Hey @warrenm, I was playing around with MPS from your tutorial http://metalbyexample.com/metal-performance-shaders-in-swift/ … now I want to try and chain some filters, Sobel and Resize for example but I'm not sure where to start. Any tips?
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Cool! So the chief thing to understand is that you can encode as much work as you want into a single command buffer; dependencies (between kernels) will be resolved automatically.
The practical upshot of this is that you can try to encode kernels in-place, while providing a backup copy allocator to minimize allocations, but chaining from the output of one kernel to the input of another—even within one command buffer—should “just work.”
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All of this goes out the window if you’re using MTLHeap, where accesses are noted less granularly, but I suspect that for now you’re not using heaps?
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Nope, not using heaps. The part where I'm kind of stranded is the source and destination textures when I encode the filters, how to make sure these are the right size and set up in the correct way in general.
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to explain the situation. Im getting some source image at a 320 x 480 resolution and apply the sobel filter for now. But the result in my mtk view is a tiny rectangle at the top right because of this resolution and so I want to resize the texture before applying the sober filter.
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Oh, you want to upsample from the source first? In that case, MPSImageScale up to the desired size (yes, you have to compute the dest size manually); at worst use Lanczos (you probably don’t need it); then feed that to your Sobel.
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Sorry if this is obtuse; I really should write a new article about all of this
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Ah I didn't even know sobel is only applied to 1:1 aspect images, I'm using it on something 320 x 240. But yes that's exactly what I'm trying to do. So the thing to do is have one intermediate texture of the same size as my drawable?
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So I can encode the resize with the image as source and intermediate texture as destination, and the sobel filter with the intermediate as source and drawable as destination. Is that correct?
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Bingo, yes. Just make sure the drawable is coming from a layer/view whose framebufferOnly property is set to false.
End of conversation
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