[OpenGL] Fix glClipControl(GL_UPPER_LEFT) rendering

src/gl/imgui_impl_opengl3.cpp

@@ -514,6 +514,14 @@ static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, int fb_wid
     if (!g_IsGLES && g_GlVersion >= 200)
         glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
 
+    bool clip_origin_lower_left = true;
+    GLenum last_clip_origin = 0;
+    if (!g_IsGLES && /*g_GlVersion >= 450*/ (glad_glClipControl || glad_glClipControlEXT)) {
+        glGetIntegerv(GL_CLIP_ORIGIN, (GLint*)&last_clip_origin); // Support for GL 4.5's glClipControl(GL_UPPER_LEFT)
+        if (last_clip_origin == GL_UPPER_LEFT)
+            clip_origin_lower_left = false;
+    }
+
     // Setup viewport, orthographic projection matrix
     // Our visible imgui space lies from draw_data->DisplayPos (top left) to draw_data->DisplayPos+data_data->DisplaySize (bottom right). DisplayPos is (0,0) for single viewport apps.
     glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
@@ -521,6 +529,7 @@ static void ImGui_ImplOpenGL3_SetupRenderState(ImDrawData* draw_data, int fb_wid
     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 (!clip_origin_lower_left) { float tmp = T; T = B; B = tmp; } // Swap top and bottom if origin is upper left
     const float ortho_projection[4][4] =
     {
         { 2.0f/(R-L),   0.0f,         0.0f,   0.0f },
@@ -598,18 +607,7 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
     GLboolean last_enable_scissor_test = glIsEnabled(GL_SCISSOR_TEST);
     // Disable and store SRGB state.
     GLboolean last_srgb_enabled = glIsEnabled(GL_FRAMEBUFFER_SRGB);
-    bool clip_origin_lower_left = true;
 
-    GLenum last_clip_origin = 0;
-    GLenum last_clip_depth_mode = 0;
-    if (!g_IsGLES && /*g_GlVersion >= 450*/ (glad_glClipControl || glad_glClipControlEXT)) {
-        glGetIntegerv(GL_CLIP_ORIGIN, (GLint*)&last_clip_origin); // Support for GL 4.5's glClipControl(GL_UPPER_LEFT)
-        glGetIntegerv(GL_CLIP_DEPTH_MODE, (GLint*)&last_clip_depth_mode);
-        if (last_clip_origin == GL_UPPER_LEFT) {
-            clip_origin_lower_left = false;
-            glClipControl(GL_LOWER_LEFT, GL_ZERO_TO_ONE);
-        }
-    }
     // 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)
     // The renderer would actually work without any VAO bound, but then our VertexAttrib calls would overwrite the default one currently bound.
@@ -656,10 +654,7 @@ 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
-                    //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 rarely used glClipControl(GL_UPPER_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));
 
                     // Bind texture, Draw
                     glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
@@ -705,10 +700,6 @@ void    ImGui_ImplOpenGL3_RenderDrawData(ImDrawData* draw_data)
 
     if (last_srgb_enabled)
         glEnable(GL_FRAMEBUFFER_SRGB);
-
-    if (!g_IsGLES && /*g_GlVersion >= 450*/ glad_glClipControl)
-        if (!clip_origin_lower_left)
-            glClipControl(last_clip_origin, last_clip_depth_mode);
 }
 
 }