(Breaking) Backends: OpenGL3: added ImGui_ImplOpenGL3_SetClipOrigin. Default to GL_LOWER_LEFT. (#2186, #3998, #3146, #3143, #8640)

backends/imgui_impl_opengl3.cpp

@@ -24,7 +24,9 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
-//  2026-10-01: OpenGL: Avoid querying glGetIntegerv(GL_CLIP_ORIGIN) again when using DrawCallback_ResetRenderState. (#2186, #3998, #3146, #3143, #8640)
+//  2026-10-01: OpenGL: Added ImGui_ImplOpenGL3_SetClipOrigin() to specify clip origins (GL_LOWER_LEFT/GL_UPPER_LEFT, or use 0 to autodetect). (#2186, #3998, #3146, #3143, #8640)
+//                      (Breaking): we now default to GL_LOWER_LEFT instead of 0=autodetect. Because 1) detection is not reliable and 2) is slow.
+//  2026-10-01: OpenGL: Avoid querying glGetIntegerv(GL_CLIP_ORIGIN) multiple times when using DrawCallback_ResetRenderState. (#2186, #3998, #3146, #3143, #8640)
 //  2026-09-17: OpenGL: Added support for platform_io.DrawCallback_SetSamplerFromTex. (#9378)
 //  2026-09-07: OpenGL: Round framebuffer dimensions to the nearest integer instead of truncating them. (#9538, 9515, #8628)
 //  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)
@@ -260,7 +262,8 @@ struct ImGui_ImplOpenGL3_Data
     bool            HasPolygonMode;
     bool            HasBindSampler;
     bool            HasClipOrigin;
-    bool            ClipOriginLowerLeft;
+    GLenum          ClipOriginRequest;      // Default = GL_LOWER_LEFT. Change using ImGui_ImplOpenGL3_SetClipOrigin().
+    GLenum          ClipOriginCurrent;
     bool            UseBufferSubData;
 #ifdef IMGUI_IMPL_OPENGL_MAY_HAVE_BIND_SAMPLER
     GLuint          TexSamplers[2];         // Used if HasBindSimpler. (0=linear, 1=nearest)
@@ -370,7 +373,7 @@ static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, ImGui_Impl
     float R = draw_data->DisplayPos.x + draw_data->DisplaySize.x;
     float T = draw_data->DisplayPos.y;
     float B = draw_data->DisplayPos.y + draw_data->DisplaySize.y;
-    if (!bd->ClipOriginLowerLeft) { float tmp = T; T = B; B = tmp; } // Swap top and bottom if origin is upper left
+    if (bd->ClipOriginCurrent == GL_UPPER_LEFT) { float tmp = T; T = B; B = tmp; } // Swap top and bottom
     const float ortho_projection[4][4] =
     {
         { 2.0f/(R-L),   0.0f,         0.0f,   0.0f },
@@ -452,6 +455,14 @@ static void ImGui_ImplOpenGL3_DrawCallback_SetSamplerFromTex(const ImDrawList*,
     render_state->UseTexParameterFilter = false;
 }
 
+// Default is GL_LOWER_LEFT since 2026/10/01. Used to be auto.
+void    ImGui_ImplOpenGL3_SetClipOrigin(unsigned int clip_origin)
+{
+    IM_ASSERT(clip_origin == 0 || clip_origin == GL_UPPER_LEFT || clip_origin == GL_LOWER_LEFT);
+    ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
+    bd->ClipOriginRequest = clip_origin;
+}
+
 // OpenGL3 Render function.
 // Note that this implementation is little overcomplicated because we are saving/setting up/restoring every OpenGL state explicitly.
 // This is in order to be able to run within an OpenGL engine that doesn't do so.
@@ -514,14 +525,15 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
 #endif
 
     // Support for GL 4.5 rarely used glClipControl(GL_UPPER_LEFT)
-    bd->ClipOriginLowerLeft = true;
+    bd->ClipOriginCurrent = bd->ClipOriginRequest;
+    if (bd->ClipOriginCurrent == 0)
+    {
+        bd->ClipOriginCurrent = GL_LOWER_LEFT;
 #if defined(GL_CLIP_ORIGIN)
         if (bd->HasClipOrigin)
-    {
-        GLenum current_clip_origin = 0; glGetIntegerv(GL_CLIP_ORIGIN, (GLint*)&current_clip_origin);
-        bd->ClipOriginLowerLeft = (current_clip_origin != GL_UPPER_LEFT);
-    }
+            glGetIntegerv(GL_CLIP_ORIGIN, (GLint*)&bd->ClipOriginCurrent);
 #endif
+    }
 
