[python-win32] win32ui and flashing box

[Tim Roberts]

Richard Bell wrote:
> I'm working on an application that automated IE and want to draw a flashing
> box around screen elements.  I can find the coordinates OK but am a bit
> unclear on how to actually draw a box in such a fashion that when the
> flashing stops the screen is as it was before it started.  A bit of
> investigation suggests that something like this ought to work:
>
> import win32gui, win32ui
> def box(hdc, x, y, w, h):
>     hdc.MoveTo(x, y)
>     hdc.LineTo(x+w, y)
>     hdc.LineTo(x+w, y+h)
>     hdc.LineTo(x, h+h)
>     hdc.LineTo(x, y)
>
> hdc = win32ui.CreateDCFromHandle(win32gui.GetDesktopWindow())
>   

CreateDCFromHandle creates a Python wrapper from a Windows HDC handle. 
You're passing it a window handle, not a DC handle.  Try this instead:

  hdc = win32ui.CreateDCFromHandle( win32gui.GetDC( 0 ) )

You can use win32gui.GetDesktopWindow() instead of the 0 if you want. 
They should do the exact same thing.

> But when I run the code I get a win32ui: LineTo failed exception.  Is there
> a simple way of doing this?
>   

This is NOT going to draw it in an erasable way.  If you want to draw a
flashing box that can be removed, you need to change the ROP2 to, for
example, R2_NOT.  That will invert the colors every time you draw it. 
Draw it once, you see it; draw it again, it disappears.

Also note that dc.Rectangle is quicker than four LineTo calls.

-- 
Tim Roberts, timr at probo.com
Providenza & Boekelheide, Inc.