Merge branch 'features/tex_antialiased_lines' (#3245)

docs/CHANGELOG.txt

@@ -35,6 +35,15 @@ HOW TO UPDATE?
  VERSION 1.78 WIP (In Progress)
 -----------------------------------------------------------------------
 
+Other Changes:
+
+- ImDrawList: Thick anti-aliased strokes (> 1.0f) with integer thickness now use a texture-based 
+  path, reducing the amount of vertices/indices and CPU/GPU usage. (#3245) [@Shironekoben]
+  - This change will facilitate the wider use of thick borders in future style changes. 
+  - Requires an extra bit of texture space (~64x64 by default), relies on GPU bilinear filtering.
+  - Clear io.AntiAliasedLinesUseTex = false; to disable rendering using this method.
+  - Clear ImFontAtlasFlags_NoBakedLines in ImFontAtlas::Flags to disable baking data in texture.
+
 
 -----------------------------------------------------------------------
  VERSION 1.77 (Released 2020-06-29)

imgui.cpp

@@ -935,6 +935,7 @@ ImGuiStyle::ImGuiStyle()
     DisplaySafeAreaPadding  = ImVec2(3,3);      // If you cannot see the edge of your screen (e.g. on a TV) increase the safe area padding. Covers popups/tooltips as well regular windows.
     MouseCursorScale        = 1.0f;             // Scale software rendered mouse cursor (when io.MouseDrawCursor is enabled). May be removed later.
     AntiAliasedLines        = true;             // Enable anti-aliased lines/borders. Disable if you are really tight on CPU/GPU.
+    AntiAliasedLinesUseTex  = true;             // Enable anti-aliased lines/borders using textures where possible. Require back-end to render with bilinear filtering.
     AntiAliasedFill         = true;             // Enable anti-aliased filled shapes (rounded rectangles, circles, etc.).
     CurveTessellationTol    = 1.25f;            // Tessellation tolerance when using PathBezierCurveTo() without a specific number of segments. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
     CircleSegmentMaxError   = 1.60f;            // Maximum error (in pixels) allowed when using AddCircle()/AddCircleFilled() or drawing rounded corner rectangles with no explicit segment count specified. Decrease for higher quality but more geometry.
@@ -3688,6 +3689,8 @@ void ImGui::NewFrame()
     g.DrawListSharedData.InitialFlags = ImDrawListFlags_None;
     if (g.Style.AntiAliasedLines)
         g.DrawListSharedData.InitialFlags |= ImDrawListFlags_AntiAliasedLines;
+    if (g.Style.AntiAliasedLinesUseTex && !(g.Font->ContainerAtlas->Flags & ImFontAtlasFlags_NoBakedLines))
+        g.DrawListSharedData.InitialFlags |= ImDrawListFlags_AntiAliasedLinesUseTex;
     if (g.Style.AntiAliasedFill)
         g.DrawListSharedData.InitialFlags |= ImDrawListFlags_AntiAliasedFill;
     if (g.IO.BackendFlags & ImGuiBackendFlags_RendererHasVtxOffset)
@@ -6158,6 +6161,7 @@ void ImGui::SetCurrentFont(ImFont* font)
 
     ImFontAtlas* atlas = g.Font->ContainerAtlas;
     g.DrawListSharedData.TexUvWhitePixel = atlas->TexUvWhitePixel;
+    g.DrawListSharedData.TexUvLines = atlas->TexUvLines;
     g.DrawListSharedData.Font = g.Font;
     g.DrawListSharedData.FontSize = g.FontSize;
 }

