA.
 !- font: better CalcTextSizeA() API, at least for simple use cases. current one is horrible (perhaps have simple vs extended versions).
  - font: a CalcTextHeight() helper could run faster than CalcTextSize().y
@@ -252,7 +250,6 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
  - font/draw: vertical and/or rotated text renderer (#705) - vertical is easier clipping wise
  - font/draw: need to be able to specify wrap start position.
  - font/draw: better reserve policy for large horizontal block of text (shouldn't reserve for all clipped lines)
- - font: imgui_freetype.h alternative renderer (#618)
  - font: optimization: for monospace font (like the default one) we can trim IndexXAdvance as long as trailing value is == FallbackXAdvance (need to make sure TAB is still correct).
  - font: add support for kerning, probably optional. A) perhaps default to (32..128)^2 matrix ~ 9K entries = 36KB, then hash for non-ascii?. B) or sparse lookup into per-char list?
  - font: add a simpler CalcTextSizeA() api? current one ok but not welcome if user needs to call it directly (without going through ImGui::CalcTextSize)

imgui.h

@@ -1182,6 +1182,7 @@ struct ImVector
 
     inline bool         empty() const                       { return Size == 0; }
     inline int          size() const                        { return Size; }
+    inline int          size_in_bytes() const               { return Size * (int)sizeof(T); }
     inline int          capacity() const                    { return Capacity; }
     inline T&           operator[](int i)                   { IM_ASSERT(i < Size); return Data[i]; }
     inline const T&     operator[](int i) const             { IM_ASSERT(i < Size); return Data[i]; }
@@ -2046,7 +2047,7 @@ struct ImFontAtlas
     ImFontAtlasFlags            Flags;              // Build flags (see ImFontAtlasFlags_)
     ImTextureID                 TexID;              // User data to refer to the texture once it has been uploaded to user's graphic systems. It is passed back to you during rendering via the ImDrawCmd structure.
     int                         TexDesiredWidth;    // Texture width desired by user before Build(). Must be a power-of-two. If have many glyphs your graphics API have texture size restrictions you may want to increase texture width to decrease height.
-    int                         TexGlyphPadding;    // Padding between glyphs within texture in pixels. Defaults to 1.
+    int                         TexGlyphPadding;    // Padding between glyphs within texture in pixels. Defaults to 1. If your rendering method doesn't rely on bilinear filtering you may set this to 0.
 
     // [Internal]
     // NB: Access texture data via GetTexData*() calls! Which will setup a default font for you.

imgui_draw.cpp

@@ -1541,11 +1541,11 @@ ImFont* ImFontAtlas::AddFont(const ImFontConfig* font_cfg)
     if (!font_cfg->MergeMode)
         Fonts.push_back(IM_NEW(ImFont));
     else
-        IM_ASSERT(!Fonts.empty()); // When using MergeMode make sure that a font has already been added before. You can use ImGui::GetIO().Fonts->AddFontDefault() to add the default imgui font.
+        IM_ASSERT(!Fonts.empty() && "Cannot use MergeMode for the first font"); // When using MergeMode make sure that a font has already been added before. You can use ImGui::GetIO().Fonts->AddFontDefault() to add the default imgui font.
 
     ConfigData.push_back(*font_cfg);
     ImFontConfig& new_font_cfg = ConfigData.back();
-    if (!new_font_cfg.DstFont)
+    if (new_font_cfg.DstFont == NULL)
         new_font_cfg.DstFont = Fonts.back();
     if (!new_font_cfg.FontDataOwnedByAtlas)
     {
@@ -1733,139 +1733,220 @@ void    ImFontAtlasBuildMultiplyRectAlpha8(const unsigned char table[256], unsig
             data[i] = table[data[i]];
 }
 
+// Temporary data for one source font (multiple source fonts can be merged into one destination ImFont)
+// (C++03 doesn't allow instancing ImVector<> with function-local types so we declare the type here.)
+struct ImFontBuildSrcData
+{
+    stbtt_fontinfo      FontInfo;
+    stbtt_pack_range    PackRange;          // Hold the list of codepoints to pack (essentially points to Codepoints.Data)
+    stbrp_rect*         Rects;              // Rectangle to pack. We first fill in their size and the packer will give us their position.
+    stbtt_packedchar*   PackedChars;        // Output glyphs
+    const ImWchar*      SrcRanges;          // Ranges as requested by user (user is allowed to request too much, e.g. 0x0020..0xFFFF)
+    int                 DstIndex;           // Index into atlas->Fonts[] and dst_tmp_array[]
+    int                 GlyphsHighest;      // Highest requested codepoint
+    int                 GlyphsCount;        // Glyph count (excluding missing glyphs and glyphs already set by an earlier source font)
+    ImBoolVector        GlyphsSet;          // Glyph bit map (random access, 1-bit per codepoint. This will be a maximum of 8KB)
+    ImVector<int>       GlyphsList;         // Glyph codepoints list (flattened version of GlyphsMap)
+};
+
+// Temporary data for one destination ImFont* (multiple source fonts can be merged into one destination ImFont)
+struct ImFontBuildDstData
+{
+    int                 SrcCount;           // Number of source fonts targeting this destination font.
+    int                 GlyphsHighest;
+    int                 GlyphsCount;
+    ImBoolVector        GlyphsSet;          // This is used to resolve collision when multiple sources are merged into a same destination font.
+};
+
+static void UnpackBoolVectorToFlatIndexList(const ImBoolVector* in, ImVector<int>* out)
+{
+    IM_ASSERT(sizeof(in->Storage.Data[0]) == sizeof(int));
+    const int* it_begin = in->Storage.begin();
+    const int* it_end = in->Storage.end();
+    for (const int* it = it_begin; it < it_end; it++)
+        if (int entries_32 = *it)
+            for (int bit_n = 0; bit_n < 32; bit_n++)
+                if (entries_32 & (1 << bit_n))
+                    out->push_back((int)((it - it_begin) << 5) + bit_n);
+}
+
 bool    ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
 {
     IM_ASSERT(atlas->ConfigData.Size > 0);
 
     ImFontAtlasBuildRegisterDefaultCustomRects(atlas);
 
+    // Clear atlas
     atlas->TexID = (ImTextureID)NULL;
     atlas->TexWidth = atlas->TexHeight = 0;
     atlas->TexUvScale = ImVec2(0.0f, 0.0f);
     atlas->TexUvWhitePixel = ImVec2(0.0f, 0.0f);
     atlas->ClearTexData();
 
-    // Count glyphs/ranges
-    int total_glyphs_count = 0;
-    int total_ranges_count = 0;
-    for (int input_i = 0; input_i < atlas->ConfigData.Size; input_i++)
-    {
-        ImFontConfig& cfg = atlas->ConfigData[input_i];
-        if (!cfg.GlyphRanges)
-            cfg.GlyphRanges = atlas->GetGlyphRangesDefault();
-        for (const ImWchar* in_range = cfg.GlyphRanges; in_range[0] && in_range[1]; in_range += 2, total_ranges_count++)
-            total_glyphs_count += (in_range[1] - in_range[0]) + 1;
-    }
-
-    // We need a width for the skyline algorithm. Using a dumb heuristic here to decide of width. User can override TexDesiredWidth and TexGlyphPadding if they wish.
-    // Width doesn't really matter much, but some API/GPU have texture size limitations and increasing width can decrease height.
-    atlas->TexWidth = (atlas->TexDesiredWidth > 0) ? atlas->TexDesiredWidth : (total_glyphs_count > 4000) ? 4096 : (total_glyphs_count > 2000) ? 2048 : (total_glyphs_count > 1000) ? 1024 : 512;
-    atlas->TexHeight = 0;
-
-    // Start packing
-    const int max_tex_height = 1024*32;
-    stbtt_pack_context spc = {};
-    if (!stbtt_PackBegin(&spc, NULL, atlas->TexWidth, max_tex_height, 0, atlas->TexGlyphPadding, NULL))
-        return false;
-    stbtt_PackSetOversampling(&spc, 1, 1);
-
-    // Pack our extra data rectangles first, so it will be on the upper-left corner of our texture (UV will have small values).
-    ImFontAtlasBuildPackCustomRects(atlas, spc.pack_info);
+    // Temporary storage for building
+    ImVector<ImFontBuildSrcData> src_tmp_array;
+    ImVector<ImFontBuildDstData> dst_tmp_array;
+    src_tmp_array.resize(atlas->ConfigData.Size);
+    dst_tmp_array.resize(atlas->Fonts.Size);
+    memset(src_tmp_array.Data, 0, (size_t)src_tmp_array.size_in_bytes());
+    memset(dst_tmp_array.Data, 0, (size_t)dst_tmp_array.size_in_bytes());
 
-    // Initialize font information (so we can error without any cleanup)
-    struct ImFontTempBuildData
+    // 1. Initialize font loading structure, check font data validity
+    for (int src_i = 0; src_i < atlas->ConfigData.Size; src_i++)
     {
-        stbtt_fontinfo      FontInfo;
-        stbrp_rect*         Rects;
-        int                 RectsCount;
-        stbtt_pack_range*   Ranges;
-        int                 RangesCount;
-    };
-    ImFontTempBuildData* tmp_array = (ImFontTempBuildData*)ImGui::MemAlloc((size_t)atlas->ConfigData.Size * sizeof(ImFontTempBuildData));
-    for (int input_i = 0; input_i < atlas->ConfigData.Size; input_i++)
-    {
-        ImFontConfig& cfg = atlas->ConfigData[input_i];
-        ImFontTempBuildData& tmp = tmp_array[input_i];
+        ImFontBuildSrcData& src_tmp = src_tmp_array[src_i];
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
         IM_ASSERT(cfg.DstFont && (!cfg.DstFont->IsLoaded() || cfg.DstFont->ContainerAtlas == atlas));
 
+        // Find index from cfg.DstFont (we allow the user to set cfg.DstFont. Also it makes casual debugging nicer than when storing indices)
+        src_tmp.DstIndex = -1;
+        for (int output_i = 0; output_i < atlas->Fonts.Size && src_tmp.DstIndex == -1; output_i++)
+            if (cfg.DstFont == atlas->Fonts[output_i])
+                src_tmp.DstIndex = output_i;
+        IM_ASSERT(src_tmp.DstIndex != -1); // cfg.DstFont not pointing within atlas->Fonts[] array?
+        if (src_tmp.DstIndex == -1)
+            return false;
+
+        // Initialize helper structure for font loading and verify that the TTF/OTF data is correct
         const int font_offset = stbtt_GetFontOffsetForIndex((unsigned char*)cfg.FontData, cfg.FontNo);
         IM_ASSERT(font_offset >= 0 && "FontData is incorrect, or FontNo cannot be found.");
-        if (!stbtt_InitFont(&tmp.FontInfo, (unsigned char*)cfg.FontData, font_offset))
-        {
-            atlas->TexWidth = atlas->TexHeight = 0; // Reset output on failure
-            ImGui::MemFree(tmp_array);
+        if (!stbtt_InitFont(&src_tmp.FontInfo, (unsigned char*)cfg.FontData, font_offset))
             return false;
-        }
+
+        // Measure highest codepoints
+        ImFontBuildDstData& dst_tmp = dst_tmp_array[src_tmp.DstIndex];
+        src_tmp.SrcRanges = cfg.GlyphRanges ? cfg.GlyphRanges : atlas->GetGlyphRangesDefault();
+        for (const ImWchar* src_range = src_tmp.SrcRanges; src_range[0] && src_range[1]; src_range += 2)
+            src_tmp.GlyphsHighest = ImMax(src_tmp.GlyphsHighest, (int)src_range[1]);
+        dst_tmp.SrcCount++;
+        dst_tmp.GlyphsHighest = ImMax(dst_tmp.GlyphsHighest, src_tmp.GlyphsHighest);
     }
 
+    // 2. For every requested codepoint, check for their presence in the font data, and handle redundancy or overlaps between source fonts to avoid unused glyphs.
+    int total_glyphs_count = 0;
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcData& src_tmp = src_tmp_array[src_i];
+        ImFontBuildDstData& dst_tmp = dst_tmp_array[src_tmp.DstIndex];
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
+        src_tmp.GlyphsSet.Resize(src_tmp.GlyphsHighest + 1);
+        if (dst_tmp.SrcCount > 1 && dst_tmp.GlyphsSet.Storage.empty())
+            dst_tmp.GlyphsSet.Resize(dst_tmp.GlyphsHighest + 1);
+
+        for (const ImWchar* src_range = src_tmp.SrcRanges; src_range[0] && src_range[1]; src_range += 2)
+            for (int codepoint = src_range[0]; codepoint <= src_range[1]; codepoint++)
+            {
+                if (cfg.MergeMode && dst_tmp.GlyphsSet.GetBit(codepoint))   // Don't overwrite existing glyphs. We could make this an option (e.g. MergeOverwrite)
+                    continue;
+                if (!stbtt_FindGlyphIndex(&src_tmp.FontInfo, codepoint))    // It is actually in the font?
+                    continue;
+                
+                // Add to avail set/counters
+                src_tmp.GlyphsCount++;
+                dst_tmp.GlyphsCount++;
+                src_tmp.GlyphsSet.SetBit(codepoint, true);
+                if (dst_tmp.SrcCount > 1)
+                    dst_tmp.GlyphsSet.SetBit(codepoint, true);
+                total_glyphs_count++;
+            }
+    }
+
+    // 3. Unpack our bit map into a flat list (we now have all the Unicode points that we know are requested _and_ available _and_ not overlapping another)
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcData& src_tmp = src_tmp_array[src_i];
+        src_tmp.GlyphsList.reserve(src_tmp.GlyphsCount);
+        UnpackBoolVectorToFlatIndexList(&src_tmp.GlyphsSet, &src_tmp.GlyphsList);
+        src_tmp.GlyphsSet.Clear();
+        IM_ASSERT(src_tmp.GlyphsList.Size == src_tmp.GlyphsCount);
+    }
+    for (int dst_i = 0; dst_i < dst_tmp_array.Size; dst_i++)
+        dst_tmp_array[dst_i].GlyphsSet.Clear();
+    dst_tmp_array.clear();
+
     // Allocate packing character data and flag packed characters buffer as non-packed (x0=y0=x1=y1=0)
-    int buf_packedchars_n = 0, buf_rects_n = 0, buf_ranges_n = 0;
-    stbtt_packedchar* buf_packedchars = (stbtt_packedchar*)ImGui::MemAlloc(total_glyphs_count * sizeof(stbtt_packedchar));
-    stbrp_rect* buf_rects = (stbrp_rect*)ImGui::MemAlloc(total_glyphs_count * sizeof(stbrp_rect));
-    stbtt_pack_range* buf_ranges = (stbtt_pack_range*)ImGui::MemAlloc(total_ranges_count * sizeof(stbtt_pack_range));
-    memset(buf_packedchars, 0, total_glyphs_count * sizeof(stbtt_packedchar));
-    memset(buf_rects, 0, total_glyphs_count * sizeof(stbrp_rect));              // Unnecessary but let's clear this for the sake of sanity.
-    memset(buf_ranges, 0, total_ranges_count * sizeof(stbtt_pack_range));
-
-    // First font pass: pack all glyphs (no rendering at this point, we are working with rectangles in an infinitely tall texture at this point)
-    for (int input_i = 0; input_i < atlas->ConfigData.Size; input_i++)
-    {
-        ImFontConfig& cfg = atlas->ConfigData[input_i];
-        ImFontTempBuildData& tmp = tmp_array[input_i];
-
-        // Setup ranges
-        int font_glyphs_count = 0;
-        int font_ranges_count = 0;
-        for (const ImWchar* in_range = cfg.GlyphRanges; in_range[0] && in_range[1]; in_range += 2, font_ranges_count++)
-            font_glyphs_count += (in_range[1] - in_range[0]) + 1;
-        tmp.Ranges = buf_ranges + buf_ranges_n;
-        tmp.RangesCount = font_ranges_count;
-        buf_ranges_n += font_ranges_count;
-        for (int i = 0; i < font_ranges_count; i++)
-        {
-            const ImWchar* in_range = &cfg.GlyphRanges[i * 2];
-            stbtt_pack_range& range = tmp.Ranges[i];
-            range.font_size = cfg.SizePixels;
-            range.first_unicode_codepoint_in_range = in_range[0];
-            range.num_chars = (in_range[1] - in_range[0]) + 1;
-            range.chardata_for_range = buf_packedchars + buf_packedchars_n;
-            buf_packedchars_n += range.num_chars;
-        }
+    // (We technically don't need to zero-clear buf_rects, but let's do it for the sake of sanity)
+    ImVector<stbrp_rect> buf_rects;
+    ImVector<stbtt_packedchar> buf_packedchars;
+    buf_rects.resize(total_glyphs_count);
+    buf_packedchars.resize(total_glyphs_count);
+    memset(buf_rects.Data, 0, (size_t)buf_rects.size_in_bytes());
+    memset(buf_packedchars.Data, 0, (size_t)buf_packedchars.size_in_bytes());
+
+    // 4. Gather glyphs sizes so we can pack them in our virtual canvas.
+    int total_surface = 0;
+    int buf_rects_out_n = 0;
+    int buf_packedchars_out_n = 0;
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcData& src_tmp = src_tmp_array[src_i];
+        if (src_tmp.GlyphsCount == 0)
+            continue;
 
-        // Gather the sizes of all rectangle we need
-        tmp.Rects = buf_rects + buf_rects_n;
-        tmp.RectsCount = font_glyphs_count;
-        buf_rects_n += font_glyphs_count;
-        stbtt_PackSetOversampling(&spc, cfg.OversampleH, cfg.OversampleV);
-        int n = stbtt_PackFontRangesGatherRects(&spc, &tmp.FontInfo, tmp.Ranges, tmp.RangesCount, tmp.Rects);
-        IM_ASSERT(n == font_glyphs_count);
-
-        // Detect missing glyphs and replace them with a zero-sized box instead of relying on the default glyphs
-        // This allows us merging overlapping icon fonts more easily.
-        int rect_i = 0;
-        for (int range_i = 0; range_i < tmp.RangesCount; range_i++)
-            for (int char_i = 0; char_i < tmp.Ranges[range_i].num_chars; char_i++, rect_i++)
-                if (stbtt_FindGlyphIndex(&tmp.FontInfo, tmp.Ranges[range_i].first_unicode_codepoint_in_range + char_i) == 0)
-                    tmp.Rects[rect_i].w = tmp.Rects[rect_i].h = 0;
-
-        // Pack
-        stbrp_pack_rects((stbrp_context*)spc.pack_info, tmp.Rects, n);
-
-        // Extend texture height
-        // Also mark missing glyphs as non-packed so we don't attempt to render into them
-        for (int i = 0; i < n; i++)
+        src_tmp.Rects = &buf_rects[buf_rects_out_n];
+        src_tmp.PackedChars = &buf_packedchars[buf_packedchars_out_n];
+        buf_rects_out_n += src_tmp.GlyphsCount;
+        buf_packedchars_out_n += src_tmp.GlyphsCount;
+
+        // Convert our ranges in the format stb_truetype wants
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
+        src_tmp.PackRange.font_size = cfg.SizePixels;
+        src_tmp.PackRange.first_unicode_codepoint_in_range = 0;
+        src_tmp.PackRange.array_of_unicode_codepoints = src_tmp.GlyphsList.Data;
+        src_tmp.PackRange.num_chars = src_tmp.GlyphsList.Size;
+        src_tmp.PackRange.chardata_for_range = src_tmp.PackedChars;
+        src_tmp.PackRange.h_oversample = (unsigned char)cfg.OversampleH;
+        src_tmp.PackRange.v_oversample = (unsigned char)cfg.OversampleV;
+
+        // Gather the sizes of all rectangles we will need to pack (this loop is based on stbtt_PackFontRangesGatherRects)
+        const float scale = (cfg.SizePixels > 0) ? stbtt_ScaleForPixelHeight(&src_tmp.FontInfo, cfg.SizePixels) : stbtt_ScaleForMappingEmToPixels(&src_tmp.FontInfo, -cfg.SizePixels);
+        const int padding = atlas->TexGlyphPadding;
+        for (int glyph_i = 0; glyph_i < src_tmp.GlyphsList.Size; glyph_i++)
         {
-            if (tmp.Rects[i].w == 0 && tmp.Rects[i].h == 0)
-                tmp.Rects[i].was_packed = 0;
-            if (tmp.Rects[i].was_packed)
-                atlas->TexHeight = ImMax(atlas->TexHeight, tmp.Rects[i].y + tmp.Rects[i].h);
+            int x0, y0, x1, y1;
+            const int glyph_index_in_font = stbtt_FindGlyphIndex(&src_tmp.FontInfo, src_tmp.GlyphsList[glyph_i]);
+            IM_ASSERT(glyph_index_in_font != 0);
+            stbtt_GetGlyphBitmapBoxSubpixel(&src_tmp.FontInfo, glyph_index_in_font, scale * cfg.OversampleH, scale * cfg.OversampleV, 0, 0, &x0, &y0, &x1, &y1);
+            src_tmp.Rects[glyph_i].w = (stbrp_coord)(x1 - x0 + padding + cfg.OversampleH - 1);
+            src_tmp.Rects[glyph_i].h = (stbrp_coord)(y1 - y0 + padding + cfg.OversampleV - 1);
+            total_surface += src_tmp.Rects[glyph_i].w * src_tmp.Rects[glyph_i].h;
         }
     }
-    IM_ASSERT(buf_rects_n == total_glyphs_count);
-    IM_ASSERT(buf_packedchars_n == total_glyphs_count);
-    IM_ASSERT(buf_ranges_n == total_ranges_count);
 
-    // Create texture
+    // We need a width for the skyline algorithm, any width!
+    // The exact width doesn't really matter much, but some API/GPU have texture size limitations and increasing width can decrease height.
+    // User can override TexDesiredWidth and TexGlyphPadding if they wish, otherwise we use a simple heuristic to select the width based on expected surface.
+    const int surface_sqrt = (int)ImSqrt((float)total_surface) + 1;
+    atlas->TexHeight = 0;
+    if (atlas->TexDesiredWidth > 0)
+        atlas->TexWidth = atlas->TexDesiredWidth;
+    else
+        atlas->TexWidth = (surface_sqrt >= 4096*0.7f) ? 4096 : (surface_sqrt >= 2048*0.7f) ? 2048 : (surface_sqrt >= 1024*0.7f) ? 1024 : 512;
+
+    // 5. Start packing
+    // Pack our extra data rectangles first, so it will be on the upper-left corner of our texture (UV will have small values).
+    const int TEX_HEIGHT_MAX = 1024 * 32;
+    stbtt_pack_context spc = {};
+    stbtt_PackBegin(&spc, NULL, atlas->TexWidth, TEX_HEIGHT_MAX, 0, atlas->TexGlyphPadding, NULL);
+    ImFontAtlasBuildPackCustomRects(atlas, spc.pack_info);
+
+    // 6. Pack each source font. No rendering yet, we are working with rectangles in an infinitely tall texture at this point.
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcData& src_tmp = src_tmp_array[src_i];
+        if (src_tmp.GlyphsCount == 0)
+            continue;
+
+        stbrp_pack_rects((stbrp_context*)spc.pack_info, src_tmp.Rects, src_tmp.GlyphsCount);
+
+        // Extend texture height and mark missing glyphs as non-packed so we won't render them.
+        // FIXME: We are not handling packing failure here (would happen if we got off TEX_HEIGHT_MAX or if a single if larger than TexWidth?)
+        for (int glyph_i = 0; glyph_i < src_tmp.GlyphsCount; glyph_i++)
+            if (src_tmp.Rects[glyph_i].was_packed)
+                atlas->TexHeight = ImMax(atlas->TexHeight, src_tmp.Rects[glyph_i].y + src_tmp.Rects[glyph_i].h);
+    }
+
+    // 7. Allocate texture
     atlas->TexHeight = (atlas->Flags & ImFontAtlasFlags_NoPowerOfTwoHeight) ? (atlas->TexHeight + 1) : ImUpperPowerOfTwo(atlas->TexHeight);
     atlas->TexUvScale = ImVec2(1.0f / atlas->TexWidth, 1.0f / atlas->TexHeight);
     atlas->TexPixelsAlpha8 = (unsigned char*)ImGui::MemAlloc(atlas->TexWidth * atlas->TexHeight);
@@ -1873,41 +1954,46 @@ bool    ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
     spc.pixels = atlas->TexPixelsAlpha8;
     spc.height = atlas->TexHeight;
 
-    // Second pass: render font characters
-    for (int input_i = 0; input_i < atlas->ConfigData.Size; input_i++)
+    // 8. Render/rasterize font characters into the texture
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
     {
-        ImFontConfig& cfg = atlas->ConfigData[input_i];
-        ImFontTempBuildData& tmp = tmp_array[input_i];
-        stbtt_PackSetOversampling(&spc, cfg.OversampleH, cfg.OversampleV);
-        stbtt_PackFontRangesRenderIntoRects(&spc, &tmp.FontInfo, tmp.Ranges, tmp.RangesCount, tmp.Rects);
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
+        ImFontBuildSrcData& src_tmp = src_tmp_array[src_i];
+        if (src_tmp.GlyphsCount == 0)
+            continue;
+
+        stbtt_PackFontRangesRenderIntoRects(&spc, &src_tmp.FontInfo, &src_tmp.PackRange, 1, src_tmp.Rects);
+
+        // Apply multiply operator
         if (cfg.RasterizerMultiply != 1.0f)
         {
             unsigned char multiply_table[256];
             ImFontAtlasBuildMultiplyCalcLookupTable(multiply_table, cfg.RasterizerMultiply);
-            for (const stbrp_rect* r = tmp.Rects; r != tmp.Rects + tmp.RectsCount; r++)
+            stbrp_rect* r = &src_tmp.Rects[0];
+            for (int glyph_i = 0; glyph_i < src_tmp.GlyphsCount; glyph_i++, r++)
                 if (r->was_packed)
-                    ImFontAtlasBuildMultiplyRectAlpha8(multiply_table, spc.pixels, r->x, r->y, r->w, r->h, spc.stride_in_bytes);
+                    ImFontAtlasBuildMultiplyRectAlpha8(multiply_table, atlas->TexPixelsAlpha8, r->x, r->y, r->w, r->h, atlas->TexWidth * 1);
         }
-        tmp.Rects = NULL;
+        src_tmp.Rects = NULL;
     }
 
     // End packing
     stbtt_PackEnd(&spc);
-    ImGui::MemFree(buf_rects);
-    buf_rects = NULL;
+    buf_rects.clear();
 
-    // Third pass: setup ImFont and glyphs for runtime
-    for (int input_i = 0; input_i < atlas->ConfigData.Size; input_i++)
+    // 9. Setup ImFont and glyphs for runtime
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
     {
-        ImFontConfig& cfg = atlas->ConfigData[input_i];
-        ImFontTempBuildData& tmp = tmp_array[input_i];
+        ImFontBuildSrcData& src_tmp = src_tmp_array[src_i];
+        if (src_tmp.GlyphsCount == 0)
+            continue;
+
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
         ImFont* dst_font = cfg.DstFont; // We can have multiple input fonts writing into a same destination font (when using MergeMode=true)
-        if (cfg.MergeMode)
-            dst_font->BuildLookupTable();
 
-        const float font_scale = stbtt_ScaleForPixelHeight(&tmp.FontInfo, cfg.SizePixels);
+        const float font_scale = stbtt_ScaleForPixelHeight(&src_tmp.FontInfo, cfg.SizePixels);
         int unscaled_ascent, unscaled_descent, unscaled_line_gap;
-        stbtt_GetFontVMetrics(&tmp.FontInfo, &unscaled_ascent, &unscaled_descent, &unscaled_line_gap);
+        stbtt_GetFontVMetrics(&src_tmp.FontInfo, &unscaled_ascent, &unscaled_descent, &unscaled_line_gap);
 
         const float ascent = ImFloor(unscaled_ascent * font_scale + ((unscaled_ascent > 0.0f) ? +1 : -1));
         const float descent = ImFloor(unscaled_descent * font_scale + ((unscaled_descent > 0.0f) ? +1 : -1));
@@ -1915,40 +2001,30 @@ bool    ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
         const float font_off_x = cfg.GlyphOffset.x;
         const float font_off_y = cfg.GlyphOffset.y + (float)(int)(dst_font->Ascent + 0.5f);
 
-        for (int i = 0; i < tmp.RangesCount; i++)
+        for (int glyph_i = 0; glyph_i < src_tmp.GlyphsCount; glyph_i++)
         {
-            stbtt_pack_range& range = tmp.Ranges[i];
-            for (int char_idx = 0; char_idx < range.num_chars; char_idx += 1)
-            {
-                const stbtt_packedchar& pc = range.chardata_for_range[char_idx];
-                if (!pc.x0 && !pc.x1 && !pc.y0 && !pc.y1)
-                    continue;
-
-                const int codepoint = range.first_unicode_codepoint_in_range + char_idx;
-                if (cfg.MergeMode && dst_font->FindGlyphNoFallback((ImWchar)codepoint))
-                    continue;
-
-                float char_advance_x_org = pc.xadvance;
-                float char_advance_x_mod = ImClamp(char_advance_x_org, cfg.GlyphMinAdvanceX, cfg.GlyphMaxAdvanceX);
-                float char_off_x = font_off_x;
-                if (char_advance_x_org != char_advance_x_mod)
-                    char_off_x += cfg.PixelSnapH ? (float)(int)((char_advance_x_mod - char_advance_x_org) * 0.5f) : (char_advance_x_mod - char_advance_x_org) * 0.5f;
-
-                stbtt_aligned_quad q;
-                float dummy_x = 0.0f, dummy_y = 0.0f;
-                stbtt_GetPackedQuad(range.chardata_for_range, atlas->TexWidth, atlas->TexHeight, char_idx, &dummy_x, &dummy_y, &q, 0);
-                dst_font->AddGlyph((ImWchar)codepoint, q.x0 + char_off_x, q.y0 + font_off_y, q.x1 + char_off_x, q.y1 + font_off_y, q.s0, q.t0, q.s1, q.t1, char_advance_x_mod);
-            }
+            const int codepoint = src_tmp.GlyphsList[glyph_i];
+            const stbtt_packedchar& pc = src_tmp.PackedChars[glyph_i];
+
+            const float char_advance_x_org = pc.xadvance;
+            const float char_advance_x_mod = ImClamp(char_advance_x_org, cfg.GlyphMinAdvanceX, cfg.GlyphMaxAdvanceX);
+            float char_off_x = font_off_x;
+            if (char_advance_x_org != char_advance_x_mod)
+                char_off_x += cfg.PixelSnapH ? (float)(int)((char_advance_x_mod - char_advance_x_org) * 0.5f) : (char_advance_x_mod - char_advance_x_org) * 0.5f;
+            
+            // Register glyph
+            stbtt_aligned_quad q;
+            float dummy_x = 0.0f, dummy_y = 0.0f;
+            stbtt_GetPackedQuad(src_tmp.PackedChars, atlas->TexWidth, atlas->TexHeight, glyph_i, &dummy_x, &dummy_y, &q, 0);
+            dst_font->AddGlyph((ImWchar)codepoint, q.x0 + char_off_x, q.y0 + font_off_y, q.x1 + char_off_x, q.y1 + font_off_y, q.s0, q.t0, q.s1, q.t1, char_advance_x_mod);
         }
     }
 
