C++ WinAPI Conflict between SetLayeredWindowAttributes and BitBlt - c++

Question

I have created a custom window using DWM. I painted the caption by using PaintCustomCaption() ,which is an example from MSDN. It worked properly until I added SetLayeredWindowAttributes().
Window before adding
SetLayeredWindowAttributes(hWnd,RGB(0,0,1),0,LWA_COLORKEY);
After adding
I tried changing RGB values but it was still black except RGB(0,0,0).
I wonder if BitBlt() works properly.
Edited:
The reason I added SetLayeredWindowAttributes is to solve this problem
Do you have other ways to paint the caption?
case WM_ACTIVATE: {
DwmExtendFrameIntoClientArea(hWnd,&m); // m={-1,-1,-1,-1};
break;
}
case WM_INITDIALOG: {
SetWindowPos(hWnd,NULL,0,0,500,500,SWP_NOMOVE|SWP_FRAMECHANGED);
SetWindowLongPtr(hWnd,GWL_STYLE,WS_VISIBLE|WS_OVERLAPPEDWINDOW);
SetWindowLongPtr(hWnd,GWL_EXSTYLE,WS_EX_LAYERED);
SetLayeredWindowAttributes(hWnd,RGB(0,0,1),0,LWA_COLORKEY);
RedrawWindow(hWnd,NULL,NULL,RDW_INVALIDATE|RDW_ERASE);
return true;
}
case WM_PAINT: {
hdc=BeginPaint(hWnd,&paintstruct);
PaintCustomCaption(hWnd,hdc)
EndPaint(hWnd,&paintstruct);
break;
}

Answer 1

If you keep the window border, you don't need to paint the caption yourself unless you want to add something to your caption.
That is, handle WM_NCCALCSIZE and WM_NCHITTEST normally.

Answer 2

First, use RGB(200,201,202) as the transparency key instead of RGB(0,0,1).
You may try other values but it is the best one so far I have tested.
Then, add this after HBITMAP hbmOld=(HBITMAP)SelectObject(hdcPaint,hbm); in PaintCustomCaption():
FillRect(hdcPaint,&rcClient,CreateSolidBrush(RGB(200,201,202)));