uniform mat4 ModelViewProjectionMatrix;
uniform float size;
uniform float outlineWidth;

in vec2 pos;
in vec4 color;
out vec4 radii;
out vec4 fillColor;

void main()
{
  gl_Position = ModelViewProjectionMatrix * vec4(pos, 0.0, 1.0);
  gl_PointSize = size;
  fillColor = color;

  /* Calculate concentric radii in pixels. */
  float radius = 0.5 * size;

  /* Start at the outside and progress toward the center. */
  radii[0] = radius;
  radii[1] = radius - 1.0;
  radii[2] = radius - outlineWidth;
  radii[3] = radius - outlineWidth - 1.0;

  /* Convert to PointCoord units. */
  radii /= size;
}