# PGPLOT Module: PGSCRL -- scroll window

SUBROUTINE PGSCRL (DX, DY)

REAL DX, DY

This routine moves the window in world-coordinate space while

leaving the viewport unchanged. On devices that have the

capability, the pixels within the viewport are scrolled

horizontally, vertically or both in such a way that graphics

previously drawn in the window are shifted so that their world

coordinates are unchanged.

If the old window coordinate range was (X1, X2, Y1, Y2), the new

coordinate range will be approximately (X1+DX, X2+DX, Y1+DY, Y2+DY).

The size and scale of the window are unchanged.

Thee window can only be shifted by a whole number of pixels

(device coordinates). If DX and DY do not correspond to integral

numbers of pixels, the shift will be slightly different from that

requested. The new window-coordinate range, and hence the exact

amount of the shift, can be determined by calling PGQWIN after this

routine.

Pixels that are moved out of the viewport by this operation are

lost completely; they cannot be recovered by scrolling back.

Pixels that are ``scrolled into'' the viewport are filled with

the background color (color index 0).

If the absolute value of DX is bigger than the width of the window,

or the aboslute value of DY is bigger than the height of the window,

the effect will be the same as zeroing all the pixels in the

viewport.

Not all devices have the capability to support this routine.

It is only available on some interactive devices that have discrete

pixels. To determine whether the current device has scroll capability,

call PGQINF.

**Arguments**

DX (input) : distance (in world coordinates) to shift the

window horizontally (positive shifts window to the

right and scrolls to the left).

DY (input) : distance (in world coordinates) to shift the

window vertically (positive shifts window up and

scrolls down).