imgui.h

@@ -60,7 +60,7 @@ Index of this file:
 // Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals. Work in progress versions typically starts at XYY99 then bounce up to XYY00, XYY01 etc. when release tagging happens)
 #define IMGUI_VERSION               "1.78 WIP"
-#define IMGUI_VERSION_NUM           17702
+#define IMGUI_VERSION_NUM           17703
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 
 // Define attributes of all API symbols declarations (e.g. for DLL under Windows)
@@ -1438,8 +1438,9 @@ struct ImGuiStyle
     ImVec2      DisplayWindowPadding;       // Window position are clamped to be visible within the display area by at least this amount. Only applies to regular windows.
     ImVec2      DisplaySafeAreaPadding;     // If you cannot see the edges of your screen (e.g. on a TV) increase the safe area padding. Apply to popups/tooltips as well regular windows. NB: Prefer configuring your TV sets correctly!
     float       MouseCursorScale;           // Scale software rendered mouse cursor (when io.MouseDrawCursor is enabled). May be removed later.
-    bool        AntiAliasedLines;           // Enable anti-aliased lines/borders. Disable if you are really tight on CPU/GPU.
-    bool        AntiAliasedFill;            // Enable anti-aliased edges around filled shapes (rounded rectangles, circles, etc.). Disable if you are really tight on CPU/GPU.
+    bool        AntiAliasedLines;           // Enable anti-aliased lines/borders. Disable if you are really tight on CPU/GPU. Latched at the beginning of the frame (copied to ImDrawList).
+    bool        AntiAliasedLinesUseTex;     // Enable anti-aliased lines/borders using textures where possible. Require back-end to render with bilinear filtering. Latched at the beginning of the frame (copied to ImDrawList).
+    bool        AntiAliasedFill;            // Enable anti-aliased edges around filled shapes (rounded rectangles, circles, etc.). Disable if you are really tight on CPU/GPU. Latched at the beginning of the frame (copied to ImDrawList).
     float       CurveTessellationTol;       // Tessellation tolerance when using PathBezierCurveTo() without a specific number of segments. Decrease for highly tessellated curves (higher quality, more polygons), increase to reduce quality.
     float       CircleSegmentMaxError;      // Maximum error (in pixels) allowed when using AddCircle()/AddCircleFilled() or drawing rounded corner rectangles with no explicit segment count specified. Decrease for higher quality but more geometry.
     ImVec4      Colors[ImGuiCol_COUNT];
@@ -1896,6 +1897,11 @@ struct ImColor
 // Hold a series of drawing commands. The user provides a renderer for ImDrawData which essentially contains an array of ImDrawList.
 //-----------------------------------------------------------------------------
 
+// The maximum line width to bake anti-aliased textures for. Build atlas with ImFontAtlasFlags_NoBakedLines to disable baking.
+#ifndef IM_DRAWLIST_TEX_LINES_WIDTH_MAX
+#define IM_DRAWLIST_TEX_LINES_WIDTH_MAX     (63)
+#endif
+
 // ImDrawCallback: Draw callbacks for advanced uses [configurable type: override in imconfig.h]
 // NB: You most likely do NOT need to use draw callbacks just to create your own widget or customized UI rendering,
 // you can poke into the draw list for that! Draw callback may be useful for example to:
@@ -1992,12 +1998,15 @@ enum ImDrawCornerFlags_
     ImDrawCornerFlags_All       = 0xF     // In your function calls you may use ~0 (= all bits sets) instead of ImDrawCornerFlags_All, as a convenience
 };
 
+// Flags for ImDrawList. Those are set automatically by ImGui:: functions from ImGuiIO settings, and generally not manipulated directly.
+// It is however possible to temporarily alter flags between calls to ImDrawList:: functions.
 enum ImDrawListFlags_
 {
     ImDrawListFlags_None                    = 0,
     ImDrawListFlags_AntiAliasedLines        = 1 << 0,  // Enable anti-aliased lines/borders (*2 the number of triangles for 1.0f wide line or lines thin enough to be drawn using textures, otherwise *3 the number of triangles)
-    ImDrawListFlags_AntiAliasedFill         = 1 << 1,  // Enable anti-aliased edge around filled shapes (rounded rectangles, circles).
-    ImDrawListFlags_AllowVtxOffset          = 1 << 2   // Can emit 'VtxOffset > 0' to allow large meshes. Set when 'ImGuiBackendFlags_RendererHasVtxOffset' is enabled.
+    ImDrawListFlags_AntiAliasedLinesUseTex  = 1 << 1,  // Enable anti-aliased lines/borders using textures when possible. Require back-end to render with bilinear filtering.
+    ImDrawListFlags_AntiAliasedFill         = 1 << 2,  // Enable anti-aliased edge around filled shapes (rounded rectangles, circles).
+    ImDrawListFlags_AllowVtxOffset          = 1 << 3   // Can emit 'VtxOffset > 0' to allow large meshes. Set when 'ImGuiBackendFlags_RendererHasVtxOffset' is enabled.
 };
 
