CODEWITHSUNDEEP
c++winapibitmapgdi
Entretoize
Entretoize

Reputation: 2251

Draw a bitmap with transparency

I am creating a user interface and actualy drawing bitmap this way:

HDC hdcMem = CreateCompatibleDC(hdc);

HBITMAP oldBmp = (HBITMAP)SelectObject(hdcMem, mouseover? bitmapover:bitmap);    

StretchBlt(hdc, xabs, yabs, width, height, hdcMem, 0, 0, worg, horg, SRCCOPY);

SelectObject(hdcMem, oldBmp);
DeleteDC(hdcMem);

But I can only draw flat images and I need to draw transparent ones (several alpha levels). I tried things with GetDIBits and SetDIBits but I failed drawing anything. I can use png or modify the bitmap pixel by pixel which is simpler, I just want to avoid using libraries with dlls or restrictive licences.

Upvotes: 1

Views: 1335

Answers (1)

user7860670
user7860670

Reputation: 37468

To draw semi-transparent bitmatps you can utilize GdiAlphaBlend function. Note that bitmap with alpha channel that you are going to draw using this API need to have premultiplied alpha.

Upvotes: 1

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