TCanvas: slow copying performance (simple animation)
lazarus / 39-Graphics

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frett · 2012-09-05 16:29

Hi there,
I've written a simple marquee text class for delphi some time ago,
which I recently ported to lazarus along with the project using it. I
encountered almost no problems, however, the cpu utilization of the
marquee animation increased by a factor of 100: compiling with delphi
2006 and executing the application, the task manager always shows 0%,
whereas the lazarus-compiled version consumes between 15% and 50% of
the cpu (enabling optimizations has no effect).

The class works as follows: a text line is drawn to an off-screen
TBitmap, and then the appropriate rectangle section of this bitmap
(depending on the current position of the animation) is copied to a
TPaintBox canvas by a repeated Timer event that also advances the
position counter.

This is the method used for copying:

Code: [Select]procedure TMarqueeText.CopySection(x1, y1, x2, y2:
Integer; source: TCanvas;
  destX, destY: Integer; dest: TCanvas);
var
  sourceRect, destRect: TRect;
begin
  sourceRect := Rect(x1, y1, x2, y2);
  destRect := Rect(destX, destY, destX+(x2-x1), destY+(y2-y1));
  dest.CopyRect(destRect, source, sourceRect);
end;
It seems that the TCanvas.Draw and CopyRect methods are very slow
compared to their VCL counterparts (at least in this particular case).

I wonder what I'm doing wrong here, simply copying an image portion to
another canvas can't be that expensive...

Development system: WinXP SP3, Lazarus 1.0

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TurboRascal · 2012-09-06 19:35

Perhaps you could draw to a TBitmap and use this instead:
Code: [Select]Canvas.Draw(x, y, Bitmap)
Among the examples that came with Lazarus there is a nice one in the
'sprites' subdirectory which uses something similar to create a smooth
animation.

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frett · 2012-09-06 22:02

I have tried that (Canvas.Draw) too, but it seems to be equally slow.
Nevertheless, thank you for the hint on the sprites example, I'll have
a look at it.