webcam_prev.glsl

// http://www.iquilezles.org/www/articles/palettes/palettes.htm
// As t runs from 0 to 1 (our normalized palette index or domain), 
//the cosine oscilates c times with a phase of d. 
//The result is scaled and biased by a and b to meet the desired constrast and brightness.
vec3 cosPalette( float t, vec3 a, vec3 b, vec3 c, vec3 d )
{
    return a + b*cos( 6.28318*(c*t+d) );
}

void main () {
    // we put the pixel coordinates in a variable for easy access
    vec2 pos = uvN();
    
    // each chanel of the vec 3 corresponds to a color chanel 
    // red, green, blue!
    vec3 brightness = vec3(0.5,0.5,0.5);
    vec3 contrast =  vec3(0.2,sin(time)*0.2,cos(time)*0.2);
    vec3 osc = vec3(0.2); // how frequently we cycles through the colors
    vec3 phase = vec3(0.5); // where does it start?
    
    // getting the cosine palette
    vec3 cp = cosPalette((time/1.0) +pos.x, brightness, contrast, osc, phase );
    // casting the cosinePalette into a vector 4 by adding a 1 at the end
    // the last number doesnt matter
    vec4 col = vec4(cp,1);
    
    // access the webcam texture at the input pixels position
    // multiplied times 1 + a small number, which returns a number
    // close to its original but modified slightly.
    vec4 web =texture2D(channel0,pos);
    
    // we get the backbuffer texture but slightly offset, 0.01 above the pixel
    // position so it has this trailing up or slitscan effect.
    vec4 prev = texture2D(backbuffer, pos - vec2(0, 0.01 ));

    // mix is a GLSL function thats like mixing paint. We mix between two
    // numbers using the last varible. The last varible is assumed to 
    // be between 0 and 1. it indicates how much of each color
    // we need, so like if the last varible is 0.5 it mixes them evenly.
    col = mix(web+col,prev,1.- web );
    // this line makes it so that the slitscan effect happens where the web is light

    gl_FragColor = col ;
    
}