Scrolling a Window

Figure 5-27 Relationship between a window and a document

Scroll Bars

Figure 5-28 The elements of a scroll bar

A scroll bar represents one dimension, top to bottom or right to left, of the entire document. The scroll box represents the relative location, in the whole document, of the portion that can be seen in the window.

If the user clicks a scroll arrow or clicks in the gray area, the document "moves" and the scroll box moves along with it. If the user drags the scroll box and releases the mouse button, the document "moves" along with it. Figure 5-29 illustrates these behaviors.

Figure 5-29 Using scroll arrows and the scroll box

If the document is no larger than the window, the scroll bars are inactive. This means that the rectangles are outlined, but there is no gray area, no scroll box, and the arrows are hollow (their outlines appear). If the document window is inactive, don't show the elements of the scroll bar at all; only the outline of the scroll bar as a whole should appear. Figure 5-30 shows an active document window with inactive scroll bars and an inactive document window with inactive scroll bars.

Figure 5-30 Inactive scroll bars in active and inactive document windows

If a document has a fixed size that is smaller than the maximum size of the window, and the user scrolls to the right or bottom edge of the document, your application can display a gray background between the edge of the document and the window frame. This background indicates to the user that the content area has a fixed size that is smaller than the maximum size of the window. Figure 5-31 shows an example of a document with this gray background.

Figure 5-31 Background between the content and the window frame

Another addition to the window that's not too intrusive is a status bar at the left side of the horizontal scroll bar. This bar doesn't take up much space, while providing useful information to the user. It also doesn't reduce the working size of the scroll bar by too much.

Figure 5-32 Acceptable additions to the scroll bar region

Some applications include a page number inside the scroll box to indicate the position of the document. This allows the user to see the page number change as the document scrolls. It also provides information without adding complexity to the window.

To ensure that the controls that you include in the window are easy to use and understand, it's best to place the majority of your features in the menus as commands. Figure 5-33 shows a window with too many controls in the scroll bars. If you really want to provide additional access to features, consider creating a utility window such as a palette with buttons. For more information on palettes, see "Tear-Off Menus and Palettes" on page 74 in Chapter 4, "Menus."

Figure 5-33 Too many controls in the scroll bar

Scrolling With the Scroll Arrows

Figure 5-34 Scrolling by clicking a scroll arrow

The scroll box moves in the direction of the arrow being clicked. It continues to represent the approximate position of the visible part of the document in comparison to the whole document.

Each click in a scroll arrow causes movement of the content a distance of one unit in the chosen direction. Your application determines what one unit equals. For example, a word processor would move one line of text for each click in the arrow. A spreadsheet would move one row or one column depending on the direction of the arrow. To ensure smooth scrolling effects, it's usually best to specify units of the same size throughout a document.

Scrolling With the Gray Area

Figure 5-35 Scrolling by clicking in the gray area

Pressing in the gray area causes the display of consecutive windowfuls of the document, until the user releases the mouse button, or until the location of the scroll box catches up to the location of the pointer. A windowful equals the height or width of the window, minus at least one unit of overlap to maintain the user's context. This unit of overlap is the same measurement determined for scroll arrow movement. By retaining this unit of information, you provide a reference point for the user.

On keyboards with function keys, the Page Up and Page Down keys also move the document view by a windowful.

Scrolling by Dragging the Scroll Box

Figure 5-36 Scrolling by dragging the scroll box

If the user starts dragging the scroll box, then moves the pointer out of the scroll bar, the scroll box stops following the pointer and snaps back to its original position. The user can move the pointer out of the scroll bar region by a little more than the width of the scroll box before the scroll box snaps back. If the user then releases the mouse button, no scrolling occurs. But if the user, still holding down the mouse button, moves the pointer back into the scroll bar, the scroll box resumes its movement in the direction of the pointer. This type of tracking is standard behavior for controls in general, such as buttons, checkboxes, and radio buttons.

Automatic Scrolling

• When your application performs an operation whose side effect is to make a new selection or move the insertion point, scroll the document to show the new selection.

  For example, when the user searches for some text, your application locates the desired text. If this text appears in a part of the document that isn't currently visible, scroll the document to the location to show the selection. Another example might occur after the user pastes something. If the insertion point appears after the end of whatever was pasted, scroll the document until the selection and the new insertion point are visible. Figure 5-37 shows the effect of automatic scrolling.

• When the user enters information from the keyboard at the edge of a window, scroll the document automatically to incorporate and display the new information.

  The user's focus will be on the new information, so don't try to maintain the document's position and record the new information out of the user's view. Your application determines the distance to scroll. In general, a word processor scrolls one line of text, a database or spreadsheet scrolls one field. Graphics applications should scroll to display an entire object when possible. Otherwise, determine how quickly your application can redraw the window contents during scrolling and adjust the amount of scrolling to reduce the amount of flashing or redrawing that is necessary. Try to ensure that the scrolling is sufficiently fast that it allows users to see the information at a rate that's useful, but don't scroll so fast that people get lost.

• When the user moves the pointer past the edge of the window while holding down the mouse button to make an extended selection, scroll the document automatically in the direction the pointer moves. The rate of scrolling can be the same as if the user were pressing on the corresponding scroll arrow. In some cases, it makes sense to vary the scrolling speed so that it is faster as the user moves the pointer farther away from the window edge.
• Sometimes the user selects something, scrolls the document to a new location, and then tries to perform an operation on the selection. In this case, scroll the window so that the selection is showing before your application performs the operation. Showing the selection makes it clear to the user what is being changed.

If your application can scroll in one orientation to reveal the selection, don't scroll in both orientations. That is, if you can scroll vertically to show the selection, don't also scroll horizontally.

When you can show context on either side of a selection, it's useful to do so. It's also better to position a selection somewhere near the middle of a window than right up against a corner. When the selection is too large to show the entire selection in the window, it might be a good idea to show some context next to it rather than having the selection fill the window. For more information about document scrolling, see Inside Macintosh: Macintosh Toolbox Essentials.