Draw on Canvas with no anti-aliasing effect in Firemonkey

Question

I am trying to make a kind of bitmap editor so I just want to draw a line on a bitmap with no anti-aliasing effect in Firemonkey. Something like this:

var
  Bmp: TBitmap;

Bmp := TBitmap.Create(2000, 2000);
if (Bmp.Canvas.BeginScene) then 
begin
  Bmp.Canvas.Stroke.Color := TAlphaColors.Aquamarine;
  Bmp.Canvas.DrawLine(PointF(5, 5), PointF(100, 100), 1);
  Bmp.Canvas.EndScene;
  Bmp.SaveToFile('c:\temp\result.bmp');
end;
FreeAndNil(Bmp);

But it doesn't work. I am trying for a while with several ideas with no luck:

• Using Map/Unmap to access the bitmap data directly is very slow with big bitmaps according to my coworkers.
• Using a TImage with DisableInterpolation=true and even GlobalUseGPUCanvas=False doesn't work.
• Using a TPaintBox component doesn't fit our needs.
• The solution would be the use of Canvas.Quality=HighPerformance but it's a read-only property. I tried to change the bitmap Canvas.Quality in different ways but it doesn't work.

So how can I simply draw a line with no anti-aliasing effect at all in Firemonkey?

PS: I am using Delphi 10.2.3 (Tokyo)

Answer 1

FireMonkey paints lines on the grid between the pixels and not on the pixels. So you have to add 0.5 to each coordinate in order to paint on the pixels:

Bmp.Canvas.DrawLine(PointF(5.5, 5.5), PointF(100.5, 100.5), 1);

This does not disable anti-aliasing, but avoids the excessive anti-aliasing that happens otherwise. I'm not aware of a FireMonkey function that disables anti-alisiasing. You would have to call a native OS function, for example CGContextSetAllowsAntialiasing on MacOS, but usually it is not needed anymore as soon as you figure out how to paint on the pixels.

Answer 2

Finally I found a way to do this. It's so simple that I am wondering if there is some hidden poison in the solution (LOL). TCanvasManager allows the creation of a HighPerformance Canvas from a given bitmap. It draws with no antialiasing according to my tests. Here the code:

var
  Bmp: TBitmap;
  TmpCanvas: TCanvas;
begin
  Bmp := TBitmap.Create(2000, 2000);
  TmpCanvas := TCanvasManager.CreateFromBitmap(Bmp, TCanvasQuality.HighPerformance);
  if (TmpCanvas.BeginScene) then
  begin
    TmpCanvas.Stroke.Color := TAlphaColors.Aquamarine;
    TmpCanvas.DrawLine(PointF(5, 5), PointF(100, 100), 1);
    TmpCanvas.EndScene;
    Bmp.SaveToFile('c:\temp\result.bmp');
  end;
  FreeAndNil(TmpCanvas);
  FreeAndNil(Bmp);

I also found that it doesn't work with the method to write text on Canvas (Canvas.FillText).

I hope this helps many others with the same problem.