[solved] rotate image problem

[speter]

I have written a program (attached) that rotates a 100x100px image; but the results are strange!

The image is of a red "racing car", enclosed in a blue circle. The program creates 35 rotated images (for angles 10..350 degrees); each rotated image is in an array; the images are visible and placed in a 6x6 grid (with the zero'th image being the initial version).

If you look at the attached image of the app some of the cars are cropped on the right and some are cropped on the left; BUT, the circle isn't cropped. I could see a reason for the image being strangely cropped, but I can't work out why only the car bits are being cropped.

I believe the issue is with my program's code, not with the LCL; but I can't work out what the error is.

Any comments / suggestions would be very welcome.

cheers
S.

[paweld]

Try BGRABitmap - it's fast and easy.

Code: Pascal  [Select][+][-]

1. uses
2.   BGRABitmap, BGRABitmapTypes, BGRAPath,
3.   BGRATransform;
4.  
5. //--------------------------------------------------------------------
6. procedure TForm_main.makeracer;
7. //--------------------------------------------------------------------
8. var
9.   a: Integer;
10.   ang: Single;
11.   bmp, bmptmp: TBGRABitmap;
12.   ms: TMemoryStream;
13.   bmptranform: TBGRAAffineBitmapTransform;
14. begin
15.   // create array of 36 racing cars :)
16.   racer[0] := image1;
17.   racer[0].parent := form_main;
18.   racer[0].setbounds(0, 0, 99, 99);
19.   racer[0].Visible := True;
20.   racer[0].top := 0;
21.   racer[0].left := 0;
22.  
23.   bmp := TBGRABitmap.Create(Image1.Picture.Bitmap);
24.  
25.   for a := 1 to 35 do
26.   begin
27.     application.ProcessMessages;
28.  
29.     racer[a] := TImage.Create(form_main);
30.     racer[a].parent := form_main;
31.     racer[a].setbounds(0, 0, 100, 100);
32.  
33.     racer[a].Visible := True;
34.     racer[a].top := 100 * (a div 6);
35.     racer[a].left := 100 * (a mod 6);
36.  
37.     ang := a * 10;
38.     //rotate image
39.     bmptmp := TBGRABitmap.Create(bmp.Width, bmp.Height, BGRAPixelTransparent);
40.     bmptranform := TBGRAAffineBitmapTransform.Create(bmp);
41.     bmptranform.Translate(-bmp.Width div 2, -bmp.Height div 2);
42.     bmptranform.RotateDeg(ang);
43.     bmptranform.Translate(bmp.Width div 2, bmp.Height div 2);
44.     bmptmp.Fill(bmptranform);
45.     bmptranform.Free;
46.     ms := TMemoryStream.Create;
47.     bmptmp.SaveToStreamAsPng(ms);
48.     ms.Position := 0;
49.     racer[a].Picture.LoadFromStream(ms);
50.     ms.Free;
51.     bmptmp.Free;
52.     //
53.   end;
54.   bmp.Free;
55. end;

[speter]

Thanks paweld, I know BGRABitmap has a rotate bitmap function.

I am not wanting to use any libraries though.

cheers
S.

[Ally]

Here is another example that rotates by 90/180/270°, but also by any angle.
When rotating by any angle, the image content is interpolated.
And the transparency is retained.

The core of the whole thing is the unit rhsBitmapRotate.pas, which I have built into the enclosed test program.

[rvk]

In your double loop you check image1.Canvas.pixels[x,y] for non transparency.
But your image1 doesn't have x 99 and y 99.
It is probably less width than height.

Change the original image1 to have width 100 and height 100 and it'll probably work better.
(Haven't tested this because I'm on a mobile)

[LeP]

It's simply because where you test the transparency, you don't rotate it but set that pixel as transparent.
YOU MUST ALSO ROTATE THE TRANSPARENT.

Code: Pascal  [Select][+][-]

1.  //if image1.Canvas.pixels[x,y] <> transparent then
2.             begin
3.               p := rotate(x,y,ang);
4.               racer[a].canvas.pixels[p.x,p.y] := image1.Canvas.pixels[x,y];
5.             end;
6.           //else
7.           //  racer[a].canvas.pixels[x,y] := transparent;

[speter]

It's simply because where you test the transparency, you don't rotate it but set that pixel as transparent.
YOU MUST ALSO ROTATE THE TRANSPARENT.

Code: Pascal  [Select][+][-]

1.  //if image1.Canvas.pixels[x,y] <> transparent then
2.             begin
3.               p := rotate(x,y,ang);
4.               racer[a].canvas.pixels[p.x,p.y] := image1.Canvas.pixels[x,y];
5.             end;
6.           //else
7.           //  racer[a].canvas.pixels[x,y] := transparent;

Thanks very much LeP.

cheers
S.

[speter]

And thanks also, to rvk and Ally.

cheers
S.