Re: Saving a Device context (DC) into a picture file

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Hi all:

I have my own code that samples pixel colour,
https://pastebin.com/4EMd765h

 and now I am trying to add the feature of saving the Device Context to a
.bmp file, so I found this code

https://books.google.ca/books?id=9MS9BQAAQBAJ

however there is one problem: The book example screenshots the whole
desktop and I only want a screenshot of a given window. Is there a way to
modify the black hat example into something that only screenshot a window
given its handle?

namely, these 4 lines.

width = win32api.GetSystemMetrics(win32con.SM_CXVIRTUALSCREEN)
height = win32api.GetSystemMetrics(win32con.SM_CYVIRTUALSCREEN)
left = win32api.GetSystemMetrics(win32con.SM_XVIRTUALSCREEN)
top = win32api.GetSystemMetrics(win32con.SM_YVIRTUALSCREEN)

Thanks!

On Fri, Apr 28, 2017 at 5:28 PM, Michael C <[email protected]>
wrote:

> Hi all:
>
> I have my own code that samples pixel colour,
> https://pastebin.com/4EMd765h
>
>  and now I am trying to add the feature of saving the Device Context to a
> .bmp file, so I found this code
>
> https://books.google.ca/books?id=9MS9BQAAQBAJ
>
> however there is one problem: The book example screenshots the whole
> desktop and I only want a screenshot of a given window. Is there a way to
> modify the black hat example into something that only screenshot a window
> given its handle?
>
> Thanks!
>
>
>
> On Sat, Apr 22, 2017 at 2:29 PM, Michael C <[email protected]
> > wrote:
>
>> neat-o
>>
>>
>> On Sat, Apr 22, 2017 at 2:27 PM, eryk sun <[email protected]> wrote:
>>
>>> On Sat, Apr 22, 2017 at 7:15 PM, Michael C
>>> <[email protected]> wrote:
>>> > Never mind, I found this
>>> > https://books.google.ca/books?id=9MS9BQAAQBAJ
>>>
>>> Thankfully a lot of the Windows code in Black Hat Python uses PyWin32.
>>> The few ctypes examples aren't top notch. For example, the author
>>> calls
>>>
>>>      user32.GetWindowThreadProcessId(hwnd, byref(pid))
>>>
>>> without setting the prototype of GetWindowThreadProcessId. In 64-bit
>>> Python 2, the value of the hwnd argument may get corrupted if the
>>> prototype isn't defined. It's only by luck of the draw that it usually
>>> works.
>>>
>>> Some WinAPI pseudohandles are non-zero in the upper DWORD, such as
>>> HWND_TOPMOST, which is defined as (HWND)(-1), i.e. 0xFFFFFFFFFFFFFFFF
>>> on a 64-bit system. This has the same problem in Python 2 if you
>>> forget to set the prototype or manually wrap the value in a pointer
>>> type. Python 3 ctypes doesn't have this problem, since it sign extends
>>> a negative argument as an intptr_t.
>>>
>>> Here's another problem in the book's example code. The default restype
>>> is a signed c_int, and here the author is calling GetTickCount without
>>> first setting GetTickCount.restype = ctypes.c_uint:
>>>
>>>     run_time = kernel32.GetTickCount()
>>>     elapsed = run_time - struct_lastinputinfo.dwTime
>>>
>>> After 24.86 days system uptime, the tick count reaches 0x80000000
>>> (milliseconds), and the signed return value wraps around to
>>> -2147483648 <(214)%20748-3648>, incrementing toward 0. The value of
>>> `elapsed` will be
>>> nonsense.
>>>
>>
>>
>

