imgui_freetype: fixed issue where glyph advances would incorrectly be snapped to pixels.

Author: ocornut

docs/CHANGELOG.txt

@@ -47,6 +47,10 @@ Breaking changes:
 Other changes:
 
 - ImDrawList: texture baked storage for thick line reduced from ~64x64 to ~32x32. (#3245)
+- imgui_freetype: fixed issue where glyph advances would incorrectly be
+  snapped to pixels. Effectively it would only be noticeable when hinting
+  is disabled with ImGuiFreeTypeBuilderFlags_NoHinting, as hinting itself
+  snaps glyph advances.
 - Examples: DirectX12: Reduced number of frame in flight from 3 to 2 in
   provided example, to reduce latency.
 - Examples: Vulkan: better handle VK_SUBOPTIMAL_KHR being returned by

misc/freetype/imgui_freetype.cpp

@@ -104,6 +104,9 @@ static FT_Error ImGuiLunasvgPortPresetSlot(FT_GlyphSlot slot, FT_Bool cache, FT_
 // Code
 //-------------------------------------------------------------------------
 
+#define FT_CEIL(X)      (((X + 63) & -64) / 64) // From SDL_ttf: Handy routines for converting from fixed point
+#define FT_SCALEFACTOR  64.0f
+
 namespace
 {
     // Glyph metrics:
@@ -182,9 +185,6 @@ namespace
         float           InvRasterizationDensity;
     };
 
-    // From SDL_ttf: Handy routines for converting from fixed point
-    #define FT_CEIL(X)  (((X + 63) & -64) / 64)
-
     bool FreeTypeFont::InitFont(FT_Library ft_library, const ImFontConfig& cfg, unsigned int extra_font_builder_flags)
     {
         FT_Error error = FT_New_Memory_Face(ft_library, (uint8_t*)cfg.FontData, (uint32_t)cfg.FontDataSize, (uint32_t)cfg.FontNo, &Face);
@@ -316,7 +316,7 @@ namespace
         out_glyph_info->Height = (int)ft_bitmap->rows;
         out_glyph_info->OffsetX = Face->glyph->bitmap_left;
         out_glyph_info->OffsetY = -Face->glyph->bitmap_top;
-        out_glyph_info->AdvanceX = (float)FT_CEIL(slot->advance.x);
+        out_glyph_info->AdvanceX = (float)slot->advance.x / FT_SCALEFACTOR;
         out_glyph_info->IsColored = (ft_bitmap->pixel_mode == FT_PIXEL_MODE_BGRA);
 
         return ft_bitmap;