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Drawing an Oscilloscope (flickerfree & fast)

Posted on 1998-08-27
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Last Modified: 2013-11-19
I want to display an oscilloscope in a window.  This oscilloscope would have a fixed grid, some fixed text, and the moving signal display.

Ideally the grid and text should be displayed BEHIND the signal, but this is not critical.

The grid and text should be flicker-free.

Finally the scope should not take too much processor time.  It is displaying the result of a fairly intensive calculation process, and I don't want to spend half my time just painting.

What is the best way to implement something like this in MFC?

Carlos
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Question by:carlosn
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psdavis earned 300 total points
ID: 1321406
Look at www.codeguru.com and there you will find two ways to perform flicker free drawing.  One uses a CMemDC method that is quite easy.  The other gives you a class that you will derive from.

Second, you may want to consider drawing all of your data into a precreated bitmap in your resource file.  (256 color is fine).  Then use LoadImage to access the bitmap and draw directly onto your bitmap.

Phillip
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by:psdavis
ID: 1321407
Also take a quick look at DrawDibDraw and it's associated functions in the Video for Windows SDK.  I've used them briefly, but if you have a lot of images to display in a row it could be useful.

Also (and possibly best) you may want to choose your signal wisely, if you use the XOR pen to draw your data, then you can just erase the signal with another XOR drawing.  Then you won't have to redraw the entire bitmap at all.  Just XOR on and XOR off the signal.

Phillip
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by:carlosn
ID: 1321408
Thank you, I'll have to check the XOR idea.

I have started using some of the memory DC, and found that the BitBlt was incredibly slow.  Is this normal?  Copying over a bitmap thats about 300x200 pixels, it was taking about 6% of the softwares time (according to the profiler).  Each BitBlt ran for about 2 ms, and the window is getting updated every 50 ms or so.
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Expert Comment

by:psdavis
ID: 1321409
Yes, BitBlt is slow.  DrawDibDraw was created to be faster.

Good luck.

Phillip
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