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<div dir=3D"ltr"><span style=3D"font-size:12.8px">Hi all:</span><div style=
=3D"font-size:12.8px"><br></div><div style=3D"font-size:12.8px">I have my o=
wn code that samples pixel colour,=C2=A0</div><div style=3D"font-size:12.8p=
x"><a href=3D"https://pastebin.com/4EMd765h" target=3D"_blank">https://past=
ebin.com/4EMd765h</a><br></div><div style=3D"font-size:12.8px"><br></div><d=
iv style=3D"font-size:12.8px">=C2=A0and now I am trying to add the feature =
of saving the Device Context to a .bmp file, so I found this code=C2=A0</di=
v><div style=3D"font-size:12.8px"><br></div><div style=3D"font-size:12.8px"=
><a href=3D"https://books.google.ca/books?id=3D9MS9BQAAQBAJ" target=3D"_bla=
nk">https://books.google.ca/books?<wbr>id=3D9MS9BQAAQBAJ</a></div><div styl=
e=3D"font-size:12.8px"><br></div><div style=3D"font-size:12.8px">however th=
ere is one problem: The book example screenshots the whole desktop and I on=
ly want a screenshot of a given window. Is there a way to modify the black =
hat example into something that only screenshot a window given its handle?<=
/div><div style=3D"font-size:12.8px"><br></div><div style=3D"font-size:12.8=
px"><span style=3D"font-size:12.8px">namely, these 4 lines.</span><div styl=
e=3D"font-size:12.8px"><br></div><div style=3D"font-size:12.8px"><div>width=
 =3D win32api.GetSystemMetrics(<wbr>win32con.SM_CXVIRTUALSCREEN)</div><div>=
height =3D win32api.GetSystemMetrics(<wbr>win32con.SM_CYVIRTUALSCREEN)</div=
><div>left =3D win32api.GetSystemMetrics(<wbr>win32con.SM_XVIRTUALSCREEN)</=
div><div>top =3D win32api.GetSystemMetrics(<wbr>win32con.SM_YVIRTUALSCREEN)=
</div></div></div><div style=3D"font-size:12.8px"><br></div><div style=3D"f=
ont-size:12.8px">Thanks!</div></div><div class=3D"gmail_extra"><br><div cla=
ss=3D"gmail_quote">On Fri, Apr 28, 2017 at 5:28 PM, Michael C <span dir=3D"=
ltr">&lt;<a href=3D"mailto:[email protected]" target=3D"_blank=
">[email protected]</a>&gt;</span> wrote:<br><blockquote class=
=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padd=
ing-left:1ex"><div dir=3D"ltr">Hi all:<div><br></div><div>I have my own cod=
e that samples pixel colour,=C2=A0</div><div><a href=3D"https://pastebin.co=
m/4EMd765h" target=3D"_blank">https://pastebin.com/4EMd765h</a><br></div><d=
iv><br></div><div>=C2=A0and now I am trying to add the feature of saving th=
e Device Context to a .bmp file, so I found this code=C2=A0</div><div><br><=
/div><div><a href=3D"https://books.google.ca/books?id=3D9MS9BQAAQBAJ" targe=
t=3D"_blank">https://books.google.ca/books?<wbr>id=3D9MS9BQAAQBAJ</a></div>=
<div><br></div><div>however there is one problem: The book example screensh=
ots the whole desktop and I only want a screenshot of a given window. Is th=
ere a way to modify the black hat example into something that only screensh=
ot a window given its handle?</div><div><br></div><div>Thanks!</div><div><b=
r></div><div><br></div></div><div class=3D"HOEnZb"><div class=3D"h5"><div c=
lass=3D"gmail_extra"><br><div class=3D"gmail_quote">On Sat, Apr 22, 2017 at=
 2:29 PM, Michael C <span dir=3D"ltr">&lt;<a href=3D"mailto:mysecretrobotfa=
[email protected]" target=3D"_blank">mysecretrobotfactory@gmail.<wbr>com</a>&=
gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 =
0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr">neat-o=
<div><br></div></div><div class=3D"m_-8829367243863059807HOEnZb"><div class=
=3D"m_-8829367243863059807h5"><div class=3D"gmail_extra"><br><div class=3D"=
gmail_quote">On Sat, Apr 22, 2017 at 2:27 PM, eryk sun <span dir=3D"ltr">&l=
t;<a href=3D"mailto:[email protected]" target=3D"_blank">[email protected]<=
/a>&gt;</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:=
0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>On Sat, Apr 2=
2, 2017 at 7:15 PM, Michael C<br>
&lt;<a href=3D"mailto:[email protected]" target=3D"_blank">mys=
[email protected]<wbr>m</a>&gt; wrote:<br>
&gt; Never mind, I found this<br>
&gt; <a href=3D"https://books.google.ca/books?id=3D9MS9BQAAQBAJ" rel=3D"nor=
eferrer" target=3D"_blank">https://books.google.ca/books?<wbr>id=3D9MS9BQAA=
QBAJ</a><br>
<br>
</span>Thankfully a lot of the Windows code in Black Hat Python uses PyWin3=
2.<br>
The few ctypes examples aren&#39;t top notch. For example, the author<br>
calls<br>
<br>
=C2=A0 =C2=A0 =C2=A0user32.GetWindowThreadProcess<wbr>Id(hwnd, byref(pid))<=
br>
<br>
without setting the prototype of GetWindowThreadProcessId. In 64-bit<br>
Python 2, the value of the hwnd argument may get corrupted if the<br>
prototype isn&#39;t defined. It&#39;s only by luck of the draw that it usua=
lly<br>
works.<br>
<br>
Some WinAPI pseudohandles are non-zero in the upper DWORD, such as<br>
HWND_TOPMOST, which is defined as (HWND)(-1), i.e. 0xFFFFFFFFFFFFFFFF<br>
on a 64-bit system. This has the same problem in Python 2 if you<br>
forget to set the prototype or manually wrap the value in a pointer<br>
type. Python 3 ctypes doesn&#39;t have this problem, since it sign extends<=
br>
a negative argument as an intptr_t.<br>
<br>
Here&#39;s another problem in the book&#39;s example code. The default rest=
ype<br>
is a signed c_int, and here the author is calling GetTickCount without<br>
first setting GetTickCount.restype =3D ctypes.c_uint:<br>
<br>
=C2=A0 =C2=A0 run_time =3D kernel32.GetTickCount()<br>
=C2=A0 =C2=A0 elapsed =3D run_time - struct_lastinputinfo.dwTime<br>
<br>
After 24.86 days system uptime, the tick count reaches 0x80000000<br>
(milliseconds), and the signed return value wraps around to<br>
-<a href=3D"tel:(214)%20748-3648" value=3D"+12147483648" target=3D"_blank">=
2147483648</a>, incrementing toward 0. The value of `elapsed` will be<br>
nonsense.<br>
</blockquote></div><br></div>
</div></div></blockquote></div><br></div>
</div></div></blockquote></div><br></div>

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