Delphi GDIPLUS change image position - image

Question

i am trying to achieve a simple task but by using GDI+ and i cannot find any example.
In my code i need to change an image position (top if to be more specific), but i have no idea if i can do it in a better way.
This is how i do it now:
procedure TForm2.Timer1Timer(Sender: TObject);
var
I: Integer;
begin
if image1.Top = -93 then
Begin
for I := -93 to -1 do
Begin
Sleep(10);
image1.Top := Image1.Top + 1;
Application.ProcessMessages;
End;
End else if image1.Top = 0 then
Begin
for I := 0 downto -92 do
Begin
Sleep(10);
image1.Top := Image1.Top - 1;
Application.ProcessMessages;
End;
End;
end;
Well it's pretty simple, but it does not go smooth, but jumps and redraws itself at each step.
I appreciate your help.
UPDATE:
Thanks to TLama and his inspiration i have found this GDIPlus implementation for delphi 2007

Answer 1

Moving control is a wrong way to animate anything, GDI+ independent. Instead, you should remember the position you want to change for the animation, modify it in the OnTimer event and tell the system that you want to invalidate the target control. Then in the control's OnPaint event you should render whatever you want by that position.
So as the first, replace your TImage component by a TPaintBox since the TImage is used mainly for static images, not for a dynamic rendering. Also use two timers. One for upward animation and one for downward animation.
The following code doesn't take into account approximation of a timer, and it uses less known Delphi 2009 GDI+ Library wrapper for Delphi:
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, ExtCtrls, GdiPlus;
type
TForm1 = class(TForm)
Timer1: TTimer;
Timer2: TTimer;
PaintBox1: TPaintBox;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure Timer1Timer(Sender: TObject);
procedure Timer2Timer(Sender: TObject);
procedure PaintBox1Paint(Sender: TObject);
private
GPImage: IGPImage;
FImageTop: Integer;
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
FImageTop := 0;
Timer1.Interval := 15;
Timer2.Interval := 15;
DoubleBuffered := True;
Timer1.Enabled := True;
Timer2.Enabled := False;
GPImage := TGPImage.Create('d:\Image.jpg');
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
// no need for the following line since it's a reference of the interface
// GPImage := nil;
end;
procedure TForm1.Timer1Timer(Sender: TObject);
begin
if (FImageTop > -93) then
begin
FImageTop := FImageTop - 1;
PaintBox1.Invalidate;
end
else
begin
Timer1.Enabled := False;
Timer2.Enabled := True;
end;
end;
procedure TForm1.Timer2Timer(Sender: TObject);
begin
if (FImageTop < 0) then
begin
FImageTop := FImageTop + 1;
PaintBox1.Invalidate;
end
else
begin
Timer2.Enabled := False;
Timer1.Enabled := True;
end;
end;
procedure TForm1.PaintBox1Paint(Sender: TObject);
var
GPGraphics: IGPGraphics;
begin
GPGraphics := TGPGraphics.Create(PaintBox1.Canvas.Handle);
GPGraphics.DrawImage(GPImage, 0, FImageTop);
end;
end.