(Breaking) Fonts: remove ImFontConfig::PixelSnapV. Post-rescale GlyphOffset is always rounded.

Amend 99f6b305c, 99bca397d8.

docs/CHANGELOG.txt

@@ -50,17 +50,21 @@ Breaking Changes:
   - This will invalidate hashes (stored in .ini data) for Tables and Windows
     that are using the "###" operators. (#713, #1698)
 - Renamed helper macro IM_ARRAYSIZE() -> IM_COUNTOF(). Kept redirection/legacy name.
-- Fonts: Fixed handling of `ImFontConfig::FontDataOwnedByAtlas = false` which
+- Fonts:
+  - Fixed handling of `ImFontConfig::FontDataOwnedByAtlas = false` which
     did erroneously make a copy of the font data, essentially defeating the purpose
     of this flag and wasting memory (undetected since July 2015 and now spotted
     by @TellowKrinkle, this is perhaps the oldest bug in Dear ImGui history,
     albeit for a rarely used feature!) (#9086, #8465)
     HOWEVER, fixing this bug is likely to surface bugs in user/app code:
     - Prior to 1.92, font data only needs to be available during the atlas->AddFontXXX() call.
-  - Since 1.92, font data needs to available until atlas->RemoveFont(), or more typically
+      Since 1.92, font data needs to available until atlas->RemoveFont(), or more typically
       until a shutdown of the owning context or font atlas.
-  - The fact that handling of `FontDataOwnedByAtlas = false` was broken
+    - The fact that handling of `FontDataOwnedByAtlas = false` was broken bypassed
-    bypassed the issue altogether.
+      the issue altogether.
+  - Removed ImFontConfig::PixelSnapV added in 1.92 which turns out is unnecessary
+    (and misdocumented). Post-rescale GlyphOffset is always rounded.
+
 
 Other Changes:
 
@@ -70,7 +74,7 @@ Other Changes:
   - imgui_freetype: fixed overwriting ImFontConfig::PixelSnapH when hinting
     is enabled, creating side-effects when later disabling hinting or
     dynamically switching to stb_truetype rasterizer.
-  which would prevent
+  - Post rescale GlyphOffset is always rounded.
 - Textures:
   - Fixed a building issue when ImTextureID is defined as a struct.
   - Fixed displaying texture # in Metrics/Debugger window.

imgui.cpp

@@ -394,13 +394,13 @@ IMPLEMENTING SUPPORT for ImGuiBackendFlags_RendererHasTextures:
  When you are not sure about an old symbol or function name, try using the Search/Find function of your IDE to look for comments or references in all imgui files.
  You can read releases logs https://github.com/ocornut/imgui/releases for more details.
 
+ - 2025/12/23 (1.92.6) - Fonts: removed ImFontConfig::PixelSnapV added in 1.92 which turns out is unnecessary (and misdocumented). Post-rescale GlyphOffset is always rounded.
  - 2025/12/17 (1.92.6) - Renamed helper macro IM_ARRAYSIZE() -> IM_COUNTOF(). Kept redirection/legacy name for now.
  - 2025/12/11 (1.92.6) - Hashing: handling of "###" operator to reset to seed within a string identifier doesn't include the "###" characters in the output hash anymore.
                          - Before: GetID("Hello###World") == GetID("###World") != GetID("World");
                          - Now:    GetID("Hello###World") == GetID("###World") == GetID("World");
                          - This has the property of facilitating concatenating and manipulating identifiers using "###", and will allow fixing other dangling issues.
-                         - This will invalidate hashes (stored in .ini data) for Tables and Windows!
+                         - This will invalidate hashes (stored in .ini data) for Tables and Windows that are using the "###" operators. (#713, #1698)
-    that are using the "###" operators. (#713, #1698)
  - 2025/11/24 (1.92.6) - Fonts: Fixed handling of `ImFontConfig::FontDataOwnedByAtlas = false` which did erroneously make a copy of the font data, essentially defeating the purpose of this flag and wasting memory.
                          (trivia: undetected since July 2015, this is perhaps the oldest bug in Dear ImGui history, albeit for a rarely used feature, see #9086)
                          HOWEVER, fixing this bug is likely to surface bugs in user code using `FontDataOwnedByAtlas = false`.
@@ -1265,7 +1265,7 @@ IMPLEMENTING SUPPORT for ImGuiBackendFlags_RendererHasTextures:
 #define IMGUI_DEBUG_NAV_RECTS       0   // Display the reference navigation rectangle for each window
 
