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I am new to win32 programming and have a very naive question.

Say there is my application window of size 1920x1280 and I create a child window over it of size 1920x2560 (double of vertical screen size). Now I load an image onto this child window which has the same size as that of child window i.e 1920x2560.

Now my question is If I use ScrollWindow for vertical scroll, will I necessarily need to repaint the dirty rect (the bottom part), since the image would be already loaded? Is it not possible to avoid that and just move the screen buffers ? Or is there any other way possible to avoid redrawing, may be using bitmaps or something?

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    Windows don't remember their contents when they're obscured. You need to repaint them when they come into view. Commented Dec 1, 2022 at 4:15
  • Thanks for the answer @JonathanPotter i also got the similar hint. Does using bitmap help here (i saw scrolling option is available in bitmap as well) or is the bitmap also limited to device screen size ? There must be something to do fast drawing. My app is taking almost 16-20 ms for single scroll event. Any suggestions here? question is specific to scrolling Commented Dec 1, 2022 at 6:23
  • If you have your image as a bitmap then instead of using ScrollWindow to shuffle the existing bits, just redraw the whole display from the new origin within the bitmap. Commented Dec 1, 2022 at 6:41
  • Say I am scrolling up, Are you suggesting that rather than doing ScrollWindow and invalidating the bottom part of the screen, I should redraw the full screen window and avoid calling ScrollWindow all together ? Will that be faster? Commented Dec 1, 2022 at 6:54
  • I wouldn't be surprised if it would be quicker. Certainly easy to test. Commented Dec 1, 2022 at 9:48

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An application draws in a window when scrolling, changing, or selecting a portion of the displayed data

but you could only draw the differences in the Update Region.
It's also noted that disabling the default handling for the WM_ERASEBKGND message makes smooth.
The disadvantage of your idea is always drawing outside of client area and how to just move the screen buffers to avoid redrawing?

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My thought was If we could simply move screen buffers, I could create a large childwindow and update the invisible part of its hwnd in some background thread as per my convenience. Since ScrollWindow moves screen buffers in 1ms , I will be practically able to handle one scroll wheelevent in 1ms and give smooth scroll experience
I'm afraid there is no so-called screen buffers concepts.

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