 // Draw command list
@@ -2216,7 +2225,8 @@ enum ImFontAtlasFlags_
 {
     ImFontAtlasFlags_None               = 0,
     ImFontAtlasFlags_NoPowerOfTwoHeight = 1 << 0,   // Don't round the height to next power of two
-    ImFontAtlasFlags_NoMouseCursors     = 1 << 1    // Don't build software mouse cursors into the atlas (save a little texture memory)
+    ImFontAtlasFlags_NoMouseCursors     = 1 << 1,   // Don't build software mouse cursors into the atlas (save a little texture memory)
+    ImFontAtlasFlags_NoBakedLines       = 1 << 2    // Don't build thick line textures into the atlas (save a little texture memory). The AntiAliasedLinesUseTex features uses them, otherwise they will be rendered using polygons (more expensive for CPU/GPU).
 };
 
 // Load and rasterize multiple TTF/OTF fonts into a same texture. The font atlas will build a single texture holding:
@@ -2317,9 +2327,11 @@ struct ImFontAtlas
     ImVector<ImFont*>           Fonts;              // Hold all the fonts returned by AddFont*. Fonts[0] is the default font upon calling ImGui::NewFrame(), use ImGui::PushFont()/PopFont() to change the current font.
     ImVector<ImFontAtlasCustomRect> CustomRects;    // Rectangles for packing custom texture data into the atlas.
     ImVector<ImFontConfig>      ConfigData;         // Configuration data
+    ImVec4                      TexUvLines[IM_DRAWLIST_TEX_LINES_WIDTH_MAX + 1];  // UVs for baked anti-aliased lines
 
     // [Internal] Packing data
     int                         PackIdMouseCursors; // Custom texture rectangle ID for white pixel and mouse cursors
+    int                         PackIdLines;        // Custom texture rectangle ID for baked anti-aliased lines
 
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
     typedef ImFontAtlasCustomRect    CustomRect;         // OBSOLETED in 1.72+

imgui_demo.cpp

@@ -3831,6 +3831,8 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
         {
             ImGui::Checkbox("Anti-aliased lines", &style.AntiAliasedLines);
             ImGui::SameLine(); HelpMarker("When disabling anti-aliasing lines, you'll probably want to disable borders in your style as well.");
+            ImGui::Checkbox("Anti-aliased lines use texture", &style.AntiAliasedLinesUseTex);
+            ImGui::SameLine(); HelpMarker("Faster lines using texture data. Require back-end to render with bilinear filtering (not point/nearest filtering).");
             ImGui::Checkbox("Anti-aliased fill", &style.AntiAliasedFill);
             ImGui::PushItemWidth(100);
             ImGui::DragFloat("Curve Tessellation Tolerance", &style.CurveTessellationTol, 0.02f, 0.10f, 10.0f, "%.2f");

imgui_draw.cpp

@@ -358,6 +358,7 @@ ImDrawListSharedData::ImDrawListSharedData()
         ArcFastVtx[i] = ImVec2(ImCos(a), ImSin(a));
     }
     memset(CircleSegmentCounts, 0, sizeof(CircleSegmentCounts)); // This will be set by SetCircleSegmentMaxError()
+    TexUvLines = NULL;
 }
 
 void ImDrawListSharedData::SetCircleSegmentMaxError(float max_error)
@@ -675,13 +676,26 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
         const float AA_SIZE = 1.0f;
         const ImU32 col_trans = col & ~IM_COL32_A_MASK;
 
