How to draw on TCanvas with performance?

Question

I use a map component named TatukGis and I need to draw some other information on map, it uses TCanvas basically to draw the maps. I'm working with Pixels to create an alpha blend effect that I'd like, but it's very slow, it seems to refresh the canvas on each operation. Some one can give some hints how to use TCanvas in the correctly way to draw the things fast ?

Tks

Yes, the `Pixels` property is *very* slow. It's almost unusable. You have to access the pixels via the `Scaline` property. [The second sample in this answer](http://stackoverflow.com/questions/4916913/draw-opacity-ellipse-in-delphi-2010/4917296#4917296) might be useful. — Andreas Rejbrand, Apr 25 '11 at 14:09

score 4 · Accepted Answer · answered Apr 25 '11 at 13:32

4

First write to a bitmap (use ScanLine if you require pixel access), then draw the bitmap to the canvas (CopyRect).

answered Apr 25 '11 at 13:32

Mike Versteeg

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Or StretchBlt, which despite the name might actually be faster than copyrect. – Warren P Apr 25 '11 at 13:37
Or `BitBlt` if you don't need to stretch. – Andreas Rejbrand Apr 25 '11 at 14:13
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BitBlt is (usually?) faster than StretchBlt. As long as your bitmaps are 1:1. – Bruce McGee Apr 25 '11 at 14:16
Or TranslateBlt in msimg32.dll. Not win95 compatible, but iirc it used to be faster that bitblt, but with less features – Marco van de Voort Apr 25 '11 at 17:57
StretchBlt=BitBlt when no stretch required – David Heffernan Apr 25 '11 at 18:44
@Marco: Really, I have to look that up. – Andreas Rejbrand Apr 25 '11 at 20:24
Andreas: saw a reference once, but at that time we already decided to convert to OpenGL, so I didn't look into it, or verify it further, other than that it exists. I do know that many webcam viewer programs use it. (from viewing with PEExplorer) – Marco van de Voort Apr 26 '11 at 12:05

How to draw on TCanvas with performance?

1 Answers1