//
// Simple passthrough fragment shader
//
varying vec2 v_vTexcoord;
varying vec4 v_vColour;

uniform sampler2D map;
uniform vec2  dimension;
uniform vec2  map_dimension;
uniform vec2  displace;
uniform float strength;
uniform float middle;
uniform int iterate;
uniform int use_rg;
uniform int sampleMode;

float bright(in vec4 col) {
	return dot(col.rgb, vec3(0.2126, 0.7152, 0.0722))  * col.a;
}

/////////////// SAMPLING ///////////////

const float PI = 3.14159265358979323846;
uniform int interpolation;
uniform vec2 sampleDimension;

const int RSIN_RADIUS = 1;

float sinc ( float x ) { return x == 0.? 1. : sin(x * PI) / (x * PI); }

vec4 texture2D_rsin( sampler2D texture, vec2 uv ) {
    vec2 tx = 1.0 / sampleDimension;
    vec2 p  = uv * sampleDimension - vec2(0.5);
    
	vec4 sum = vec4(0.0);
    float weights = 0.;
    
    for (int x = -RSIN_RADIUS; x <= RSIN_RADIUS; x++)
	for (int y = -RSIN_RADIUS; y <= RSIN_RADIUS; y++) {
        float a = length(vec2(float(x), float(y))) / float(RSIN_RADIUS);
		if(a > 1.) continue;
        float w = sinc(a * PI * tx.x) * sinc(a * PI * tx.y);
        vec2 offset = vec2(float(x), float(y)) * tx;
        vec4 sample = texture2D(texture, (p + offset + vec2(0.5)) / sampleDimension);
        sum += w * sample;
        weights += w;
    }
	
    return sum / weights;
}

vec4 texture2D_bicubic( sampler2D texture, vec2 uv ) {
	uv = uv * sampleDimension + 0.5;
	vec2 iuv = floor( uv );
	vec2 fuv = fract( uv );
	uv = iuv + fuv * fuv * (3.0 - 2.0 * fuv);
	uv = (uv - 0.5) / sampleDimension;
	return texture2D( texture, uv );
}

vec4 texture2Dintp( sampler2D texture, vec2 uv ) {
	if(interpolation == 2)		return texture2D_bicubic( texture, uv );
	else if(interpolation == 3)	return texture2D_rsin( texture, uv );
	return texture2D( texture, uv );
}

/////////////// SAMPLING ///////////////

vec4 sampleTexture(vec2 pos) {
	if(pos.x >= 0. && pos.y >= 0. && pos.x <= 1. && pos.y <= 1.)
		return texture2Dintp(gm_BaseTexture, pos);
	
	if(sampleMode == 0) 
		return vec4(0.);
	if(sampleMode == 1) 
		return texture2Dintp(gm_BaseTexture, clamp(pos, 0., 1.));
	if(sampleMode == 2) 
		return texture2Dintp(gm_BaseTexture, fract(pos));
	
	return vec4(0.);
}

vec2 shiftMap(in vec2 pos, in float str) {
	vec4 disP = texture2Dintp( map, pos );
	vec2 sam_pos;
	vec2 raw_displace = displace / dimension;
	float _str;
	
	if(use_rg == 1) {
		vec2 _disp = vec2(disP.r - middle, disP.g - middle) * vec2((disP.r + disP.g + disP.b) / 3. - middle) * str;
		
		sam_pos = pos + _disp;
	} else if(use_rg == 2) {
		float _ang = disP.r * PI * 2.;
		_str = (disP.g - middle) * str;
		
		sam_pos = pos + _str * vec2(cos(_ang), sin(_ang));
	} else {
		_str = (bright(disP) - middle) * str;
		
		sam_pos = pos + _str * raw_displace;
	}
	
	return sam_pos;
}

void main() {
	vec2 samPos = v_vTexcoord;
	
	if(iterate == 1) {
		for(float i = 0.; i < strength; i++) 
			samPos = shiftMap(samPos, 1.);
	} else
		samPos = shiftMap(samPos, strength);
	
	vec4 col = sampleTexture( samPos );
	
    gl_FragColor = col;
}