Fixed ImFontConfig::GlyphExtraSpacing and ImFontConfig::PixelSnapH settings being pulled from the merged/target font settings when merging fonts, instead of being pulled from the source font settings.

docs/CHANGELOG.txt

@@ -47,6 +47,9 @@ Other Changes:
   clipping, more than 16 KB characters are visible in the same low-level ImDrawList::RenderText
   call. ImGui-level functions such as TextUnformatted() are not affected. This is quite rare
   but it will be addressed later). (#3349)
+- Fonts: Fixed ImFontConfig::GlyphExtraSpacing and ImFontConfig::PixelSnapH settings being pulled
+  from the merged/target font settings when merging fonts, instead of being pulled from the source
+  font settings.
 - 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.

imgui.h

@@ -2386,7 +2386,7 @@ struct ImFont
     IMGUI_API void              BuildLookupTable();
     IMGUI_API void              ClearOutputData();
     IMGUI_API void              GrowIndex(int new_size);
-    IMGUI_API void              AddGlyph(ImWchar c, float x0, float y0, float x1, float y1, float u0, float v0, float u1, float v1, float advance_x);
+    IMGUI_API void              AddGlyph(ImFontConfig* src_cfg, ImWchar c, float x0, float y0, float x1, float y1, float u0, float v0, float u1, float v1, float advance_x);
     IMGUI_API void              AddRemapChar(ImWchar dst, ImWchar src, bool overwrite_dst = true); // Makes 'dst' character/glyph points to 'src' character/glyph. Currently needs to be called AFTER fonts have been built.
     IMGUI_API void              SetGlyphVisible(ImWchar c, bool visible);
     IMGUI_API void              SetFallbackChar(ImWchar c);

imgui_draw.cpp

@@ -2285,8 +2285,11 @@ bool    ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
         if (src_tmp.GlyphsCount == 0)
             continue;
 
+        // When merging fonts with MergeMode=true:
+        // - We can have multiple input fonts writing into a same destination font.
+        // - dst_font->ConfigData is != from cfg which is our source configuration.
         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)
+        ImFont* dst_font = cfg.DstFont;
 
         const float font_scale = stbtt_ScaleForPixelHeight(&src_tmp.FontInfo, cfg.SizePixels);
         int unscaled_ascent, unscaled_descent, unscaled_line_gap;
@@ -2300,20 +2303,13 @@ bool    ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
 
         for (int glyph_i = 0; glyph_i < src_tmp.GlyphsCount; glyph_i++)
         {
+            // Register glyph
             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 ? ImFloor((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);
+            dst_font->AddGlyph(&cfg, (ImWchar)codepoint, q.x0 + font_off_x, q.y0 + font_off_y, q.x1 + font_off_x, q.y1 + font_off_y, q.s0, q.t0, q.s1, q.t1, pc.xadvance);
         }
     }
 
@@ -2468,10 +2464,11 @@ void ImFontAtlasBuildFinish(ImFontAtlas* atlas)
         if (r->Font == NULL || r->GlyphID == 0)
             continue;
 
+        // Will ignore ImFontConfig settings: GlyphMinAdvanceX, GlyphMinAdvanceY, GlyphExtraSpacing, PixelSnapH
         IM_ASSERT(r->Font->ContainerAtlas == atlas);
         ImVec2 uv0, uv1;
         atlas->CalcCustomRectUV(r, &uv0, &uv1);
-        r->Font->AddGlyph((ImWchar)r->GlyphID, r->GlyphOffset.x, r->GlyphOffset.y, r->GlyphOffset.x + r->Width, r->GlyphOffset.y + r->Height, uv0.x, uv0.y, uv1.x, uv1.y, r->GlyphAdvanceX);
+        r->Font->AddGlyph(NULL, (ImWchar)r->GlyphID, r->GlyphOffset.x, r->GlyphOffset.y, r->GlyphOffset.x + r->Width, r->GlyphOffset.y + r->Height, uv0.x, uv0.y, uv1.x, uv1.y, r->GlyphAdvanceX);
     }
 
     // Build all fonts lookup tables
@@ -2881,8 +2878,29 @@ void ImFont::GrowIndex(int new_size)
 
