From ff2dfc84226aaeab4200aa2334c4715590e9dc9e Mon Sep 17 00:00:00 2001
From: Elliot Prior <1709938+Quogu@users.noreply.github.com>
Date: Tue, 22 Jul 2025 18:21:43 +0100
Subject: [PATCH] Fonts: fixed a crash when modifying different texture format
 with a legacy backend. (#8824)

---
 docs/CHANGELOG.txt | 3 +++
 imgui_draw.cpp     | 6 +-----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 21008e01d..049007155 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -50,6 +50,9 @@ Other Changes:
   specified but the target font doesn't. Usually either all fonts should
   have a reference size (only required when specifying e.g. GlyphOffset),
   or none should have a reference size. 
+- Fonts: fixed a crash when changing texture format when using a legacy
+  backend. Most commonly would happen when calling GetTexDataAsRGBA32()
+  then immediately GetTexDataAsAlpha8(). (#8824)
 - Windows: fixed an issue where resizable child windows would emit border
   logic when hidden/non-visible (e.g. when in a docked window that is not
   selected), impacting code not checking for BeginChild() return value. (#8815)
diff --git a/imgui_draw.cpp b/imgui_draw.cpp
index ca1f912a4..8109ca6e0 100644
--- a/imgui_draw.cpp
+++ b/imgui_draw.cpp
@@ -3363,11 +3363,7 @@ void ImFontAtlasBuildMain(ImFontAtlas* atlas)
 {
     IM_ASSERT(!atlas->Locked && "Cannot modify a locked ImFontAtlas!");
     if (atlas->TexData && atlas->TexData->Format != atlas->TexDesiredFormat)
-    {
-        ImVec2i new_tex_size = ImFontAtlasTextureGetSizeEstimate(atlas);
-        ImFontAtlasBuildDestroy(atlas);
-        ImFontAtlasTextureAdd(atlas, new_tex_size.x, new_tex_size.y);
-    }
+        ImFontAtlasBuildClear(atlas); 
 
     if (atlas->Builder == NULL)
         ImFontAtlasBuildInit(atlas);