Package drawutil contains draw related utility functions.
MouseScrollSize computes the number of lines of text that should be scrolled in response to a mouse scroll wheel click. Maxlines is the number of lines visible in the text window.
The default scroll increment is one line. This default can be overridden by setting the $mousescrollsize environment variable to an integer, which specifies a constant number of lines, or to a real number followed by a percent character, indicating that the scroll increment should be a percentage of the total number of lines in the window. For example, setting $mousescrollsize to 50% causes a half-window scroll increment.