Support for TWAIN-Compatible Applications
In order to support TWAIN applications with private capabilities, WIA drivers can use a technique known as pass-through functionality. The pass-through mechanism refers to the way a TWAIN-compatible application communicates with a WIA driver, using the data source manager and the TWAIN compatibility layer as intermediaries. It is important to note that TWAIN capability pass-through is supported only in Windows XP and later operating system versions.
All communication between a TWAIN-compatible application and the WIA driver goes first to the data source manager (twain_32.dll), which in turn calls into the TWAIN compatibility layer (wiadss.dll). The TWAIN compatibility layer then calls the IWiaItemExtras::Escape method, which calls the IStiUSD::Escape method. The TWAIN compatibility layer calls only the IWiaItemExtras::Escape method. The driver developer should be concerned only with the device receiving an IStiUSD::Escape call. For more information about IWiaItemExtras::Escape, see the Microsoft Windows SDK documentation.
The following topics are discussed in this section: