uniform sampler2D de;
uniform sampler2D it;
uniform sampler2D tt;

uniform vec3 interior;
uniform vec3 border;
uniform vec3 exterior;

void main(void) {
  float d = texture2D(de, gl_TexCoord[0].st).x;
  float i = texture2D(it, gl_TexCoord[0].st).x;
  float t = texture2D(tt, gl_TexCoord[0].st).x;
  vec4 c = vec4(interior, 1.0);
  if (i > 0.0) {
    float k = tanh(clamp(d, 0.0, 4.0));
    c.rgb = mix(border, exterior, k);
  }
  gl_FragColor = c;
}