Combines the source object's bitmap with the calling objects bitmap so that one appears to be an underlying texture for the other. This is most effective when the underlying image is a filtered one, such as an embossed image.


#include "ltwrappr.h"

virtual L_INT LBitmapBase::Underlay(LUnderlayBmp, uFlags=UB_TILE)


LBitmapBase& LUnderlayBmp

The LBitmapBase object. This objects bitmap will be used as an underlay for the calling object's bitmap.

L_UINT uFlags

Flag that indicates how the underlying image is to be positioned. Possible values are:

Value Meaning
UB_TILE [0x00] Tile the underlay. This repeats the underlying image, so that it fills the target image. This function does not do any resizing; you are responsible for the size of the tiles.
UB_STRETCH [0x01] Stretch the underlay to fit the dimensions of the target image.


Value Meaning
SUCCESS The function was successful.
< 1 An error occurred. Refer to Return Codes.


This function changes the colors of the underlay to grayscale as it combines the images. It updates the target bitmap (pBitmapDst), leaving the second bitmap (pUnderlay) unchanged. The underlying image can either be stretched or tiled to fill the target image, as shown in the following illustration:


To update a status bar or detect a user interrupt during execution of this function, refer to LBase::EnableStatusCallBack.

If a region is defined for the target bitmap, the underlay is applied to the region, not to the whole bitmap. (Any region defined for the underlay bitmap is ignored.)

Note: The LUnderlayBmp parameter is passed by reference, and is a required parameter.

Required DLLs and Libraries


Win32, x64.

See Also




L_INT LBitmapBase__UnderlayExample() 
   L_INT nRet; 
   LBitmapBase MyBitmap,Bitmap2; 
   nRet =MyBitmap.Load(); 
   if(nRet !=SUCCESS) 
      return nRet; 
   nRet =Bitmap2.Load(); 
   if(nRet !=SUCCESS) 
      return nRet; 
   nRet =MyBitmap.Underlay(Bitmap2, UB_TILE); 
   if(nRet !=SUCCESS) 
      return nRet; 
   return SUCCESS; 
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