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procedure BresenhamCircle(CenterX, CenterY, Radius: Integer; Canvas: TCanvas; Color: TColor);
{
Bresenham's Line Algorithm
Bresenham's Circle Algorithm
fra denne side:
http://www.funducode.com/freec/graphics/graphics2.htm
}
procedure PlotCircle(x, y, x1, y1: Integer);
begin
  Canvas.Pixels[x + x1, y + y1] := Color;
  Canvas.Pixels[x - x1, y + y1] := Color;
  Canvas.Pixels[x + x1, y - y1] := Color;
  Canvas.Pixels[x - x1, y - y1] := Color;
  Canvas.Pixels[x + y1, y + x1] := Color;
  Canvas.Pixels[x - y1, y + x1] := Color;
  Canvas.Pixels[x + y1, y - x1] := Color;
  Canvas.Pixels[x - y1, y - x1] := Color;
end;
var
  x, y, r: Integer;
  x1, y1, p: Integer;
begin
  x := CenterX;
  y := CenterY;
  r := Radius;
  x1 := 0;
  y1 := r;
  p := 3 - 2 * r;
  while ( x1 < y1 ) do
  begin
    plotcircle ( x, y, x1, y1) ;
    if ( p < 0 ) then
      p := p + 4 * x1 + 6
    else
      begin
        p := p + 4 * ( x1 - y1 ) + 10 ;
        y1 := y1 - 1 ;
      end;
    x1 := x1 + 1 ;
  end;
  if ( x1 = y1 ) then
    plotcircle ( x, y, x1, y1) ;
end;					

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for y:=1 to Image1.Height DO
  for x:=1 to Image1.Width DO
  begin
  if sqrt(sqr(x)+sqr(y)) <= r then
    Image1.Canvas.Pixels[x,y]:=clBlack;
  end;
for y:=1 to Image1.Height DO
  for x:=1 to Image1.Width DO
  begin
  if sqrt(sqr(x)+sqr(y)) <= r then
    Image2.Canvas.Pixels[x,Image2.Height-y]:=clBlack;
  end;
for y:=1 to Image1.Height DO
  for x:=1 to Image1.Width DO
  begin
  if sqrt(sqr(x)+sqr(y)) <= r then
    Image3.Canvas.Pixels[Image3.Width-x,y]:=clBlack;
  end;
for y:=1 to Image1.Height DO
  for x:=1 to Image1.Width DO
  begin
  if sqrt(sqr(x)+sqr(y)) <= r then
    Image4.Canvas.Pixels[Image4.Width-x,Image4.Height-y]:=clBlack;
  end;					

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for y:=1 to Image1.Height do
 begin
  for x:=1 to Image1.Width do
   begin
    if sqrt(sqr(x)+sqr(y)) <= r then
     begin
      Image1.Canvas.Pixels[x,y]:=clBlack;
      Image2.Canvas.Pixels[x,Image2.Height-y]:=clBlack;
      Image3.Canvas.Pixels[Image3.Width-x,y]:=clBlack;
      Image4.Canvas.Pixels[Image4.Width-x,Image4.Height-y]:=clBlack; 
     end
   end
 end;					

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procedure FilledCircle(Canvas: TCanvas; x0, y0, r: Integer);
var
 x, y: Integer;
begin
  with Canvas do
   for y := -(r-1) to r-1 do
   begin
    x := round(sqrt(sqr(r)-sqr(y)));
    MoveTo(-x+x0, y+y0);
    Lineto(x+x0, y+y0);
   end;
end;