Merge pull request #50 from dimateos/pr/fix-modalbg

FIX: modal background + improve clipping

Author: seanchas116

src/ImGuiRenderer.cpp

@@ -158,6 +158,10 @@ void ImGuiRenderer::renderDrawList(ImDrawData *draw_data)
     glUniformMatrix4fv(g_AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
     glBindVertexArray(g_VaoHandle);
 
+    // Will project scissor/clipping rectangles into framebuffer space
+    ImVec2 clip_off = draw_data->DisplayPos;         // (0,0) unless using multi-viewports
+    ImVec2 clip_scale = draw_data->FramebufferScale; // (1,1) unless using retina display which are often (2,2)
+
     for (int n = 0; n < draw_data->CmdListsCount; n++)
     {
         const ImDrawList* cmd_list = draw_data->CmdLists[n];
@@ -178,11 +182,19 @@ void ImGuiRenderer::renderDrawList(ImDrawData *draw_data)
             }
             else
             {
+                // Project scissor/clipping rectangles into framebuffer space
+                ImVec2 clip_min((pcmd->ClipRect.x - clip_off.x) * clip_scale.x, (pcmd->ClipRect.y - clip_off.y) * clip_scale.y);
+                ImVec2 clip_max((pcmd->ClipRect.z - clip_off.x) * clip_scale.x, (pcmd->ClipRect.w - clip_off.y) * clip_scale.y);
+                if (clip_max.x <= clip_min.x || clip_max.y <= clip_min.y)
+                    continue;
+
+                // Apply scissor/clipping rectangle (Y is inverted in OpenGL)
+                glScissor((int)clip_min.x, (int)(fb_height - clip_max.y), (int)(clip_max.x - clip_min.x), (int)(clip_max.y - clip_min.y));
+
+                 // Bind texture, Draw
                 glBindTexture(GL_TEXTURE_2D, (GLuint)(size_t)pcmd->TextureId);
-                glScissor((int)pcmd->ClipRect.x, (int)(fb_height - pcmd->ClipRect.w), (int)(pcmd->ClipRect.z - pcmd->ClipRect.x), (int)(pcmd->ClipRect.w - pcmd->ClipRect.y));
-                glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer_offset);
+                glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer_offset + pcmd->IdxOffset);
             }
-            idx_buffer_offset += pcmd->ElemCount;
         }
     }