how to use MTLSamplerState instead of declaring a sampler in my fragment shader code?

Question

I have the shader below where I define a sampler (constexpr sampler textureSampler (mag_filter::linear,min_filter::linear);).

    using namespace metal;

    struct ProjectedVertex {
      'float4 position [[position]];
      'float2 textureCoord;
    };

    fragment float4 fragmentShader(const ProjectedVertex in [[stage_in]],
                                   const texture2d<float> colorTexture [[texture(0)]],
                                   constant float4 &opacity [[buffer(1)]]){

      constexpr sampler textureSampler (mag_filter::linear,min_filter::linear);
      const float4 colorSample = colorTexture.sample(textureSampler, in.textureCoord);
      return colorSample*opacity[0];

    }

Now I would like to avoid to hardly define this sampler inside my shader code. I found MTLSamplerState But I don't know how to use it

Answer 1

To create a sampler, first create a MTLSamplerDescriptor object and configure the descriptor’s properties. Then call the newSamplerStateWithDescriptor: method on the MTLDevice object that will use this sampler. After you create the sampler, you can release the descriptor or reconfigure its properties to create other samplers.

// Create default sampler state
MTLSamplerDescriptor *samplerDesc = [MTLSamplerDescriptor new];
samplerDesc.rAddressMode = MTLSamplerAddressModeRepeat;
samplerDesc.sAddressMode = MTLSamplerAddressModeRepeat;
samplerDesc.tAddressMode = MTLSamplerAddressModeRepeat;
samplerDesc.minFilter = MTLSamplerMinMagFilterLinear;
samplerDesc.magFilter = MTLSamplerMinMagFilterLinear;
samplerDesc.mipFilter = MTLSamplerMipFilterNotMipmapped;
id<MTLSamplerState> ss = [device newSamplerStateWithDescriptor:samplerDesc];

Sets a sampler state for the fragment function:

    id<MTLRenderCommandEncoder> encoder = [commandBuffer renderCommandEncoderWithDescriptor: passDescriptor];
     ...
    [encoder setFragmentSamplerState: ss atIndex:0];

Accessing from the shader:

fragment float4 albedoMainFragment(ImageColor in [[stage_in]],
                                texture2d<float> diffuseTexture [[texture(0)]],
                                sampler smp [[sampler(0)]]) {

    float4 color = diffuseTexture.sample(smp, in.texCoord);
    return color;
}