Zoom image using delphi - delphi

Question

I am working with delphi. I have TImage, to which I assign a bitmap.
imgmain.Picture.Bitmap := bmpMain;
imgmain.Picture.Bitmap.PixelFormat := pf24bit;
imgmain is object of TImage and bmpMain is object of TBitmap
I want to zoom my image. I have one trackbar on my form and as I click on trackbar the image should get zoom. What should I do?
Thank You.
Edit :
I found some solution at here It works but it cut my image.

Answer 1

The code you refer to sets up a transformation from one coordinate space to another, I didn't notice anything that would cut/crop your image there. However, instead of having an inversely proportional zoom factor I'd rather have, easy to understand, linear scaling. Also, I see no reason switching map modes depending on the scaling factor, I would modify the SetCanvasZoomFactor like this;
procedure SetCanvasZoomPercent(Canvas: TCanvas; AZoomPercent: Integer);
begin
SetMapMode(Canvas.Handle, MM_ISOTROPIC);
SetWindowExtEx(Canvas.Handle, 100, 100, nil);
SetViewportExtEx(Canvas.Handle, AZoomPercent, AZoomPercent, nil);
end;
A simplified (no error checking) working example with a bitmap loaded to a TImage, scaled via a TrackBar could be like the below. Note that the above function is inlined in the TrackBar's OnChange event.
type
TForm1 = class(TForm)
imgmain: TImage;
TrackBar1: TTrackBar;
Label1: TLabel;
procedure FormCreate(Sender: TObject);
procedure TrackBar1Change(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
bmpmain: TBitmap;
[..]
[...]
procedure TForm1.FormCreate(Sender: TObject);
begin
bmpmain := TBitmap.Create;
bmpmain.LoadFromFile(ExtractFilePath('samplebitmap.bmp');
bmpmain.PixelFormat := pf32bit; // No significance, just seems faster here than pf24bit
TrackBar1.Min := 10;
TrackBar1.Max := 200;
TrackBar1.Frequency := 10;
TrackBar1.PageSize := 10;
TrackBar1.Position := 100; // Fires OnChange
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
bmpmain.Free;
end;
procedure TForm1.TrackBar1Change(Sender: TObject);
var
Zoom, x, y: Integer;
begin
Zoom := TrackBar1.Position;
if not (Visible or (Zoom = 100)) or (Zoom = 0) then
Exit;
SetMapMode(imgmain.Canvas.Handle, MM_ISOTROPIC);
SetWindowExtEx(imgmain.Canvas.Handle, 100, 100, nil);
SetViewportExtEx(imgmain.Canvas.Handle, Zoom, Zoom, nil);
x := imgmain.Width * 50 div Zoom - bmpmain.Width div 2;
y := imgmain.Height * 50 div Zoom - bmpmain.Height div 2;
imgmain.Canvas.Draw(x, y, bmpmain);
if (x > 0) or (y > 0) then begin
imgmain.Canvas.Brush.Color := clWhite;
ExcludeClipRect(imgmain.Canvas.Handle, x, y, x + bmpmain.Width, y + bmpmain.Height);
imgmain.Canvas.FillRect(imgmain.Canvas.ClipRect);
end;
Label1.Caption := 'Zoom: ' + IntToStr(TrackBar1.Position) + '%';
end;
edit: same code with a TImage in a ScrollBox;
type
TForm1 = class(TForm)
TrackBar1: TTrackBar;
Label1: TLabel;
ScrollBox1: TScrollBox;
imgmain: TImage;
procedure FormCreate(Sender: TObject);
procedure TrackBar1Change(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
bmpmain: TBitmap;
[...]
[...]
const
FULLSCALE = 100;
procedure TForm1.FormCreate(Sender: TObject);
begin
imgmain.Left := 0;
imgmain.Top := 0;
bmpmain := TBitmap.Create;
bmpmain.LoadFromFile(ExtractFilePath(Application.ExeName) + '610x.bmp');
bmpmain.PixelFormat := pf32bit;
TrackBar1.Min := FULLSCALE div 10; // %10
TrackBar1.Max := FULLSCALE * 2; // %200
TrackBar1.PageSize := (TrackBar1.Max - TrackBar1.Min) div 19;
TrackBar1.Frequency := TrackBar1.PageSize;
TrackBar1.Position := FULLSCALE;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
bmpmain.Free;
end;
procedure TForm1.TrackBar1Change(Sender: TObject);
var
Zoom: Integer;
begin
Zoom := TrackBar1.Position;
if not (Visible or (Zoom = FULLSCALE)) or (Zoom = 0) then
Exit;
SetMapMode(imgmain.Canvas.Handle, MM_ISOTROPIC);
SetWindowExtEx(imgmain.Canvas.Handle, FULLSCALE, FULLSCALE, nil);
SetViewportExtEx(imgmain.Canvas.Handle, Zoom, Zoom, nil);
imgmain.Width := Round(bmpmain.Width * Zoom / FULLSCALE);
imgmain.Height := Round(bmpmain.Height * Zoom / FULLSCALE);
if Assigned(imgmain.Picture.Graphic) then begin
imgmain.Picture.Graphic.Width := imgmain.Width;
imgmain.Picture.Graphic.Height := imgmain.Height;
end;
imgmain.Canvas.Draw(0, 0, bmpmain);
Label1.Caption := 'Zoom: ' +
IntToStr(Round(TrackBar1.Position / FULLSCALE * 100)) + '%';
end;