What’s new in Metal at WWDC21

This year has been an incremental one for the Metal framework. The Metal Shading Language (MSL) is now at version 2.4, however, the GPU families and feature set tables are unchanged since last year, with the Apple7 GPU family including the M1 . Let’s get to all the exciting additions at WWDC21 and start with the new ray tracing features.

Normally, you have a compute pass after each render pass and you are saving intermediate render attachments to system memory after each pass so they can communicate to each other. Apple GPUs use the tile memory to hold the processed data for the current pass. At the end of the pass the tile memory is copied to system memory and before the new pass begins the tile memory is loaded again from system memory:

However, this is not the most performant way to intersperse render and compute because of the multiple copies from/to memory. With the new additions to the API this year, you can now simply integrate your ray tracing code into your render pass and only have one write to system memory at the end:

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