CDC::BitBlt

This method copies a bitmap from the source device context to the device context

針對第八個參數
DWORD dwRop
Raster-operation codes define how the GDI combines colors in output operations that involve a brush, a possible source bitmap, and a destination bitmap
負責定義 用什麼方式去結合 src and dest.

可以有四個選擇

• SRCAND: src AND dest
• SRCCOPY:直接將src 複製到 dest
• SRCINVERT: src XOR dest
• SRCPAINT: src OR dest
  

Reference:
http://www.moon-soft.com/program/bbs/readelite903754.htm