frag.glsl

#version 300 es

precision highp float;

in float v_height;
in vec3 v_local_pos;
in float v_primitiveID;

uniform int u_display;

uniform vec3 u_light_direction;
uniform vec3 u_top_color;
uniform vec3 u_bottom_color;

out vec4 fragColor;

vec3 intToColor(int i) {
  int r = (i * 127) & 255;
  int g = (i * 251) & 255;
  int b = (i * 373) & 255;
  
  return vec3(float(r), float(g), float(b)) / 255.0;
}

void main() {
  vec4 low_color  = vec4(u_bottom_color, 1.0);
  vec4 high_color = vec4(u_top_color, 1.0);

  vec3 light_dir = normalize(u_light_direction);

  vec3 normal = normalize(cross(dFdx(v_local_pos), dFdy(v_local_pos)));

  float diffuse = dot(normal, light_dir);
  
  if (u_display == 0 || u_display == 4) {
    fragColor = mix(low_color, high_color, v_height);
    fragColor.rgb *= 0.5 + 0.5 * (1.0 - diffuse);
  } else if (u_display == 1) {
    fragColor = vec4(vec3(diffuse), 1.0);
  } else if (u_display == 2) {
    fragColor = vec4(0.5 + 0.5 * normal, 1.0);
  } else if (u_display == 3) {
    fragColor = vec4(intToColor(int(v_primitiveID)), 1.0);
  }
}