 // Default font size if unspecified in both style.FontSizeBase and AddFontXXX() calls.
-static const float FONT_DEFAULT_SIZE = 20.0f;
+static const float FONT_DEFAULT_SIZE_BASE = 20.0f;
 
 // When using Ctrl+Tab (or Gamepad Square+L/R) we delay the visual a little in order to reduce visual noise doing a fast switch.
 static const float NAV_WINDOWING_HIGHLIGHT_DELAY            = 0.20f;    // Time before the highlight and screen dimming starts fading in
@@ -8903,7 +8903,7 @@ void ImGui::UpdateFontsNewFrame()
     // Apply default font size the first time
     ImFont* font = ImGui::GetDefaultFont();
     if (g.Style.FontSizeBase <= 0.0f)
-        g.Style.FontSizeBase = (font->LegacySize > 0.0f ? font->LegacySize : FONT_DEFAULT_SIZE);
+        g.Style.FontSizeBase = (font->LegacySize > 0.0f ? font->LegacySize : FONT_DEFAULT_SIZE_BASE);
 
     // Set initial font
     g.Font = font;

imgui.h

@@ -30,7 +30,7 @@
 // Library Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals, e.g. '#if IMGUI_VERSION_NUM >= 12345')
 #define IMGUI_VERSION       "1.92.6 WIP"
-#define IMGUI_VERSION_NUM   19257
+#define IMGUI_VERSION_NUM   19258
 #define IMGUI_HAS_TABLE             // Added BeginTable() - from IMGUI_VERSION_NUM >= 18000
 #define IMGUI_HAS_TEXTURES          // Added ImGuiBackendFlags_RendererHasTextures - from IMGUI_VERSION_NUM >= 19198
 
@@ -3528,7 +3528,6 @@ struct ImFontConfig
     // Options
     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.
     bool            PixelSnapH;             // false    // Align every glyph AdvanceX to pixel boundaries. Prevents fractional font size from working correctly! Useful e.g. if you are merging a non-pixel aligned font with the default font. If enabled, you can set OversampleH/V to 1.
-    bool            PixelSnapV;             // false    // Align Scaled GlyphOffset.y to pixel boundaries. Prevents fractional font size from working correctly!.
     ImS8            OversampleH;            // 0 (2)    // Rasterize at higher quality for sub-pixel positioning. 0 == auto == 1 or 2 depending on size. Note the difference between 2 and 3 is minimal. You can reduce this to 1 for large glyphs save memory. Read https://github.com/nothings/stb/blob/master/tests/oversample/README.md for details.
     ImS8            OversampleV;            // 0 (1)    // Rasterize at higher quality for sub-pixel positioning. 0 == auto == 1. This is not really useful as we don't use sub-pixel positions on the Y axis.
     ImWchar         EllipsisChar;           // 0        // Explicitly specify Unicode codepoint of ellipsis character. When fonts are being merged first specified ellipsis will be used.
@@ -3553,6 +3552,9 @@ struct ImFontConfig
     const ImFontLoader* FontLoader;         // Custom font backend for this source (default source is the one stored in ImFontAtlas)
     void*           FontLoaderData;         // Font loader opaque storage (per font config)
 
