Metal Core Image passing sampler arguments

Question

Created Nov ’21

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I am trying to use a CIColorKernel or CIBlendKernel with sampler arguments but the program crashes. Here is my shader code which compiles successfully.

extern "C" float4 wipeLinear(coreimage::sampler t1, coreimage::sampler t2, float time) {
    float2 coord1 = t1.coord();
    float2 coord2 = t2.coord();

    float4 innerRect = t2.extent();

    float minX = innerRect.x + time*innerRect.z;
    float minY = innerRect.y + time*innerRect.w;
    float cropWidth = (1 - time) * innerRect.w;
    float cropHeight = (1 - time) * innerRect.z;

    float4 s1 = t1.sample(coord1);
    float4 s2 = t2.sample(coord2);

   if ( coord1.x > minX && coord1.x < minX + cropWidth && coord1.y > minY && coord1.y <= minY + cropHeight) {
       return s1;
   } else {
      return s2;
   }
}

And it crashes on initialization.

class CIWipeRenderer: CIFilter {
var backgroundImage:CIImage?
var foregroundImage:CIImage?
var  inputTime: Float = 0.0

static var kernel:CIColorKernel = { () -> CIColorKernel in

    let url = Bundle.main.url(forResource: "AppCIKernels", withExtension: "ci.metallib")!
    let data = try! Data(contentsOf: url)
    return try! CIColorKernel(functionName: "wipeLinear", fromMetalLibraryData: data) //Crashes here!!!!
    
}()

override var outputImage: CIImage? {
    guard let backgroundImage = backgroundImage else {
        return nil
    }
    
    guard let foregroundImage = foregroundImage else {
        return nil
    }
    
    return CIWipeRenderer.kernel.apply(extent: backgroundImage.extent, arguments: [backgroundImage, foregroundImage, inputTime])
}
}

It crashes in the try line with the following error:

Fatal error: 'try!' expression unexpectedly raised an error: Foundation._GenericObjCError.nilError

If I replace the kernel code with the following, it works like a charm:

extern "C" float4 wipeLinear(coreimage::sample_t s1, coreimage::sample_t s2, float time)
{
     return mix(s1, s2, time);
}

Boost

Answer 1

SergeyPekar OP

Oct ’23

You are using either wrong CIKernel type or kernel function input type.

CIColorKernel accepts only sample_t1 (which can be treated as a single pixel colorl) while CIKernel accepts zero or more input images each input image is represented by a parameter of type sampler.

So typical CIColorKernel will look like this:

#include <CoreImage/CoreImage.h>
 
extern "C" {
    namespace coreimage {
        float4 do_nothing(sample_t s) {
            return s;
        }
    }
}

While CIKernel will work with this code:

 
extern "C" {
    namespace coreimage {
        float4 do_nothing(sampler src) { // It can have multiple samplers, vectors, floats or may not have parameters at all
            return src.sample(src.coord());
        }
    }
}

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