init-auto-scrollbars in canvas%

Enables and initializes automatic scrollbars for the canvas. A horizontal or vertical scrollbar can be activated only in a canvas that was created with the 'hscroll or 'vscroll style flag, respectively.

With automatic scrollbars, the programmer specifies the desired virtual size of the canvas, and the scrollbars are automatically handled to allow the user to scroll around the virtual area. The scrollbars are not automatically hidden if they are unneeded; see show-scrollbars.

See also init-manual-scrollbars for information about manual scrollbars. The horizontal and vertical scrollbars are always either both manual or both automatic, but they are independently enabled. Automatic scrollbars can be re-initialized as manual, and vice-versa.

• (send a-canvas init-auto-scrollbars horiz-pixels vert-pixels h-value v-value) -> void
     horiz-pixels : exact integer in [1, 10000] or #f
   vert-pixels : exact integer in [1, 10000] or #f
   h-value : real number in [0.0, 1.0]
     v-value : real number in [0.0, 1.0]

  Initializes the scrollbars and resets the canvas's virtual size to the given values. If either horiz-pixels or vert-pixels is #f, the scrollbar is not enabled in the corresponding direction, and the canvas's virtual size in that direction is the same as its client size.

  The h-value and v-value arguments specify the initial values of the scrollbars as a fraction of the scrollbar's range. A 0.0 value initializes the scrollbar to its left/top, while a 1.0 value initializes the scrollbar to its right/bottom.

  See also on-scroll and get-virtual-size.