- 1 year ago
How to use CAP_REWINDPAGE as TWAIN api in C/C++?
The CAP_REWINDPAGE
capability in the TWAIN API is used to indicate whether the data source should rewind the physical document page or not after acquiring an image. When the CAP_REWINDPAGE
capability is set to TRUE, the data source will rewind the physical document page after acquiring the image, allowing the application to acquire the same page again. If CAP_REWINDPAGE
is set to FALSE, the data source will not rewind the page, and the application will acquire the next page instead.
To use the CAP_REWINDPAGE
capability in C/C++ with the TWAIN API, you need to follow these steps:
Initialize the TWAIN session and select a data source using the
TWAIN_32
orTWAIN_64
DSM (Data Source Manager) functions. This step is required to interact with TWAIN-compatible scanners and cameras.Query the data source for the supported capabilities using the
DG_CONTROL/DAT_CAPABILITY/MSG_GET
triplet. Check if theCAP_REWINDPAGE
capability is supported by the data source.If the
CAP_REWINDPAGE
capability is supported, you can set its value using theDG_CONTROL/DAT_CAPABILITY/MSG_SET
triplet.
Here's an example of how to use CAP_REWINDPAGE
in C/C++ with the TWAIN API:
c++#include <windows.h>
#include <twain.h>
int main() {
TW_IDENTITY appId;
TW_IDENTITY sourceId;
TW_CAPABILITY cap;
TW_UINT16 capValue;
// Step 1: Initialize TWAIN session and select a data source
TWAIN_32.DSM_Entry(&appId, NULL, DG_CONTROL, DAT_PARENT, MSG_OPENDSM, (TW_MEMREF)&hwndApp);
TWAIN_32.DSM_Entry(&sourceId, NULL, DG_CONTROL, DAT_IDENTITY, MSG_USERSELECT, (TW_MEMREF)&appId);
// Step 2: Query data source for supported capabilities
cap.Cap = CAP_REWINDPAGE;
cap.ConType = TWON_DONTCARE16;
cap.hContainer = NULL;
TWAIN_32.DSM_Entry(&sourceId, NULL, DG_CONTROL, DAT_CAPABILITY, MSG_GET, (TW_MEMREF)&cap);
// Check if CAP_REWINDPAGE is supported
if (cap.Capability != TWCC_SUCCESS) {
printf("CAP_REWINDPAGE is not supported by the data source.\n");
return -1;
}
// Step 3: Set CAP_REWINDPAGE to TRUE or FALSE
capValue = TRUE; // Set to TRUE to rewind the page after acquiring
cap.hContainer = GlobalAlloc(GHND, sizeof(TW_ONEVALUE));
TW_ONEVALUE* oneValue = (TW_ONEVALUE*)GlobalLock(cap.hContainer);
oneValue->ItemType = TWTY_BOOL;
oneValue->Item = capValue;
GlobalUnlock(cap.hContainer);
TWAIN_32.DSM_Entry(&sourceId, NULL, DG_CONTROL, DAT_CAPABILITY, MSG_SET, (TW_MEMREF)&cap);
// Cleanup and close TWAIN session
TWAIN_32.DSM_Entry(&sourceId, NULL, DG_CONTROL, DAT_IDENTITY, MSG_CLOSEDS, (TW_MEMREF)&sourceId);
TWAIN_32.DSM_Entry(&appId, NULL, DG_CONTROL, DAT_PARENT, MSG_CLOSEDSM, (TW_MEMREF)&hwndApp);
return 0;
}
Please note that this example assumes you have properly linked to the TWAIN 32-bit or TWAIN 64-bit library and have the necessary header files included in your project. Additionally, this code is a basic example and may require additional error handling and resource management for real-world applications.