-    // Cleanup temporaries
-    ImGui::MemFree(buf_packedchars);
-    ImGui::MemFree(buf_ranges);
-    ImGui::MemFree(tmp_array);
+    // Cleanup temporary (ImVector doesn't honor destructor)
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+        src_tmp_array[src_i].~ImFontBuildSrcData();
 
     ImFontAtlasBuildFinish(atlas);
-
     return true;
 }
 
@@ -1976,16 +2052,16 @@ void ImFontAtlasBuildSetupFont(ImFontAtlas* atlas, ImFont* font, ImFontConfig* f
     font->ConfigDataCount++;
 }
 
-void ImFontAtlasBuildPackCustomRects(ImFontAtlas* atlas, void* pack_context_opaque)
+void ImFontAtlasBuildPackCustomRects(ImFontAtlas* atlas, void* stbrp_context_opaque)
 {
-    stbrp_context* pack_context = (stbrp_context*)pack_context_opaque;
+    stbrp_context* pack_context = (stbrp_context*)stbrp_context_opaque;
 
     ImVector<ImFontAtlas::CustomRect>& user_rects = atlas->CustomRects;
     IM_ASSERT(user_rects.Size >= 1); // We expect at least the default custom rects to be registered, else something went wrong.
 
     ImVector<stbrp_rect> pack_rects;
     pack_rects.resize(user_rects.Size);
-    memset(pack_rects.Data, 0, sizeof(stbrp_rect) * user_rects.Size);
+    memset(pack_rects.Data, 0, (size_t)pack_rects.size_in_bytes());
     for (int i = 0; i < user_rects.Size; i++)
     {
         pack_rects[i].w = user_rects[i].Width;

imgui_internal.h

@@ -236,6 +236,18 @@ static inline ImVec2 ImRotate(const ImVec2& v, float cos_a, float sin_a)
 static inline float  ImLinearSweep(float current, float target, float speed)    { if (current < target) return ImMin(current + speed, target); if (current > target) return ImMax(current - speed, target); return current; }
 static inline ImVec2 ImMul(const ImVec2& lhs, const ImVec2& rhs)                { return ImVec2(lhs.x * rhs.x, lhs.y * rhs.y); }
 
+// Helper: ImBoolVector. Store 1-bit per value.
+// Note that Resize() currently clears the whole vector.
+struct ImBoolVector
+{
+    ImVector<int>   Storage;
+    ImBoolVector()  { }
+    void            Resize(int sz)          { Storage.resize((sz + 31) >> 5); memset(Storage.Data, 0, (size_t)Storage.Size * sizeof(Storage.Data[0])); }
+    void            Clear()                 { Storage.clear(); }
+    bool            GetBit(int n) const     { int off = (n >> 5); int mask = 1 << (n & 31); return (Storage[off] & mask) != 0; }
+    void            SetBit(int n, bool v)   { int off = (n >> 5); int mask = 1 << (n & 31); if (v) Storage[off] |= mask; else Storage[off] &= ~mask; }
+};
+
 // Helper: ImPool<>. Basic keyed storage for contiguous instances, slow/amortized insertion, O(1) indexable, O(Log N) queries by ID over a dense/hot buffer,
 // Honor constructor/destructor. Add/remove invalidate all pointers. Indexes have the same lifetime as the associated object.
 typedef int ImPoolIdx;
@@ -1440,7 +1452,7 @@ namespace ImGui
 IMGUI_API bool              ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas);
 IMGUI_API void              ImFontAtlasBuildRegisterDefaultCustomRects(ImFontAtlas* atlas);
 IMGUI_API void              ImFontAtlasBuildSetupFont(ImFontAtlas* atlas, ImFont* font, ImFontConfig* font_config, float ascent, float descent);
-IMGUI_API void              ImFontAtlasBuildPackCustomRects(ImFontAtlas* atlas, void* spc);
+IMGUI_API void              ImFontAtlasBuildPackCustomRects(ImFontAtlas* atlas, void* stbrp_context_opaque);
 IMGUI_API void              ImFontAtlasBuildFinish(ImFontAtlas* atlas);
 IMGUI_API void              ImFontAtlasBuildMultiplyCalcLookupTable(unsigned char out_table[256], float in_multiply_factor);
 IMGUI_API void              ImFontAtlasBuildMultiplyRectAlpha8(const unsigned char table[256], unsigned char* pixels, int x, int y, int w, int h, int stride);

misc/freetype/README.md

@@ -1,14 +1,14 @@
 # imgui_freetype
 
-This is an attempt to replace stb_truetype (the default imgui's font rasterizer) with FreeType. 
-Currently not optimal and probably has some limitations or bugs.
-By [Vuhdo](https://github.com/Vuhdo) (Aleksei Skriabin). Improvements by @mikesart. Maintained by @ocornut.
+Build font atlases using FreeType instead of stb_truetype (the default imgui's font rasterizer).
+<br>by @vuhdo, @mikesart, @ocornut.
 
-**Usage**
-1. Get latest FreeType binaries or build yourself.
+### Usage
+
+1. Get latest FreeType binaries or build yourself (under Windows you may use vcpkg with `vcpkg install freetype`).
 2. Add imgui_freetype.h/cpp alongside your imgui sources.
 3. Include imgui_freetype.h after imgui.h.
-4. Call ImGuiFreeType::BuildFontAtlas() *BEFORE* calling ImFontAtlas::GetTexDataAsRGBA32() or ImFontAtlas::Build() (so normal Build() won't be called):
+4. Call `ImGuiFreeType::BuildFontAtlas()` *BEFORE* calling `ImFontAtlas::GetTexDataAsRGBA32()` or `ImFontAtlas::Build()` (so normal Build() won't be called):
 
 ```cpp
 // See ImGuiFreeType::RasterizationFlags
@@ -17,13 +17,14 @@ ImGuiFreeType::BuildFontAtlas(io.Fonts, flags);
 io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);
 ```
 
-**Gamma Correct Blending**
+### Gamma Correct Blending
+
 FreeType assumes blending in linear space rather than gamma space.
 See FreeType note for [FT_Render_Glyph](https://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html#FT_Render_Glyph).
 For correct results you need to be using sRGB and convert to linear space in the pixel shader output.
 The default imgui styles will be impacted by this change (alpha values will need tweaking).
 
-**Test code Usage**
+### Test code Usage
 ```cpp
 #include "misc/freetype/imgui_freetype.h"
 #include "misc/freetype/imgui_freetype.cpp"
@@ -42,16 +43,15 @@ while (true)
    if (freetype_test.UpdateRebuild())
    {
       // REUPLOAD FONT TEXTURE TO GPU
-      // e.g ImGui_ImplGlfwGL3_InvalidateDeviceObjects() + ImGui_ImplGlfwGL3_CreateDeviceObjects()
+      // e.g ImGui_ImplOpenGL3_DestroyDeviceObjects() + ImGui_ImplOpenGL3_CreateDeviceObjects()
    }
    ImGui::NewFrame();
    freetype_test.ShowFreetypeOptionsWindow();
    ...
-   }
 }
 ```
 
-**Test code**
+### Test code
 ```cpp
 #include "misc/freetype/imgui_freetype.h"
 #include "misc/freetype/imgui_freetype.cpp"
@@ -61,7 +61,7 @@ struct FreeTypeTest
     enum FontBuildMode
     {
         FontBuildMode_FreeType,
-        FontBuildMode_Stb,
+        FontBuildMode_Stb
     };
 
     FontBuildMode BuildMode;
@@ -120,14 +120,7 @@ struct FreeTypeTest
 };
 ```
 
-**Known issues**
-- Output texture has excessive resolution (lots of vertical waste).
+### Known issues
 - FreeType's memory allocator is not overridden.
 - `cfg.OversampleH`, `OversampleV` are ignored (but perhaps not so necessary with this rasterizer).
 
-**Obligatory comparison screenshots**
-
-Using Windows built-in segoeui.ttf font. Open in new browser tabs, view at 1080p+.
-
-![freetype rasterizer](https://raw.githubusercontent.com/wiki/ocornut/imgui_club/images/freetype_20170817.png)
-

misc/freetype/imgui_freetype.cpp

@@ -1,6 +1,6 @@
-// Wrapper to use Freetype (instead of stb_truetype) for Dear ImGui
+// Wrapper to use FreeType (instead of stb_truetype) for Dear ImGui
 // Get latest version at https://github.com/ocornut/imgui/tree/master/misc/freetype
-// Original code by @Vuhdo (Aleksei Skriabin). Improvements by @mikesart. Maintained by @ocornut
+// Original code by @vuhdo (Aleksei Skriabin). Improvements by @mikesart. Maintained and v0.60+ by @ocornut.
 
 // Changelog:
 // - v0.50: (2017/08/16) imported from https://github.com/Vuhdo/imgui_freetype into http://www.github.com/ocornut/imgui_club, updated for latest changes in ImFontAtlas, minor tweaks.
@@ -10,6 +10,7 @@
 // - v0.54: (2018/01/22) fix for addition of ImFontAtlas::TexUvscale member
 // - v0.55: (2018/02/04) moved to main imgui repository (away from http://www.github.com/ocornut/imgui_club)
 // - v0.56: (2018/06/08) added support for ImFontConfig::GlyphMinAdvanceX, GlyphMaxAdvanceX
+// - v0.60: (2019/01/10) re-factored to match big update in STB builder. fixed texture height waste. fixed redundant glyphs when merging. support for glyph padding.
 
