Window and Display Features: Windows and the Display Surface

Windows and the Display Surface

A window is really a viewport into a display. The display can be larger or smaller than the window. If the display is larger than the window, you can use scrolling commands to move the surface under the window (or equivalently, move the window over the display surface). The scrolling commands are as follows:

RIGHT $\text{[math]}$: scrolls right.
LEFT $\text{[math]}$: scrolls left.
FORWARD $\text{[math]}$: scrolls forward (down).
BACKWARD $\text{[math]}$: scrolls backward (up).
TOP: scrolls to the top of the display surface.
BOTTOM: scrolls to the bottom of the display surface.

The argument $\text{[math]}$ is an optional numeric argument that indicates the number of positions to scroll. The default is 5.

Only one window is active at a time. You can move, zoom, enlarge, shrink, or recolor inactive windows, but you cannot scroll or enter data.

Each display starts with the same standard lines: first a command line for entering commands, then a message line for displaying messages (such as error messages).

The remainder of the display is up to you to design. You can put fields in any positive row and column position of the display surface, even if it is off the displayed viewport.