From e3927dc004a05f4cc7b4ebe5f1fe204efbbb4f29 Mon Sep 17 00:00:00 2001
From: Turtle Dove <paul.dev.co@outlook.com>
Date: Wed, 15 Jul 2026 07:58:39 -0500
Subject: [PATCH] Backends: OpenGL2/3: Backup and restore GL_UNPACK state in
 UpdateTexture() (#9473, #8802)

---
 backends/imgui_impl_opengl2.cpp | 11 +++++++++++
 backends/imgui_impl_opengl3.cpp | 20 +++++++++++++++++++-
 2 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/backends/imgui_impl_opengl2.cpp b/backends/imgui_impl_opengl2.cpp
index 6cbaaac77..23afa1d33 100644
--- a/backends/imgui_impl_opengl2.cpp
+++ b/backends/imgui_impl_opengl2.cpp
@@ -30,6 +30,7 @@
 //  2026-03-12: OpenGL: Fixed invalid assert in ImGui_ImplOpenGL3_UpdateTexture() if ImTextureID_Invalid is defined to be != 0, which became the default since 2026-03-12. (#9295)
 //  2025-09-18: Call platform_io.ClearRendererHandlers() on shutdown.
 //  2025-07-15: OpenGL: Set GL_UNPACK_ALIGNMENT to 1 before updating textures. (#8802)
+//  2026-07-15: OpenGL: Backup and restore GL_UNPACK_ROW_LENGTH and GL_UNPACK_ALIGNMENT in UpdateTexture() to avoid corrupting caller GL state. (#8802, #9473)
 //  2025-06-11: OpenGL: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas. Removed ImGui_ImplOpenGL2_CreateFontsTexture() and ImGui_ImplOpenGL2_DestroyFontsTexture().
 //  2024-10-07: OpenGL: Changed default texture sampler to Clamp instead of Repeat/Wrap.
 //  2024-06-28: OpenGL: ImGui_ImplOpenGL2_NewFrame() recreates font texture if it has been destroyed by ImGui_ImplOpenGL2_DestroyFontsTexture(). (#7748)
@@ -262,6 +263,12 @@ void ImGui_ImplOpenGL2_RenderDrawData(ImDrawData* draw_data)
 
 void ImGui_ImplOpenGL2_UpdateTexture(ImTextureData* tex)
 {
+    // Backup GL_UNPACK state that we modify, restore on exit.
+    // This prevents corrupting the caller's pixel store state when ImGui
+    // creates or updates textures mid-frame. (#8802, #9473)
+    GLint last_unpack_row_length = 0; GL_CALL(glGetIntegerv(GL_UNPACK_ROW_LENGTH, &last_unpack_row_length));
+    GLint last_unpack_alignment = 0; GL_CALL(glGetIntegerv(GL_UNPACK_ALIGNMENT, &last_unpack_alignment));
+
     if (tex->Status == ImTextureStatus_WantCreate)
     {
         // Create and upload new texture to graphics system
@@ -318,6 +325,10 @@ void ImGui_ImplOpenGL2_UpdateTexture(ImTextureData* tex)
         tex->SetTexID(ImTextureID_Invalid);
         tex->SetStatus(ImTextureStatus_Destroyed);
     }
+
+    // Restore GL_UNPACK state
+    GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, last_unpack_row_length));
+    GL_CALL(glPixelStorei(GL_UNPACK_ALIGNMENT, last_unpack_alignment));
 }
 
 bool    ImGui_ImplOpenGL2_CreateDeviceObjects()
diff --git a/backends/imgui_impl_opengl3.cpp b/backends/imgui_impl_opengl3.cpp
index 1f96c6fe8..8e21a3a5f 100644
--- a/backends/imgui_impl_opengl3.cpp
+++ b/backends/imgui_impl_opengl3.cpp
@@ -32,6 +32,7 @@
 //  2025-09-18: Call platform_io.ClearRendererHandlers() on shutdown.
 //  2025-07-22: OpenGL: Add and call embedded loader shutdown during ImGui_ImplOpenGL3_Shutdown() to facilitate multiple init/shutdown cycles in same process. (#8792)
 //  2025-07-15: OpenGL: Set GL_UNPACK_ALIGNMENT to 1 before updating textures (#8802) + restore non-WebGL/ES update path that doesn't require a CPU-side copy.
+//  2026-07-15: OpenGL: Backup and restore GL_UNPACK_ROW_LENGTH and GL_UNPACK_ALIGNMENT in UpdateTexture() to avoid corrupting caller GL state. (#8802, #9473)
 //  2025-06-11: OpenGL: Added support for ImGuiBackendFlags_RendererHasTextures, for dynamic font atlas. Removed ImGui_ImplOpenGL3_CreateFontsTexture() and ImGui_ImplOpenGL3_DestroyFontsTexture().
 //  2025-06-04: OpenGL: Made GLES 3.20 contexts not access GL_CONTEXT_PROFILE_MASK nor GL_PRIMITIVE_RESTART. (#8664)
 //  2025-02-18: OpenGL: Lazily reinitialize embedded GL loader for when calling backend from e.g. other DLL boundaries. (#8406)
@@ -666,7 +667,16 @@ static void ImGui_ImplOpenGL3_DestroyTexture(ImTextureData* tex)
 
 void ImGui_ImplOpenGL3_UpdateTexture(ImTextureData* tex)
 {
-    // FIXME: Consider backing up and restoring
+    // Backup GL_UNPACK state that we modify, restore on exit.
+    // This prevents corrupting the caller's pixel store state when ImGui
+    // creates or updates textures mid-frame. (#8802, #9473)
+#ifdef GL_UNPACK_ROW_LENGTH
+    GLint last_unpack_row_length = 0; GL_CALL(glGetIntegerv(GL_UNPACK_ROW_LENGTH, &last_unpack_row_length));
+#endif
+#ifdef GL_UNPACK_ALIGNMENT
+    GLint last_unpack_alignment = 0; GL_CALL(glGetIntegerv(GL_UNPACK_ALIGNMENT, &last_unpack_alignment));
+#endif
+
     if (tex->Status == ImTextureStatus_WantCreate || tex->Status == ImTextureStatus_WantUpdates)
     {
 #ifdef GL_UNPACK_ROW_LENGTH // Not on WebGL/ES
@@ -738,6 +748,14 @@ void ImGui_ImplOpenGL3_UpdateTexture(ImTextureData* tex)
     }
     else if (tex->Status == ImTextureStatus_WantDestroy && tex->UnusedFrames > 0)
         ImGui_ImplOpenGL3_DestroyTexture(tex);
+
+    // Restore GL_UNPACK state
+#ifdef GL_UNPACK_ROW_LENGTH
+    GL_CALL(glPixelStorei(GL_UNPACK_ROW_LENGTH, last_unpack_row_length));
+#endif
+#ifdef GL_UNPACK_ALIGNMENT
+    GL_CALL(glPixelStorei(GL_UNPACK_ALIGNMENT, last_unpack_alignment));
+#endif
 }
 
 // If you get an error please report on github. You may try different GL context version or GLSL version. See GL<>GLSL version table at the top of this file.