Textures: fixed an issue preventing multi-contexts from using each others' fonts if context 2 runs after context 1's Render() function. (#9039)

docs/CHANGELOG.txt

@@ -60,6 +60,9 @@ Other Changes:
   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]
+- Textures:
+  - Fixed an issue preventing multi-contexts from using each others' fonts
+    if context 2 runs after context 1's Render() function. (#9039)
 - MultiSelect: added ImGuiMultiSelectFlags_NoSelectOnRightClick to disable default
   right-click processing, which selects item on mouse down and is designed for
   context-menus. (#8200, #9015)

imgui_draw.cpp

@@ -3909,6 +3909,11 @@ void ImFontAtlasRemoveDrawListSharedData(ImFontAtlas* atlas, ImDrawListSharedDat
 void ImFontAtlasUpdateDrawListsTextures(ImFontAtlas* atlas, ImTextureRef old_tex, ImTextureRef new_tex)
 {
     for (ImDrawListSharedData* shared_data : atlas->DrawListSharedDatas)
+    {
+        // If Context 2 uses font owned by Context 1 which already called EndFrame()/Render(), we don't want to mess with draw commands for Context 1
+        if (shared_data->Context && !shared_data->Context->WithinFrameScope)
+            continue;
+
         for (ImDrawList* draw_list : shared_data->DrawLists)
         {
             // Replace in command-buffer
@@ -3922,6 +3927,7 @@ void ImFontAtlasUpdateDrawListsTextures(ImFontAtlas* atlas, ImTextureRef old_tex
                 if (stacked_tex == old_tex)
                     stacked_tex = new_tex;
         }
+    }
 }
 
 // Update texture coordinates in all draw list shared context