text: #include "Halide.h"
  
  namespace {
  
  class EdgeDetect : public Halide::Generator<EdgeDetect> {
  public:
      ImageParam input{ UInt(8), 2, "input" };
  
      Func build() {
          Var x, y;
  
          Func clamped = Halide::BoundaryConditions::repeat_edge(input);
  
          // Upcast to 16-bit
          Func in16;
          in16(x, y) = cast<int16_t>(clamped(x, y));
  
          // Gradients in x and y.
          Func gx;
          Func gy;
          gx(x, y) = (in16(x + 1, y) - in16(x - 1, y)) / 2;
          gy(x, y) = (in16(x, y + 1) - in16(x, y - 1)) / 2;
  
          // Gradient magnitude.
          Func grad_mag;
          grad_mag(x, y) = (gx(x, y) * gx(x, y) + gy(x, y) * gy(x, y));
  
          // Draw the result
          Func result;
          result(x, y) = cast<uint8_t>(clamp(grad_mag(x, y), 0, 255));
  
          // CPU schedule:
          //   Parallelize over scan lines, 4 scanlines per task.
          //   Independently, vectorize in x.
          result
              .compute_root()
              .vectorize(x, 8)
              .parallel(y, 8);
  
          // Cope with rotated inputs
          input.dim(0).set_stride(Expr());
          result.specialize(input.dim(0).stride() == 1);
          result.specialize(input.dim(0).stride() == -1);
  
          return result;
      }
  };
  
  Halide::RegisterGenerator<EdgeDetect> register_edge_detect{ "edge_detect" };
  
  }  // namespace
  