Render: draw dimmed background earlier to match docking code. (#6716)

Amend f422e78

docs/CHANGELOG.txt

@@ -50,6 +50,8 @@ Other changes:
   through proper navigation logic: honor scrolling and selection. (#1079, #1131)
 - Sliders: Fixed an integer overflow and div-by-zero in SliderInt() when
   v_max=INT_MAX (#6675, #6679) [@jbarthelmes]
+- ImDrawData: Fixed an issue where TotalVtxCount/TotalIdxCount does not match the sum
+  of individual ImDrawList's buffer sizes when a dimming/modal background is rendered. (#6716)
 - ImDrawList: Fixed OOB access in _CalcCircleAutoSegmentCount when passing excessively
   large radius to AddCircle(). (#6657, #5317) [@EggsyCRO, @jdpatdiscord]
 - Debug Tools: Metrics: Fixed "Drawlists" section and per-viewport equivalent

imgui.cpp

@@ -5083,6 +5083,10 @@ void ImGui::Render()
 
     CallContextHooks(&g, ImGuiContextHookType_RenderPre);
 
+    // Draw modal/window whitening backgrounds
+    if (first_render_of_frame)
+        RenderDimmedBackgrounds();
+
     // Add background ImDrawList (for each active viewport)
     for (int n = 0; n != g.Viewports.Size; n++)
     {
@@ -5092,10 +5096,6 @@ void ImGui::Render()
             AddDrawListToDrawDataEx(&viewport->DrawDataP, viewport->DrawDataBuilder.Layers[0], GetBackgroundDrawList(viewport));
     }
 
-    // Draw modal/window whitening backgrounds
-    if (first_render_of_frame)
-        RenderDimmedBackgrounds();
-
     // Add ImDrawList to render
     ImGuiWindow* windows_to_render_top_most[2];
     windows_to_render_top_most[0] = (g.NavWindowingTarget && !(g.NavWindowingTarget->Flags & ImGuiWindowFlags_NoBringToFrontOnFocus)) ? g.NavWindowingTarget->RootWindow : NULL;