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Metal Single Pass Downsampler (SPD)

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Kiriakos Gavras

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Description

Metal Single Pass Downsampler (SPD) is a February 2026 technical article by Kiriakos Gavras porting AMD FidelityFX SPD to Metal for depth pyramid generation.

It explains multi-pass mip bandwidth and sync costs, then a 64x64 threadgroup where 16x16 threads load 4x4 blocks, write mip 0, and reduce with max (or min for reverse-Z) in threadgroup memory. An atomic global counter lets the last finished group finish remaining mips, with Metal barriers and kernel excerpts.

It is for advanced Metal and occlusion-culling engineers who already know compute shaders and hierarchical Z.

The post is a free blog with figures, code listings, and full source referenced at the end.

It is useful as a concrete Metal SPD walkthrough focused on depth pyramids rather than a generic drop-in.