uniform vec4 color;
uniform vec4 innerColor;

out vec4 fragColor;

void main()
{
  vec2 centered = abs(gl_PointCoord - vec2(0.5));
  float dist = max(centered.x, centered.y);

  float fac = dist * dist * 4.0;
  fragColor = mix(innerColor, color, 0.45 + fac * 0.65);

  /* Make the effect more like a fresnel by offsetting
   * the depth and creating mini-spheres.
   * Disabled as it has performance impact. */
  // gl_FragDepth = gl_FragCoord.z + 1e-6 * fac;
}