我有一个源纹理（大小为480x480），创建时设置了mipmapped为true（为简化此文章，省略了错误检查），和一个目标纹理（大小为100x100）：
// source texture
var textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: MTLPixelFormat.r8Unorm, width: Int(480), height: Int(480), mipmapped: true)
textureDescriptor.usage = .unknown // .shaderWrite .shaderRead
srcTexture = metalDevice!.makeTexture(descriptor: textureDescriptor)
// Dest texture
textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: MTLPixelFormat.r8Unorm, width: Int(100), height: Int(100), mipmapped: false)
textureDescriptor.usage = .shaderWrite
destTexture = metalDevice!.makeTexture(descriptor: textureDescriptor)
采样器被定义为：
let samplerDescriptor = MTLSamplerDescriptor()
samplerDescriptor.magFilter = .linear
samplerDescriptor.minFilter = .linear
samplerDescriptor.rAddressMode = .clampToZero
samplerDescriptor.sAddressMode = .clampToZero
samplerDescriptor.tAddressMode = .clampToZero
samplerDescriptor.normalizedCoordinates = true
textureSampler = metalDevice!.makeSamplerState(descriptor: samplerDescriptor)
我把src纹理用一张图片填充了。
然后生成了mipmap：
let blitEncoder = metalCommandBuffer!.makeBlitCommandEncoder()
blitEncoder!.pushDebugGroup("Dispatch mipmap kernel")
blitEncoder!.generateMipmaps(for: srcTexture!);
blitEncoder!.popDebugGroup()
blitEncoder!.endEncoding()
在同一命令缓冲区中，运行了调整大小内核：
let computeEncoder = metalCommandBuffer!.makeComputeCommandEncoder()
computeEncoder!.pushDebugGroup("Dispatch resize image kernel")
computeEncoder!.setComputePipelineState(resizeImagePipeline)
computeEncoder!.setTexture(srcTexture, index: 0)
computeEncoder!.setTexture(destTexture, index: 1)
computeEncoder!.setSamplerState(textureSampler, index: 0)
let threadGroupCount = MTLSizeMake(20, 10, 1)
let threadGroups = MTLSizeMake(destTexture!.width / threadGroupCount.width, destTexture!.height / threadGroupCount.height, 1)
computeEncoder!.dispatchThreadgroups(threadGroups, threadsPerThreadgroup: threadGroupCount)
computeEncoder!.popDebugGroup()
computeEncoder!.endEncoding()
计算内核是（请记住，这不是片段着色器，它不会自动设置纹理的mipmap细节级别）：
kernel void resizeImage(
texture2d<half, access::sample> sourceTexture [[texture(0)]],
texture2d<half, access::write> destTexture [[texture(1)]],
sampler samp [[sampler(0)]],
uint2 gridPosition [[thread_position_in_grid]])
{
float2 srcSize = float2(sourceTexture.get_width(0),
sourceTexture.get_height(0));
float2 destSize = float2(destTexture.get_width(0),
destTexture.get_height(0));
float2 sourceCoords = float2(gridPosition) / destSize;
/*+ The following attempts all produced a pixelated image
(no edges smoothed out like a fragment shader would)
half4 color = sourceTexture.sample(samp, sourceCoords);
float lod = srcSize.x / destSize.x;
float lod = 0.0;
float lod = 1.0;
float lod = 2.0;
float lod = 3.0;
float lod = 4.0;
float lod = 4.5;
float lod = 5.0;
float lod = 5.5;
*/
float lod = 6.0;
half4 color = sourceTexture.sample(samp, sourceCoords, level(lod));
destTexture.write(color, gridPosition);
}
无论lod设置为什么，我都得到相同的像素化结果。为什么mipmapping不起作用？ 感谢您提供的任何帮助。