How to read out an .rgba16Float MTLTexture via getBytes()

Question

I have problems reading out an MTLTexture which has a pixel format of .rgba16Float, the main reason is that Swift does not seem to have a corresponding SIMD4 format.

For .rgba32Float I can simply use the SIMD4< Float > format, like so

if let texture = texture {
    let region = MTLRegionMake2D(x, y, 1, 1)

    let texArray = Array<SIMD4<Float>>(repeating: SIMD4<Float>(repeating: 0), count: 1)
    texture.getBytes(UnsafeMutableRawPointer(mutating: texArray), bytesPerRow: (MemoryLayout<SIMD4<Float>>.size * texture.width), from: region, mipmapLevel: 0)
    let value = texArray[0]
}

This works fine as the Swift Float data type is 32bit, how can I do the same for a 16 bit .rgba16Float texture ?

Answer 1

You can use vImage to convert the buffer from 16-bit to 32-bit float first. Check out vImageConvert_Planar16FtoPlanarF. But not that the documentation on the site is wrong (it's from another function...). I found this utility that demonstrate the process.

It would be more efficient, however, if you could use Metal to convert the texture into 32-bit float (or directly render into a 32-bit texture in the first place).