Blur

Box Blur

Gaussian Blur

O(n^2)

Discrete Sample

  // discrete sample gaussian blur vs
  attribute vec4 a_position;
  attribute vec2 a_texcoord;

  uniform vec2 blurSize;
  
  varying vec2 vblurtexcoord[9];
  
  void main()
  {
    gl_Position = a_position;
    
    vec2 offset1 = 1.0 * blurSize;
    vec2 offset2 = 2.0 * blurSize;
    vec2 offset3 = 3.0 * blurSize;
    vec2 offset4 = 4.0 * blurSize;
    
    vblurtexcoord[0] = a_texcoord - offset4;
    vblurtexcoord[1] = a_texcoord - offset3;
    vblurtexcoord[2] = a_texcoord - offset2;
    vblurtexcoord[3] = a_texcoord - offset1;
    vblurtexcoord[4] = a_texcoord;
    vblurtexcoord[5] = a_texcoord + offset1;
    vblurtexcoord[6] = a_texcoord + offset2;
    vblurtexcoord[7] = a_texcoord + offset3;
    vblurtexcoord[8] = a_texcoord + offset4;
  }

  // discrete sample gaussian blur fs
  
  precision mediump float;
  uniform sampler2D  inputTexture;
  
  varying vec2 vblurtexcoord[9];
  
  void main()
  {
    lowp vec3 sample = texture2D(inputTexture, vblurtexcoord[0]).rgb * 0.05;
    sample += texture2D(inputTexture, vblurtexcoord[1]).rgb * 0.09;
    sample += texture2D(inputTexture, vblurtexcoord[2]).rgb * 0.12;
    sample += texture2D(inputTexture, vblurtexcoord[3]).rgb * 0.15;
    sample += texture2D(inputTexture, vblurtexcoord[4]).rgb * 0.18;
    sample += texture2D(inputTexture, vblurtexcoord[5]).rgb * 0.15;
    sample += texture2D(inputTexture, vblurtexcoord[6]).rgb * 0.12;
    sample += texture2D(inputTexture, vblurtexcoord[7]).rgb * 0.09;
    sample += texture2D(inputTexture, vblurtexcoord[8]).rgb * 0.05;
    
    gl_FragColor = vec4(sample, 1.0);
  }

Linear Sample

  // linear sample gaussian blur vs
  attribute vec4 a_position;
  attribute vec2 a_texcoord;

  uniform vec2 blurSize;
  
  varying vec2 vblurtexcoord[5];
  
  void main()
  {
    gl_Position = a_position;
    vec2 firstOffset = 1.3846153846 * blurSize;
    vec2 secondOffset = 3.2307692308 * blurSize;
    
    vblurtexcoord[0] = a_texcoord - secondOffset;
    vblurtexcoord[1] = a_texcoord - firstOffset;
    vblurtexcoord[2] = a_texcoord;
    vblurtexcoord[3] = a_texcoord + firstOffset;
    vblurtexcoord[4] = a_texcoord + secondOffset;
  }

  // linear sample gaussian blur fs
  
  precision mediump float;
  uniform sampler2D  inputTexture;
  
  varying vec2 vblurtexcoord[5];
  
  void main()
  {
    lowp vec3 sample = texture2D(inputTexture, vblurtexcoord[0]).rgb * 0.0702702703;
    sample += texture2D(inputTexture, vblurtexcoord[1]).rgb * 0.3162162162;
    sample += texture2D(inputTexture, vblurtexcoord[2]).rgb * 0.2270270270;
    sample += texture2D(inputTexture, vblurtexcoord[3]).rgb * 0.3162162162;
    sample += texture2D(inputTexture, vblurtexcoord[4]).rgb * 0.0702702703;
    
    gl_FragColor = vec4(sample, 1.0);
  }

Stack Blur

Reference