shadowmap

//vertex fragment
#ifdef GL_ES
precision mediump float;
#endif
uniform float invFar; //   actually this is inverse of distance from camera to frustum corner
const vec4 bitShift = vec4( 256.0, 1.0, 256.0, 1.0);
const vec4 bitMask = vec4(0.0, 1.0 / 256.0, 0.0, 1.0 / 256.0);
varying vec3 pos;

void main() {
    float depth = length(pos) * invFar;
    float moment2 = depth * depth;
    vec4 comp = fract(vec4depth, depth, moment2, moment2) * bitShift);
    gl_FragColor = comp - comp.xxzz * bitMask; //this give more precission
}

//vertex
attribute vec4 a_position;
uniform mat4 u_projectionViewMatrix;
uniform vec3 lightPos;
varying vec3 pos;

void main()
{
    pos = (a_position.rgb - lightPos);
    gl_Position = u_projectionViewMatrix * a_position;
}