#version 330

in vec2 f_texCoord;
out vec4 fragColor;

uniform sampler2D tex;
uniform vec2 min_uv;
uniform vec2 max_uv;

float c_x0 = -1.0;
float c_x1 =  0.0;
float c_x2 =  1.0;
float c_x3 =  2.0;

//=======================================================================================
vec4 clampedSmaple(sampler2D tex, vec2 uv)
{
   vec2 clmapedUv = clamp(uv, min_uv, max_uv);
   return texture2D(tex, clmapedUv);
}

//=======================================================================================
vec3 CubicHermite (vec3 A, vec3 B, vec3 C, vec3 D, float t)
{
	float t2 = t*t;
   float t3 = t*t*t;
   vec3 a = -A/2.0 + (3.0*B)/2.0 - (3.0*C)/2.0 + D/2.0;
   vec3 b = A - (5.0*B)/2.0 + 2.0*C - D / 2.0;
   vec3 c = -A/2.0 + C/2.0;
   vec3 d = B;
   
   return a*t3 + b*t2 + c*t + d;
}

//=======================================================================================
vec3 BicubicHermiteTextureSample (sampler2D sam, vec2 P, float textureSize)
{
   float onePixel = (1.0 / textureSize);
   float twoPixels = (2.0 / textureSize);
   vec2 pixel = P * textureSize + 0.5;
   
   vec2 frac = fract(pixel);
   pixel = floor(pixel) / textureSize - vec2(onePixel/2.0);
   
   vec3 C00 = clampedSmaple(sam, pixel + vec2(-onePixel ,-onePixel)).rgb;
   vec3 C10 = clampedSmaple(sam, pixel + vec2( 0.0        ,-onePixel)).rgb;
   vec3 C20 = clampedSmaple(sam, pixel + vec2( onePixel ,-onePixel)).rgb;
   vec3 C30 = clampedSmaple(sam, pixel + vec2( twoPixels,-onePixel)).rgb;
   
   vec3 C01 = clampedSmaple(sam, pixel + vec2(-onePixel , 0.0)).rgb;
   vec3 C11 = clampedSmaple(sam, pixel + vec2( 0.0        , 0.0)).rgb;
   vec3 C21 = clampedSmaple(sam, pixel + vec2( onePixel , 0.0)).rgb;
   vec3 C31 = clampedSmaple(sam, pixel + vec2( twoPixels, 0.0)).rgb;    
   
   vec3 C02 = clampedSmaple(sam, pixel + vec2(-onePixel , onePixel)).rgb;
   vec3 C12 = clampedSmaple(sam, pixel + vec2( 0.0        , onePixel)).rgb;
   vec3 C22 = clampedSmaple(sam, pixel + vec2( onePixel , onePixel)).rgb;
   vec3 C32 = clampedSmaple(sam, pixel + vec2( twoPixels, onePixel)).rgb;    
   
   vec3 C03 = clampedSmaple(sam, pixel + vec2(-onePixel , twoPixels)).rgb;
   vec3 C13 = clampedSmaple(sam, pixel + vec2( 0.0        , twoPixels)).rgb;
   vec3 C23 = clampedSmaple(sam, pixel + vec2( onePixel , twoPixels)).rgb;
   vec3 C33 = clampedSmaple(sam, pixel + vec2( twoPixels, twoPixels)).rgb;    
   
   vec3 CP0X = CubicHermite(C00, C10, C20, C30, frac.x);
   vec3 CP1X = CubicHermite(C01, C11, C21, C31, frac.x);
   vec3 CP2X = CubicHermite(C02, C12, C22, C32, frac.x);
   vec3 CP3X = CubicHermite(C03, C13, C23, C33, frac.x);
   
   return CubicHermite(CP0X, CP1X, CP2X, CP3X, frac.y);
}
    
//=======================================================================================
vec3 CubicLagrange (vec3 A, vec3 B, vec3 C, vec3 D, float t)
{
   return
      A * 
      (
         (t - c_x1) / (c_x0 - c_x1) * 
         (t - c_x2) / (c_x0 - c_x2) *
         (t - c_x3) / (c_x0 - c_x3)
      ) +
      B * 
      (
         (t - c_x0) / (c_x1 - c_x0) * 
         (t - c_x2) / (c_x1 - c_x2) *
         (t - c_x3) / (c_x1 - c_x3)
      ) +
      C * 
      (
         (t - c_x0) / (c_x2 - c_x0) * 
         (t - c_x1) / (c_x2 - c_x1) *
         (t - c_x3) / (c_x2 - c_x3)
      ) +       
      D * 
      (
         (t - c_x0) / (c_x3 - c_x0) * 
         (t - c_x1) / (c_x3 - c_x1) *
         (t - c_x2) / (c_x3 - c_x2)
      );
}