+#ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+    bool            PixelSnapV;             // true    // [Obsoleted in 1.91.6] Align Scaled GlyphOffset.y to pixel boundaries.
+#endif
     IMGUI_API ImFontConfig();
 };
 

imgui_draw.cpp

@@ -3121,11 +3121,11 @@ ImFont* ImFontAtlas::AddFontDefault(const ImFontConfig* font_cfg_template)
         font_cfg.PixelSnapH = true;
     }
     if (font_cfg.SizePixels <= 0.0f)
-        font_cfg.SizePixels = 13.0f * 1.0f;
+        font_cfg.SizePixels = 13.0f; // This only serves (1) as a reference for GlyphOffset.y setting and (2) as a default for pre-1.92 backend.
     if (font_cfg.Name[0] == '\0')
         ImFormatString(font_cfg.Name, IM_COUNTOF(font_cfg.Name), "ProggyClean.ttf");
     font_cfg.EllipsisChar = (ImWchar)0x0085;
-    font_cfg.GlyphOffset.y += 1.0f * IM_TRUNC(font_cfg.SizePixels / 13.0f);  // Add +1 offset per 13 units
+    font_cfg.GlyphOffset.y += 1.0f * (font_cfg.SizePixels / 13.0f); // Add +1 offset per 13 units
 
     int ttf_compressed_size = 0;
     const char* ttf_compressed = GetDefaultCompressedFontDataTTF(&ttf_compressed_size);
@@ -4721,12 +4721,8 @@ static bool ImGui_ImplStbTrueType_FontBakedLoadGlyph(ImFontAtlas* atlas, ImFontC
 
         const float ref_size = baked->OwnerFont->Sources[0]->SizePixels;
         const float offsets_scale = (ref_size != 0.0f) ? (baked->Size / ref_size) : 1.0f;
-        float font_off_x = (src->GlyphOffset.x * offsets_scale);
+        float font_off_x = ImFloor(src->GlyphOffset.x * offsets_scale + 0.5f); // Snap scaled offset.
-        float font_off_y = (src->GlyphOffset.y * offsets_scale);
+        float font_off_y = ImFloor(src->GlyphOffset.y * offsets_scale + 0.5f);
-        if (src->PixelSnapH) // Snap scaled offset. This is to mitigate backward compatibility issues for GlyphOffset, but a better design would be welcome.
-            font_off_x = IM_ROUND(font_off_x);
-        if (src->PixelSnapV)
-            font_off_y = IM_ROUND(font_off_y);
         font_off_x += sub_x;
         font_off_y += sub_y + IM_ROUND(baked->Ascent);
         float recip_h = 1.0f / (oversample_h * rasterizer_density);

misc/freetype/imgui_freetype.cpp

@@ -538,12 +538,8 @@ static bool ImGui_ImplFreeType_FontBakedLoadGlyph(ImFontAtlas* atlas, ImFontConf
 
         const float ref_size = baked->OwnerFont->Sources[0]->SizePixels;
         const float offsets_scale = (ref_size != 0.0f) ? (baked->Size / ref_size) : 1.0f;
-        float font_off_x = (src->GlyphOffset.x * offsets_scale);
+        float font_off_x = ImFloor(src->GlyphOffset.x * offsets_scale + 0.5f); // Snap scaled offset.
-        float font_off_y = (src->GlyphOffset.y * offsets_scale) + baked->Ascent;
+        float font_off_y = ImFloor(src->GlyphOffset.y * offsets_scale + 0.5f) + baked->Ascent;
-        if (src->PixelSnapH || (bd_font_data->UserFlags & ImGuiFreeTypeLoaderFlags_NoHinting) == 0) // Snap scaled offset. This is to mitigate backward compatibility issues for GlyphOffset, but a better design would be welcome.
-            font_off_x = IM_ROUND(font_off_x);
-        if (src->PixelSnapV)
-            font_off_y = IM_ROUND(font_off_y);
         float recip_h = 1.0f / rasterizer_density;
         float recip_v = 1.0f / rasterizer_density;