Info Catalog elisp: Accessing Mouse elisp: Input Events elisp: Strings of Events

elisp: Accessing Scroll

 
 20.7.14 Accessing Scroll Bar Events
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 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) RATIO by 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
      ‘scroll-bar-event-ratio’.
 
      This function is handy for scaling a position on a scroll bar into
      a buffer position.  Here’s how to do that:
 
           (+ (point-min)
              (scroll-bar-scale
                 (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.
 

Info Catalog elisp: Accessing Mouse elisp: Input Events elisp: Strings of Events