​

uniform sampler2D uTexture;

uniform vec2 uResolution;

uniform float uIntensity;

​

void main() {

  // Translate our coordinates from pixels with a top left origin to normalized coordinates in [0, 1] with a lower left origin for GLSL

  vec2 uv = gl_FragCoord.xy / uResolution;

  uv.y = 1.0 - uv.y;

  // and read our image's RGBA data with these normalized coordinates

  vec4 color = texture2D(uTexture, uv);

​

  // Calculate the brightness of the pixel

  float brightness = (color.r + color.g + color.b) / 3.0;

​

  // Blur the image by taking the average of the surrounding pixels

  float blur = 0.0;

  for (float x = -5.0; x <= 5.0; x++) {

    for (float y = -5.0; y <= 5.0; y++) {

      vec2 offset = vec2(x, y) / uResolution;

      blur += texture2D(uTexture, uv + offset).r;

    }

  }

  blur /= 121.0;

​

  // Add the blurred image back to the original, with some scaling to control the intensity

  vec4 bloom = vec4(color.rgb + uIntensity * blur, 1.0);

  // Output the final color

  gl_FragColor = mix(color, bloom, brightness);

}