Designing Gestural Interfaces

TWO FINGERS TO SCROLL

WHAT

With two fingers (the index and middle fingers, typically) on the screen together (usually but not necessarily side by side), the user is able to scroll a list of items or the entire screen up/down or left/right.

USE WHEN

Used mainly on trackpads, this gesture allows users to manipulate the overall screen (and its accompanying scroll bar) with both fingers while still being able to control the cursor on the visible screen with a single finger (see Drag to Move Object). If there is no cursor to move, Slide to Scroll could be used instead.

WHY

This pattern allows for control of metalevel objects such as scroll bars while retaining control of individual objects via a cursor.

HOW

The touchscreen needs to be sensitive enough to detect multitouch; otherwise, the system has to compensate by looking for a wider touch area than a single finger would typically create.

EXAMPLES

Figure 3-31. The HP TouchSmart IQ500 Series PC allows users to use the Two Finger Scroll gesture right on the screen. Courtesy Hewlett-Packard.

Figure 3-32. Apple's laptop trackpads, such as the one on this PowerBook, allow for two-finger scrolling. Courtesy Bill Selak.