Development Issues

Since DTWAIN operates as a generic Windows 32 or 64 bit Dynamic Link Library (DLL), any Windows environment that allows calls to external DLL's can use DTWAIN. This includes Visual Basic, Delphi, FoxPro, Access, Java (using JNI), and many others. If you are already familiar with how to use third-party DLL's within your application, you can skip this topic.

Note for Visual Basic programmers: DTWAIN DLL is not an ActiveX DLL. The following topics discuss the various programming environments and the interface to DTWAIN.

Consult the user's manual of your programming environment for information on how to make calls to external DLL's. If you need to set up an interface to the DTWAIN functions and are not sure how to set up the parameters for the DTWAIN functions, the best approach is to see how your environment defines the parameters when calling a Windows API function such as CreateWindow, BitBlt, GetWindowText, etc. Almost all programming documentation for various languages have code samples of calling a Windows API function, so you can use this as a template when interfacing to DTWAIN.

Most of the DTWAIN function parameter types match as closely as possible to the usual parameter types that you will see associated with Windows API functions. For example, LPCSTR, LPVOID, LONG, BOOL, etc. that DTWAIN uses are exactly the same types as used with the Windows API functions.

Here is a small table of how to interpret the various DTWAIN types using the standard 'C' language types:

DTWAIN Type	Definition	'C' / Windows equivalent
DTWAIN_SOURCE	32-bit integer	LONG
LPDTWAIN_SOURCE	32-bit void pointer	void FAR * (or LPVOID)
DTWAIN_ARRAY	32-bit integer	LONG
LPDTWAIN_ARRAY	32-bit void pointer	void FAR * (or LPVOID)
DTWAIN_IDENTITY	32-bit integer	LONG
DTWAIN_STRING	array of 256 chars	LPSTR
DTWAIN_LONGSTRING	array of 1,024 chars	LPSTR
DTWAIN_FLOAT	8 byte IEEE floating point	double
DTWAIN_LONG	32-bit integer	LONG
DTWAIN_BOOL	32-bit integer	LONG
DTWAIN_LONG64	64-bit integer	LONGLONG (or __int64)

For 64-bit applications, some of the above definitions will be 64-bit integers and pointers. Here is a table of the differences between the 32-bit definitions and 64-bit definitions:

DTWAIN Type	Definition	'C' / Windows equivalent
DTWAIN_SOURCE	64-bit integer	LONGLONG (or __int64)
LPDTWAIN_SOURCE	64-bit void pointer	void FAR * (or LPVOID)
DTWAIN_ARRAY	64-bit integer	LONGLONG (or __int64)
LPDTWAIN_ARRAY	64-bit void pointer	void FAR * (or LPVOID)
DTWAIN_IDENTITY	64-bit integer	LONGLONG (or __int64)

Unless you're calling DTWAIN functions that automatically create image files from scanned images (for example, DTWAIN_AcquireFile), by default TWAIN returns Device Independent Bitmaps (DIBs) to your application, therefore you should be familiar with how to handle this image type within your language and application. An example of DTWAIN functions that return DIBS are DTWAIN_AcquireNative and DTWAIN_AcquireBuffered (when acquiring uncompressed image data)

Since DIB's are one of the most common formats in the Windows environment, you should be able to consult documentation on how to handle this format. If you have libraries that handle Windows BMP files, the same library or code can be used to handle a DIB. The example programs found in the /EXAMPLES/C and /EXAMPLES/C++ directory include portions of the DIBVIEW program that demonstrates handling of Device Independent Bitmaps.

If you are not familiar with handling DIB's, we suggest that you get one of the many ActiveX or third party libraries that can display or manipulate Device Independent Bitmaps. Here are a few libraries with their web site address: