Abstract:
For one rotation of the wheel, never scroll the window by more than one page.

Created by Peter Kankowski
Last changed
Filed under Win32 programming

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Corrections to Raymond Chen's wheel scrolling code

In 2003, Raymond Chen published a long series of articles about scrolling in Win32. Unfortunately, the wheel scrolling technique has a subtle bug: if the window height is less than 3 lines (more precisely, less than the scroll delta, which has a default value of 3), several lines will be skipped when scrolling.

Before scrolling: He took his vorpal blade in hand / Long time before the manxsome for he sought. After scrolling: And stood awhile in thought

As you can see, one line (about the Tumturn tree :) is missing. A better program will never scroll the window by more than one page for one rotation of the wheel. Change these lines:

if(uScroll == WHEEL_PAGESCROLL) {
   uScroll = g_cLinesPerPage;
}

to the following ones:

if(uScroll > g_cLinesPerPage) {
   uScroll = g_cLinesPerPage;
}

WHEEL_PAGESCROLL is defined as UINT_MAX, so the modified code will handle WHEEL_PAGESCROLL as well as the small window height.

The code for handling sub-detent wheel mice also was simplified in the program below. Such beasts currently do not exist, so instead of writing the sophisticated code for line-by-line scrolling with them, you could scroll by 3 lines as with usual mouse. The function is simpler this way.

Download the full code (MSVC++ 2005 or Pelles C, 6 KB zip archive)

Peter Kankowski
Peter Kankowski

About the author

Peter is the developer of Aba Search and Replace, a tool for replacing text in multiple files. He likes to program in C with a bit of C++, also in x86 assembly language, Python, and PHP. He can be reached at kankowski@gmail.com.

Created by Peter Kankowski
Last changed

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