-        const int idx_count = thick_line ? count * 18 : count * 12;
-        const int vtx_count = thick_line ? points_count * 4 : points_count * 3;
+        // Thicknesses <1.0 should behave like thickness 1.0
+        thickness = ImMax(thickness, 1.0f);
+        const int integer_thickness = (int)thickness;
+        const float fractional_thickness = thickness - integer_thickness;
+
+        // Do we want to draw this line using a texture?
+        // - For now, only draw integer-width lines using textures to avoid issues with the way scaling occurs, could be improved.
+        // - If AA_SIZE is not 1.0f we cannot use the texture path.
+        const bool use_texture = (Flags & ImDrawListFlags_AntiAliasedLinesUseTex) && (integer_thickness < IM_DRAWLIST_TEX_LINES_WIDTH_MAX) && (fractional_thickness <= 0.00001f);
+
+        // We should never hit this, because NewFrame() doesn't set ImDrawListFlags_AntiAliasedLinesUseTex unless ImFontAtlasFlags_NoBakedLines is off
+        IM_ASSERT_PARANOID(!use_texture || !(_Data->Font->ContainerAtlas->Flags & ImFontAtlasFlags_NoBakedLines));
+
+        const int idx_count = use_texture ? (count * 6) : (thick_line ? count * 18 : count * 12);
+        const int vtx_count = use_texture ? (points_count * 2) : (thick_line ? points_count * 4 : points_count * 3);
         PrimReserve(idx_count, vtx_count);
 
         // Temporary buffer
         // The first <points_count> items are normals at each line point, then after that there are either 2 or 4 temp points for each line point
-        ImVec2* temp_normals = (ImVec2*)alloca(points_count * (thick_line ? 5 : 3) * sizeof(ImVec2)); //-V630
+        ImVec2* temp_normals = (ImVec2*)alloca(points_count * ((use_texture || !thick_line) ? 3 : 5) * sizeof(ImVec2)); //-V630
         ImVec2* temp_points = temp_normals + points_count;
 
         // Calculate normals (tangents) for each line segment
@@ -697,14 +711,23 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
         if (!closed)
             temp_normals[points_count - 1] = temp_normals[points_count - 2];
 
-        if (!thick_line)
+        // If we are drawing a one-pixel-wide line without a texture, or a textured line of any width, we only need 2 or 3 vertices per point
+        if (use_texture || !thick_line)
         {
+            // [PATH 1] Texture-based lines (thick or non-thick)
+            // [PATH 2] Non texture-based lines (non-thick)
+
+            // The width of the geometry we need to draw - this is essentially <thickness> pixels for the line itself, plus one pixel for AA
+            // We don't use AA_SIZE here because the +1 is tied to the generated texture and so alternate values won't work without changes to that code
+            const float half_draw_size = use_texture ? ((thickness * 0.5f) + 1) : AA_SIZE;
+
+            // If line is not closed, the first and last points need to be generated differently as there are no normals to blend
             if (!closed)
             {
-                temp_points[0] = points[0] + temp_normals[0] * AA_SIZE;
-                temp_points[1] = points[0] - temp_normals[0] * AA_SIZE;
-                temp_points[(points_count-1)*2+0] = points[points_count-1] + temp_normals[points_count-1] * AA_SIZE;
-                temp_points[(points_count-1)*2+1] = points[points_count-1] - temp_normals[points_count-1] * AA_SIZE;
+                temp_points[0] = points[0] + temp_normals[0] * half_draw_size;
+                temp_points[1] = points[0] - temp_normals[0] * half_draw_size;
+                temp_points[(points_count-1)*2+0] = points[points_count-1] + temp_normals[points_count-1] * half_draw_size;
+                temp_points[(points_count-1)*2+1] = points[points_count-1] - temp_normals[points_count-1] * half_draw_size;
             }
 
             // Generate the indices to form a number of triangles for each line segment, and the vertices for the line edges
@@ -713,15 +736,15 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
             unsigned int idx1 = _VtxCurrentIdx; // Vertex index for start of line segment
             for (int i1 = 0; i1 < count; i1++) // i1 is the first point of the line segment
             {
-                const int i2 = (i1 + 1) == points_count ? 0 : i1 + 1;
-                const unsigned int idx2 = (i1 + 1) == points_count ? _VtxCurrentIdx : idx1 + 3;
+                const int i2 = (i1 + 1) == points_count ? 0 : i1 + 1; // i2 is the second point of the line segment
+                const unsigned int idx2 = ((i1 + 1) == points_count) ? _VtxCurrentIdx : (idx1 + (use_texture ? 2 : 3)); // Vertex index for end of segment
 
