Paint Icon with win32api c++ - c++

Question

I'm trying to paint an Icon onto my window with the win32 api. Here is where I load the image.
case WM_CREATE: {
HANDLE image = (HICON)LoadImage(NULL, TEXT("Button.ico"), IMAGE_ICON, 16, 16, LR_LOADFROMFILE | LR_LOADTRANSPARENT);
break;
}
Here is where I try to paint the icon onto the screen.
case WM_NCPAINT: {
PAINTSTRUCT ps;
BITMAP bm;
HDC hdc = BeginPaint(ParentHwnd, &ps);
HDC hdcMem = CreateCompatibleDC(hdc);
HBITMAP hbmOld = SelectObject(hdcMem, image);
GetObject(image, sizeof(bm), &bm);
BitBlt(hdc, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
SelectObject(hdcMem, hbmOld);
DeleteDC(hdcMem);
EndPaint(ParentHwnd, &ps);
break;
}
For some reason, I get this error on SelectObject();
E0144 a value of type "HGDIOBJ" cannot be used to initialize an entity of type "HBITMAP"
I'm using Visual Studio community 2019. I've looked all over the place for an answer. Thank you in advance for your efforts to help.

Answer 1

One, you are not supposed to use BeginPaint() in a WM_NCPAINT handler, only in a WM_PAINT handler. Per the WM_NCPAINT documentation, use GetDCEx() instead.
Two, you likely have STRICT Type Checking turned on (which is a good thing), that is why you are getting the compiler error. Under STRICT, an HGDIOBJ (aka void*) cannot be assigned to an HBITMAP (aka struct HBITMAP__*), so you would need to explicitly type-cast the return value of SelectObject(). However, you are loading an HICON, which you can't select as-is into an HDC, so you will have to either:
load a BMP file instead of an ICO file.
convert the HICON data to an actual HBITMAP.
use DrawIcon() or DrawIconEx().
Three, in your WM_CREATE handler, your image variable is local to that message handler, so whatever image you are accessing in the WM_NCPAINT handler is not the same variable.
Try this instead:
HBITMAP image;
...
case WM_CREATE: {
HICON icon = (HICON) LoadImage(NULL, TEXT("Button.ico"), IMAGE_ICON, 16, 16, LR_LOADFROMFILE | LR_LOADTRANSPARENT);
// convert icon to image as needed...
DestroyIcon(icon);
break;
}
case WM_NCPAINT: {
BITMAP bm;
HDC hdc = GetDCEx(hwnd, (HRGN)wParam, DCX_WINDOW | DCX_INTERSECTRGN);
HDC hdcMem = CreateCompatibleDC(hdc);
HBITMAP hbmOld = (HBITMAP) SelectObject(hdcMem, image);
GetObject(image, sizeof(bm), &bm);
BitBlt(hdc, 0, 0, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
SelectObject(hdcMem, hbmOld);
DeleteDC(hdcMem);
ReleaseDC(hwnd, hdc);
break;
}
Or this:
HICON image;
...
case WM_CREATE: {
image = (HICON) LoadImage(NULL, TEXT("Button.ico"), IMAGE_ICON, 16, 16, LR_LOADFROMFILE | LR_LOADTRANSPARENT);
break;
}
case WM_DESTROY: {
DestroyIcon(image);
break;
}
case WM_NCPAINT: {
HDC hdc = GetDCEx(hwnd, (HRGN)wParam, DCX_WINDOW|DCX_INTERSECTRGN);
DrawIcon(hdc, 0, 0, image);
ReleaseDC(hwnd, hdc);
break;
}