Empty windows with SDL2 renderer on macOS

[JacobCZ]

Version/Branch of Dear ImGui:

Version: 1.89.1
Branch: master

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_sdl.h, imgui_impl_sdlrenderer.h; SDL2 using Metal
Compiler: Apple clang 14.0.0 (am64-apple-darwin22.1.0)
Operating System: macOS Ventura 13.0

My Issue/Question:

I'm trying to render the demo window and one additional window. The window frames are both shown but only the additional window has a title and both of the windows are completely empty. The mouse also seems to be strangely offset. At first I thought this might somehow be a font issue because of the missing text but adding a custom font made no difference.

Screenshots/Video

Standalone, minimal, complete and verifiable example:

(error handling omitted for brevity)

int main(it argc, char* argv[]) {
  // Create SDL window and renderer
  SDL_Init(SDL_INIT_EVERYTHING);
  window = SDL_CreateWindow("Hello World", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, 640, 480, SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI | SDL_WINDOW_METAL);
  renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);

  // ImGui Init
  IMGUI_CHECKVERSION();
  ImGui::CreateContext();
  ImGuiIO& io = ImGui::GetIO();
  io.Fonts->AddFontDefault();
  ImGui_ImplSDL2_InitForSDLRenderer(window, renderer);
  ImGui_ImplSDLRenderer_Init(renderer);
  ImGui::StyleColorsDark();

  SDL_Event evt;
  while(true) {
    while(SDL_PollEvent(&evt)) {
      ImGui_ImplSDL2_ProcessEvent(&evt);
    }

    ImGui_ImplSDLRenderer_NewFrame();
    ImGui_ImplSDL2_NewFrame();
    ImGui::NewFrame();

    ImGui::ShowDemoWindow();

    ImGui::Begin("Debug");
    ImGui::Text("Hello World");
    ImGui::End();

    ImGui::Render();
    SDL_SetRenderDrawColor(renderer, 0x0, 0x0, 0x0, 0xFF);
    SDL_RenderClear(renderer);
    ImGui_ImplSDLRenderer_RenderDrawData(ImGui::GetDrawData());
    SDL_RenderPresent(renderer);
  }
}

[ocornut]

1. can you confirm that example_sdl_sdlrenderer/main.cpp is exhibit the same issue?

2. The rendering issue seems like the scissoring is off:

• either related to FrameBufferScale
• either the same offset you have with the mouse are applied to scissoring rectangle, meaning text is clipped.

3. Perhaps mouse issue is also a FrameBufferScale issue?

Out of curiosity try to remove the SDL_WINDOW_ALLOW_HIGHDPI flag.

We haven't really standardized setting/applying framebufferscale but it is currently a bit of a mess, hence my rather obtuse answer ( = I don't have full answer).

Links:
https://github.com/ocornut/imgui/issues?q=label%3Aosx%2Fios+label%3Adpi
dpi

Notice in ImGui_ImplSDLRenderer_RenderDrawData():

// If there's a scale factor set by the user, use that instead
// If the user has specified a scale factor to SDL_Renderer already via SDL_RenderSetScale(), SDL will scale whatever we pass
// to SDL_RenderGeometryRaw() by that scale factor. In that case we don't want to be also scaling it ourselves here.
float rsx = 1.0f;
float rsy = 1.0f;
SDL_RenderGetScale(bd->SDLRenderer, &rsx, &rsy);
ImVec2 render_scale;
render_scale.x = (rsx == 1.0f) ? draw_data->FramebufferScale.x : 1.0f;
render_scale.y = (rsy == 1.0f) ? draw_data->FramebufferScale.y : 1.0f;

[JacobCZ]

example_sdl_sdlrenderer/main.cpp has the same issue...

Removing SDL_WINDOW_ALLOW_HIGHDPI seems to fix the issue and everything seems to be rendering at a reasonable scale for a 14 inch retina screen (with a very slightly blurry text with the default font, not visible on a screenshot and looks fine on a 1080p screen so probably not an ImGUI problem). Also solves the mouse offset issue.

[ocornut]

Can you debug step into the beginning of ImGui_ImplSDLRenderer_RenderDrawData() and report all the values?

They are not hard problems to solve but I don’t have a Mac, I’ll want to spend more time on backend dpi issue on Mac for 1.90

[ocornut]

Hello,
I have added SDL_RenderSetScale() in 5a3f82e to make this consistent across examples for now. Fuller hi-dpi support on Mac in the examples app will be address separately but this fixes this issue.