#version 150
//OVE shader_name: Inverted Page Curl
//OVE shader_description: by Hewlett-Packard / Sergey Kosarevsky (Licence BSD 3 Clause)


//OVE end

#define LINEAR_CURVE 0
#define EXPONENTIAL_CURVE 1
#define LOGARITHMIC_CURVE 2

uniform sampler2D out_block_in;
uniform sampler2D in_block_in;
uniform bool out_block_in_enabled;
uniform bool in_block_in_enabled;
uniform int curve_in;

/* animated from 0 to 1 */
uniform float ove_tprog_all;

in vec2 ove_texcoord;
out vec4 frag_color;

vec4 getFromColor( vec2 p)
{
  return texture( in_block_in, p);
}

vec4 getToColor( vec2 p)
{
  return texture( out_block_in, p);
}

float TransformCurve(float linear) {
  if (curve_in == EXPONENTIAL_CURVE) {
    return linear * linear;
  } else if (curve_in == LOGARITHMIC_CURVE) {
    return sqrt(linear);
  } else {
    return linear;
  }
}


const float MIN_AMOUNT = -0.16;
const float MAX_AMOUNT = 1.5;
const float PI = 3.141592653589793;
const float scale = 512.0;
const float sharpness = 3.0;

float progress;
float amount;
float cylinderCenter;
float cylinderAngle;

const float cylinderRadius = 1.0 / PI / 2.0;

vec3 hitPoint(float hitAngle, float yc, vec3 point, mat3 rrotation)
{
  float hitPoint = hitAngle / (2.0 * PI);
  point.y = hitPoint;
  return rrotation * point;
}

vec4 antiAlias(vec4 color1, vec4 color2, float distanc)
{
  distanc *= scale;
  if (distanc < 0.0) return color2;
  if (distanc > 2.0) return color1;
  float dd = pow(1.0 - distanc / 2.0, sharpness);
  return ((color2 - color1) * dd) + color1;
}

float distanceToEdge(vec3 point)
{
  float dx = abs(point.x > 0.5 ? 1.0 - point.x : point.x);
  float dy = abs(point.y > 0.5 ? 1.0 - point.y : point.y);
  if (point.x < 0.0) dx = -point.x;
  if (point.x > 1.0) dx = point.x - 1.0;
  if (point.y < 0.0) dy = -point.y;
  if (point.y > 1.0) dy = point.y - 1.0;
  if ((point.x < 0.0 || point.x > 1.0) && (point.y < 0.0 || point.y > 1.0))
    return sqrt(dx * dx + dy * dy);

  return min(dx, dy);
}

vec4 seeThrough(float yc, vec2 p, mat3 rotation, mat3 rrotation)
{
  float hitAngle = PI - (acos(yc / cylinderRadius) - cylinderAngle);
  vec3 point = hitPoint(hitAngle, yc, rotation * vec3(p, 1.0), rrotation);
  if (yc <= 0.0 && (point.x < 0.0 || point.y < 0.0 || point.x > 1.0 || point.y > 1.0))
  {
    return getToColor(p);
  }

  if (yc > 0.0) return getFromColor(p);

  vec4 color = getFromColor(point.xy);
  vec4 tcolor = vec4(0.0);

  return antiAlias(color, tcolor, distanceToEdge(point));
}

vec4 seeThroughWithShadow(float yc, vec2 p, vec3 point, mat3 rotation, mat3 rrotation)
{
  float shadow = distanceToEdge(point) * 30.0;
  shadow = (1.0 - shadow) / 3.0;

  if (shadow < 0.0) shadow = 0.0; else shadow *= amount;

  vec4 shadowColor = seeThrough(yc, p, rotation, rrotation);
  shadowColor.r -= shadow;
  shadowColor.g -= shadow;
  shadowColor.b -= shadow;