 // Gamma Correct Blending:
 //  FreeType assumes blending in linear space rather than gamma space.
@@ -17,18 +18,16 @@
 //  For correct results you need to be using sRGB and convert to linear space in the pixel shader output.
 //  The default imgui styles will be impacted by this change (alpha values will need tweaking).
 
-// TODO:
-// - Output texture has excessive resolution (lots of vertical waste).
-// - FreeType's memory allocator is not overridden.
-// - cfg.OversampleH, OversampleV are ignored (but perhaps not so necessary with this rasterizer).
+// FIXME: FreeType's memory allocator is not overridden.
+// FIXME: cfg.OversampleH, OversampleV are not supported (but perhaps not so necessary with this rasterizer).
 
 #include "imgui_freetype.h"
-#include "imgui_internal.h"   // ImMin,ImMax,ImFontAtlasBuild*,
+#include "imgui_internal.h"     // ImMin,ImMax,ImFontAtlasBuild*,
 #include <stdint.h>
 #include <ft2build.h>
-#include FT_FREETYPE_H
-#include FT_GLYPH_H
-#include FT_SYNTHESIS_H
+#include FT_FREETYPE_H          // <freetype/freetype.h>
+#include FT_GLYPH_H             // <freetype/ftglyph.h>
+#include FT_SYNTHESIS_H         // <freetype/ftsynth.h>
 
 #ifdef _MSC_VER
 #pragma warning (disable: 4505) // unreferenced local function has been removed (stb stuff)
@@ -74,15 +73,15 @@ namespace
     /// A structure that describe a glyph.
     struct GlyphInfo 
     {
-        float Width;		// Glyph's width in pixels.
-        float Height;		// Glyph's height in pixels.
-        float OffsetX;		// The distance from the origin ("pen position") to the left of the glyph.
-        float OffsetY;		// The distance from the origin to the top of the glyph. This is usually a value < 0.
-        float AdvanceX;		// The distance from the origin to the origin of the next glyph. This is usually a value > 0.
+        int         Width;              // Glyph's width in pixels.
+        int         Height;             // Glyph's height in pixels.
+        FT_Int      OffsetX;            // The distance from the origin ("pen position") to the left of the glyph.
+        FT_Int      OffsetY;            // The distance from the origin to the top of the glyph. This is usually a value < 0.
+        float       AdvanceX;           // The distance from the origin to the origin of the next glyph. This is usually a value > 0.
     };
 
     // Font parameters and metrics.
-    struct FontInfo 
+    struct FontInfo
     {
         uint32_t    PixelHeight;        // Size this font was generated with.
         float       Ascender;           // The pixel extents above the baseline in pixels (typically positive).
@@ -96,82 +95,80 @@ namespace
     // NB: No ctor/dtor, explicitly call Init()/Shutdown()
     struct FreeTypeFont
     {
-        bool        Init(const ImFontConfig& cfg, unsigned int extra_user_flags);   // Initialize from an external data buffer. Doesn't copy data, and you must ensure it stays valid up to this object lifetime.
-        void        Shutdown();
-        void        SetPixelHeight(int pixel_height);                               // Change font pixel size. All following calls to RasterizeGlyph() will use this size
-
-        bool        CalcGlyphInfo(uint32_t codepoint, GlyphInfo& glyph_info, FT_Glyph& ft_glyph, FT_BitmapGlyph& ft_bitmap);
-        void        BlitGlyph(FT_BitmapGlyph ft_bitmap, uint8_t* dst, uint32_t dst_pitch, unsigned char* multiply_table = NULL);
+        bool                    InitFont(FT_Library ft_library, const ImFontConfig& cfg, unsigned int extra_user_flags); // Initialize from an external data buffer. Doesn't copy data, and you must ensure it stays valid up to this object lifetime.
+        void                    CloseFont();
+        void                    SetPixelHeight(int pixel_height); // Change font pixel size. All following calls to RasterizeGlyph() will use this size
+        const FT_Glyph_Metrics* LoadGlyph(uint32_t in_codepoint);
+        const FT_Bitmap*        RenderGlyphAndGetInfo(GlyphInfo* out_glyph_info);
+        void                    BlitGlyph(const FT_Bitmap* ft_bitmap, uint8_t* dst, uint32_t dst_pitch, unsigned char* multiply_table = NULL);
+        ~FreeTypeFont()         { CloseFont(); }
 
         // [Internals]
         FontInfo        Info;               // Font descriptor of the current font.
+        FT_Face         Face;
         unsigned int    UserFlags;          // = ImFontConfig::RasterizerFlags
-        FT_Library      FreetypeLibrary;
-        FT_Face         FreetypeFace;
-        FT_Int32        FreetypeLoadFlags;
+        FT_Int32        LoadFlags;
     };
 
     // From SDL_ttf: Handy routines for converting from fixed point
     #define FT_CEIL(X)  (((X + 63) & -64) / 64)
 
-    bool FreeTypeFont::Init(const ImFontConfig& cfg, unsigned int extra_user_flags)
+    bool FreeTypeFont::InitFont(FT_Library ft_library, const ImFontConfig& cfg, unsigned int extra_user_flags)
     {
         // FIXME: substitute allocator
-        FT_Error error = FT_Init_FreeType(&FreetypeLibrary);
-        if (error != 0)
-            return false;
-        error = FT_New_Memory_Face(FreetypeLibrary, (uint8_t*)cfg.FontData, (uint32_t)cfg.FontDataSize, (uint32_t)cfg.FontNo, &FreetypeFace);
+        FT_Error error = FT_New_Memory_Face(ft_library, (uint8_t*)cfg.FontData, (uint32_t)cfg.FontDataSize, (uint32_t)cfg.FontNo, &Face);
         if (error != 0)
             return false;
-        error = FT_Select_Charmap(FreetypeFace, FT_ENCODING_UNICODE);
+        error = FT_Select_Charmap(Face, FT_ENCODING_UNICODE);
         if (error != 0)
             return false;
 
         memset(&Info, 0, sizeof(Info));
         SetPixelHeight((uint32_t)cfg.SizePixels);
 
-        // Convert to freetype flags (nb: Bold and Oblique are processed separately)
+        // Convert to FreeType flags (NB: Bold and Oblique are processed separately)
         UserFlags = cfg.RasterizerFlags | extra_user_flags;
-        FreetypeLoadFlags = FT_LOAD_NO_BITMAP;
-        if (UserFlags & ImGuiFreeType::NoHinting)      FreetypeLoadFlags |= FT_LOAD_NO_HINTING;
-        if (UserFlags & ImGuiFreeType::NoAutoHint)     FreetypeLoadFlags |= FT_LOAD_NO_AUTOHINT;
-        if (UserFlags & ImGuiFreeType::ForceAutoHint)  FreetypeLoadFlags |= FT_LOAD_FORCE_AUTOHINT;
-        if (UserFlags & ImGuiFreeType::LightHinting)   
-            FreetypeLoadFlags |= FT_LOAD_TARGET_LIGHT;
-        else if (UserFlags & ImGuiFreeType::MonoHinting)   
-            FreetypeLoadFlags |= FT_LOAD_TARGET_MONO;
+        LoadFlags = FT_LOAD_NO_BITMAP;
+        if (UserFlags & ImGuiFreeType::NoHinting)
+            LoadFlags |= FT_LOAD_NO_HINTING;
+        if (UserFlags & ImGuiFreeType::NoAutoHint)
+            LoadFlags |= FT_LOAD_NO_AUTOHINT;
+        if (UserFlags & ImGuiFreeType::ForceAutoHint)
+            LoadFlags |= FT_LOAD_FORCE_AUTOHINT;
+        if (UserFlags & ImGuiFreeType::LightHinting)
+            LoadFlags |= FT_LOAD_TARGET_LIGHT;
+        else if (UserFlags & ImGuiFreeType::MonoHinting)
+            LoadFlags |= FT_LOAD_TARGET_MONO;
         else                                                
-            FreetypeLoadFlags |= FT_LOAD_TARGET_NORMAL;
+            LoadFlags |= FT_LOAD_TARGET_NORMAL;
 
         return true;
     }
 
-    void FreeTypeFont::Shutdown()
+    void FreeTypeFont::CloseFont()
     {
-        if (FreetypeFace) 
+        if (Face) 
         {
-            FT_Done_Face(FreetypeFace);
-            FreetypeFace = NULL;
-            FT_Done_FreeType(FreetypeLibrary);
-            FreetypeLibrary = NULL;
+            FT_Done_Face(Face);
+            Face = NULL;
         }
     }
 
     void FreeTypeFont::SetPixelHeight(int pixel_height) 
     {
-        // I'm not sure how to deal with font sizes properly.
-        // As far as I understand, currently ImGui assumes that the 'pixel_height' is a maximum height of an any given glyph,
-        // i.e. it's the sum of font's ascender and descender. Seems strange to me.
+        // Vuhdo: I'm not sure how to deal with font sizes properly. As far as I understand, currently ImGui assumes that the 'pixel_height' 
+        // is a maximum height of an any given glyph, i.e. it's the sum of font's ascender and descender. Seems strange to me.
+        // NB: FT_Set_Pixel_Sizes() doesn't seem to get us the same result.
         FT_Size_RequestRec req;
         req.type = FT_SIZE_REQUEST_TYPE_REAL_DIM;
         req.width = 0;
         req.height = (uint32_t)pixel_height * 64;
         req.horiResolution = 0;
         req.vertResolution = 0;
-        FT_Request_Size(FreetypeFace, &req);
+        FT_Request_Size(Face, &req);
 
-        // update font info
-        FT_Size_Metrics metrics = FreetypeFace->size->metrics;
+        // Update font info
+        FT_Size_Metrics metrics = Face->size->metrics;
         Info.PixelHeight = (uint32_t)pixel_height;
         Info.Ascender = (float)FT_CEIL(metrics.ascender);
         Info.Descender = (float)FT_CEIL(metrics.descender);
@@ -180,52 +177,58 @@ namespace
         Info.MaxAdvanceWidth = (float)FT_CEIL(metrics.max_advance);
     }
 
