金属 RGB 到 YUV 转换计算着色器 [英] Metal RGB to YUV conversion compute shader

问题描述

我正在尝试编写用于从 RGB 转换为 YUV 的 Metal 计算着色器，但出现构建错误.

I am trying to write a Metal compute shader for converting from RGB to YUV, but am getting build errors.

typedef struct {
   float3x3 matrix;
   float3   offset;
} ColorConversion;

  // Compute kernel
 kernel void kernelRGBtoYUV(texture2d<half, access::sample> inputTexture [[ texture(0) ]],
                       texture2d<half, access::write> textureY [[ texture(1) ]],
                       texture2d<half, access::write> textureCbCr [[ texture(2) ]],
                       constant ColorConversion &colorConv [[ buffer(0) ]],
                       uint2 gid [[thread_position_in_grid]])
{
  // Make sure we don't read or write outside of the texture
  if ((gid.x >= inputTexture.get_width()) || (gid.y >= inputTexture.get_height())) {
      return;
  }



  float3 inputColor = float3(inputTexture.read(gid).rgb);

  float3 yuv = colorConv.matrix*inputColor + colorConv.offset;

  half2 uv = half2(yuv.gb);

  textureY.write(half(yuv.x), gid);

  if (gid.x % 2 == 0 && gid.y % 2 == 0) {
      textureCbCr.write(uv, uint2(gid.x / 2, gid.y / 2));
  }
} 

最后一行，即写入textureCbCr会抛出错误:

The last line, i.e. write to textureCbCr throws an error:

  no matching member function for call to 'write'

我做错了什么?

推荐答案

根据Metal Shading Language Specification，write在texture2d<>的所有重载的第一个参数code> 是 4 元素向量.即使您正在写入的纹理少于 4 个组件也是如此.因此，您可以通过将错误的行替换为:

According to the Metal Shading Language Specification, the first parameter of all overloads of write on texture2d<> are 4-element vectors. This is the case even if the texture you're writing to has fewer than 4 components. So you can fix this by replacing the erroneous line with:

textureCbCr.write(half4(yuv.xyzz), uint2(gid.x / 2, gid.y / 2));

并且在执行写入时会屏蔽掉多余的组件.

And the superfluous components will be masked out when performing the write.

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