Android Canvas Demonstration 2b

The use of a palette to display the Mandelbrot set is rewarding. You can try changing values in the palette to customise the appearance of the output. As stated when we used similar code in Pascal demonstrations, it is an instructive and enjoyable exercise to study the effects of slight changes to the code.

Screenshot

The code of MainActivity.pas

namespace org.me.canvas_demo2b;

interface

uses
  java.util,
  android.app,
  android.content,
  android.os,
  android.util,
  android.view,
  android.graphics;

type
  MainActivity = public class(Activity)
  private
    drawView : DrawView;    
  public
    class var maxX, maxY : Integer;
    method onCreate(savedInstanceState: Bundle); override;
  end;

  DrawView = class (View)
  private      
    paint : Paint  := new Paint;    
  public
    method onDraw(canvas : Canvas); override;
end;

implementation

method MainActivity.onCreate(savedInstanceState: Bundle);
begin
  inherited;
  drawView := new DrawView(self);
  drawView.setBackgroundColor(Color.WHITE);
  setContentView(drawView);
  maxX := drawView.Width;
  maxY := drawView.Height;
end; 

method DrawView.onDraw(canvas : Canvas);
var
  iMaxX, iMaxY : Integer;
  iNewColor, iI, iJ, CurrentColour : Integer;
  rU, rV, rX, rY, rZ : Single;
  palette: array[0 .. 255] of Integer :=
      [$000000,$A80000,$00A800,$A8A800,$0000A8,$A800A8,$0054A8,$A8A8A8,
       $545454,$FC8484,$54FC54,$FCFC54,$5454FC,$FC54FC,$54FCFC,$FCFCFC,
       $000000,$141414,$202020,$2C2C2C,$383838,$444444,$505050,$606060,
       $707070,$808080,$909090,$A0A0A0,$B4B4B4,$C8C8C8,$E0E0E0,$FCFCFC,
       $FC0000,$FC0040,$FC007C,$FC00BC,$FC00FC,$BC00FC,$7C00FC,$4000FC,
       $0000FC,$0040FC,$007CFC,$00BCFC,$00FCFC,$00FCBC,$00FC7C,$00FC40,
       $00FC00,$40FC00,$7CFC00,$BCFC00,$FCFC00,$FCBC00,$FC7C00,$FC4000,
       $FC7C7C,$FC7C9C,$FC7CBC,$FC7CDC,$FC7CFC,$DC7CFC,$BC7CFC,$9C7CFC,
       $7C7CFC,$FC9CFC,$7CBCFC,$7CDCFC,$7CFCFC,$7CFCDC,$7CFCBC,$7CFC9C,
       $7CFC7C,$9CFC7C,$BCFC7C,$DCFC7C,$FCFC7C,$FCDC7C,$FCBC7C,$FC9C7C,
       $FCB4B4,$FCB4C4,$FCB4D8,$FCB4E8,$FCB4FC,$E8B4FC,$D8B4FC,$C4B4FC,
       $B4B4FC,$B4C4FC,$B4D8FC,$B4E8FC,$B4FCFC,$B4FCE8,$B4FCD8,$B4FCC4,
       $B4FCB4,$C4FCB4,$D8FCB4,$E8FCB4,$FCFCB4,$FCE8B4,$FCD8B4,$FCC4B4,
       $700000,$70001C,$700038,$700054,$700070,$540070,$380070,$1C0070,
       $000070,$001C70,$003870,$005470,$007070,$007054,$007038,$00701C,
       $007000,$1C7000,$387000,$547000,$707000,$705400,$703800,$701C00,
       $703838,$703844,$703854,$703860,$703870,$603870,$543870,$443870,
       $383870,$384470,$385470,$386070,$387070,$387060,$387054,$387044,
       $387038,$447038,$547038,$607038,$707038,$706038,$705438,$704438,
       $705050,$705058,$705060,$705068,$705070,$685070,$605070,$585070,
       $505070,$505870,$506070,$506870,$507070,$507068,$507060,$507058,
       $507050,$587050,$607050,$687050,$707050,$706850,$706050,$705850,
       $400000,$400010,$400020,$400030,$400040,$300040,$200040,$100040,
       $000040,$001040,$002040,$003040,$004040,$004030,$004020,$004010,
       $004000,$104000,$204000,$304000,$404000,$403000,$402000,$401000,
       $402020,$402028,$402030,$402038,$402040,$382040,$302040,$282040,
       $202040,$202840,$203040,$203840,$204040,$204038,$204030,$204028,
       $204020,$284020,$304020,$384020,$404020,$403820,$403020,$402820,
       $402C2C,$402C30,$402C34,$402C3C,$402C40,$3C2C40,$342C40,$302C40,
       $2C3040,$2C3440,$2C3C40,$2C4040,$2C403C,$2C4034,$2C4030,$2C402C,
       $30402C,$34402C,$3C402C,$40402C,$403C2C,$40342C,$40302C,$000000,
       $000000,$000000,$000000,$000000,$000000,$000000,$000000,$000000];
begin
  iMaxX := 450;
  iMaxY := 700;
  for iI := 0 to iMaxX do
    begin
      for iJ := 0 to iMaxY do
        begin
          //Centre and scale along real (x) axis
          rX := -0.85 + 3 * Single(iI) / iMaxX;
          //Centre and scale along imaginary (y) axis
          rY := -1.2 + 2.4 * Single(iJ) / iMaxY;
          iNewColor := 0;
          rU := 0;
          rV := 0;
          repeat
            rZ := rU * rU - rV * rV - rX;
            rV := 2 * rU * rV - rY;
            rU := rZ;
            inc(iNewColor);
          until (rU * rU + rV * rV > 4) or (iNewColor = 255);
          if iNewColor = 255 then
            iNewColor := 0;
          paint.setColor(palette[iNewColor]);
          paint.setAlpha(255);
          canvas.drawPoint(iI, iJ, paint);         
        end;
    end;
end;

end.

Strings File

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="app_name">Canvas Demo 2b</string>
</resources>