uniform float ambient;
uniform vec3 diffuse;
uniform float ring;
uniform float shininess;
uniform float specular;
uniform int lights;
uniform int style;
varying vec3 eye;
varying vec3 normal;
varying vec3 vertex;
uniform float thickness;

float balance(float sample, float weight) {
  if (weight < 1.0)
    weight = sample + weight;
  return clamp(pow(weight, 5.0), 0.0, 1.0);
}

float diagonal(float sample) {
  vec2 pixel = floor(vec2(gl_FragCoord));
  float a = 1.0;
  float b = mod(pixel.x - pixel.y, thickness);
  float c = thickness / 2.0;
  if (b < thickness) 
    a = abs(b - c) / c;
  return balance(sample, a);  
}

float waves(float sample) {
  vec2 pixel = floor(vec2(gl_FragCoord));
  float a = 1.0;
  float b = mod(pixel.y + sin(pixel.x / 10.0) * 4.0, thickness);
  float c = thickness / 2.0;
  if (b < thickness) 
    a = abs(b - c) / c;
  return balance(sample, a);  
}

float circles(float sample) {
  vec2 pixel = floor(vec2(gl_FragCoord));
  float b = thickness / 2.0;
  if (mod((pixel.y), thickness * 2.0) > thickness)
    pixel.x += b;
  pixel = mod(pixel, vec2(thickness));
  float a = distance(pixel, vec2(b)) / (thickness * 0.65);
  return balance(sample, a);  
}

vec3 shade(int index, vec3 eye, vec3 normal, vec3 color) {
  vec3 light = gl_LightSource[index].position.xyz + eye;
  vec3 c = gl_LightSource[index].diffuse.rgb;
  float w = gl_LightSource[index].position.w;
  vec3 l = normalize(light);
  float b = dot(normal, l) * w;
  if (b > 0.0) {
    color += diffuse * b * c;  
    vec3 r = reflect(-l, normal);
    float s = pow(max(dot(r, eye), 0.0), shininess) * w;
    s = smoothstep(ring, 1.0, s);
    color += s * specular;
  }
  return color;
}

void main(void) {
  vec3 color = diffuse * ambient;
  vec3 e = normalize(eye);
  vec3 n = normalize(normal);
  for (int i = 0; i < lights; i++)
    color = shade(i, e, n, color);
  float hatch;
  float scale = color.r;
  if (style == 0)
    hatch = diagonal(scale);
  else if (style == 1)
    hatch = waves(scale);
  else if (style == 2)
    hatch = circles(scale);
  else 
    hatch = 1.0;
  if (hatch > 0.25)  
    color = vec3(1.0);
  gl_FragColor = vec4(color * hatch, 1);
}