From 99712515740102ad6ea4db96300ed319453fa1fc Mon Sep 17 00:00:00 2001
From: ocornut <omar@miracleworld.net>
Date: Wed, 10 Dec 2025 21:42:07 +0100
Subject: [PATCH] Fonts: amend/comment on FontDataOwnedByAtlas=false fix being
 a breaking change. (#9086, #8465)

---
 docs/CHANGELOG.txt | 17 ++++++++++++-----
 docs/FONTS.md      |  1 +
 imgui.cpp          |  6 ++++++
 imgui.h            |  2 +-
 4 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 824e05990..faf1ebb2c 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -41,14 +41,21 @@ HOW TO UPDATE?
 
 Breaking Changes:
 
+- 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
+    until a shutdown of the owning context or font atlas.
+  - The fact that handling of `FontDataOwnedByAtlas = false` was broken
+    bypassed the issue altogether.
+
 Other Changes:
 
 - 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)
   - Fixed an issue related to EllipsisChar handling, while changing
     font loader or font loader flags dynamically in Style->Fonts menus.
 - Textures:
diff --git a/docs/FONTS.md b/docs/FONTS.md
index 072ca9762..1a466be8d 100644
--- a/docs/FONTS.md
+++ b/docs/FONTS.md
@@ -228,6 +228,7 @@ ImFontConfig font_cfg;
 font_cfg.FontDataOwnedByAtlas = false;
 ImFont* font = io.Fonts->AddFontFromMemoryTTF(data, data_size, size_pixels, &font_cfg);
 ```
+IMPORTANT: Since 1.92, when using `FontDataOwnedByAtlas = false`, font data needs to available until `atlas->RemoveFont()`, or more typically until a shutdown of the owning context or font atlas. It was not immediately noticeable in 1.92.0 due to a bug in handling `FontDataOwnedByAtlas = false`, which was fixed in 1.92.6.
 
 ##### [Return to Index](#index)
 
diff --git a/imgui.cpp b/imgui.cpp
index a977c773c..52b4f0f66 100644
--- a/imgui.cpp
+++ b/imgui.cpp
@@ -394,6 +394,12 @@ 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.
 
+ - 2025/11/24 (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`.
+                         - Prior to 1.92, font data only needed to be available during the atlas->AddFontXXX() call.
+                         - 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 bypassed the issue altogether.
  - 2025/11/06 (1.92.5) - BeginChild: commented out some legacy names which were obsoleted in 1.90.0 (Nov 2023), 1.90.9 (July 2024), 1.91.1 (August 2024):
                          - ImGuiChildFlags_Border                    --> ImGuiChildFlags_Borders
                          - ImGuiWindowFlags_NavFlattened             --> ImGuiChildFlags_NavFlattened (moved to ImGuiChildFlags). BeginChild(name, size, 0, ImGuiWindowFlags_NavFlattened) --> BeginChild(name, size, ImGuiChildFlags_NavFlattened, 0)
diff --git a/imgui.h b/imgui.h
index 7f8b6f3ac..09fef133f 100644
--- a/imgui.h
+++ b/imgui.h
@@ -3521,7 +3521,7 @@ struct ImFontConfig
     char            Name[40];               // <auto>   // Name (strictly to ease debugging, hence limited size buffer)
     void*           FontData;               //          // TTF/OTF data
     int             FontDataSize;           //          // TTF/OTF data size
-    bool            FontDataOwnedByAtlas;   // true     // TTF/OTF data ownership taken by the owner ImFontAtlas (will delete memory itself).
+    bool            FontDataOwnedByAtlas;   // true     // TTF/OTF data ownership taken by the owner ImFontAtlas (will delete memory itself). SINCE 1.92, THE DATA NEEDS TO PERSIST FOR WHOLE DURATION OF ATLAS.
 
     // 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.