     // Setup desired GL state
     // Recreate the VAO every time (this is to easily allow multiple GL contexts to be rendered to. VAO are not shared among GL contexts)
@@ -1149,6 +1161,7 @@ bool    ImGui_ImplOpenGL3_Init(const char* glsl_version)
             bd->HasClipOrigin = true;
     }
 #endif
+    bd->ClipOriginCurrent = bd->ClipOriginRequest = GL_LOWER_LEFT;
 
     return true;
 }

backends/imgui_impl_opengl3.h

@@ -44,6 +44,9 @@ IMGUI_IMPL_API void     ImGui_ImplOpenGL3_DestroyDeviceObjects();
 // (Advanced) Use e.g. if you need to precisely control the timing of texture updates (e.g. for staged rendering), by setting ImDrawData::Textures = nullptr to handle this manually.
 IMGUI_IMPL_API void     ImGui_ImplOpenGL3_UpdateTexture(ImTextureData* tex);
 
+// (Advanced) Specify clip origin, same value as glClipControl() or 0 for auto-detection.
+IMGUI_IMPL_API void     ImGui_ImplOpenGL3_SetClipOrigin(unsigned int gl_clip_origin);
+
 // Configuration flags to add in your imconfig file:
 //#define IMGUI_IMPL_OPENGL_ES2     // Enable ES 2 (Auto-detected on Emscripten)
 //#define IMGUI_IMPL_OPENGL_ES3     // Enable ES 3 (Auto-detected on iOS/Android)

backends/imgui_impl_opengl3_loader.h

@@ -303,6 +303,7 @@ typedef khronos_uint16_t GLushort;
 #define GL_LINK_STATUS                    0x8B82
 #define GL_INFO_LOG_LENGTH                0x8B84
 #define GL_CURRENT_PROGRAM                0x8B8D
+#define GL_LOWER_LEFT                     0x8CA1
 #define GL_UPPER_LEFT                     0x8CA2
 typedef void (APIENTRYP PFNGLBLENDEQUATIONSEPARATEPROC) (GLenum modeRGB, GLenum modeAlpha);
 typedef void (APIENTRYP PFNGLATTACHSHADERPROC) (GLuint program, GLuint shader);

docs/CHANGELOG.txt

@@ -53,6 +53,9 @@ Breaking Changes:
   - DirectX12: Removed support for legacy `ImGui_ImplDX12_Init()` signature, which was
     obsoleted in 1.91.6 (December 2014), because it needed to forcefully disable support
     for `ImGuiBackendFlags_RendererHasTextures`. Use the new signature! (#9487)
+  - OpenGL3: Does not attempt to read `GL_CLIP_ORIGIN` by default as the detection is
+    sub-optimal and not reliable on some setup. Use `ImGui_ImplOpenGL3_SetClipOrigin(0)`
+    to  enable auto-detection, or e.g. `ImGui_ImplOpenGL3_SetClipOrigin(GL_UPPER_LEFT)`.
 
 Other Changes:
 
@@ -148,8 +151,11 @@ Other Changes:
     callback to request using the sampler associated already associated to a texture. (#9378)
   - OpenGL2, OpenGL3: fixed `DrawCallback_ResetRenderState` handler not reseting all states
     in the glTexParameter() path. (#9378)
-  - OpenGL3: avoid querying `glGetIntegerv(GL_CLIP_ORIGIN)` again when using `DrawCallback_ResetRenderState`,
-    at it appear to stall some drivers. (#2186, #3998, #3146, #3143, #8640)
+  - OpenGL3: added `ImGui_ImplOpenGL3_SetClipOrigin()` to specify origin between
+    `GL_LOWER_LEFT` (new default), `GL_UPPER_LEFT` and `0` (autodetect, old default).
+  - OpenGL3: avoid querying `glGetIntegerv(GL_CLIP_ORIGIN)` multiple times when using
+    when using default and using `DrawCallback_ResetRenderState`, at it appear to stall
+    some drivers. (#2186, #3998, #3146, #3143, #8640)
   - SDL2: fixed querying framebuffer scale/density when using Metal without
     going through a SDL_Renderer. (#5592) [@lailoken]
   - SDLRenderer3: restore any temporarily modified texture scale modes at the of `RenderDrawData()`. (#9378)