Imagination PowerVR SDK Blog

Scissor vs. stencil test


#1

Picking through our GL call traces for more PowerVR optimization ideas, I noticed that we are using scissor rectangles for viewports (GL_SCISSOR_TEST). I see that in one of the PowerVR docs, it recommends that developers prefer stencil to scissor (assuming one is really required) as it is performed completely on-chip.

Is this recommendation still recommended for PowerVR Series 6 GPUs? Or is this an old Series 5/SGX tip?

Also on Series 6, is this implemented with an internal fragment shader modification or with fixed-function hardware?

Thanks!


#2

Hello Dark_Photon,

Scissors are efficient on Series6 and are not a major performance concern. We are in the process of updating our recommendations specifically for Series6 and this should be available soon.

If you require more detail about the hardware please create a support ticket as the internals are subject to NDA.

Thanks,
Paul


#3

Ok, thank you Paul! We won’t spend much time trying to measure a performance cost then.