VuoImageMapColors.c

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#include "VuoImageRenderer.h"
#include <OpenGL/CGLMacro.h>
 
#ifdef VUO_COMPILER
VuoModuleMetadata({
                     "title" : "VuoImageMapColors",
                     "dependencies" : [
                         "VuoImageRenderer"
                     ]
                 });
#endif
 
VuoImage VuoImage_mapColors(VuoImage image, VuoList_VuoColor colors, VuoReal filterOpacity)
{
    if (!image)
        return NULL;
 
    if (!colors)
        return image;
 
    static const char * fragmentShaderSource = VUOSHADER_GLSL_SOURCE(120,
 
        uniform float gradientCount;
        uniform sampler2D image;        // the unfiltered image
        uniform sampler2D gradientStrip;// the gradient strip to map against
        uniform float amount;           // the amount to mix gradient and image
        varying vec2 fragmentTextureCoordinate;
 
        // https://stackoverflow.com/questions/596216/formula-to-determine-brightness-of-rgb-color
        float brightness(vec3 col)
        {
            // Digital CCIR601 (gives more weight to the green and red components):
            return 0.299*col.r + 0.587*col.g + 0.114*col.b;
        }
 
        void main(void)
        {
            vec4 orig = texture2D(image, fragmentTextureCoordinate);
 
            float lum = brightness(orig.rgb/orig.a);
 
            float gradientWidth = (1./gradientCount)/2.;
            lum = lum * (1-gradientWidth*2) + gradientWidth;
 
            vec4 color = texture2D(gradientStrip, vec2(clamp(lum, gradientWidth, 1-gradientWidth), .5));
 
            vec4 mixed = mix(orig, color, amount);
            mixed *= orig.a;
 
            gl_FragColor = mixed;
        }
    );
 
    int len = VuoListGetCount_VuoColor(colors);
 
    unsigned char* pixels = (unsigned char*)malloc(sizeof(unsigned char)*len*4);
    int n = 0;
    for(int i = 1; i <= len; i++)
    {
        VuoColor col = VuoListGetValue_VuoColor(colors, i);
        // VuoColor is non-premultiplied, but VuoImage_makeFromBuffer() expects premultiplied colors, so premultiply them.
        pixels[n++] = (unsigned int)(col.a*col.b*255);
        pixels[n++] = (unsigned int)(col.a*col.g*255);
        pixels[n++] = (unsigned int)(col.a*col.r*255);
        pixels[n++] = (unsigned int)(col.a*255);
    }
 
    VuoImage gradientStrip = VuoImage_makeFromBuffer(pixels, GL_BGRA, len, 1, VuoImageColorDepth_8, ^(void *buffer){ free(buffer); });
 
    VuoShader shader = VuoShader_make("Map Image Brightness to Gradient Shader");
    VuoShader_addSource(shader, VuoMesh_IndividualTriangles, NULL, NULL, fragmentShaderSource);
    VuoRetain(shader);
 
    // Set `image` before `gradientStrip`, so that `image`'s scaleFactor is used for the output image.
    VuoShader_setUniform_VuoImage(shader, "image", image);
    VuoShader_setUniform_VuoImage(shader, "gradientStrip", gradientStrip);
    VuoShader_setUniform_VuoReal (shader, "gradientCount", (float)len);
    VuoShader_setUniform_VuoReal (shader, "amount", filterOpacity);
 
    // Render.
    VuoImage mappedImage = VuoImageRenderer_render(shader, image->pixelsWide, image->pixelsHigh, VuoImage_getColorDepth(image));
 
    VuoRelease(shader);
 
    return mappedImage;
}