These functions are useful for decoding scroll bar events.
function scroll-bar-event-ratio event
This function returns the fractional vertical position of a scroll bar event within the scroll bar. The value is a cons cell
(portion . whole) containing two integers whose ratio is the fractional position.
function scroll-bar-scale ratio total
This function multiplies (in effect)
total, rounding the result to an integer. The argument
ratio is not a number, but rather a pair
(num . denom)—typically a value returned by
This function is handy for scaling a position on a scroll bar into a buffer position. Here’s how to do that:
(posn-x-y (event-start event))
(- (point-max) (point-min))))
Recall that scroll bar events have two integers forming a ratio, in place of a pair of x and y coordinates.