[Win32] How draw a rectangle on the desktop

[Member 2965471]

Hi, I'm trying to draw a rectangle on the screen with MouseHook, but i can't:

LRESULT CALLBACK MouseProc(int nCode,WPARAM wParam,LPARAM lParam)
{
LPMOUSEHOOKSTRUCT info=(LPMOUSEHOOKSTRUCT) lParam;
static BOOL capturing = 0;
Pen p(Color(255,255,0,0),5);
Graphics g(GetDC(0));

switch(wParam)
{
case WM_LBUTTONDOWN:
capturing = TRUE;
rcCaptured.left = info->pt.x;
rcCaptured.top = info->pt.y;
break;
case WM_LBUTTONUP:
if( capturing )
{
rcCaptured.right = info->pt.x;
rcCaptured.bottom = info->pt.y;
capturing = FALSE;
}
break;
case WM_MOUSEMOVE:
InvalidateRect(GetDesktopWindow(),NULL,FALSE);
g.DrawRectangle(&p,rcCaptured.left,rcCaptured.top,info->pt.x-rcCaptured.left,info->pt.y-rcCaptured.top);
break;
}
}

how can force repaint of the screen? and how remove hook after select a rectangle?

[Mark Salsbery]

I'm guessing your InvalidateRect() call is causing a repaint that ends up covering up what you just drawed to the screen. What is happening with your current code??

Mark Salsbery Microsoft MVP - Visual C++ :java:

[Member 2965471]

InvalidateRect doesn't work, the screen is still dirty.

[Mark Salsbery]

Yes, you'd have to set the erase background flag to true in the call and call UpdateWindow() to force an immediate paint. That worked on older OSs but on Windows 7 the updates don't happen while you have the mouse button pressed it seems. It does work on the LBUTTONUP message (just tested it). You may have to double buffer - grab the image for the rect from the screen, draw your rectangle, draw the captured image back to the screen to erase, etc.

Mark Salsbery Microsoft MVP - Visual C++ :java:

[bob16972]

Deja Voodoo. It almost feels like I posted an answer[^] to this problem some days back? Use SetROP2 to rubberband it. Yes, you can mix GDI and GDI+ together in the same application. You just need to understand how each works to make them complement each other.