                 // Average normals
                 float dm_x = (temp_normals[i1].x + temp_normals[i2].x) * 0.5f;
                 float dm_y = (temp_normals[i1].y + temp_normals[i2].y) * 0.5f;
                 IM_FIXNORMAL2F(dm_x, dm_y);
-                dm_x *= AA_SIZE;
-                dm_y *= AA_SIZE;
+                dm_x *= half_draw_size; // dm_x, dm_y are offset to the outer edge of the AA area
+                dm_y *= half_draw_size;
 
                 // Add temporary vertexes for the outer edges
                 ImVec2* out_vtx = &temp_points[i2 * 2];
@@ -730,28 +753,63 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
                 out_vtx[1].x = points[i2].x - dm_x;
                 out_vtx[1].y = points[i2].y - dm_y;
 
-                // Add indexes for four triangles
-                _IdxWritePtr[0] = (ImDrawIdx)(idx2+0); _IdxWritePtr[1] = (ImDrawIdx)(idx1+0); _IdxWritePtr[2] = (ImDrawIdx)(idx1+2);
-                _IdxWritePtr[3] = (ImDrawIdx)(idx1+2); _IdxWritePtr[4] = (ImDrawIdx)(idx2+2); _IdxWritePtr[5] = (ImDrawIdx)(idx2+0);
-                _IdxWritePtr[6] = (ImDrawIdx)(idx2+1); _IdxWritePtr[7] = (ImDrawIdx)(idx1+1); _IdxWritePtr[8] = (ImDrawIdx)(idx1+0);
-                _IdxWritePtr[9] = (ImDrawIdx)(idx1+0); _IdxWritePtr[10]= (ImDrawIdx)(idx2+0); _IdxWritePtr[11]= (ImDrawIdx)(idx2+1);
-                _IdxWritePtr += 12;
+                if (use_texture)
+                {
+                    // Add indices for two triangles
+                    _IdxWritePtr[0] = (ImDrawIdx)(idx2 + 0); _IdxWritePtr[1] = (ImDrawIdx)(idx1 + 0); _IdxWritePtr[2] = (ImDrawIdx)(idx1 + 1); // Right tri
+                    _IdxWritePtr[3] = (ImDrawIdx)(idx2 + 1); _IdxWritePtr[4] = (ImDrawIdx)(idx1 + 1); _IdxWritePtr[5] = (ImDrawIdx)(idx2 + 0); // Left tri
+                    _IdxWritePtr += 6;
+                }
+                else
+                {
+                    // Add indexes for four triangles
+                    _IdxWritePtr[0] = (ImDrawIdx)(idx2 + 0); _IdxWritePtr[1] = (ImDrawIdx)(idx1 + 0); _IdxWritePtr[2] = (ImDrawIdx)(idx1 + 2); // Right tri 1
+                    _IdxWritePtr[3] = (ImDrawIdx)(idx1 + 2); _IdxWritePtr[4] = (ImDrawIdx)(idx2 + 2); _IdxWritePtr[5] = (ImDrawIdx)(idx2 + 0); // Right tri 2
+                    _IdxWritePtr[6] = (ImDrawIdx)(idx2 + 1); _IdxWritePtr[7] = (ImDrawIdx)(idx1 + 1); _IdxWritePtr[8] = (ImDrawIdx)(idx1 + 0); // Left tri 1
+                    _IdxWritePtr[9] = (ImDrawIdx)(idx1 + 0); _IdxWritePtr[10] = (ImDrawIdx)(idx2 + 0); _IdxWritePtr[11] = (ImDrawIdx)(idx2 + 1); // Left tri 2
+                    _IdxWritePtr += 12;
+                }
 
