Delphi, Canvas: Complicated background animation under [blinding] image - delphi

Question

I have some troubles with rendering my canvas. Actually I'm trying to write game like space invaders, without using any OpenGL or DirectX. So at the background I have moving sky, and jet moving over it. But the jet is blinding, and sky moves not uniformly. Here's my code
sky := TBitmap.Create;
sky.LoadFromFile('sky.bmp');
jet := TBitmap.Create;
jet.LoadFromFile('jet.bmp');
jet.Transparent := True;
while True do
begin
for k := 0 to sky.Height do
begin
for i := -1 to (pbMain.Height div sky.Height) do
begin
for j := 0 to (pbMain.Width div sky.Width) do
begin
pbMain.Canvas.Draw(nx, ny, jet);
pbMain.Canvas.Draw(j*sky.Width, k + i*sky.Height, sky);
end;
Application.ProcessMessages;
end;
Sleep(1);
end;
end;
Thank you.

Answer 1

You can't write a standard Windows app like that. You have to do your painting in response to WM_PAINT messages. In Delphi terms this equates to overriding the Paint method of a TWinControl descendent, or perhaps using a TPaintBox and providing an OnPaint event handler. I'm going to assume that you use a TPaintBox.
If you need to avoid flicker it is common practice to draw to an off-screen bitmap and then show this when you are asked to paint.
Your application should probably use a timer control to provide a regular pulse. Then, on each pulse, update your off-screen bitmap. Then call Invalidate on your paint box to force a paint cycle.
The code might look like this:
procedure TMainForm.RefreshTimerTimer(Sender: TObject);
begin
RedrawOffscreenBitmap;
PaintBox.Invalidate;
end;
procedure TMainForm.RedrawOffscreenBitmap;
begin
//paint to FOffscreenBitmap
end;
procedure TMainForm.PaintBoxBox(Sender: TObject);
begin
PaintBox.Canvas.Draw(0, 0, FOffscreenBitmap);
end;