 // x0/y0/x1/y1 are offset from the character upper-left layout position, in pixels. Therefore x0/y0 are often fairly close to zero.
 // Not to be mistaken with texture coordinates, which are held by u0/v0/u1/v1 in normalized format (0.0..1.0 on each texture axis).
-void ImFont::AddGlyph(ImWchar codepoint, float x0, float y0, float x1, float y1, float u0, float v0, float u1, float v1, float advance_x)
+// 'cfg' is not necessarily == 'this->ConfigData' because multiple source fonts+configs can be used to build one target font.
+void ImFont::AddGlyph(ImFontConfig* cfg, ImWchar codepoint, float x0, float y0, float x1, float y1, float u0, float v0, float u1, float v1, float advance_x)
 {
+    if (cfg != NULL)
+    {
+        // Clamp & recenter if needed
+        const float advance_x_original = advance_x;
+        advance_x = ImClamp(advance_x, cfg->GlyphMinAdvanceX, cfg->GlyphMaxAdvanceX);
+        if (advance_x != advance_x_original)
+        {
+            float char_off_x = cfg->PixelSnapH ? ImFloor((advance_x - advance_x_original) * 0.5f) : (advance_x - advance_x_original) * 0.5f;
+            x0 += char_off_x;
+            x1 += char_off_x;
+        }
+
+        // Snap to pixel
+        if (cfg->PixelSnapH)
+            advance_x = IM_ROUND(advance_x);
+
+        // Bake spacing
+        advance_x += cfg->GlyphExtraSpacing.x;
+    }
+
     Glyphs.resize(Glyphs.Size + 1);
     ImFontGlyph& glyph = Glyphs.back();
     glyph.Codepoint = (unsigned int)codepoint;
@@ -2895,14 +2913,13 @@ void ImFont::AddGlyph(ImWchar codepoint, float x0, float y0, float x1, float y1,
     glyph.V0 = v0;
     glyph.U1 = u1;
     glyph.V1 = v1;
-    glyph.AdvanceX = advance_x + ConfigData->GlyphExtraSpacing.x;  // Bake spacing into AdvanceX
+    glyph.AdvanceX = advance_x;
-
-    if (ConfigData->PixelSnapH)
-        glyph.AdvanceX = IM_ROUND(glyph.AdvanceX);
 
     // Compute rough surface usage metrics (+1 to account for average padding, +0.99 to round)
+    // We use (U1-U0)*TexWidth instead of X1-X0 to account for oversampling.
+    float pad = ContainerAtlas->TexGlyphPadding + 0.99f;
     DirtyLookupTables = true;
-    MetricsTotalSurface += (int)((glyph.U1 - glyph.U0) * ContainerAtlas->TexWidth + 1.99f) * (int)((glyph.V1 - glyph.V0) * ContainerAtlas->TexHeight + 1.99f);
+    MetricsTotalSurface += (int)((glyph.U1 - glyph.U0) * ContainerAtlas->TexWidth + pad) * (int)((glyph.V1 - glyph.V0) * ContainerAtlas->TexHeight + pad);
 }
 
 void ImFont::AddRemapChar(ImWchar dst, ImWchar src, bool overwrite_dst)

misc/freetype/imgui_freetype.cpp

@@ -544,8 +544,11 @@ bool ImFontAtlasBuildWithFreeType(FT_Library ft_library, ImFontAtlas* atlas, uns
         if (src_tmp.GlyphsCount == 0)
             continue;
 
+        // When merging fonts with MergeMode=true:
+        // - We can have multiple input fonts writing into a same destination font.
+        // - dst_font->ConfigData is != from cfg which is our source configuration.
         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)
+        ImFont* dst_font = cfg.DstFont;
 
         const float ascent = src_tmp.Font.Info.Ascender;
         const float descent = src_tmp.Font.Info.Descender;
@@ -576,14 +579,8 @@ bool ImFontAtlasBuildWithFreeType(FT_Library ft_library, ImFontAtlas* atlas, uns
             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 ? IM_FLOOR((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 x0 = info.OffsetX + font_off_x;
             float y0 = info.OffsetY + font_off_y;
             float x1 = x0 + info.Width;
             float y1 = y0 + info.Height;
@@ -591,7 +588,7 @@ bool ImFontAtlasBuildWithFreeType(FT_Library ft_library, ImFontAtlas* atlas, uns
             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);
+            dst_font->AddGlyph(&cfg, (ImWchar)src_glyph.Codepoint, x0, y0, x1, y1, u0, v0, u1, v1, info.AdvanceX);
         }
 
         src_tmp.Rects = NULL;