I know nothing about SSAO, but wikipedia indicates that the method has the following advantages:
- Independent from scene complexity.
- No data pre-processing needed, no loading time and no memory allocations in system memory.
- Works with dynamic scenes.
- Works in the same consistent way for every pixel on the screen.
- No CPU usage – it can be executed completely on the GPU.
- May be easily integrated into any modern graphics pipeline
If framerates increase when SSAO is turned off, doesn't this indicate serious issues between the game code & most GPU's?