precision mediump float;

varying vec2 vTextureCoord;
uniform float exposure;
uniform float decay;
uniform float density;
uniform float weight;
uniform vec2 lightPositionOnScreen;
uniform sampler2D uSampler;

const int NUM_SAMPLES = 100;

void main()
{
    vec2 deltaTextCoord = vec2( vTextureCoord - lightPositionOnScreen.xy );
    vec2 textCoo = vTextureCoord;
    deltaTextCoord *= 1.0 /  float(NUM_SAMPLES) * density;
    float illuminationDecay = 1.0;
   
    for(int i=0; i < NUM_SAMPLES ; i++)
    {
             textCoo -= deltaTextCoord;
             vec4 sample = texture2D(uSampler, textCoo );

             sample *= illuminationDecay * weight;

             gl_FragColor += sample;

             illuminationDecay *= decay;
     }
    
     gl_FragColor *= exposure;
}