Text: Tweaked rendering of three-dots "..." ellipsis variant. Baking more data. (#2775, #4269)

Ideally we're bake a single glyph but it's currently difficult to setup in our font building process.

docs/CHANGELOG.txt

@@ -40,6 +40,7 @@ All changes:
 - Text: Fix clipping of single-character "..." ellipsis (U+2026 or U+0085) when font
   is scaled. Scaling wasn't taken into account, leading to ellipsis character straying
   slightly out of its expected boundaries. (#2775)
+- Text: Tweaked rendering of three-dots "..." ellipsis variant. (#2775, #4269)
 
 
 -----------------------------------------------------------------------

imgui.cpp

@@ -3261,29 +3261,10 @@ void ImGui::RenderTextEllipsis(ImDrawList* draw_list, const ImVec2& pos_min, con
         const float font_size = draw_list->_Data->FontSize;
         const float font_scale = font_size / font->FontSize;
         const char* text_end_ellipsis = NULL;
-
-        ImWchar ellipsis_char = font->EllipsisChar;
-        int ellipsis_char_count = 1;
-        if (ellipsis_char == (ImWchar)-1)
-        {
-            ellipsis_char = font->DotChar;
-            ellipsis_char_count = 3;
-        }
-        const ImFontGlyph* glyph = font->FindGlyph(ellipsis_char);
-
-        float ellipsis_glyph_width = glyph->X1 * font_scale;    // Width of the glyph with no padding on either side
-        float ellipsis_total_width = ellipsis_glyph_width;      // Full width of entire ellipsis
-
-        if (ellipsis_char_count > 1)
-        {
-            // Full ellipsis size without free spacing after it.
-            const float spacing_between_dots = 1.0f * font_scale;
-            ellipsis_glyph_width = (glyph->X1 - glyph->X0) * font_scale + spacing_between_dots;
-            ellipsis_total_width = ellipsis_glyph_width * (float)ellipsis_char_count - spacing_between_dots;
-        }
+        const float ellipsis_width = font->EllipsisWidth * font_scale;
 
         // We can now claim the space between pos_max.x and ellipsis_max.x
-        const float text_avail_width = ImMax((ImMax(pos_max.x, ellipsis_max_x) - ellipsis_total_width) - pos_min.x, 1.0f);
+        const float text_avail_width = ImMax((ImMax(pos_max.x, ellipsis_max_x) - ellipsis_width) - pos_min.x, 1.0f);
         float text_size_clipped_x = font->CalcTextSizeA(font_size, text_avail_width, 0.0f, text, text_end_full, &text_end_ellipsis).x;
         if (text == text_end_ellipsis && text_end_ellipsis < text_end_full)
         {
@@ -3300,13 +3281,10 @@ void ImGui::RenderTextEllipsis(ImDrawList* draw_list, const ImVec2& pos_min, con
 
         // Render text, render ellipsis
         RenderTextClippedEx(draw_list, pos_min, ImVec2(clip_max_x, pos_max.y), text, text_end_ellipsis, &text_size, ImVec2(0.0f, 0.0f));
-        float ellipsis_x = pos_min.x + text_size_clipped_x;
-        if (ellipsis_x + ellipsis_total_width <= ellipsis_max_x)
-            for (int i = 0; i < ellipsis_char_count; i++)
-            {
-                font->RenderChar(draw_list, font_size, ImVec2(ellipsis_x, pos_min.y), GetColorU32(ImGuiCol_Text), ellipsis_char);
-                ellipsis_x += ellipsis_glyph_width;
-            }
+        ImVec2 ellipsis_pos = ImFloor(ImVec2(pos_min.x + text_size_clipped_x, pos_min.y));
+        if (ellipsis_pos.x + ellipsis_width <= ellipsis_max_x)
+            for (int i = 0; i < font->EllipsisCharCount; i++, ellipsis_pos.x += font->EllipsisCharStep * font_scale)
+                font->RenderChar(draw_list, font_size, ellipsis_pos, GetColorU32(ImGuiCol_Text), font->EllipsisChar);
     }
     else
     {

imgui.h

@@ -2859,8 +2859,10 @@ struct ImFont
     const ImFontConfig*         ConfigData;         // 4-8   // in  //            // Pointer within ContainerAtlas->ConfigData
     short                       ConfigDataCount;    // 2     // in  // ~ 1        // Number of ImFontConfig involved in creating this font. Bigger than 1 when merging multiple font sources into one ImFont.
     ImWchar                     FallbackChar;       // 2     // out // = FFFD/'?' // Character used if a glyph isn't found.
-    ImWchar                     EllipsisChar;       // 2     // out // = '...'    // Character used for ellipsis rendering.
-    ImWchar                     DotChar;            // 2     // out // = '.'      // Character used for ellipsis rendering (if a single '...' character isn't found)
+    ImWchar                     EllipsisChar;       // 2     // out // = '...'/'.'// Character used for ellipsis rendering.
+    short                       EllipsisCharCount;  // 1     // out // 1 or 3
+    float                       EllipsisWidth;      // 4     // out               // Width
+    float                       EllipsisCharStep;   // 4     // out               // Step between characters when EllipsisCount > 0
     bool                        DirtyLookupTables;  // 1     // out //
     float                       Scale;              // 4     // in  // = 1.f      // Base font scale, multiplied by the per-window font scale which you can adjust with SetWindowFontScale()
     float                       Ascent, Descent;    // 4+4   // out //            // Ascent: distance from top to bottom of e.g. 'A' [0..FontSize]

imgui_draw.cpp

@@ -3112,7 +3112,8 @@ ImFont::ImFont()
     FallbackAdvanceX = 0.0f;
     FallbackChar = (ImWchar)-1;
     EllipsisChar = (ImWchar)-1;
-    DotChar = (ImWchar)-1;
+    EllipsisWidth = EllipsisCharStep = 0.0f;
+    EllipsisCharCount = 0;
     FallbackGlyph = NULL;
     ContainerAtlas = NULL;
     ConfigData = NULL;
@@ -3200,8 +3201,20 @@ void ImFont::BuildLookupTable()
     const ImWchar dots_chars[] = { (ImWchar)'.', (ImWchar)0xFF0E };
     if (EllipsisChar == (ImWchar)-1)
         EllipsisChar = FindFirstExistingGlyph(this, ellipsis_chars, IM_ARRAYSIZE(ellipsis_chars));
-    if (DotChar == (ImWchar)-1)
-        DotChar = FindFirstExistingGlyph(this, dots_chars, IM_ARRAYSIZE(dots_chars));
+    const ImWchar dot_char = FindFirstExistingGlyph(this, dots_chars, IM_ARRAYSIZE(dots_chars));
+    if (EllipsisChar != (ImWchar)-1)
+    {
+        EllipsisCharCount = 1;
+        EllipsisWidth = EllipsisCharStep = FindGlyph(EllipsisChar)->X1;
+    }
+    else if (dot_char != (ImWchar)-1)
+    {
+        const ImFontGlyph* glyph = FindGlyph(dot_char);
+        EllipsisChar = dot_char;
+        EllipsisCharCount = 3;
+        EllipsisCharStep = (glyph->X1 - glyph->X0) + 1.0f;
+        EllipsisWidth = EllipsisCharStep * 3.0f - 1.0f;
+    }
 
     // Setup fallback character
     const ImWchar fallback_chars[] = { (ImWchar)IM_UNICODE_CODEPOINT_INVALID, (ImWchar)'?', (ImWchar)' ' };