Hi Eric et al: Okay, I have just established that the documentation is incorrect (at least for a MacBook Pro 15"), because SDL_CreateWindow does behave differently when given different widths and heights in fullscreen mode. When I pass it 2880x1800 I get a very crisp, clear display with the mouse pointer looking (almost?) exactly as it does during general use of the computer. OTOH, if I pass it 1024x768 I get blurry scaled, large and blocky drawing including the mouse pointer.
BTW, I'm using OpenGL directly as in SDL 1.2, not using any of the exotic new 2D drawing stuff in SDL 2.0.
And this makes sense... if you were unable to choose a resolution for your fullscreen app, what would be the point in looping through the display modes with SDL_GetDisplayMode() to store the widths and heights for multiple resolutions in an SDL_DisplayMode structure?
Anyway, I've discovered on my MacBook Pro that I need to first request a resolution with SDL_CreateWindow, then check for what resolution I actually got by calling SDL_GL_GetDrawableSize(WINDOW,&w,&h). This is the only way to make it behave sanely.
Hope this helps someone.