-    bool FreeTypeFont::CalcGlyphInfo(uint32_t codepoint, GlyphInfo &glyph_info, FT_Glyph& ft_glyph, FT_BitmapGlyph& ft_bitmap)
+    const FT_Glyph_Metrics* FreeTypeFont::LoadGlyph(uint32_t codepoint)
     {
-        uint32_t glyph_index = FT_Get_Char_Index(FreetypeFace, codepoint);
+        uint32_t glyph_index = FT_Get_Char_Index(Face, codepoint);
         if (glyph_index == 0)
-            return false;
-        FT_Error error = FT_Load_Glyph(FreetypeFace, glyph_index, FreetypeLoadFlags);
+            return NULL;
+        FT_Error error = FT_Load_Glyph(Face, glyph_index, LoadFlags);
         if (error)
-            return false;
+            return NULL;
 
         // Need an outline for this to work
-        FT_GlyphSlot slot = FreetypeFace->glyph;
+        FT_GlyphSlot slot = Face->glyph;
         IM_ASSERT(slot->format == FT_GLYPH_FORMAT_OUTLINE);
 
+        // Apply convenience transform (this is not picking from real "Bold"/"Italic" fonts! Merely applying FreeType helper transform. Oblique == Slanting)
         if (UserFlags & ImGuiFreeType::Bold)
             FT_GlyphSlot_Embolden(slot);
         if (UserFlags & ImGuiFreeType::Oblique)
+        {
             FT_GlyphSlot_Oblique(slot);
+            //FT_BBox bbox;
+            //FT_Outline_Get_BBox(&slot->outline, &bbox);
+            //slot->metrics.width = bbox.xMax - bbox.xMin;
+            //slot->metrics.height = bbox.yMax - bbox.yMin;
+        }
 
-        // Retrieve the glyph
-        error = FT_Get_Glyph(slot, &ft_glyph);
-        if (error != 0)
-            return false;
+        return &slot->metrics;
+    }
 
-        // Rasterize
-        error = FT_Glyph_To_Bitmap(&ft_glyph, FT_RENDER_MODE_NORMAL, NULL, true);
+    const FT_Bitmap* FreeTypeFont::RenderGlyphAndGetInfo(GlyphInfo* out_glyph_info)
+    {
+        FT_GlyphSlot slot = Face->glyph;
+        FT_Error error = FT_Render_Glyph(slot, FT_RENDER_MODE_NORMAL);
         if (error != 0)
-            return false;
+            return NULL;
 
-        ft_bitmap = (FT_BitmapGlyph)ft_glyph;
-        glyph_info.AdvanceX = (float)FT_CEIL(slot->advance.x);
-        glyph_info.OffsetX = (float)ft_bitmap->left;
-        glyph_info.OffsetY = -(float)ft_bitmap->top;
-        glyph_info.Width = (float)ft_bitmap->bitmap.width;
-        glyph_info.Height = (float)ft_bitmap->bitmap.rows;
+        FT_Bitmap* ft_bitmap = &Face->glyph->bitmap;
+        out_glyph_info->Width = (int)ft_bitmap->width;
+        out_glyph_info->Height = (int)ft_bitmap->rows;
+        out_glyph_info->OffsetX = Face->glyph->bitmap_left;
+        out_glyph_info->OffsetY = -Face->glyph->bitmap_top;
+        out_glyph_info->AdvanceX = (float)FT_CEIL(slot->advance.x);
 
-        return true;
+        return ft_bitmap;
     }
 
-    void FreeTypeFont::BlitGlyph(FT_BitmapGlyph ft_bitmap, uint8_t* dst, uint32_t dst_pitch, unsigned char* multiply_table)
+    void FreeTypeFont::BlitGlyph(const FT_Bitmap* ft_bitmap, uint8_t* dst, uint32_t dst_pitch, unsigned char* multiply_table)
     {
         IM_ASSERT(ft_bitmap != NULL);
-
-        const uint32_t w = ft_bitmap->bitmap.width;
-        const uint32_t h = ft_bitmap->bitmap.rows;
-        const uint8_t* src = ft_bitmap->bitmap.buffer;
-        const uint32_t src_pitch = ft_bitmap->bitmap.pitch;
+        const uint32_t w = ft_bitmap->width;
+        const uint32_t h = ft_bitmap->rows;
+        const uint8_t* src = ft_bitmap->buffer;
+        const uint32_t src_pitch = ft_bitmap->pitch;
 
         if (multiply_table == NULL)
         {
@@ -246,143 +249,332 @@ namespace
 #define STB_RECT_PACK_IMPLEMENTATION
 #include "imstb_rectpack.h"
 
-bool ImGuiFreeType::BuildFontAtlas(ImFontAtlas* atlas, unsigned int extra_flags)
+struct ImFontBuildSrcGlyphFT
+{
+    GlyphInfo           Info;
+    uint32_t            Codepoint;
+    unsigned char*      BitmapData;         // Point within one of the dst_tmp_bitmap_buffers[] array
+};
+
+struct ImFontBuildSrcDataFT
+{
+    FreeTypeFont        Font;
+    stbrp_rect*         Rects;              // Rectangle to pack. We first fill in their size and the packer will give us their position.
+    const ImWchar*      SrcRanges;          // Ranges as requested by user (user is allowed to request too much, e.g. 0x0020..0xFFFF)
+    int                 DstIndex;           // Index into atlas->Fonts[] and dst_tmp_array[]
+    int                 GlyphsHighest;      // Highest requested codepoint
+    int                 GlyphsCount;        // Glyph count (excluding missing glyphs and glyphs already set by an earlier source font)
+    ImBoolVector        GlyphsSet;          // Glyph bit map (random access, 1-bit per codepoint. This will be a maximum of 8KB)
+    ImVector<ImFontBuildSrcGlyphFT>   GlyphsList;
+};
+
+// Temporary data for one destination ImFont* (multiple source fonts can be merged into one destination ImFont)
+struct ImFontBuildDstDataFT
+{
+    int                 SrcCount;           // Number of source fonts targeting this destination font.
+    int                 GlyphsHighest;
+    int                 GlyphsCount;
+    ImBoolVector        GlyphsSet;          // This is used to resolve collision when multiple sources are merged into a same destination font.
+};
+
+bool ImFontAtlasBuildWithFreeType(FT_Library ft_library, ImFontAtlas* atlas, unsigned int extra_flags)
 {
     IM_ASSERT(atlas->ConfigData.Size > 0);
-    IM_ASSERT(atlas->TexGlyphPadding == 1); // Not supported
 
     ImFontAtlasBuildRegisterDefaultCustomRects(atlas);
 
-    atlas->TexID = NULL;
+    // Clear atlas
+    atlas->TexID = (ImTextureID)NULL;
     atlas->TexWidth = atlas->TexHeight = 0;
     atlas->TexUvScale = ImVec2(0.0f, 0.0f);
     atlas->TexUvWhitePixel = ImVec2(0.0f, 0.0f);
     atlas->ClearTexData();
 
-    ImVector<FreeTypeFont> fonts;
-    fonts.resize(atlas->ConfigData.Size);
+    // Temporary storage for building
+    ImVector<ImFontBuildSrcDataFT> src_tmp_array;
+    ImVector<ImFontBuildDstDataFT> dst_tmp_array;
+    src_tmp_array.resize(atlas->ConfigData.Size);
+    dst_tmp_array.resize(atlas->Fonts.Size);
+    memset(src_tmp_array.Data, 0, (size_t)src_tmp_array.size_in_bytes());
+    memset(dst_tmp_array.Data, 0, (size_t)dst_tmp_array.size_in_bytes());
 
-    ImVec2 max_glyph_size(1.0f, 1.0f);
-
-    // Count glyphs/ranges, initialize font
-    int total_glyphs_count = 0;
-    int total_ranges_count = 0;
-    for (int input_i = 0; input_i < atlas->ConfigData.Size; input_i++) 
+    // 1. Initialize font loading structure, check font data validity
+    for (int src_i = 0; src_i < atlas->ConfigData.Size; src_i++)
     {
-        ImFontConfig& cfg = atlas->ConfigData[input_i];
-        FreeTypeFont& font_face = fonts[input_i];
+        ImFontBuildSrcDataFT& src_tmp = src_tmp_array[src_i];
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
+        FreeTypeFont& font_face = src_tmp.Font;
         IM_ASSERT(cfg.DstFont && (!cfg.DstFont->IsLoaded() || cfg.DstFont->ContainerAtlas == atlas));
 
-        if (!font_face.Init(cfg, extra_flags))
+        // Find index from cfg.DstFont (we allow the user to set cfg.DstFont. Also it makes casual debugging nicer than when storing indices)
+        src_tmp.DstIndex = -1;
+        for (int output_i = 0; output_i < atlas->Fonts.Size && src_tmp.DstIndex == -1; output_i++)
+            if (cfg.DstFont == atlas->Fonts[output_i])
+                src_tmp.DstIndex = output_i;
+        IM_ASSERT(src_tmp.DstIndex != -1); // cfg.DstFont not pointing within atlas->Fonts[] array?
+        if (src_tmp.DstIndex == -1)
             return false;
 
