mandelbrot.etch

  // TWS, April 28th, Mandelbrot Set (simple):
  function main()
    //
    printLn("Mandelbrot Set");
    //
    // The "screen" size and the screen itself (double height for mirrored set):
    var xMax : Int32 = 100;
    var yMax : Int32 = 32;
    var halfOffset : Int32 = yMax * xMax;
    var screen = Array<String>(xMax * (yMax * 2));
    var maxIterations : Int32 = 230;
    var maxSprites : Float64 = 32.0;
    //
    // Draw the mandelbrot set:  
    for (pixelY in 0:yMax - 1)  
      for (pixelX in 0:xMax - 1)
        //
        // Scale X to mandlebrot scale (x -2.5 to 1):
        var xLocal : Float64 = toFloat64(pixelX);
        xLocal = ((xLocal / toFloat64(xMax)) * 3.5) - 2.5;
        //
        // Now Y to -1 to 1:
        var yLocal : Float64 = toFloat64(pixelY);
        yLocal = yLocal / toFloat64(yMax);
        //
        // Now let's do the algorithm bit:
        var x : Float64 = 0.0;
        var y : Float64 = 0.0;
        var iteration : Int32 = 0;
        while (((x * x) + (y * y)) <= 4.0 && iteration < maxIterations)
          var xTemp = (x * x) - (y * y) + xLocal;
          y = 2.0 * x * y + yLocal;
          x = xTemp;
          iteration++;
          endwhile
        //
        // Render based on iteration achieved:
        var colourSlide : Float64 = (toFloat64(iteration) / toFloat64(maxIterations));
        var colourIndex : Int32 = toInt32(colourSlide * maxSprites);
        //
        // Pick a character according to colourIndex (iterations achieved):
        var insertCharacter : String = " ";
        if (colourIndex < 2)
          insertCharacter = " ";
        elseif (colourIndex < 6)
          insertCharacter = ".";
        elseif (colourIndex < 10)
          insertCharacter = "'";
        elseif (colourIndex < 20)
          insertCharacter = "+";
        else
          insertCharacter = "*";
        endif
        //
        // Bottom half of mandlebrot set:
        var bIndex : Int32 = halfOffset + (pixelY * xMax) + pixelX;
        screen[bIndex] = insertCharacter;
        //
        // Top mirror half:
        var inverseY = yMax - pixelY;
        var tIndex : Int32 = (inverseY * xMax) + pixelX;
        screen[tIndex] = insertCharacter;
        endfor
      endfor
      //
      // Render the buffer out:
      for (y in 0:(yMax * 2) - 1)   
        var line : String = "";
        for (x in 0:xMax - 1)      
          //
          // Build the line, deal with my own stupidity with the screen array
          // by testing for NULL:
          var index : Int32 = (y * xMax) + x; 
          if (screen[index] == null)
            line = line + " ";
          else
            line = line + screen[index];
          endif
          endfor
        //
        // Output this line and proceed to next:
        printLn(line);
        endfor
    
  endfunction