#version 450

/**
* Practical Elliptical Texture Filtering on the GPU
* Copyright 2010-2011 Pavlos Mavridis, All rights reserved.
*
* Version: 0.6 - 12 / 7 / 2011 (DD/MM/YY)
*/

layout(push_constant) uniform Push
{
	vec4 SourceSize;
	vec4 OriginalSize;
	vec4 OutputSize;
	uint FrameCount;
	float distortion;
} params;

#pragma parameter distortion "EWA Curvature" 0.15 0.0 1.0 0.01

layout(std140, set = 0, binding = 0) uniform UBO
{
	mat4 MVP;
} global;

#pragma stage vertex
layout(location = 0) in vec4 Position;
layout(location = 1) in vec2 TexCoord;
layout(location = 0) out vec2 vTexCoord;

void main()
{
   gl_Position = global.MVP * Position;
   vTexCoord = TexCoord;
}

#pragma stage fragment
layout(location = 0) in vec2 vTexCoord;
layout(location = 0) out vec4 FragColor;
layout(set = 0, binding = 2) uniform sampler2D Source;

//{========= TEXTURE FILTERING (EWA) PARAMETERS =========
#define MAX_ECCENTRICITY 1
#define FILTER_WIDTH 0.8
#define FILTER_SHARPNESS 1.0
#define TEXELS_PER_PIXEL 1.0
#define TEXEL_LIMIT 32
#define FILTER_FUNC gaussFilter
//}======================================================

#define M_PI 3.14159265358979323846

#define SourceImage Source

//{========================= FILTER FUNCTIONS =======================
// We only use the Gaussian filter function. The other filters give
// very similar results.
 
float boxFilter(float r2){
    return 1.0;
}
 
float gaussFilter(float r2){
    float alpha = FILTER_SHARPNESS;
    return exp(-alpha * r2);
}
 
float triFilter(float r2){
    float alpha = FILTER_SHARPNESS;
    float r= sqrt(r2);
    return max(0, 1.-r);///alpha);
}
 
float sinc(float x){
    return sin(M_PI*x)/(M_PI*x);
}
 
float lanczosFilter(float r2){
    if (r2==0)
        return 1;
    float r= sqrt(r2);
    return sinc(r)*sinc(r/1.3);
}
 
//catmull-rom filter
float crFilter(float r2){
    float r = sqrt(r2);
    return (r>=2.)?.0:(r<1.)?(3.*r*r2-5.*r2+2.):(-r*r2+5.*r2-8*r+4.);
}
 
float quadraticFilter(float r2){
    float a = FILTER_SHARPNESS;
    return 1.0 - r2/(a*a);
}
 
float cubicFilter(float r2){
    float a = FILTER_SHARPNESS;
    float r = sqrt(r2);
    return 1.0 - 3*r2/(a*a) + 2*r*r2/(a*a*a);
}

//}

//==================== EWA ( reference / 2-tex / 4-tex) ====================
 
/**
*   EWA filter
*   Adapted from an ANSI C implementation from Matt Pharr
*/
vec4 ewaFilter(sampler2D Source, vec2 p0, vec2 du, vec2 dv, int scale){

    vec4 foo = texture(Source,p0);
   
    //don't bother with elliptical filtering if the scale is very small
    if(scale<2)
        return foo;
 
    p0 -=vec2(0.5,0.5)/scale;
    vec2 p = scale * p0;
 
    float ux = FILTER_WIDTH * du.s * scale;
    float vx = FILTER_WIDTH * du.t * scale;
    float uy = FILTER_WIDTH * dv.s * scale;
    float vy = FILTER_WIDTH * dv.t * scale;
 
    // compute ellipse coefficients
    // A*x*x + B*x*y + C*y*y = F.
    float A = vx*vx+vy*vy+1;
    float B = -2*(ux*vx+uy*vy);
    float C = ux*ux+uy*uy+1;
    float F = A*C-B*B/4.;
 
    // Compute the ellipse's (u,v) bounding box in texture space
    float bbox_du = 2. / (-B*B+4.0*C*A) * sqrt((-B*B+4.0*C*A)*C*F);
    float bbox_dv = 2. / (-B*B+4.0*C*A) * sqrt(A*(-B*B+4.0*C*A)*F);
 
    //the ellipse bbox             
    int u0 = int(floor(p.s - bbox_du));
    int u1 = int(ceil (p.s + bbox_du));
    int v0 = int(floor(p.t - bbox_dv));
    int v1 = int(ceil (p.t + bbox_dv));
 
    // Heckbert MS thesis, p. 59; scan over the bounding box of the ellipse
    // and incrementally update the value of Ax^2+Bxy*Cy^2; when this
    // value, q, is less than F, we're inside the ellipse so we filter
    // away..
    vec4 num= vec4(0., 0., 0., 1.);
    float den = 0;
    float ddq = 2 * A;
    float U = u0 - p.s;
   
    for (int v = v0; v <= v1; ++v) {
        float V = v - p.t;
        float dq = A*(2*U+1) + B*V;
        float q = (C*V + B*U)*V + A*U*U;

        for (int u = u0; u <= u1; ++u) {
            if (q < F)
            {
                float r2 = q / F;
                float weight = FILTER_FUNC(r2);
           
                num += weight* texture(Source, vec2(u+0.5,v+0.5)/scale);
                den += weight;
            }
            q += dq;
            dq += ddq;
        }

    }
 
 
    vec4 color = num*(1./den);
    return color;
}

vec4 texture2DEWA(sampler2D tex, vec2 coords){
 
    vec2 du = dFdx(coords);
    vec2 dv = dFdy(coords);
   
    int scale = textureSize(tex, 0).x;
 
    return ewaFilter(tex, coords, du, dv, scale );
 
}

vec2 radialDistortion(vec2 coord) {
  vec2 cc = coord - vec2(0.5);
  float dist = dot(cc, cc) * params.distortion;
  return coord + cc * (1.0 - dist) * dist;
}

void main()
{
   FragColor = texture2DEWA(SourceImage,radialDistortion(vTexCoord));
}