Metal Shader Debugging - Capture GPU Frame

Question

I want to debug my metal shader, tho the "Capture GPU Frame" button is not visible and unavailable in the debug menu.

My scheme was initially set up like this:

• Capture GPU Frame: Automatically Enabled
• Metal API Validation: Enabled

Tho when I change the Capture GPU Frame option to Metal, I do see the capture button, tho my app crashes when I'm trying to make the render command encoder:

commandBuffer.makeRenderCommandEncoder(descriptor: ...)

validateRenderPassDescriptor:644: failed assertion `Texture at colorAttachment[0] has usage (0x01) which doesn't specify MTLTextureUsageRenderTarget (0x04)'

Question one: Why do I need to specify the usage? (It works in Automatically Enabled mode)

Question two: How do I specify the MTLTextureUsageRenderTarget?

Running betas; Xcode 10 and iOS 12.

Answer 1

With newer versions of Xcode you need to explicitly set MTLTextureDescriptor.usage, for my case (a render target) that looks like this:

textureDescriptor.usage = MTLTextureUsageRenderTarget|MTLTextureUsageShaderRead;

The above setting indicates that a texture can be used as a render target and that it could also be read after that by another shader. As the comment above mentioned, you may also want to set the framebufferOnly property, here is how I do that:

if (isCaptureRenderedTextureEnabled) {
  mtkView.framebufferOnly = false;
}

Note that this framebufferOnly only setting is left as the default of true when for the optimized case (isCaptureRenderedTextureEnabled = false) which makes it easy to inspect the data that will be rendered in the view (the output of the shader).