Magic Music Visuals

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/*{
	"DESCRIPTION": "Fill the bockground with recursive copies of inputImage",
	"CREDIT": "@SelfDrivingCarp",
	"ISFVSN": "2",
	"CATEGORIES": [
		"Effect"
	],
	"INPUTS": [
		{
			"NAME": "inputImage",
			"TYPE": "image"
		}
	],
	"PASSES": [
		{
			"TARGET":"lastOutput",
            		"PERSISTENT": true
		},
		{
			"DESCRIPTION": "output"
		}
	]
	
}*/

vec4 baseImage(vec2 p) {
    // read this pixel from inputImage
    vec4 col = IMG_NORM_PIXEL(inputImage, p);
    
    // grab th color that would go under it. If it's on the left side, we'll
    // from lastOutput rotated and scaled one way, on the right, the other way
    vec2 underCoord;
    if (p.x < 0.5) {
        underCoord.x = p.y;
        underCoord.y = p.x*2.0;
    } else {
        underCoord.x = 1.0-p.y;
        underCoord.y = (1.0-p.x)*2.0;
    }
    
    // grab the underneath pixel from lastOutput. Add some transparency
    vec4 under = IMG_NORM_PIXEL(lastOutput, underCoord);
    under.a *= 0.9;
    
    // combine the input color with the under color according to the alpha
    // channel of the input color. For the resulting alpha channel, use the
    // higher alpha value of input and under color
    col.rgb = (col.rgb * col.a) + (under.rgb * (1.0-col.a));
    col.a = max(col.a,under.a);
    return col;
}


void main()	{
	vec4		inputPixelColor;
	
	if (PASSINDEX == 0) {
            // Our first pass composites the new input with the previous frame,
            // writing the output to the persistent lastOutput buffer
	    inputPixelColor = baseImage(isf_FragNormCoord.xy);
	} else {
            // Our second pass copies from the persistent buffer to our output
	    inputPixelColor = IMG_NORM_PIXEL(lastOutput, isf_FragNormCoord.xy);
	}
	
	gl_FragColor = inputPixelColor;
}