Version/Branch of Dear ImGui:

Branch: docking

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_sdl.cpp + imgui_impl_opengl3.cpp
Compiler: Apple clang version 11.0.3 (clang-1103.0.32.62)
Operating System: MacOS 12.6.2

My Issue/Question:

Running the DockSpace example, example_sdl_opengl3, I noticed that quite a bit of time was being spent in rendering the UI when using high dpi mode on a 2019 16-inch macbook pro with an AMD Radeon Pro 5500M 4 GB.

To profile, I used glGenQueries/glBeginQuery functions and surrounded the rendering function, ImGui_ImplOpenGL3_RenderDrawData. What I found was that running the example and docking both windows took 4.5ms to render when maximized (resolution of 3584x2134). If PassthruCentralNode is set, it drops to 2.5ms per frame.

Now, I'm trying to understand if, first of all, these numbers are normal, given the high rendering resolution, and what exactly causes the performance to be nearly doubled when setting PassthruCentralNode. On the latter, my understanding is that dear imgui is rendering a big rectangle, but would that have such a big impact on performance? Does blending have something to do with it perhaps?