ImFont: Store the texture surface used to get an idea of how costly each font is.

imgui.h

@@ -1367,6 +1367,7 @@ struct ImFont
     ImFontConfig*               ConfigData;         //              // Pointer within ContainerAtlas->ConfigData
     ImFontAtlas*                ContainerAtlas;     //              // What we has been loaded into
     float                       Ascent, Descent;    //              // Ascent: distance from top to bottom of e.g. 'A' [0..FontSize]
+    int                         MetricsTotalSurface;//              // Total surface in pixels to get an idea of the font rasterization/texture cost (not exact, we approximate the cost of padding between glyphs)
 
     // Methods
     IMGUI_API ImFont();

imgui_demo.cpp

@@ -1750,10 +1750,11 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
                 ImGui::SameLine(); ShowHelpMarker("Note than the default embedded font is NOT meant to be scaled.\n\nFont are currently rendered into bitmaps at a given size at the time of building the atlas. You may oversample them to get some flexibility with scaling. You can also render at multiple sizes and select which one to use at runtime.\n\n(Glimmer of hope: the atlas system should hopefully be rewritten in the future to make scaling more natural and automatic.)");
                 ImGui::Text("Ascent: %f, Descent: %f, Height: %f", font->Ascent, font->Descent, font->Ascent - font->Descent);
                 ImGui::Text("Fallback character: '%c' (%d)", font->FallbackChar, font->FallbackChar);
+                ImGui::Text("Texture surface: %d pixels (approx)", font->MetricsTotalSurface);
                 for (int config_i = 0; config_i < font->ConfigDataCount; config_i++)
                 {
                     ImFontConfig* cfg = &font->ConfigData[config_i];
-                    ImGui::BulletText("Input %d: \'%s\'\nOversample: (%d,%d), PixelSnapH: %d", config_i, cfg->Name, cfg->OversampleH, cfg->OversampleV, cfg->PixelSnapH);
+                    ImGui::BulletText("Input %d: \'%s\', Oversample: (%d,%d), PixelSnapH: %d", config_i, cfg->Name, cfg->OversampleH, cfg->OversampleV, cfg->PixelSnapH);
                 }
                 if (ImGui::TreeNode("Glyphs", "Glyphs (%d)", font->Glyphs.Size))
                 {

imgui_draw.cpp

@@ -1386,7 +1386,7 @@ bool    ImFontAtlas::Build()
     {
         ImFontConfig& cfg = ConfigData[input_i];
         ImFontTempBuildData& tmp = tmp_array[input_i];
-        ImFont* dst_font = cfg.DstFont;
+        ImFont* dst_font = cfg.DstFont; // We can have multiple input fonts writing into a same destination font (when using MergeMode=true)
 
         float font_scale = stbtt_ScaleForPixelHeight(&tmp.FontInfo, cfg.SizePixels);
         int unscaled_ascent, unscaled_descent, unscaled_line_gap;
@@ -1403,6 +1403,7 @@ bool    ImFontAtlas::Build()
             dst_font->Ascent = ascent;
             dst_font->Descent = descent;
             dst_font->Glyphs.resize(0);
+            dst_font->MetricsTotalSurface = 0;
         }
         dst_font->ConfigDataCount++;
         float off_y = (cfg.MergeMode && cfg.MergeGlyphCenterV) ? (ascent - dst_font->Ascent) * 0.5f : 0.0f;
@@ -1435,6 +1436,7 @@ bool    ImFontAtlas::Build()
                 glyph.XAdvance = (pc.xadvance + cfg.GlyphExtraSpacing.x);  // Bake spacing into XAdvance
                 if (cfg.PixelSnapH)
                     glyph.XAdvance = (float)(int)(glyph.XAdvance + 0.5f);
+                dst_font->MetricsTotalSurface += (int)(glyph.X1 - glyph.X0 + 1.99f) * (int)(glyph.Y1 - glyph.Y0 + 1.99f); // +1 to account for average padding, +0.99 to round
             }
         }
         cfg.DstFont->BuildLookupTable();
@@ -1703,6 +1705,7 @@ void    ImFont::Clear()
     ConfigData = NULL;
     ContainerAtlas = NULL;
     Ascent = Descent = 0.0f;
+    MetricsTotalSurface = 0;
 }
 
 void ImFont::BuildLookupTable()