Fonts: minor/shallow amends (#6925)

docs/CHANGELOG.txt

@@ -201,6 +201,12 @@ Other changes:
   - Better assert during load when passing truncated font data or wrong data size. (#6822)
   - Ensure calling AddFontXXX function doesn't invalidates ImFont's ConfigData pointers
     prior to building again. (#6825)
+  - Added ImFontConfig::RasterizerDensity field to increase texture size of rendered glyphs
+    without altering other metrics. Among other things, this makes it easier to have zooming code
+    swapping between 2 fonts (e.g. a 100% and a 400% fonts) depending on current scale. (#6925) [@thedmd]
+    Important: if you increase this it is expected that you would render the font with a scale of
+    similar value or magnitude. Merely increasing this without increasing scale may lower quality.
+  - imgui_freetype: Added support for RasterizerDensity. (#6925) [@thedmd]
   - imgui_freetype: Fixed a warning and leak in IMGUI_ENABLE_FREETYPE_LUNASVG support. (#6842, #6591)
 - Inputs: Added IsKeyChordPressed() helper function e.g. IsKeyChordPressed(ImGuiMod_Ctrl | ImGuiKey_S).
   (note that ImGuiMod_Shortcut may be used as an alias for Cmd on OSX and Ctrl on other systems).

imgui.h

@@ -2848,8 +2848,8 @@ struct ImFontConfig
     float           GlyphMaxAdvanceX;       // FLT_MAX  // Maximum AdvanceX for glyphs
     bool            MergeMode;              // false    // Merge into previous ImFont, so you can combine multiple inputs font into one ImFont (e.g. ASCII font + icons + Japanese glyphs). You may want to use GlyphOffset.y when merge font of different heights.
     unsigned int    FontBuilderFlags;       // 0        // Settings for custom font builder. THIS IS BUILDER IMPLEMENTATION DEPENDENT. Leave as zero if unsure.
-    float           RasterizerMultiply;     // 1.0f     // Brighten (>1.0f) or darken (<1.0f) font output. Brightening small fonts may be a good workaround to make them more readable.
+    float           RasterizerMultiply;     // 1.0f     // Linearly brighten (>1.0f) or darken (<1.0f) font output. Brightening small fonts may be a good workaround to make them more readable. This is a silly thing we may remove in the future.
-    float           RasterizerDensity;      // 1.0f     // DPI scale for rasterization. Bigger DPI for higher quality.
+    float           RasterizerDensity;      // 1.0f     // DPI scale for rasterization, not altering other font metrics: make it easy to swap between e.g. a 100% and a 400% fonts for a zooming display. IMPORTANT: If you increase this it is expected that you increase font scale accordingly, otherwise quality may look lowered.
     ImWchar         EllipsisChar;           // -1       // Explicitly specify unicode codepoint of ellipsis character. When fonts are being merged first specified ellipsis will be used.
 
     // [Internal]

imgui_draw.cpp

@@ -2576,7 +2576,7 @@ static bool ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
         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 * cfg.RasterizerDensity) : stbtt_ScaleForMappingEmToPixels(&src_tmp.FontInfo, -cfg.SizePixels * cfg.RasterizerDensity);
+        const float scale = (cfg.SizePixels > 0.0f) ? stbtt_ScaleForPixelHeight(&src_tmp.FontInfo, cfg.SizePixels * cfg.RasterizerDensity) : stbtt_ScaleForMappingEmToPixels(&src_tmp.FontInfo, -cfg.SizePixels * cfg.RasterizerDensity);
         const int padding = atlas->TexGlyphPadding;
         for (int glyph_i = 0; glyph_i < src_tmp.GlyphsList.Size; glyph_i++)
         {

misc/freetype/imgui_freetype.cpp

@@ -6,6 +6,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2023/11/13: added support for ImFontConfig::RasterizationDensity field for scaling render density without scaling metrics.
 //  2023/08/01: added support for SVG fonts, enable by using '#define IMGUI_ENABLE_FREETYPE_LUNASVG' (#6591)
 //  2023/01/04: fixed a packing issue which in some occurrences would prevent large amount of glyphs from being packed correctly.
 //  2021/08/23: fixed crash when FT_Render_Glyph() fails to render a glyph and returns NULL.