A confusing issue with the CIKernel's sample() method. Assigning the result of samplerTransform() to a variable and then using it in the sample() method breaks everything.

Confusion.cikernel

// This works.
kernel vec4 simpleFilter(sampler p)
{
  vec2 dc = destCoord();
  return sample(p, samplerTransform(p, dc));
}

// This does not. It produces [0, 0, 0, 255] for the first 255 pixels and then [0, 0, 0, 0] thereafter.
kernel vec4 simpleFilter(sampler p)
{
  vec2 dc = destCoord();
  vec2 tc = samplerTransform(p, dc);
  return sample(p, tc);
}

Seeing the same, many years later :))))) 😭