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Passing an empty SDL_Rect {0, 0, 0, 0} to SDL_RenderSetViewport() raises a SDL_Error for OpenGL, but fails to set an appropriate error message, leading to confusing output for the developer.

The issue can be found in GL_UpdateViewport:


if (!renderer->viewport.w || !renderer->viewport.h) {
   /* The viewport isn't set up yet, ignore it */
   return -1;
}
  
The return value is passed back to SDL_RenderSetViewport(), which returns it without any additional error message setting.

Ideally, the above code is changed in a way that it supports empty viewports or it sets the appropriate error message:

if (!renderer->viewport.w || !renderer->viewport.h) {
   /* The viewport isn't set up yet, ignore it */
   SDL_SetError("empty viewports are not supported for the OpenGL renderer")
   return -1;
}

Find attached a small test case, which tries to apply an empty SDL_Rect as viewport to all renderers found on the system.

On a side note: a render component in bugzilla would be nice ;-).