Examples: OpenGL3: Added support for GL 4.5's glClipControl(GL_UPPER_LEFT). (#2186)

docs/CHANGELOG.txt

@@ -79,6 +79,7 @@ Other Changes:
 - Examples: DirectX10, DirectX11: Removed seemingly unnecessary calls to invalidate and recreate device objects
   in the WM_SIZE handler. (#2088) [@ice1000]
 - Examples: GLFW: User previously installed GLFW callbacks are now saved and chain-called by the default callbacks. (#1759)
+- Examples: OpenGL3: Added support for GL 4.5's glClipControl(GL_UPPER_LEFT). (#2186)
 - Examples: OpenGL3+GLFW: Fixed error condition when using the GLAD loader. (#2157) [@blackball]
 - Examples: OpenGL3+GLFW/SDL: Made main.cpp compile with IMGUI_IMPL_OPENGL_LOADER_CUSTOM (may be missing init). (#2178) [@doug-moen]
 

examples/imgui_impl_opengl3.cpp

@@ -11,6 +11,7 @@
 
 // CHANGELOG
 // (minor and older changes stripped away, please see git history for details)
+//  2018-11-13: OpenGL: Support for GL 4.5's glClipControl(GL_UPPER_LEFT).
 //  2018-08-29: OpenGL: Added support for more OpenGL loaders: glew and glad, with comments indicative that any loader can be used.
 //  2018-08-09: OpenGL: Default to OpenGL ES 3 on iOS and Android. GLSL version default to "#version 300 ES".
 //  2018-07-30: OpenGL: Support for GLSL 300 ES and 410 core. Fixes for Emscripten compilation.
@@ -162,6 +163,11 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     GLboolean last_enable_cull_face = glIsEnabled(GL_CULL_FACE);
     GLboolean last_enable_depth_test = glIsEnabled(GL_DEPTH_TEST);
     GLboolean last_enable_scissor_test = glIsEnabled(GL_SCISSOR_TEST);
+    bool clip_origin_lower_left = true;
+#ifdef GL_CLIP_ORIGIN
+    GLenum last_clip_origin; glGetIntegerv(GL_CLIP_ORIGIN, (GLint*)&last_clip_origin); // Support for GL 4.5's glClipControl(GL_UPPER_LEFT)
+    clip_origin_lower_left = (last_clip_origin == GL_LOWER_LEFT);
+#endif
 
     // Setup render state: alpha-blending enabled, no face culling, no depth testing, scissor enabled, polygon fill
     glEnable(GL_BLEND);
@@ -234,7 +240,10 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
                 if (clip_rect.x < fb_width && clip_rect.y < fb_height && clip_rect.z >= 0.0f && clip_rect.w >= 0.0f)
                 {
                     // Apply scissor/clipping rectangle
-                    glScissor((int)clip_rect.x, (int)(fb_height - clip_rect.w), (int)(clip_rect.z - clip_rect.x), (int)(clip_rect.w - clip_rect.y));
+                    if (clip_origin_lower_left)
+                        glScissor((int)clip_rect.x, (int)(fb_height - clip_rect.w), (int)(clip_rect.z - clip_rect.x), (int)(clip_rect.w - clip_rect.y));
+                    else
+                        glScissor((int)clip_rect.x, (int)clip_rect.y, (int)clip_rect.z, (int)clip_rect.w); // Support for GL 4.5's glClipControl(GL_UPPER_LEFT)
 
                     // Bind texture, Draw
                     glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);