  return shadowColor;
}

vec4 backside(float yc, vec3 point)
{
  vec4 color = getFromColor(point.xy);
  float gray = (color.r + color.b + color.g) / 15.0;
  gray += (8.0 / 10.0) * (pow(1.0 - abs(yc / cylinderRadius), 2.0 / 10.0) / 2.0 + (5.0 / 10.0));
  color.rgb = vec3(gray);
  return color;
}

vec4 behindSurface(vec2 p, float yc, vec3 point, mat3 rrotation)
{
  float shado = (1.0 - ((-cylinderRadius - yc) / amount * 7.0)) / 6.0;
  shado *= 1.0 - abs(point.x - 0.5);

  yc = (-cylinderRadius - cylinderRadius - yc);

  float hitAngle = (acos(yc / cylinderRadius) + cylinderAngle) - PI;
  point = hitPoint(hitAngle, yc, point, rrotation);

  if (yc < 0.0 && point.x >= 0.0 && point.y >= 0.0 && point.x <= 1.0 && point.y <= 1.0 && (hitAngle < PI || amount > 0.5))
  {
    shado = 1.0 - (sqrt(pow(point.x - 0.5, 2.0) + pow(point.y - 0.5, 2.0)) / (71.0 / 100.0));
    shado *= pow(-yc / cylinderRadius, 3.0);
    shado *= 0.5;
  }
  else
  {
    shado = 0.0;
  }
  return vec4(getToColor(p).rgb - shado, 1.0);
}

vec4 transition(vec2 p) {

  const float angle = 100.0 * PI / 180.0;
  float c = cos(-angle);
  float s = sin(-angle);

  mat3 rotation = mat3( c, s, 0,
                        -s, c, 0,
                        -0.801, 0.8900, 1
                        );
  c = cos(angle);
  s = sin(angle);

  mat3 rrotation = mat3( c, s, 0,
                         -s, c, 0,
                         0.98500, 0.985, 1
                         );

  vec3 point = rotation * vec3(p, 1.0);

  float yc = point.y - cylinderCenter;

  if (yc < -cylinderRadius)
  {
          // Behind surface
          return behindSurface(p,yc, point, rrotation);
  }

  if (yc > cylinderRadius)
  {
    // Flat surface
    return getFromColor(p);
  }

  float hitAngle = (acos(yc / cylinderRadius) + cylinderAngle) - PI;

  float hitAngleMod = mod(hitAngle, 2.0 * PI);
  if ((hitAngleMod > PI && amount < 0.5) || (hitAngleMod > PI/2.0 && amount < 0.0))
  {
    return seeThrough(yc, p, rotation, rrotation);
  }

  point = hitPoint(hitAngle, yc, point, rrotation);

  if (point.x < 0.0 || point.y < 0.0 || point.x > 1.0 || point.y > 1.0)
  {
    return seeThroughWithShadow(yc, p, point, rotation, rrotation);
  }

  vec4 color = backside(yc, point);

  vec4 otherColor;
  if (yc < 0.0)
  {
    float shado = 1.0 - (sqrt(pow(point.x - 0.5, 2.0) + pow(point.y - 0.5, 2.0)) / 0.71);
    shado *= pow(-yc / cylinderRadius, 3.0);
    shado *= 0.5;
    otherColor = vec4(0.0, 0.0, 0.0, shado);
  }
  else
  {
    otherColor = getFromColor(p);
  }

  color = antiAlias(color, otherColor, cylinderRadius - abs(yc));

  vec4 cl = seeThroughWithShadow(yc, p, point, rotation, rrotation);
  float dist = distanceToEdge(point);

  return antiAlias(color, cl, dist);
}


void main(void) {
  progress = TransformCurve(1.0 - ove_tprog_all);
  amount = progress * (MAX_AMOUNT - MIN_AMOUNT) + MIN_AMOUNT;
  cylinderCenter = amount;
  // 360 degrees * amount
  cylinderAngle = 2.0 * PI * amount;
  frag_color = transition( ove_texcoord.xy);
}