// (c) 2008 OpenTK.net

uniform sampler1D COLORTABLE;
uniform float CETX;
uniform float CETY;
uniform float SCALINGX;
uniform float SCALINGY;

const int MAXIterations = 16; // *must* be > 0

void main(void)
{
  float XPos = gl_FragCoord.x / SCALINGX - 1.6;
  float YPos = gl_FragCoord.y / SCALINGY - 1.6;
  float XQuad = pow( XPos, 2.0 );
  float YQuad = pow( YPos, 2.0 );
  int TableIndex = -1;
  int LoopCount = 0;
  while ( LoopCount <= MAXIterations )
    {
      YPos = 2.0 * XPos * YPos + CETY;
      XPos = XQuad - YQuad + CETX;
      XQuad = pow( XPos, 2.0 );
      YQuad = pow( YPos, 2.0 );
      TableIndex++;
      if ( (XQuad + YQuad) > 4.0 )
      { 
//         if (TableIndex == 0)
//           discard;
         LoopCount = MAXIterations;
      }
      LoopCount++;
    }
  float FinalTableIndex = float( TableIndex ) / float( MAXIterations );

  gl_FragColor.rgb = vec3( FinalTableIndex ); // outputs greyscale
  // gl_FragColor = texture1D( COLORTABLE, FinalTableIndex ); // outputs color
}