Fonts: calling ImFontAtlas::Clear() mid-frame without re-adding a font will lead to a more explicit crash. (#9067)

+ reformat Changelog.

docs/CHANGELOG.txt

@@ -79,17 +79,21 @@ Other Changes:
     to auto-size on a given axis would keep marking ini settings as dirty.
 - Disabled: fixed a bug when a previously enabled item that got nav focus
   and then turns disabled could still be activated using keyboard. (#9036)
-- InputText: when buffer is not resizable, trying to paste contents that
-  cannot fit will now truncate text to nearest UTF-8 codepoint boundaries,
-  instead of completely ignoring the paste. (#9029)
-- InputText: avoid continuously overwriting ownership of ImGuiKey_Enter/_KeypadEnter
-  keys in order to allow e.g. external Shortcut override behavior. (#9004)
-- InputText: when using a callback to reduce/manipulate the value of BufTextLen,
-  we do not require anymore that CursorPos be clamped by user code. (#9029)
-- InputTextMultiline: fixed a crash when using ImGuiInputTextFlags_WordWrap and
-  resizing the parent window while keeping the multi-line field active (which is
-  most typically achieved when resizing programmatically or via a docking layout
-  reacting to a platform window resize). (#3237, #9007) [@anton-kl, @ocornut]
+- InputText:
+  - When buffer is not resizable, trying to paste contents that cannot
+    fit will now truncate text to nearest UTF-8 codepoint boundaries,
+    instead of completely ignoring the paste. (#9029)
+  - Avoid continuously overwriting ownership of ImGuiKey_Enter/_KeypadEnter
+    keys in order to allow e.g. external Shortcut override behavior. (#9004)
+  - When using a callback to reduce/manipulate the value of BufTextLen,
+    we do not require anymore that CursorPos be clamped by user code. (#9029)
+  - InputTextMultiline: fixed a crash when using ImGuiInputTextFlags_WordWrap and
+    resizing the parent window while keeping the multi-line field active (which is
+    most typically achieved when resizing programmatically or via a docking layout
+    reacting to a platform window resize). (#3237, #9007) [@anton-kl, @ocornut]
+- Fonts:
+  - Calling ImFontAtlas::Clear() mid-frame without re-adding a font will
+    lead to a more explicit crash.
 - Textures:
   - Fixed an issue preventing multi-contexts from using each others' fonts
     if context 2 runs after context 1's Render() function. (#9039)

imgui.h

@@ -3638,7 +3638,7 @@ struct ImFontAtlas
     IMGUI_API ImFont*           AddFontFromMemoryCompressedBase85TTF(const char* compressed_font_data_base85, float size_pixels = 0.0f, const ImFontConfig* font_cfg = NULL, const ImWchar* glyph_ranges = NULL);              // 'compressed_font_data_base85' still owned by caller. Compress with binary_to_compressed_c.cpp with -base85 parameter.
     IMGUI_API void              RemoveFont(ImFont* font);
 
-    IMGUI_API void              Clear();                    // Clear everything (input fonts, output glyphs/textures)
+    IMGUI_API void              Clear();                    // Clear everything (input fonts, output glyphs/textures).
     IMGUI_API void              CompactCache();             // Compact cached glyphs and texture.
     IMGUI_API void              SetFontLoader(const ImFontLoader* font_loader); // Change font loader at runtime.
 

imgui_draw.cpp

@@ -2656,6 +2656,7 @@ ImFontAtlas::~ImFontAtlas()
     TexData = NULL;
 }
 
+// If you call this mid-frame, you would need to add new font and bind them!
 void ImFontAtlas::Clear()
 {
     bool backup_renderer_has_textures = RendererHasTextures;
@@ -2706,6 +2707,8 @@ void ImFontAtlas::ClearFonts()
 {
     // FIXME-NEWATLAS: Illegal to remove currently bound font.
     IM_ASSERT(!Locked && "Cannot modify a locked ImFontAtlas!");
+    for (ImFont* font : Fonts)
+        ImFontAtlasBuildNotifySetFont(this, font, NULL);
     ImFontAtlasBuildDestroy(this);
     ClearInputData();
     Fonts.clear_delete();
@@ -3200,7 +3203,7 @@ ImFont* ImFontAtlas::AddFontFromMemoryCompressedBase85TTF(const char* compressed
 
 // On font removal we need to remove references (otherwise we could queue removal?)
 // We allow old_font == new_font which forces updating all values (e.g. sizes)
-static void ImFontAtlasBuildNotifySetFont(ImFontAtlas* atlas, ImFont* old_font, ImFont* new_font)
+void ImFontAtlasBuildNotifySetFont(ImFontAtlas* atlas, ImFont* old_font, ImFont* new_font)
 {
     for (ImDrawListSharedData* shared_data : atlas->DrawListSharedDatas)
     {

imgui_internal.h

@@ -3856,6 +3856,7 @@ IMGUI_API void              ImFontAtlasBuildInit(ImFontAtlas* atlas);
 IMGUI_API void              ImFontAtlasBuildDestroy(ImFontAtlas* atlas);
 IMGUI_API void              ImFontAtlasBuildMain(ImFontAtlas* atlas);
 IMGUI_API void              ImFontAtlasBuildSetupFontLoader(ImFontAtlas* atlas, const ImFontLoader* font_loader);
+IMGUI_API void              ImFontAtlasBuildNotifySetFont(ImFontAtlas* atlas, ImFont* old_font, ImFont* new_font);
 IMGUI_API void              ImFontAtlasBuildUpdatePointers(ImFontAtlas* atlas);
 IMGUI_API void              ImFontAtlasBuildRenderBitmapFromString(ImFontAtlas* atlas, int x, int y, int w, int h, const char* in_str, char in_marker_char);
 IMGUI_API void              ImFontAtlasBuildClear(ImFontAtlas* atlas); // Clear output and custom rects