                 idx1 = idx2;
             }
 
             // Add vertexes for each point on the line
-            for (int i = 0; i < points_count; i++)
+            if (use_texture)
+            {
+                // If we're using textures we only need to emit the left/right edge vertices
+                ImVec4 tex_uvs = _Data->TexUvLines[integer_thickness];
+                if (fractional_thickness != 0.0f)
+                {
+                    const ImVec4 tex_uvs_1 = _Data->TexUvLines[integer_thickness + 1];
+                    tex_uvs.x = tex_uvs.x + (tex_uvs_1.x - tex_uvs.x) * fractional_thickness; // inlined ImLerp()
+                    tex_uvs.y = tex_uvs.y + (tex_uvs_1.y - tex_uvs.y) * fractional_thickness;
+                    tex_uvs.z = tex_uvs.z + (tex_uvs_1.z - tex_uvs.z) * fractional_thickness;
+                    tex_uvs.w = tex_uvs.w + (tex_uvs_1.w - tex_uvs.w) * fractional_thickness;
+                }
+                ImVec2 tex_uv0(tex_uvs.x, tex_uvs.y);
+                ImVec2 tex_uv1(tex_uvs.z, tex_uvs.w);
+                for (int i = 0; i < points_count; i++)
+                {
+                    _VtxWritePtr[0].pos = temp_points[i * 2 + 0]; _VtxWritePtr[0].uv = tex_uv0; _VtxWritePtr[0].col = col; // Left-side outer edge
+                    _VtxWritePtr[1].pos = temp_points[i * 2 + 1]; _VtxWritePtr[1].uv = tex_uv1; _VtxWritePtr[1].col = col; // Right-side outer edge
+                    _VtxWritePtr += 2;
+                }
+            }
+            else
             {
-                _VtxWritePtr[0].pos = points[i];          _VtxWritePtr[0].uv = opaque_uv; _VtxWritePtr[0].col = col;
-                _VtxWritePtr[1].pos = temp_points[i*2+0]; _VtxWritePtr[1].uv = opaque_uv; _VtxWritePtr[1].col = col_trans;
-                _VtxWritePtr[2].pos = temp_points[i*2+1]; _VtxWritePtr[2].uv = opaque_uv; _VtxWritePtr[2].col = col_trans;
-                _VtxWritePtr += 3;
+                // If we're not using a texture, we need the center vertex as well
+                for (int i = 0; i < points_count; i++)
+                {
+                    _VtxWritePtr[0].pos = points[i];              _VtxWritePtr[0].uv = opaque_uv; _VtxWritePtr[0].col = col;       // Center of line
+                    _VtxWritePtr[1].pos = temp_points[i * 2 + 0]; _VtxWritePtr[1].uv = opaque_uv; _VtxWritePtr[1].col = col_trans; // Left-side outer edge
+                    _VtxWritePtr[2].pos = temp_points[i * 2 + 1]; _VtxWritePtr[2].uv = opaque_uv; _VtxWritePtr[2].col = col_trans; // Right-side outer edge
+                    _VtxWritePtr += 3;
+                }
             }
         }
         else
         {
-            // Non texture-based lines (thick): we need to draw the solid line core and thus require four vertices per point
+            // [PATH 2] Non texture-based lines (thick): we need to draw the solid line core and thus require four vertices per point
             const float half_inner_thickness = (thickness - AA_SIZE) * 0.5f;
 
             // If line is not closed, the first and last points need to be generated differently as there are no normals to blend
@@ -823,7 +881,7 @@ void ImDrawList::AddPolyline(const ImVec2* points, const int points_count, ImU32
     }
     else
     {
-        // Non texture-based, Non anti-aliased lines
+        // [PATH 4] Non texture-based, Non anti-aliased lines
         const int idx_count = count * 6;
         const int vtx_count = count * 4;    // FIXME-OPT: Not sharing edges
         PrimReserve(idx_count, vtx_count);
@@ -1663,7 +1721,7 @@ ImFontAtlas::ImFontAtlas()
     TexWidth = TexHeight = 0;
     TexUvScale = ImVec2(0.0f, 0.0f);
     TexUvWhitePixel = ImVec2(0.0f, 0.0f);
-    PackIdMouseCursors = -1;
+    PackIdMouseCursors = PackIdLines = -1;
 }
 
 ImFontAtlas::~ImFontAtlas()
@@ -1691,7 +1749,7 @@ void    ImFontAtlas::ClearInputData()
         }
     ConfigData.clear();
     CustomRects.clear();
-    PackIdMouseCursors = -1;
+    PackIdMouseCursors = PackIdLines = -1;
 }
 
 void    ImFontAtlas::ClearTexData()
@@ -2331,6 +2389,36 @@ static void ImFontAtlasBuildRenderDefaultTexData(ImFontAtlas* atlas)
     atlas->TexUvWhitePixel = ImVec2((r->X + 0.5f) * atlas->TexUvScale.x, (r->Y + 0.5f) * atlas->TexUvScale.y);
 }
 
