Improve RichTextBox scrolling logic

[Xanfre]

Currently, the control only checks if the mouse wheel distance is greater or less than zero while ignoring the distance itself, which can result in the scroll procedure being sent far too frequently under some circumstances. Here, we can store the mouse wheel accumulation and increment or decrement it when the scroll procedure is sent to prevent this from happening.

[FenPhoenix]

Works fine, although I'm unable to notice a difference myself. Do you mean that it was sometimes scrolling multiple times when it should have only scrolled once? Out of curiosity, how did you make it happen?

[Xanfre]

It only happens, from what I can tell, on high-resolution mouse wheels. No issue occurs at all on a notched wheel since the distance is reported at each notch; however, moving a modern laptop's trackpad will scroll a disproportionate distance in the control because the distance is reported more frequently.

This modified procedure will only scroll the control at distance intervals of 120, which is one notch in a standard mouse wheel.

[FenPhoenix]

Okay, cool. Merging. Thanks for the continued improvements.