//=======================================================================================
vec3 BicubicLagrangeTextureSample (sampler2D sam, vec2 P, float textureSize)
{
   float onePixel = (1.0 / textureSize);
   float twoPixels = (2.0 / textureSize);

   vec2 pixel = P * textureSize + 0.5;
   
   vec2 frac = fract(pixel);
   pixel = floor(pixel) / textureSize - vec2(onePixel/2.0);
   
   vec3 C00 = clampedSmaple(sam, pixel + vec2(-onePixel ,-onePixel)).rgb;
   vec3 C10 = clampedSmaple(sam, pixel + vec2( 0.0        ,-onePixel)).rgb;
   vec3 C20 = clampedSmaple(sam, pixel + vec2( onePixel ,-onePixel)).rgb;
   vec3 C30 = clampedSmaple(sam, pixel + vec2( twoPixels,-onePixel)).rgb;
   
   vec3 C01 = clampedSmaple(sam, pixel + vec2(-onePixel , 0.0)).rgb;
   vec3 C11 = clampedSmaple(sam, pixel + vec2( 0.0        , 0.0)).rgb;
   vec3 C21 = clampedSmaple(sam, pixel + vec2( onePixel , 0.0)).rgb;
   vec3 C31 = clampedSmaple(sam, pixel + vec2( twoPixels, 0.0)).rgb;    
   
   vec3 C02 = clampedSmaple(sam, pixel + vec2(-onePixel , onePixel)).rgb;
   vec3 C12 = clampedSmaple(sam, pixel + vec2( 0.0        , onePixel)).rgb;
   vec3 C22 = clampedSmaple(sam, pixel + vec2( onePixel , onePixel)).rgb;
   vec3 C32 = clampedSmaple(sam, pixel + vec2( twoPixels, onePixel)).rgb;    
   
   vec3 C03 = clampedSmaple(sam, pixel + vec2(-onePixel , twoPixels)).rgb;
   vec3 C13 = clampedSmaple(sam, pixel + vec2( 0.0        , twoPixels)).rgb;
   vec3 C23 = clampedSmaple(sam, pixel + vec2( onePixel , twoPixels)).rgb;
   vec3 C33 = clampedSmaple(sam, pixel + vec2( twoPixels, twoPixels)).rgb;    
   
   vec3 CP0X = CubicLagrange(C00, C10, C20, C30, frac.x);
   vec3 CP1X = CubicLagrange(C01, C11, C21, C31, frac.x);
   vec3 CP2X = CubicLagrange(C02, C12, C22, C32, frac.x);
   vec3 CP3X = CubicLagrange(C03, C13, C23, C33, frac.x);
   
   return CubicLagrange(CP0X, CP1X, CP2X, CP3X, frac.y);
}

//=======================================================================================
vec4 cubic(float v){
    vec4 n = vec4(1.0, 2.0, 3.0, 4.0) - v;
    vec4 s = n * n * n;
    float x = s.x;
    float y = s.y - 4.0 * s.x;
    float z = s.z - 4.0 * s.y + 6.0 * s.x;
    float w = 6.0 - x - y - z;
    return vec4(x, y, z, w) * (1.0/6.0);
}

//=======================================================================================
vec4 textureBicubic(sampler2D sampler, vec2 texCoords){

   vec2 texSize = textureSize(sampler, 0);
   vec2 invTexSize = 1.0 / texSize;
   
   texCoords = texCoords * texSize - 0.5;

   
    vec2 fxy = fract(texCoords);
    texCoords -= fxy;

    vec4 xcubic = cubic(fxy.x);
    vec4 ycubic = cubic(fxy.y);

    vec4 c = texCoords.xxyy + vec2 (-0.5, +1.5).xyxy;
    
    vec4 s = vec4(xcubic.xz + xcubic.yw, ycubic.xz + ycubic.yw);
    vec4 offset = c + vec4 (xcubic.yw, ycubic.yw) / s;
    
    offset *= invTexSize.xxyy;
    
    vec4 sample0 = clampedSmaple(sampler, offset.xz);
    vec4 sample1 = clampedSmaple(sampler, offset.yz);
    vec4 sample2 = clampedSmaple(sampler, offset.xw);
    vec4 sample3 = clampedSmaple(sampler, offset.yw);

    float sx = s.x / (s.x + s.y);
    float sy = s.z / (s.z + s.w);

    return mix(
       mix(sample3, sample2, sx), mix(sample1, sample0, sx)
    , sy);
}

//=======================================================================================
vec4 textureNice( sampler2D sam, vec2 uv )
{
    float textureResolution = float(textureSize(sam,0).x);
    uv = uv*textureResolution + 0.5;
    vec2 iuv = floor( uv );
    vec2 fuv = fract( uv );
    uv = iuv + fuv*fuv*(3.0-2.0*fuv);
    uv = (uv - 0.5)/textureResolution;
    return clampedSmaple( sam, uv );
}

void main(void)
{
   // fragColor = textureBicubic(tex, f_texCoord.xy);

   // fragColor = texture2D(tex, f_texCoord.xy);  

   // fragColor = textureNice(tex, f_texCoord.xy);

   // vec3 color;
   // float textureResolution = float(textureSize(tex,0).x);
   // color = BicubicLagrangeTextureSample(tex, f_texCoord.xy, textureResolution);
   // fragColor = vec4(color, 1.0);

   vec3 color;
   
   float textureResolution = float(textureSize(tex,0).x);
   color = BicubicHermiteTextureSample(tex, f_texCoord.xy, textureResolution);
   fragColor = vec4(color, 1.0);

   //fragColor = vec4(0.5, 0.7, 0.6, 1);
}