The GetSystemMetrics function provides access to the SM_PENWINDOWS constant that indicates when a pen is installed. For more information about this function, see the documentation included in the Microsoft Win32 Software Development Kit (SDK).
Systems with a Windows pen driver installed support user input using tapping or writing on the surface of the screen or a tablet with a pen, and in some cases with a finger.
Note
The GetSystemMetrics function provides access to the SM_PENWINDOWS constant that indicates when a pen is installed. For more information about this function, see the documentation included in the Microsoft Win32 Software Development Kit (SDK).
Depending on the placement of the pen, you can use it for both pointing and writing. For example, if you move the pen over menus or most controls, it acts as a pointing device. Because of the pointing capabilities of the pen, the user can perform most mouse-based operations. When over a text entry or drawing area, the pen becomes a writing or drawing tool; the pointer changes to a pen shape to provide feedback to the user. When the tip of the pen touches the input surface, the pen starts inking — that is, tracing lines on the screen. The user can then draw shapes, characters, and other patterns; these patterns remain on the screen exactly as drawn or can be recognized, interpreted, and redisplayed.
The pen can retain the functionality of a pointing device (such as a mouse) even in contexts where it would normally function as a writing or drawing tool. For example, you can use timing to differentiate operations; that is, if the user holds the pen tip in the same location for a predetermined period of time, a different action may be inferred. However, this method is often unreliable or inefficient for many operations, so it may be better to use toolbar buttons to switch to different modes of operation. Choosing a particular button allows the user to define whether to use the pen for entering information (writing or drawing) or as a pointing device.
You can also provide the user with access to other operations using an action handle. An action handle is a special graphic displayed for a selection. An action handle can be used to support direct manipulation operations or to provide access to pop-up menus.
Note
For more information about action handles, see Chapter 5, "General Interaction Techniques."
Following are the fundamental behaviors defined for a pen.
|
Action |
Description |
|
Pressing |
Positioning and pressing the tip to the input surface. A pen press is equivalent to a mouse press and typically identifies a particular pen action. |
|
Tapping |
Pressing the pen tip on the input surface and lifting it without moving the pen. In general, tapping is equivalent to clicking mouse button 1. Therefore, this action typically selects an object, setting a text insertion point or activating a button |
|
Double-tapping |
Pressing and lifting the pen tip twice in rapid succession. Double-tapping is usually interpreted as the equivalent to double-clicking mouse button 1. |
|
Dragging |
Pressing the pen tip on the input surface and keeping it pressed while moving the pen. In inking contexts, you can use dragging for the input of pen strokes for writing, drawing, gestures, or for direct manipulation, depending on which is most appropriate for the context. In noninking contexts, it is the equivalent of a mouse drag. |
Note 
A user may move the pen more between taps when double-tapping than a user double-clicking with a mouse. As a result, you may want to slightly increase your hot zones for detecting a double-tap when of a pen device has been installed.
Some pens include buttons on the pen barrel that can be pressed. For pens that support barrel buttons, the following behaviors may be supported.
|
Action |
Description |
|
Barrel-tapping |
Holding down the barrel button of the pen while tapping. Barrel-tapping is equivalent to clicking with mouse button 2. |
|
Barrel-dragging |
Holding down the barrel button of the pen while dragging the pen. Barrel-dragging is equivalent to dragging with mouse button 2. |
Note
Because not all pens support barrel buttons, any behaviors that you support using a barrel button should also be supported by other techniques in the interface.
Pen input is delimited, by the lifting of the pen tip, an explicit termination tap (such as tapping the pen on another window or as the completion of a gesture), or a time-out without further input. You can also explicitly define an application-specific recognition time-out.
Proximity is the ability to detect the position of the pen without it touching the input surface. While Windows provides support for pen proximity, avoid depending on proximity as the exclusive means of access to basic functions, because not all pen hardware supports this feature. Even pen hardware that does support proximity may allow other non-pen input, such as touch input, where proximity cannot be supported.