-        max_glyph_size.x = ImMax(max_glyph_size.x, font_face.Info.MaxAdvanceWidth);
-        max_glyph_size.y = ImMax(max_glyph_size.y, font_face.Info.Ascender - font_face.Info.Descender);
+        // Load font
+        if (!font_face.InitFont(ft_library, cfg, extra_flags))
+            return false;
+
+        // Measure highest codepoints
+        ImFontBuildDstDataFT& dst_tmp = dst_tmp_array[src_tmp.DstIndex];
+        src_tmp.SrcRanges = cfg.GlyphRanges ? cfg.GlyphRanges : atlas->GetGlyphRangesDefault();
+        for (const ImWchar* src_range = src_tmp.SrcRanges; src_range[0] && src_range[1]; src_range += 2)
+            src_tmp.GlyphsHighest = ImMax(src_tmp.GlyphsHighest, (int)src_range[1]);
+        dst_tmp.SrcCount++;
+        dst_tmp.GlyphsHighest = ImMax(dst_tmp.GlyphsHighest, src_tmp.GlyphsHighest);
+    }
+
+    // 2. For every requested codepoint, check for their presence in the font data, and handle redundancy or overlaps between source fonts to avoid unused glyphs.
+    int total_glyphs_count = 0;
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcDataFT& src_tmp = src_tmp_array[src_i];
+        ImFontBuildDstDataFT& dst_tmp = dst_tmp_array[src_tmp.DstIndex];
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
+        src_tmp.GlyphsSet.Resize(src_tmp.GlyphsHighest + 1);
+        if (dst_tmp.SrcCount > 1 && dst_tmp.GlyphsSet.Storage.empty())
+            dst_tmp.GlyphsSet.Resize(dst_tmp.GlyphsHighest + 1);
+
+        for (const ImWchar* src_range = src_tmp.SrcRanges; src_range[0] && src_range[1]; src_range += 2)
+            for (int codepoint = src_range[0]; codepoint <= src_range[1]; codepoint++)
+            {
+                if (cfg.MergeMode && dst_tmp.GlyphsSet.GetBit(codepoint))               // Don't overwrite existing glyphs. We could make this an option (e.g. MergeOverwrite)
+                    continue;
+                uint32_t glyph_index = FT_Get_Char_Index(src_tmp.Font.Face, codepoint); // It is actually in the font? (FIXME-OPT: We are not storing the glyph_index..)
+                if (glyph_index == 0)
+                    continue;
+
+                // Add to avail set/counters
+                src_tmp.GlyphsCount++;
+                dst_tmp.GlyphsCount++;
+                src_tmp.GlyphsSet.SetBit(codepoint, true);
+                if (dst_tmp.SrcCount > 1)
+                    dst_tmp.GlyphsSet.SetBit(codepoint, true);
+                total_glyphs_count++;
+            }
+    }
 
-        if (!cfg.GlyphRanges)
-            cfg.GlyphRanges = atlas->GetGlyphRangesDefault();
-        for (const ImWchar* in_range = cfg.GlyphRanges; in_range[0] && in_range[ 1 ]; in_range += 2, total_ranges_count++) 
-            total_glyphs_count += (in_range[1] - in_range[0]) + 1;
+    // 3. Unpack our bit map into a flat list (we now have all the Unicode points that we know are requested _and_ available _and_ not overlapping another)
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcDataFT& src_tmp = src_tmp_array[src_i];
+        src_tmp.GlyphsList.reserve(src_tmp.GlyphsCount);
+
+        IM_ASSERT(sizeof(src_tmp.GlyphsSet.Storage.Data[0]) == sizeof(int));
+        const int* it_begin = src_tmp.GlyphsSet.Storage.begin();
+        const int* it_end = src_tmp.GlyphsSet.Storage.end();
+        for (const int* it = it_begin; it < it_end; it++)
+            if (int entries_32 = *it)
+                for (int bit_n = 0; bit_n < 32; bit_n++)
+                    if (entries_32 & (1 << bit_n))
+                    {
+                        ImFontBuildSrcGlyphFT src_glyph;
+                        memset(&src_glyph, 0, sizeof(src_glyph));
+                        src_glyph.Codepoint = (ImWchar)(((it - it_begin) << 5) + bit_n);
+                        //src_glyph.GlyphIndex = 0; // FIXME-OPT: We had this info in the previous step and lost it..
+                        src_tmp.GlyphsList.push_back(src_glyph);
+                    }
+        src_tmp.GlyphsSet.Clear();
+        IM_ASSERT(src_tmp.GlyphsList.Size == src_tmp.GlyphsCount);
     }
+    for (int dst_i = 0; dst_i < dst_tmp_array.Size; dst_i++)
+        dst_tmp_array[dst_i].GlyphsSet.Clear();
+    dst_tmp_array.clear();
+
+    // Allocate packing character data and flag packed characters buffer as non-packed (x0=y0=x1=y1=0)
+    // (We technically don't need to zero-clear buf_rects, but let's do it for the sake of sanity)
+    ImVector<stbrp_rect> buf_rects;
+    buf_rects.resize(total_glyphs_count);
+    memset(buf_rects.Data, 0, (size_t)buf_rects.size_in_bytes());
+
+    // Allocate temporary rasterization data buffers. 
+    // We could not find a way to retrieve accurate glyph size without rendering them.
+    // (e.g. slot->metrics->width not always matching bitmap->width, especially considering the Oblique transform)
+    // We allocate in chunks of 256 KB to not waste too much extra memory ahead. Hopefully users of FreeType won't find the temporary allocations.
+    const int BITMAP_BUFFERS_CHUNK_SIZE = 256 * 1024;
+    int buf_bitmap_current_used_bytes = 0;
+    ImVector<unsigned char*> buf_bitmap_buffers;
+    buf_bitmap_buffers.push_back((unsigned char*)ImGui::MemAlloc(BITMAP_BUFFERS_CHUNK_SIZE));
+
+    // 4. Gather glyphs sizes so we can pack them in our virtual canvas.
+    // 8. Render/rasterize font characters into the texture
+    int total_surface = 0;
+    int buf_rects_out_n = 0;
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcDataFT& src_tmp = src_tmp_array[src_i];
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
+        if (src_tmp.GlyphsCount == 0)
+            continue;
 
-    // We need a width for the skyline algorithm. Using a dumb heuristic here to decide of width. User can override TexDesiredWidth and TexGlyphPadding if they wish.
-    // Width doesn't really matter much, but some API/GPU have texture size limitations and increasing width can decrease height.
-    atlas->TexWidth = (atlas->TexDesiredWidth > 0) ? atlas->TexDesiredWidth : (total_glyphs_count > 4000) ? 4096 : (total_glyphs_count > 2000) ? 2048 : (total_glyphs_count > 1000) ? 1024 : 512;
+        src_tmp.Rects = &buf_rects[buf_rects_out_n];
+        buf_rects_out_n += src_tmp.GlyphsCount;
 
-    // We don't do the original first pass to determine texture height, but just rough estimate.
-    // Looks ugly inaccurate and excessive, but AFAIK with FreeType we actually need to render glyphs to get exact sizes.
-    // Alternatively, we could just render all glyphs into a big shadow buffer, get their sizes, do the rectangle packing and just copy back from the 
-    // shadow buffer to the texture buffer. Will give us an accurate texture height, but eat a lot of temp memory. Probably no one will notice.)
-    const int total_rects = total_glyphs_count + atlas->CustomRects.size();
-    float min_rects_per_row = ceilf((atlas->TexWidth / (max_glyph_size.x + 1.0f)));
-    float min_rects_per_column = ceilf(total_rects / min_rects_per_row);
-    atlas->TexHeight = (int)(min_rects_per_column * (max_glyph_size.y + 1.0f));
+        // Compute multiply table if requested
+        const bool multiply_enabled = (cfg.RasterizerMultiply != 1.0f);
+        unsigned char multiply_table[256];
+        if (multiply_enabled)
+            ImFontAtlasBuildMultiplyCalcLookupTable(multiply_table, cfg.RasterizerMultiply);
 
-    // Create texture
+        // Gather the sizes of all rectangles we will need to pack
+        const int padding = atlas->TexGlyphPadding;
+        for (int glyph_i = 0; glyph_i < src_tmp.GlyphsList.Size; glyph_i++)
+        {
+            ImFontBuildSrcGlyphFT& src_glyph = src_tmp.GlyphsList[glyph_i];
+
+            const FT_Glyph_Metrics* metrics = src_tmp.Font.LoadGlyph(src_glyph.Codepoint);
+            IM_ASSERT(metrics != NULL);
+            if (metrics == NULL)
+                continue;
+
+            // Render glyph into a bitmap (currently held by FreeType)
+            const FT_Bitmap* ft_bitmap = src_tmp.Font.RenderGlyphAndGetInfo(&src_glyph.Info);
+            IM_ASSERT(ft_bitmap);
+
+            // Allocate new temporary chunk if needed
+            const int bitmap_size_in_bytes = src_glyph.Info.Width * src_glyph.Info.Height;
+            if (buf_bitmap_current_used_bytes + bitmap_size_in_bytes > BITMAP_BUFFERS_CHUNK_SIZE)
+            {
+                buf_bitmap_current_used_bytes = 0;
+                buf_bitmap_buffers.push_back((unsigned char*)ImGui::MemAlloc(BITMAP_BUFFERS_CHUNK_SIZE));
+            }
+
+            // Blit rasterized pixels to our temporary buffer and keep a pointer to it.
+            src_glyph.BitmapData = buf_bitmap_buffers.back() + buf_bitmap_current_used_bytes;
+            buf_bitmap_current_used_bytes += bitmap_size_in_bytes;
+            src_tmp.Font.BlitGlyph(ft_bitmap, src_glyph.BitmapData, src_glyph.Info.Width * 1, multiply_enabled ? multiply_table : NULL);
+
+            src_tmp.Rects[glyph_i].w = (stbrp_coord)(src_glyph.Info.Width + padding);
+            src_tmp.Rects[glyph_i].h = (stbrp_coord)(src_glyph.Info.Height + padding);
+            total_surface += src_tmp.Rects[glyph_i].w * src_tmp.Rects[glyph_i].h;
+        }
+    }
+
+    // We need a width for the skyline algorithm, any width!
+    // The exact width doesn't really matter much, but some API/GPU have texture size limitations and increasing width can decrease height.
+    // User can override TexDesiredWidth and TexGlyphPadding if they wish, otherwise we use a simple heuristic to select the width based on expected surface.
+    const int surface_sqrt = (int)ImSqrt((float)total_surface) + 1;
+    atlas->TexHeight = 0;
+    if (atlas->TexDesiredWidth > 0)
+        atlas->TexWidth = atlas->TexDesiredWidth;
+    else
+        atlas->TexWidth = (surface_sqrt >= 4096*0.7f) ? 4096 : (surface_sqrt >= 2048*0.7f) ? 2048 : (surface_sqrt >= 1024*0.7f) ? 1024 : 512;
+
+    // 5. Start packing
+    // Pack our extra data rectangles first, so it will be on the upper-left corner of our texture (UV will have small values).
+    const int TEX_HEIGHT_MAX = 1024 * 32;
+    const int num_nodes_for_packing_algorithm = atlas->TexWidth - atlas->TexGlyphPadding;
+    ImVector<stbrp_node> pack_nodes;
+    pack_nodes.resize(num_nodes_for_packing_algorithm);
+    stbrp_context pack_context;
+    stbrp_init_target(&pack_context, atlas->TexWidth, TEX_HEIGHT_MAX, pack_nodes.Data, pack_nodes.Size);
+    ImFontAtlasBuildPackCustomRects(atlas, &pack_context);
+
+    // 6. Pack each source font. No rendering yet, we are working with rectangles in an infinitely tall texture at this point.
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcDataFT& src_tmp = src_tmp_array[src_i];
+        if (src_tmp.GlyphsCount == 0)
+            continue;
+
+        stbrp_pack_rects(&pack_context, src_tmp.Rects, src_tmp.GlyphsCount);
+
+        // Extend texture height and mark missing glyphs as non-packed so we won't render them.
+        // FIXME: We are not handling packing failure here (would happen if we got off TEX_HEIGHT_MAX or if a single if larger than TexWidth?)
+        for (int glyph_i = 0; glyph_i < src_tmp.GlyphsCount; glyph_i++)
+            if (src_tmp.Rects[glyph_i].was_packed)
+                atlas->TexHeight = ImMax(atlas->TexHeight, src_tmp.Rects[glyph_i].y + src_tmp.Rects[glyph_i].h);
+    }
+
+    // 7. Allocate texture
     atlas->TexHeight = (atlas->Flags & ImFontAtlasFlags_NoPowerOfTwoHeight) ? (atlas->TexHeight + 1) : ImUpperPowerOfTwo(atlas->TexHeight);
     atlas->TexUvScale = ImVec2(1.0f / atlas->TexWidth, 1.0f / atlas->TexHeight);
     atlas->TexPixelsAlpha8 = (unsigned char*)ImGui::MemAlloc(atlas->TexWidth * atlas->TexHeight);
     memset(atlas->TexPixelsAlpha8, 0, atlas->TexWidth * atlas->TexHeight);
 
