C + + Set Transparent background picture _c language

Background:

There are two pictures, one is the target background picture, the other is a color picture with its own background color

The color picture is first drawn to the target background image, which can be achieved by BitBlt. But the effect is: the target picture, painted up color pictures with its own background.

The problem is, we want to remove the background color picture itself, how should we solve?

Workaround:

Using API functions: TransparentBlt This function draws a picture from the original DC to the target DC and sets the original shape's transparent color on the target graphic.

BOOL TransparentBlt ( 
 HDC hdcdest,    //handle to destination DC 
 int nxorigindest,  //X-coord of Destination Upper-left corner 
 int nyorigindest,  //Y-coord of destination Upper-left 
 -corner int nwidthdest,   //width of destination rectangle 
 int hheightdest,  //height of destination rectangle 
 HDC HDCSRC,
   //handle to source DC 
 int nxoriginsrc,  //X-coord of source upper-left corner 
 int nyoriginsrc,  //Y -coord of source upper-left corner 
 int nwidthsrc,   //width of source rectangle 
 int nheightsrc,   //Hei Ght of source Rectangle 
 UINT crtransparent//color to make transparent 
);

In this example, when the transparent color is set to a color graphic with its background color, the resulting color of the colored graphic on the final shape is eliminated when the function is used.

cdc* pdc=getdc (); 
 
CBitmap bmp; 
Bmp. LoadBitmap (IDB_BITMAP1); 
 
BITMAP Bmpinfo; 
Bmp. GetObject (sizeof (BITMAP), &bmpinfo); 
 
 
CDC Imagedc; 
Imagedc.createcompatibledc (PDC); 
 
CBitmap *poldimagebmp=imagedc.selectobject (&bmp); 
 
 
CBitmap bmpbk; 
Bmpbk.loadbitmap (IDB_BITMAP2); 
 
BITMAP Bmpbkinfo; 
  Bmpbk.getobject (sizeof (BITMAP), &bmpbkinfo); 
 
CDC BKDC; 
Bkdc.createcompatibledc (PDC); 
 
Bkdc.selectobject (&BMPBK); 
 
TransparentBlt (Bkdc.m_hdc,100,150,bmpinfo.bmwidth,bmpinfo.bmheight,imagedc.m_hdc,0,0,bmpinfo.bmwidth, Bmpinfo.bmheight,rgb (255,0,0)); Set red to Transparent color 
 
BitBlt (pdc->m_hdc,0,0,bmpbkinfo.bmwidth,bmpbkinfo.bmheight,bkdc.m_hdc,0,0,srccopy);//Draw to screen

Principle: By setting the mask bitmap to implement

1 Create mask Bitmap first
2 Using a mask bitmap to the color of the original image, get a new map (transparent color is black, the other area is the primary color)
3 Use mask bitmap and target background image (transparent area is transparent, other area is black)
4 Use the new variant and the target background image or, get the final diagram

The above mentioned is the entire content of this article, I hope you can enjoy.