typedef struct _UNDERLAYDLGPARAMS 
   L_UINT uStructSize; 
   pBITMAPHANDLE pBitmap; 
   L_BOOL bZoomToFit; 
   L_UINT32 uUnderlayFlags; 
   L_INT nUnderlayBitmapIndex; 
   L_UINT32 uDlgFlags; 
   LTCOMMDLGHELPCB pfnHelpCallback; 
   L_VOID *pHelpCallBackUserData; 

The UNDERLAYDLGPARAMS structure provides information used to initialize the dialog box created by the L_DlgUnderlay function. After the user closes the dialog box, this structure is updated with information about the user's selections.



Size of this structure, in bytes. Use the sizeof operator to calculate this value.


Pointer to the bitmap handle that references the bitmap used for preview or processing.


Flag that indicates the initial zoom level for previewing the image. Possible values are:

Value Meaning
TRUE Set the initial zoom level to "Zoom to fit".
FALSE Set the initial zoom level to "Normal (1:1)".


Flags that indicate how the underlying image is to be positioned. Possible values are:

Value Meaning
UB_TILE [0x00] Tile the underlay image. This repeats the underlying image, so that it fills the target image.
UB_STRETCH [0x01] Stretch the underlay image to fit the dimensions of the target image.


Index of the selected tile bitmap to use for underlay. This index points to an entry in pBitmapList member.


Pointer to a DLGBITMAPLIST structure that references the images in the image picker. Set this to initialize the image picker in the dialog.


User interface flags for this dialog, which determines the layout and action of the dialog. Possible values are:

Value Meaning
DLG_UNDERLAY_AUTOPROCESS [0x0001] process the image on OK. The pBitmap member of this structure should contain a valid bitmap.
DLG_UNDERLAY_SHOW_CONTEXTHELP [0x0002] dialog should contain a context sensitive help icon.
DLG_UNDERLAY_SHOW_PREVIEW [0x0004] show a preview of the image in the dialog. The pBitmap member of this structure should contain a valid bitmap.
DLG_UNDERLAY_SHOW_TOOL_ZOOMLEVEL [0x0008] show the "Zoom to fit" and "Zoom Normal" toolbar buttons. The DLG_UNDERLAY_SHOW_PREVIEW flag must be set in order to show these buttons.


Pointer to an optional help callback function. If you do not wish to provide help to this dialog, use NULL as the value of this parameter. To provide help to this dialog, use the function pointer as the value of this parameter. The callback function must adhere to the prototype described in LTCOMMDLGHELPCB.


Void pointer that you can use to pass one or more additional parameters that the callback function needs. To use this feature, assign a value to a variable or create a structure that contains as many fields as you need. Then, in this parameter, pass the address of the variable or structure, casting it to L_VOID *. The callback function, which receives the address in its own pHelpCallBackUserData parameter, can cast it to a pointer of the appropriate data type to access your variable or structure. If the additional parameters are not needed, you can pass NULL in this parameter.

Help Version 21.0.2021.4.7
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LEADTOOLS Common Dialog C API Help