[SOLVED] How to draw on canvas with semi-transparency?

[artem101]

Task is very simple - draw red circle on TImage canvas with 50% transparency fill.

I tried to set different values (0, $ffff, $ffff div 2) to Brush.FPColor alpha, but result is the same - no transparency.

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. begin
3.   with Image1.Canvas do
4.   begin
5.     DrawingMode := dmAlphaBlend; // no any effect with/without this
6.  
7.     Brush.Color:=clBlack;
8.     Pen.Style:=psClear;
9.     Clear;
10.  
11.     Brush.Color:=clGreen;
12.     Ellipse(50, 50, 150, 150);
13.  
14.     // How to draw second circle with 50% transparency?
15.     //Brush.Color:=clRed;
16.     Brush.FPColor:=FPColor($ffff,0000,0000, $ffff div 2);
17.     Ellipse(80, 80, 200, 200);
18.  
19.   end;
20. end;  

How to make this?

Thanks.

[paweld]

https://wiki.freepascal.org/Developing_with_Graphics#Creating_and_drawing_a_transparent_bitmap_for_a_TImage

[ADMGNS]

hello

with RGBABitmap:

Code: Pascal  [Select][+][-]

1. uses
2. ..., BGRABitmap, BGRABitmapTypes;
3.  
4.  
5. procedure TForm1.FormPaint(Sender: TObject);
6. var
7.   Bmp: TBGRABitmap;
8. begin
9.   Bmp := TBGRABitmap.Create(256, 256, BGRA(240, 240, 240, 128)); // no transparency effect
10.   try
11.     Bmp.FillRect(50, 50, 200, 200, BGRA(255, 0, 0, 128));
12.  
13.     // together, use same color, 150 is transparency in RGBA()
14.     Bmp.FillEllipseAntialias(100, 100, 80, 80, BGRA(0, 255, 0, 150));
15.     Bmp.EllipseAntialias(100, 100, 80, 80, BGRA(0, 255, 0, 150), 1);
16.  
17.     Bmp.Draw(Canvas, (ClientWidth-bmp.Width) div 2, (ClientHeight-bmp.Height) div 2, True);
18.   finally
19.     Bmp.Free;
20.   end;
21. end;
22.  

[artem101]

Thank you!

Result:

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. var
3.   Bmp: TBGRABitmap;
4. begin
5.   Bmp := TBGRABitmap.Create(Image1.Width, Image1.Height, BGRA(0,0,0));
6.   try
7.     bmp.FillEllipseInRect(Rect(50, 50, 150, 150), BGRA(0,255,0));
8.     bmp.FillEllipseInRect(Rect(80, 80, 200, 200), BGRA(255,0,0,255 div 2));
9.  
10.     Bmp.Draw(Image1.Canvas, (ClientWidth-bmp.Width) div 2, (ClientHeight-bmp.Height) div 2, True);
11.   finally
12.     Bmp.Free;
13.   end;
14. end;