gistfile1.txt

// It's an angled sobel operator.
// Pseudocode follows:

// input is RGB, output is greyscale
auto edge_detect (u8 input_image[W][L][3]) → u8[W][L] {
    u8 output_image[W][L] = {0};
    
    constexpr double angle = -135.0;
    double radians = angle * 2.0 * PI / 360.0;

    // Calculate kernel to convolve with.
    constepxr double dr = PI / 4.0;
    double kernel[3][3];
    kernel[0][0] = cos(radians + dr);
    kernel[0][1] = cos(radians + 2.0 * dr);
    kernel[0][2] = cos(radians + 3.0 * dr);
    kernel[1][0] = cos(radians);
    kernel[1][1] = 0;
    kernel[1][2] = cos(radians + 4.0 * dr);
    kernel[2][0] = cos(radians - dr);
    kernel[2][1] = cos(radians - 2.0 * dr);
    kernel[2][2] = cos(radians - 3.0 * dr);
    
    for (image_y = 1..H-2)
    for (image_x = 1..W-2) {
        double R = 0.0;
        double G = 0.0;
        double B = 0.0;
    
        for (i = 0..2)
        for (j = 0..2) {
            std::array<u8, 3> in_px = input_image[image_x + i - 1][image_y + j - 1];

            R += in_px[0] * kernel[i][j];
            G += in_px[1] * kernel[i][j];
            B += in_px[2] * kernel[i][j];
        }
        
        R = Clamp(R, 0, 255);
        G = Clamp(G, 0, 255);
        B = Clamp(B, 0, 255);
        
        output_image[image_x][image_y] = (R+B+G)/3.0;
    }

    return output_image;
}