Broken rendering in "Custom rendering"-window of example

[JayFoxRox]

There's some broken garbage in the background of some primitives from the start:

However, the primitives also break further when changing the thickness (I moved it away from 3.0, then back to 3.0):

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This seems to be a side-effect of #6, where the SDL_RenderClear in Device::UseAsRenderTarget doesn't work correctly.

It can be worked around by SDL_RenderSetClipRect(Renderer, (SDL_Rect*)texture); (hack to workaround SDL bug; any non-nullptr is fine) in Device::UseAsRenderTarget. You also have to move the CurrentDevice->DisableClip(); call to after CurrentDevice->UseAsRenderTarget(cache);

This bug should be fixed by the next SDL release. I'm just leaving it here to document what's going on. It should only affect GL (and GL ES) based SDL_Render backends.