10.6. Scroll Bars

When the data being displayed in a panel is too large to be visible all at once, scroll bars are added to allow the contents of the panel to be moved such that any part of it can be made visible. If the panel is too wide to fit, a horizontal scroll bar appears on the bottom of the panel; if too tall, a vertical scroll bar appears on the right of the panel. You control what part of the data is visible by manipulating the scroll bar.

The vertical scroll bar to the right is used to move the data vertically; the horizontal scroll bar below is used to move the data horizontally. The discussion below about how to control the scroll bar assumes a vertical scroll bar that moves the data up and down. The horizontal scroll bar works in exactly the same manner, but with "up" and "down" (or "above" and "below" ) replaced by "left" and "right", respectively.

A Scroll Bar contains two arrows and a scrolling region. The scrolling region has an active area called the thumb. The size of the thumb as a fraction of the size of the scrolling region indicates the amount of data visible at once as a fraction of the total amount of data. Thus, if the thumb takes up half of the scrolling region, then you can see half of the data at once; if the thumb takes up a tenth of the scrolling region, you can see a tenth of the data at once. The smaller the thumb, the more data there is.

To move the data by a small amount, click on the up or down arrow in the scroll bar. This will move the thumb by a small amount up or down, which will move the visible data in the other direction by a small amount (the viewing region moves through the data in the same direction as the thumb, so the visible data on the screen moves in the other direction).

To move the data by one page (i.e. by an amount equal to the height of the displayed data), move the pointer to the scrolling region above or below the thumb and click the left mouse button. This will move the thumb up or down by one thumb-length, which will move the visible data in the other direction by one page.

To move the data by an arbitrary amount, move the pointer on to the thumb, then press the left mouse button and drag the pointer up or down to move the thumb up or down. The data will move as you move the pointer. Release the button when you reach the desired point in the data.