Accessing the Pen API from Applications

As Figure 1.5 shows, applications that accept user input are divided into two categories: pen-aware and pen-unaware applications. A pen-unaware application, as the name implies, is written to expect input only through the keyboard or mouse, unaware of the existence of Windows pen services. However, if a pen device is present, Windows 95 supports its use both as a mouse and for text entry with a pen-unaware application. For details about how Windows allows the use of a pen with an application not written to accept pen input, see "Pen-Unaware Applications" in Chapter 2, "Starting Out with System Defaults."

The Pen API is designed for small handheld systems with limited memory and power, so its API consists of 16-bit functions. Therefore, Windows provides a thunk layer for 32-bit applications to call through to the API. The thunk layer automatically converts 32-bit function parameters and structure data to 16-bit equivalents. The application must ensure its data will fit into the smaller sizes before calling into the Pen API. See Appendix B for information about using the 32-bit API.

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