#define FOG_START 100
#define FOG_END 500

uniform mat4 projection;
uniform mat4 view;
uniform mat4 model;

attribute vec3 position;
varying float fogAmount;

#pragma glslify: fog_linear = require(glsl-fog/linear)

void main() {
  gl_Position = projection * view * model * vec4(positon, 1.0);
  float fogDistance = length(gl_Position.xyz);
  fogAmount = fog_linear(fogDistance, FOG_START, FOG_END);
}

#define FOG_DENSITY 0.05

varying vec4 vertexColor;

// Take your pick: these should be usable interchangeably.
#pragma glslify: fog_exp2 = require(glsl-fog/exp2)
#pragma glslify: fog_exp = require(glsl-fog/exp)

void main() {
  float fogDistance = gl_FragCoord.z / gl_FragCoord.w;
  float fogAmount = fog_exp2(fogDistance, FOG_DENSITY);
  const float fogColor = vec4(1.0); // white

  gl_FragColor = mix(vertexColor, fogColor, fogAmount);
}