[ch]

Hey I’m trying to debug something and I can’t capture Metal frames with the debugger because I’m not directly presenting this render pass to the UI, is there a way to manually invoke insertDebugCaptureBoundary or get the MTLCommandQueue from a vulkan type?

[Bill Hollings]

@ch

MoltenVK automatically handles that for you as part of the Vulkan vkQueuePresentKHR() call…so that you can capture GPU frames.

As with any app, you need to ensure that within your Xcode Scheme, your app is being run in Debug mode and GPU Frame Capture is enabled.

Please try it out with the Demo apps that come with MoltenVK, and confirm that it is working. If you are still having trouble, please expand on how you are using it, and what might be different between your app and the MoltenVK Demo apps.

…Bill

[ch]

@bill I know the Molten does it as part of queue present however I am trying to write the equivalent of a glReadPixel thing, I’m rendering into a VkImage and transferring that to a staging VkImage, mapping it, and using the pixel data for something else. There is no need to present the image to the swapchain. This currently isn’t working under Molten and I’d like to run a frame capture on the queue to see what’s missing. I previously had it backed with a swapchain image and it rendered fine.

[Bill Hollings]

@ch

Is the problem that your effort is not happening in a queue that ends up being presented at all?

…Bill

[ch]

correct, that queue is not presented to the swapchain, so the implicit insertDebugCaptureBoundary do not get submitted

[Bill Hollings]

@ch

Right. Unfortunately…there is nothing in the current version of MoltenVK that can help with that. We can look to add the capability to make a distinct call to insert a debug capture boundary in a future release.

In the meantime…I assume you are using multiple queues for performance through concurrency? Is it possible to temporarily use your presentation queue for your texture manipulation efforts, until you determine what the problem is through a GPU frame trace?

…Bill

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