[英]Init a Metal texture with the type of 3D
最近,我正在玩SceneKit,我找到了colorGrading属性。 医生说
此材料属性的内容值必须是3D颜色查找表,或者表示排列在水平条带中的此类表格的2D纹理图像。
并且3D颜色查找表可以从Metal纹理中读取。
您可以将此立方体格式的数据提供为具有type3D纹理类型的Metal纹理。
那我该如何设置scnCamera.colorGrading.contents
属性呢?
如果您有一个包含适当布局中的图像数据的缓冲区,则创建3D纹理与创建2D纹理非常相似。 我猜你已经有了。 以下是如何创建纹理本身,将数据复制到其中,并将其设置为颜色分级纹理:
var dim = 16
var values: UnsafeMutablePointer<Float> = ... // alloc and populate 3D array of pixels
let textureDescriptor = MTLTextureDescriptor()
textureDescriptor.textureType = .type3D
textureDescriptor.pixelFormat = .rgba32Float
textureDescriptor.width = dim
textureDescriptor.height = dim
textureDescriptor.depth = dim
textureDescriptor.usage = .shaderRead
let texture = device.makeTexture(descriptor: textureDescriptor)
texture.replace(region: MTLRegionMake3D(0, 0, 0, dim, dim, dim),
mipmapLevel:0,
slice:0,
withBytes:values,
bytesPerRow:dim * MemoryLayout<Float>.size * 4,
bytesPerImage:dim * dim * MemoryLayout<Float>.size * 4)
camera.colorGrading.contents = texture
编辑
这是一个完整的解析器,它将.cube文件转换为适合与此属性一起使用的MTLTexture
:
import Metal
class AdobeLUTParser {
static func texture(withContentsOf url: URL, device: MTLDevice) -> MTLTexture? {
let lutString = try! NSString(contentsOf: url, encoding: String.Encoding.utf8.rawValue)
let lines = lutString.components(separatedBy: "\r\n") as [NSString]
var dim = 2
var values: UnsafeMutablePointer<Float>? = nil
var index = 0
for line in lines {
if line.length == 0 { continue; } // skip blanks
let firstChar = line.character(at: 0)
if firstChar < 58 /*':'*/ {
if values == nil {
print("Error: Got data before size in LUT")
break;
}
let numbers = line.components(separatedBy: " ") as [NSString]
if numbers.count == 3 {
let r = numbers[0].floatValue
let g = numbers[1].floatValue
let b = numbers[2].floatValue
let a = Float(1)
values![index * 4 + 0] = r
values![index * 4 + 1] = g
values![index * 4 + 2] = b
values![index * 4 + 3] = a
index += 1
}
} else {
if line.hasPrefix("LUT_3D_SIZE") {
let sizeString = line.components(separatedBy: " ")[1] as NSString
dim = Int(sizeString.intValue)
if dim < 2 || dim > 512 {
print("Error: insane LUT size: \(dim)")
}
let rawPointer = malloc(dim * dim * dim * 4 * MemoryLayout<Float>.size)
values = rawPointer!.bindMemory(to: Float.self, capacity: dim * dim * dim * 4)
} else if line.hasPrefix("LUT_1D_SIZE") {
print("Error: 1D LUTs not supported")
break
}
}
}
if values == nil {
print("Did not parse LUT successfully")
return nil
}
let textureDescriptor = MTLTextureDescriptor()
textureDescriptor.textureType = .type3D
textureDescriptor.pixelFormat = .rgba32Float
textureDescriptor.width = dim
textureDescriptor.height = dim
textureDescriptor.depth = dim
textureDescriptor.usage = .shaderRead
let texture = device.makeTexture(descriptor: textureDescriptor)
texture.replace(region: MTLRegionMake3D(0, 0, 0, dim, dim, dim),
mipmapLevel:0,
slice:0,
withBytes:values!,
bytesPerRow:dim * MemoryLayout<Float>.size * 4,
bytesPerImage:dim * dim * MemoryLayout<Float>.size * 4)
return texture
}
}
用法:
let mtlDevice = MTLCreateSystemDefaultDevice()
let lutURL = Bundle.main.url(forResource: "MyGradingTexture", withExtension: "cube")
let lutTexture = AdobeLUTParser.texture(withContentsOf: lutURL!, device: mtlDevice!)
camera.colorGrading.contents = lutTexture
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