-    // Start packing
-    ImVector<stbrp_node> pack_nodes;
-    pack_nodes.resize(total_rects);
-    stbrp_context context;
-    stbrp_init_target(&context, atlas->TexWidth, atlas->TexHeight, pack_nodes.Data, total_rects);
+    // 8. Copy rasterized font characters back into the main texture
+    // 9. Setup ImFont and glyphs for runtime
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+    {
+        ImFontBuildSrcDataFT& src_tmp = src_tmp_array[src_i];
+        if (src_tmp.GlyphsCount == 0)
+            continue;
 
-    // Pack our extra data rectangles first, so it will be on the upper-left corner of our texture (UV will have small values).
-    ImFontAtlasBuildPackCustomRects(atlas, &context);
+        ImFontConfig& cfg = atlas->ConfigData[src_i];
+        ImFont* dst_font = cfg.DstFont; // We can have multiple input fonts writing into a same destination font (when using MergeMode=true)
 
-    // Render characters, setup ImFont and glyphs for runtime
-    for (int input_i = 0; input_i < atlas->ConfigData.Size; input_i++)
-    {
-        ImFontConfig& cfg = atlas->ConfigData[input_i];
-        FreeTypeFont& font_face = fonts[input_i];
-        ImFont* dst_font = cfg.DstFont;
-        if (cfg.MergeMode)
-            dst_font->BuildLookupTable();
-
-        const float ascent = font_face.Info.Ascender;
-        const float descent = font_face.Info.Descender;
+        const float ascent = src_tmp.Font.Info.Ascender;
+        const float descent = src_tmp.Font.Info.Descender;
         ImFontAtlasBuildSetupFont(atlas, dst_font, &cfg, ascent, descent);
         const float font_off_x = cfg.GlyphOffset.x;
         const float font_off_y = cfg.GlyphOffset.y + (float)(int)(dst_font->Ascent + 0.5f);
 
-        bool multiply_enabled = (cfg.RasterizerMultiply != 1.0f);
-        unsigned char multiply_table[256];
-        if (multiply_enabled)
-            ImFontAtlasBuildMultiplyCalcLookupTable(multiply_table, cfg.RasterizerMultiply);
-
-        for (const ImWchar* in_range = cfg.GlyphRanges; in_range[0] && in_range[1]; in_range += 2) 
+        const int padding = atlas->TexGlyphPadding;
+        for (int glyph_i = 0; glyph_i < src_tmp.GlyphsCount; glyph_i++)
         {
-            for (uint32_t codepoint = in_range[0]; codepoint <= in_range[1]; ++codepoint) 
-            {
-                if (cfg.MergeMode && dst_font->FindGlyphNoFallback((ImWchar)codepoint))
-                    continue;
-
-                FT_Glyph ft_glyph = NULL;
-                FT_BitmapGlyph ft_glyph_bitmap = NULL; // NB: will point to bitmap within FT_Glyph
-                GlyphInfo glyph_info;
-                if (!font_face.CalcGlyphInfo(codepoint, glyph_info, ft_glyph, ft_glyph_bitmap))
-                    continue;
-
-                // Pack rectangle
-                stbrp_rect rect;
-                rect.w = (uint16_t)glyph_info.Width + 1; // Account for texture filtering
-                rect.h = (uint16_t)glyph_info.Height + 1;
-                stbrp_pack_rects(&context, &rect, 1);
-
-                // Copy rasterized pixels to main texture
-                uint8_t* blit_dst = atlas->TexPixelsAlpha8 + rect.y * atlas->TexWidth + rect.x;
-                font_face.BlitGlyph(ft_glyph_bitmap, blit_dst, atlas->TexWidth, multiply_enabled ? multiply_table : NULL);
-                FT_Done_Glyph(ft_glyph);
-
-                float char_advance_x_org = glyph_info.AdvanceX;
-                float char_advance_x_mod = ImClamp(char_advance_x_org, cfg.GlyphMinAdvanceX, cfg.GlyphMaxAdvanceX);
-                float char_off_x = font_off_x;
-                if (char_advance_x_org != char_advance_x_mod)
-                    char_off_x += cfg.PixelSnapH ? (float)(int)((char_advance_x_mod - char_advance_x_org) * 0.5f) : (char_advance_x_mod - char_advance_x_org) * 0.5f;
-
-                // Register glyph
-                dst_font->AddGlyph((ImWchar)codepoint, 
-                    glyph_info.OffsetX + char_off_x, 
-                    glyph_info.OffsetY + font_off_y, 
-                    glyph_info.OffsetX + char_off_x + glyph_info.Width, 
-                    glyph_info.OffsetY + font_off_y + glyph_info.Height,
-                    rect.x / (float)atlas->TexWidth, 
-                    rect.y / (float)atlas->TexHeight, 
-                    (rect.x + glyph_info.Width) / (float)atlas->TexWidth, 
-                    (rect.y + glyph_info.Height) / (float)atlas->TexHeight,
-                    char_advance_x_mod);
-            }
+            ImFontBuildSrcGlyphFT& src_glyph = src_tmp.GlyphsList[glyph_i];
+            stbrp_rect& pack_rect = src_tmp.Rects[glyph_i];
+            IM_ASSERT(pack_rect.was_packed);
+
+            GlyphInfo& info = src_glyph.Info;
+            IM_ASSERT(info.Width + padding <= pack_rect.w);
+            IM_ASSERT(info.Height + padding <= pack_rect.h);
+            const int tx = pack_rect.x + padding;
+            const int ty = pack_rect.y + padding;
+
+            // Blit from temporary buffer to final texture
+            size_t blit_src_stride = (size_t)src_glyph.Info.Width;
+            size_t blit_dst_stride = (size_t)atlas->TexWidth;
+            unsigned char* blit_src = src_glyph.BitmapData;
+            unsigned char* blit_dst = atlas->TexPixelsAlpha8 + (ty * blit_dst_stride) + tx;
+            for (int y = info.Height; y > 0; y--, blit_dst += blit_dst_stride, blit_src += blit_src_stride)
+                memcpy(blit_dst, blit_src, blit_src_stride);
+
+            float char_advance_x_org = info.AdvanceX;
+            float char_advance_x_mod = ImClamp(char_advance_x_org, cfg.GlyphMinAdvanceX, cfg.GlyphMaxAdvanceX);
+            float char_off_x = font_off_x;
+            if (char_advance_x_org != char_advance_x_mod)
+                char_off_x += cfg.PixelSnapH ? (float)(int)((char_advance_x_mod - char_advance_x_org) * 0.5f) : (char_advance_x_mod - char_advance_x_org) * 0.5f;
+            
+            // Register glyph
+            float x0 = info.OffsetX + char_off_x;
+            float y0 = info.OffsetY + font_off_y;
+            float x1 = x0 + info.Width;
+            float y1 = y0 + info.Height;
+            float u0 = (tx) / (float)atlas->TexWidth;
+            float v0 = (ty) / (float)atlas->TexHeight;
+            float u1 = (tx + info.Width) / (float)atlas->TexWidth;
+            float v1 = (ty + info.Height) / (float)atlas->TexHeight;
+            dst_font->AddGlyph((ImWchar)src_glyph.Codepoint, x0, y0, x1, y1, u0, v0, u1, v1, char_advance_x_mod);
         }
+
+        src_tmp.Rects = NULL;
     }
 
     // Cleanup
-    for (int n = 0; n < fonts.Size; n++)
-        fonts[n].Shutdown();
+    for (int buf_i = 0; buf_i < buf_bitmap_buffers.Size; buf_i++)
+        ImGui::MemFree(buf_bitmap_buffers[buf_i]);
+    for (int src_i = 0; src_i < src_tmp_array.Size; src_i++)
+        src_tmp_array[src_i].~ImFontBuildSrcDataFT();
 
     ImFontAtlasBuildFinish(atlas);
 
     return true;
 }
+
+bool ImGuiFreeType::BuildFontAtlas(ImFontAtlas* atlas, unsigned int extra_flags)
+{
+    FT_Library ft_library;
+    FT_Error error = FT_Init_FreeType(&ft_library);
+    if (error != 0)
+        return false;
+
+    bool ret = ImFontAtlasBuildWithFreeType(ft_library, atlas, extra_flags);
+    FT_Done_FreeType(ft_library);
+
+    return ret;
+}

misc/freetype/imgui_freetype.h

@@ -1,4 +1,4 @@
-// Wrapper to use Freetype (instead of stb_truetype) for Dear ImGui
+// Wrapper to use FreeType (instead of stb_truetype) for Dear ImGui
 // Get latest version at https://github.com/ocornut/imgui/tree/master/misc/freetype
 // Original code by @Vuhdo (Aleksei Skriabin), maintained by @ocornut