​

uniform sampler2D uTexture;

uniform vec2 uTextureSize;

uniform vec2 uCanvasSize;

uniform float uOffset;

uniform vec4 uShadeColor;

uniform float uShadeExponent;

uniform float uDeltaAngle;

​

varying vec2 vTexCoord;

​

const int BlurSampleCount = 39;

#define PI 3.1415926535897932

​

const float EPS = 1.0e-6;

#define APPROX(a, b) abs(a - b) <= EPS

​

​

vec2 Map(vec2 uv)

{

  return vec2(uv.x, 1.0 - acos(2.0 * uv.y - 1.0) / PI);

}

​

​

void main()

{

  float diameter = uTextureSize.y / PI;

  vec2 pixCoord = floor(gl_FragCoord.xy) / (uCanvasSize - 2.0);

  float dist = abs(2.0 * pixCoord.y - 1.0);

  float t = pow(1.0 - pow(dist, uShadeExponent), 1.0 / uShadeExponent);

  vec2 uv = fract(vTexCoord - vec2(0.0, uOffset));

  vec2 sampleFrom = Map(uv);

  vec4 sampledColor = texture2D(uTexture, sampleFrom);

  float totalWeight = 1.0;

  const int loopCount = (BlurSampleCount - 1) / 2;

  for (int i = 0; i < loopCount; ++i)

  {

    float dist = float(i + 1) / float(loopCount);

    // vec2 sampleOffset = vec2(0.0, uDeltaAngle * float(i) / uTextureSize.y);

    vec2 sampleOffset = vec2(0.0, uDeltaAngle * dist);

    vec2 lowerSampleFrom = Map(fract(uv + sampleOffset));

    vec2 upperSampleFrom = Map(fract(uv - sampleOffset));

    sampledColor += texture2D(uTexture, lowerSampleFrom);

    sampledColor += texture2D(uTexture, upperSampleFrom);

    totalWeight += 2.0 * (1.0 - dist);

  }

  sampledColor /= totalWeight;

  gl_FragColor = mix(uShadeColor, sampledColor, t);

  // gl_FragColor = vec4(0.0, uv.y, 1.0, 1.0);

  // gl_FragColor = APPROX(gl_FragCoord.y, 100.5) ?

  //   vec4(1.0) : vec4(vec3(0.0), 1.0);

}

​