OVERLAYCALLBACK pfnCallback;

/* your callback function */

L_VOID L_FAR * ppUserData;

/* pointer to more parameters for the callback */

L_UINT uFlags;

/* procedure flag */

Parameter

Description

pfnCallback

Your callback function that asks the user for the overlay bitmap, when loading a file containing an overlay. The callback function must adhere to the syntax specified in OVERLAYCALLBACK. Pass NULL If there is no overlay callback function. If a callback function is set, the callback function will be used only if OVERLAY_LOADONLY is not set in uFlags.

pUserData

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 L_FAR *. The callback function, which receives the address in its own pUserData 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.

uFlags

Flags that indicate the method(s) to use when loading an overlay bitmap and the order in which to perform those methods. Possible values are:

Value

Meaning

OVERLAY_LOADCALL

[0x0001] First, try loading the overlay bitmap from disk. If the load fails, the overlay callback will be asked to provide the overlay bitmap.

OVERLAY_CALLLOAD

[0x0002] First, call the overlay callback. If the callback did not supply an overlay bitmap, try loading the overlay bitmap from disk.

OVERLAY_CALLONLY

[0x003] Call the overlay callback. If there is no callback function set, there is no overlay bitmap.

OVERLAY_LOADONLY

[0x0004] Try to load the overlay bitmap from disk. If the load fails, there is no overlay.

SUCCESS

The function was successful.

< 1

An error occurred. Refer to Return Codes.

LTFIL

For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.

Functions:

L_GetOverlayCallback, OVERLAYCALLBACK

Topics:

Raster Image Functions: Loading Files

Loading and Saving Images