Fonts: fixed assertion failure when ImFontAtlasRectEntry::Generation overflows. (#8906)

docs/CHANGELOG.txt

@@ -45,6 +45,8 @@ Other Changes:
 
 - Scrollbar, Style: added configurable style.ScrollbarPadding value and corresponding
   ImGuiStyleVar_ScrollbarPadding enum, instead of hardcoded computed default. (#8895)
+- Fonts: fixed an assertion failure when a rectangle entry has been reused
+  1024 times (e.g. due to constant change of font types). (#8906) [@cfillion]
 - Fixed Bullet() fixed tesselation amount which looked out of place in very large sizes.
 - DrawList: Fixed CloneOutput() unnecessarily taking a copy of the ImDrawListSharedData
   pointer, which could to issue when deleting the cloned list. (#8894, #1860)

imgui_draw.cpp

@@ -4293,6 +4293,8 @@ void ImFontAtlasPackDiscardRect(ImFontAtlas* atlas, ImFontAtlasRectId id)
     index_entry->IsUsed = false;
     index_entry->TargetIndex = builder->RectsIndexFreeListStart;
     index_entry->Generation++;
+    if (index_entry->Generation == 0)
+        index_entry->Generation++; // Keep non-zero on overflow
 
     const int pack_padding = atlas->TexGlyphPadding;
     builder->RectsIndexFreeListStart = index_idx;

imgui_internal.h

@@ -3736,12 +3736,12 @@ inline bool operator==(const ImTextureRef& lhs, const ImTextureRef& rhs)    { re
 inline bool operator!=(const ImTextureRef& lhs, const ImTextureRef& rhs)    { return lhs._TexID != rhs._TexID || lhs._TexData != rhs._TexData; }
 
 // Refer to ImFontAtlasPackGetRect() to better understand how this works.
-#define ImFontAtlasRectId_IndexMask_        (0x000FFFFF)    // 20-bits: index to access builder->RectsIndex[].
+#define ImFontAtlasRectId_IndexMask_        (0x0007FFFF)    // 20-bits signed: index to access builder->RectsIndex[].
 #define ImFontAtlasRectId_GenerationMask_   (0x3FF00000)    // 10-bits: entry generation, so each ID is unique and get can safely detected old identifiers.
 #define ImFontAtlasRectId_GenerationShift_  (20)
-inline int               ImFontAtlasRectId_GetIndex(ImFontAtlasRectId id)       { return id & ImFontAtlasRectId_IndexMask_; }
-inline int               ImFontAtlasRectId_GetGeneration(ImFontAtlasRectId id)  { return (id & ImFontAtlasRectId_GenerationMask_) >> ImFontAtlasRectId_GenerationShift_; }
-inline ImFontAtlasRectId ImFontAtlasRectId_Make(int index_idx, int gen_idx)     { IM_ASSERT(index_idx < ImFontAtlasRectId_IndexMask_ && gen_idx < (ImFontAtlasRectId_GenerationMask_ >> ImFontAtlasRectId_GenerationShift_)); return (ImFontAtlasRectId)(index_idx | (gen_idx << ImFontAtlasRectId_GenerationShift_)); }
+inline int               ImFontAtlasRectId_GetIndex(ImFontAtlasRectId id)       { return (id & ImFontAtlasRectId_IndexMask_); }
+inline unsigned int      ImFontAtlasRectId_GetGeneration(ImFontAtlasRectId id)  { return (unsigned int)(id & ImFontAtlasRectId_GenerationMask_) >> ImFontAtlasRectId_GenerationShift_; }
+inline ImFontAtlasRectId ImFontAtlasRectId_Make(int index_idx, int gen_idx)     { IM_ASSERT(index_idx >= 0 && index_idx <= ImFontAtlasRectId_IndexMask_ && gen_idx <= (ImFontAtlasRectId_GenerationMask_ >> ImFontAtlasRectId_GenerationShift_)); return (ImFontAtlasRectId)(index_idx | (gen_idx << ImFontAtlasRectId_GenerationShift_)); }
 
 // Packed rectangle lookup entry (we need an indirection to allow removing/reordering rectangles)
 // User are returned ImFontAtlasRectId values which are meant to be persistent.
@@ -3751,7 +3751,7 @@ inline ImFontAtlasRectId ImFontAtlasRectId_Make(int index_idx, int gen_idx)
 struct ImFontAtlasRectEntry
 {
     int                 TargetIndex : 20;   // When Used: ImFontAtlasRectId -> into Rects[]. When unused: index to next unused RectsIndex[] slot to consume free-list.
-    int                 Generation : 10;    // Increased each time the entry is reused for a new rectangle.
+    unsigned int        Generation : 10;    // Increased each time the entry is reused for a new rectangle.
     unsigned int        IsUsed : 1;
 };