ios - 金属 RGB 到 YUV 转换计算着色器

Question

我正在尝试编写一个用于从 RGB 转换为 YUV 的金属计算着色器，但出现构建错误。

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 会引发错误：

  no matching member function for call to 'write'

我究竟做错了什么？

Answer 1

根据 Metal Shading Language Specification，writeon所有重载的第一个参数texture2d<>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：

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

并且在执行写入时将屏蔽掉多余的组件。