Processing order of vertices and fragments in arm gpu

Hi Shawn, 

Older Mali GPUs (Utgard, Midgard) render vertices in incrementing index order, between min and max referenced index, ignoring the actual order in the index buffer. 

Newer Mali GPUs (Bifrost) render vertices in the order in the index buffer (in contiguous blocks of 4), and can skip ranges that are not referenced (except those that are in the same block of 4 as a referenced vertex).  

Using mesh conditioning tools such as meshoptimizer are a very good idea; the algorithms applied will work well for both types of Mali GPU, either to minimize bandwidth or reduce shading cost.

HTH, 
Pete

Peter Harris said:

Older Mali GPUs (Utgard, Midgard) render vertices in incrementing index order, between min and max referenced index, ignoring the actual order in the index buffer. 

Thank you very much for your reply, but this reply gave me new questions. For example, there are vertices 0, 1, 2, 3, 4, 5, 6, and 7 in the vertex buffer. In actual drawing, the index buffer only uses three vertices 0, 5, and 7. But the GPU side will also execute the calculation of the five vertices 1, 2, 3, 4, and 6?

Shawn Chang said:

In actual drawing, the index buffer only uses three vertices 0, 5, and 7. But the GPU side will also execute the calculation of the five vertices 1, 2, 3, 4, and 6?

Yes. Don't leave unused indices in the active index range, aim to reference every vertex between min and max. 

For implementing mesh level-of-detail, duplicate vertices and have a compacted index range for each LOD, don't make low resolution meshes by sparsely sample from the LOD 0 mesh.

Shawn Chang said:

In actual drawing, the index buffer only uses three vertices 0, 5, and 7. But the GPU side will also execute the calculation of the five vertices 1, 2, 3, 4, and 6?

Yes. Don't leave unused indices in the active index range, aim to reference every vertex between min and max. 

For implementing mesh level-of-detail, duplicate vertices and have a compacted index range for each LOD, don't make low resolution meshes by sparsely sample from the LOD 0 mesh.