+static void ImFontAtlasBuildRenderLinesTexData(ImFontAtlas* atlas)
+{
+    if (atlas->Flags & ImFontAtlasFlags_NoBakedLines)
+        return;
+
+    // This generates a triangular shape in the texture, with the various line widths stacked on top of each other to allow interpolation between them
+    ImFontAtlasCustomRect* r = atlas->GetCustomRectByIndex(atlas->PackIdLines);
+    IM_ASSERT(r->IsPacked());
+    for (unsigned int n = 0; n < IM_DRAWLIST_TEX_LINES_WIDTH_MAX + 1; n++) // +1 because of the zero-width row
+    {
+        // Each line consists of at least two empty pixels at the ends, with a line of solid pixels in the middle
+        unsigned int y = n;
+        unsigned int line_width = n;
+        unsigned int pad_left = (r->Width - line_width) / 2;
+        unsigned int pad_right = r->Width - (pad_left + line_width);
+
+        // Write each slice
+        IM_ASSERT(pad_left + line_width + pad_right == r->Width && y < r->Height); // Make sure we're inside the texture bounds before we start writing pixels
+        unsigned char* write_ptr = &atlas->TexPixelsAlpha8[r->X + ((r->Y + y) * atlas->TexWidth)];
+        memset(write_ptr, 0x00, pad_left);
+        memset(write_ptr + pad_left, 0xFF, line_width);
+        memset(write_ptr + pad_left + line_width, 0x00, pad_right);
+
+        // Calculate UVs for this line
+        ImVec2 uv0 = ImVec2((float)(r->X + pad_left - 1), (float)(r->Y + y)) * atlas->TexUvScale;
+        ImVec2 uv1 = ImVec2((float)(r->X + pad_left + line_width + 1), (float)(r->Y + y + 1)) * atlas->TexUvScale;
+        float half_v = (uv0.y + uv1.y) * 0.5f; // Calculate a constant V in the middle of the row to avoid sampling artifacts
+        atlas->TexUvLines[n] = ImVec4(uv0.x, half_v, uv1.x, half_v);
+    }
+}
 
 // Note: this is called / shared by both the stb_truetype and the FreeType builder
 void ImFontAtlasBuildInit(ImFontAtlas* atlas)
@@ -2343,6 +2431,14 @@ void ImFontAtlasBuildInit(ImFontAtlas* atlas)
         else
             atlas->PackIdMouseCursors = atlas->AddCustomRectRegular(2, 2);
     }
+
+    // Register texture region for thick lines
+    // The +2 here is to give space for the end caps, whilst height +1 is to accommodate the fact we have a zero-width row
+    if (atlas->PackIdLines < 0)
+    {
+        if (!(atlas->Flags & ImFontAtlasFlags_NoBakedLines))
+            atlas->PackIdLines = atlas->AddCustomRectRegular(IM_DRAWLIST_TEX_LINES_WIDTH_MAX + 2, IM_DRAWLIST_TEX_LINES_WIDTH_MAX + 1);
+    }
 }
 
 // This is called/shared by both the stb_truetype and the FreeType builder.
@@ -2351,6 +2447,7 @@ void ImFontAtlasBuildFinish(ImFontAtlas* atlas)
     // Render into our custom data blocks
     IM_ASSERT(atlas->TexPixelsAlpha8 != NULL);
     ImFontAtlasBuildRenderDefaultTexData(atlas);
+    ImFontAtlasBuildRenderLinesTexData(atlas);
 
     // Register custom rectangle glyphs
     for (int i = 0; i < atlas->CustomRects.Size; i++)

imgui_internal.h

@@ -544,6 +544,7 @@ struct IMGUI_API ImDrawListSharedData
     // [Internal] Lookup tables
     ImVec2          ArcFastVtx[12 * IM_DRAWLIST_ARCFAST_TESSELLATION_MULTIPLIER];  // FIXME: Bake rounded corners fill/borders in atlas
     ImU8            CircleSegmentCounts[64];    // Precomputed segment count for given radius (array index + 1) before we calculate it dynamically (to avoid calculation overhead)
+    const ImVec4*   TexUvLines;                 // UV of anti-aliased lines in the atlas
 
     ImDrawListSharedData();
     void SetCircleSegmentMaxError(float max_error);