Transparent camera causes unnecessary draw calls

[ACrazyTown]

In #3459, FlxCamera.fill() was changed to always fill the camera, even if the alpha is 0. As a result, even though this fill rect is entirely invisible, it still gets pushed and drawn by OpenGL, which we can see by using an OpenGL debugger like RenderDoc:

Here's a replay of the draw process, in video form to better illustrate my point. Notice how the first glDrawElements() call doesn't change anything visually (because it's entirely transparent).

2026-01-14.17-24-52.mp4

The alpha check was added back in 2013 in 5dde99f with the intention of solving performance related issues mentioned in #502. I believe we should re-add the check, and the memory leak from #3459 should be investigated further.

[Geokureli]

What kind of performance hit is this causing? The original poster boasted 15fps increase on ios, but maybe we should add this back once the leak is actually fixed?

[ACrazyTown]

What kind of performance hit is this causing?

Hmmm I don't think it's a significant performance hit, the time taken (by the draw call at least) is in microseconds so nothing too bad! Perhaps it's worse on older/weaker hardware. It's still unnecessary work tho!

but maybe we should add this back once the leak is actually fixed?

Yeah I think this is the way to go