[kruseborn]

I am trying to upload 3D texture data larger than 1 gig. It looks like the maximum buffer length on OSX is 1024 MB and 256 MB on Ipad. How would this be done in MoltenVk? Upload the data in smaller chunks with vkMapMemory? If this works, can I still have a descriptorSet to one contiguous memory?

Something like this:

VkDeviceSize first = maxSize; // 1024 MB
VkDeviceSize second = size - maxSize;
checkResult(vkMapMemory(vkContext.device, memory, 0, first, 0, &pData));
memcpy(pData, data, first);
vkUnmapMemory(vkContext.device, memory);
        
checkResult(vkMapMemory(vkContext.device, memory, first, second, 0, &pData));
memcpy(pData, data, second);
vkUnmapMemory(vkContext.device, memory);

However, when I am trying to do this I am still getting an error:

-[MTLDebugDevice validateNewBufferArgs:options:]:306: failed assertion newBufferWith*:length 0x4cd90400 must not exceed 1024 MB.

[Bill Hollings]

@kruseborn

Under Vulkan, device memory is allocated and populated separately from the creation of a buffer or image on that memory.

In order to support this behaviour in the general sense, currently, all device memory allocations under MoltenVK are backed by a MTLBuffer. Consequently, device memory allocations are limited by the size of a MTLBuffer on the runtime platform.

…Bill

[kruseborn]

It looks like you can allocate larger textures than buffer memory in Metal. I have been able to create a 512MB 3D texture on an iPad in Metal.
Is this something that can been done in MoltenVK? And if its not, is there something I can write to create a texture with
let texture = device.makeTexture(descriptor: textureDescriptor) And still somehow get a Vulkan-descriptorset from MoltenVK to point to that texture memory?

[Bill Hollings]

@kruseborn

Good feedback. I appreciate you letting us know your results with that texture size.

Unfortunately…it’s not currently possible to do either of what you are asking.

The VkDeviceMemory objects that back Vulkan image objects, are in turn backed by MTLBuffers. Based on your feedback, we can look at re-factoring how memory management works with textures within MoltenVK, but that will require some development effort, and wouldn’t be available for several weeks.

And unfortunately, the other option…of applying an existing MTLTexture to a VkImage…does not exist within the MoltenVK API.

What is your timing on needing this kind of capability?

…Bill

[kruseborn]

We are going to release the product in the end of the year, so like 2,3 month would not be a problem for us. But the in the final product we are dependent on really large textures and would really appreciate if you would look in to it. The max buffer size on iPad was only 256 MB, its strange that Apple has different limitations for textures and buffers.

best regards
kruseborn

[Bill Hollings]

@kruseborn

We are making these changes now. Do you have a sample app that includes a large texture…so we can test it to make sure it works in the way you are using it?

…Bill

[Bill Hollings]

@kruseborn

MoltenVK 0.18.1 is available for download now, and includes support for larger textures.

Please download and let us know whether this fixes the issue for you.

…Bill

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