Pixel-Composer/shaders/sh_jpeg_dct/sh_jpeg_dct.fsh

#define PI    3.1415972
#define SQRT2 0.70710678118

varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform vec2  dimension;
uniform int   patch;
uniform int   transform;
uniform float compression;
uniform float phase;

float DCTcoeff(vec2 k, vec2 x) { return cos(PI * k.x * x.x + phase) * cos(PI * k.y * x.y + phase); }
float ZIGcoeff(vec2 k, vec2 x) { 
	float a, b;
	
	float fx = fract(k.x * x.x + phase / PI / 2. + .5);
	a = fx < 0.5? fx * 2. : (1. - fx) * 2.;
	a = a * 2. - 1.;
	
	float fy = fract(k.y * x.y + phase / PI / 2. + .5);
	b = fy < 0.5? fy * 2. : (1. - fy) * 2.;
	b = b * 2. - 1.;
	
	return a * b;
}

float SMTcoeff(vec2 k, vec2 x) { 
	float a, b;
	
	float fx = fract(k.x * x.x + phase / PI / 2. + .5);
	a = fx < 0.5? fx * 2. : (1. - fx) * 2.;
	a = smoothstep(0., 1., a);
	a = a * 2. - 1.;
	
	float fy = fract(k.y * x.y + phase / PI / 2. + .5);
	b = fy < 0.5? fy * 2. : (1. - fy) * 2.;
	b = smoothstep(0., 1., b);
	b = b * 2. - 1.;
	
	return a * b;
}

float STPcoeff(vec2 k, vec2 x) { 
	float a, b;
	float sp = 1. / 2.;
	
	float _fx = fract(k.x * x.x + phase / PI / 2.);
	float fx  = _fx >= 0.5 - sp && _fx <= 0.5 + sp? 0. : step(0.5, _fx);
	a = a * 2. - 1.;
	
	float _fy = fract(k.y * x.y + phase / PI / 2.);
	float fy  = _fy >= 0.5 - sp && _fy <= 0.5 + sp? 0. : step(0.5, _fy);
	b = b * 2. - 1.;
	
	return a * b;
}

float round(float val) { return fract(val) > 0.5? ceil(val) : floor(val); }
vec4  round(vec4  val) { return vec4(round(val.x), round(val.y), round(val.z), round(val.w)); }

void main() {
    vec2 tx = dimension * v_vTexcoord;
    
    vec2 k = mod(tx, float(patch)) - .5;
    vec2 K = floor(tx - k);
    
    vec4 val = vec4(0.);
    
    for(int x = 0; x < patch; ++x)
	for(int y = 0; y < patch; ++y) {
	    vec4  s = texture2D( gm_BaseTexture, (K + vec2(x, y) + .5) / dimension);
	    float c = 0.;
	    
	    	 if(transform == 0) c = DCTcoeff(k, (vec2(x, y) + .5) / float(patch));
	    else if(transform == 1) c = ZIGcoeff(k, (vec2(x, y) + .5) / float(patch));
	    else if(transform == 2) c = SMTcoeff(k, (vec2(x, y) + .5) / float(patch));
	    else if(transform == 3) c = STPcoeff(k, (vec2(x, y) + .5) / float(patch));
	    
	    c *= k.x < .5? SQRT2 : 1.;
	    c *= k.y < .5? SQRT2 : 1.;
	    
        val += s * c;
	}
        
    vec4 c = val / float(patch) * 2.;
    if(compression != 0.)
        c = round(c / float(patch) * compression) / compression * float(patch);
    c.a = 1.;
    
    gl_FragColor = c;
}