Draw a filled circle

[Carver413]

well I suppose that works but what if you want a 6 sided circle or an ellipse or a half circle. might be better to use a more conventual routine with a fill routine.

[User137]

Sometimes, but fill routine makes it much slower. It is checking for pixels on every draw to find where the borders are, and could also be allocating dynamic arrays for point data, depending on algorithm. You can modify algorithms to make filled half circle etc. And if you need to draw the circle on top of a complex drawing, fill no longer works. And it's in addition that you would use sin/cos/sqrt for outline anyway

Here's algorithm for above given function translated, filled and non-filled circle. (Drawing to TForm.canvas directly was bad idea, i know... but it showed it at least.)

procedure DrawPixel(x, y: longint; color: TColor);
begin
  form1.Canvas.Pixels[x, y]:=color;
end;

procedure DrawLine(x1, x2, y: longint; color: TColor);
var x: integer;
begin
  for x:=x1 to x2 do
    form1.Canvas.Pixels[x, y]:=color;
end;

procedure retro_circle(xc, yc, r: longint; color: TColor);
var x, y, d: longint;
begin
  x:=0; y:=r;
  d:=1 - r;
  while x < y do begin
    if d < 0 then
      d:=d + 2*x + 3
    else begin
      d:=d + 2*x - 2*y + 5;
      dec(y);
    end;
    DrawPixel(xc + x, yc - y, color); // Top
    DrawPixel(xc - x, yc - y, color);
    DrawPixel(xc + y, yc - x, color); // Upper middle
    DrawPixel(xc - y, yc - x, color);
    DrawPixel(xc + y, yc + x, color); // Lower middle
    DrawPixel(xc - y, yc + x, color);
    DrawPixel(xc + x, yc + y, color); // Bottom
    DrawPixel(xc - x, yc + y, color);
    inc(x);
  end;
end;

procedure retro_fill_circle(xc, yc, r: longint; color: TColor);
var x, y, d: longint;
begin
  x:=0; y:=r;
  d:=1 - r;
  while x < y do begin
    if d < 0 then
      d:=d + 2*x + 3
    else begin
      d:=d + 2*x - 2*y + 5;
      dec(y);
    end;
    DrawLine(xc - x, xc + x, yc - y, color);
    DrawLine(xc - y, xc + y, yc - x, color);
    DrawLine(xc - y, xc + y, yc + x, color);
    DrawLine(xc - x, xc + x, yc + y, color);
    inc(x);
  end;
end;

Also as far as i see, the fill function may draw some pixels overlapped. Not perfectly optimal this way.