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#version 120

// www.OpenTK.net GLSL Julia Set (c) 2008 Christoph Brandtner

uniform sampler1D COLORTABLE;

uniform float CETX;

uniform float CETY;

uniform float SCALINGX;

uniform float SCALINGY;

uniform float OFFSETX;

uniform float OFFSETY;

const int MAXIterations = 32; // *must* be > 0

void main(void)

{

  float XPos = gl_FragCoord.x / SCALINGX - OFFSETX;

  float YPos = gl_FragCoord.y / SCALINGY - OFFSETY;

  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 = texture1D( COLORTABLE, FinalTableIndex ); // lookup texture for output

  // gl_FragColor.rgb = vec3( FinalTableIndex ); // Debug: output greyscale

}