Can't load large jpeg into a MTLTexture with MTKTextureLoader - metal

Question

I'm trying to load a large image into a MTLTexture and it works with 4000x6000 images. But when I try with 6000x8000 it can't.
func setTexture(device: MTLDevice, imageName: String) -> MTLTexture? {
let textureLoader = MTKTextureLoader(device: device)
var texture: MTLTexture? = nil
// In iOS 10 the origin was changed.
let textureLoaderOptions: [MTKTextureLoader.Option: Any]
if #available(iOS 10.0, *) {
let origin = MTKTextureLoader.Origin.bottomLeft.rawValue
textureLoaderOptions = [MTKTextureLoader.Option.origin : origin]
} else {
textureLoaderOptions = [:]
}
if let textureURL = Bundle.main.url(forResource: imageName, withExtension: nil, subdirectory: "Images") {
do {
texture = try textureLoader.newTexture(URL: textureURL, options: textureLoaderOptions)
} catch {
print("Texture not created.")
}
}
return texture
}
Pretty basic code. I'm running it in an iPad Pro with A9 chip, GPU family 3. It should handle textures this large. Should I manually tile it somehow if it doesn't accept this size? In that case, what's the best approach: using MTLRegionMake to copy bytes, slicing in Core Image or a Core Graphics context...
I appreciate any help

Answer 1

Following your helpful comments I decided to load it manually drawing to a CGContext and copying to a MTLTexture. I'm adding the solution code below. The context shouldn't be created each time a texture is created, it's better to put it outside the function and keep reusing it.
// Grab the CGImage, w = width, h = height...
let context = CGContext(data: nil, width: w, height: h, bitsPerComponent: bpc, bytesPerRow: (bpp / 8) * w, space: colorSpace!, bitmapInfo: bitmapInfo.rawValue)
let flip = CGAffineTransform(a: 1, b: 0, c: 0, d: -1, tx: 0, ty: CGFloat(h))
context?.concatenate(flip)
context?.draw(cgImage, in: CGRect(x: 0, y: 0, width: CGFloat(w), height: CGFloat(h)))
let textureDescriptor = MTLTextureDescriptor()
textureDescriptor.pixelFormat = .rgba8Unorm
textureDescriptor.width = w
textureDescriptor.height = h
guard let data = context?.data else {print("No data in context."); return nil}
let texture = device.makeTexture(descriptor: textureDescriptor)
texture?.replace(region: MTLRegionMake2D(0, 0, w, h), mipmapLevel: 0, withBytes: data, bytesPerRow: 4 * w)
return texture

Answer 2

I had this issue before, a texture would load on one device and not on another. I think it is a bug with the texture loader.
You can load in a texture manually using CGImage and a CGContext, draw the image into the context. Create a MTLTexture buffer, then copy the bytes from the CGContext into the texture using a MTLRegion.
It's not fool proof, you have to make sure to use the correct pixel format for the metal buffer or you'll get strange results, so either you code for one specific format of image you're importing, or do a lot of checking. Apples' Basic Texturing example shows how you can change the color order before writing the bytes to the texture using MTLRegion.