Allow HWND to be passed to ImageGrab.grab() on Windows #8516

radarhere · 2024-10-31T08:21:39Z

Resolves #4415

Adds a handle argument to ImageGrab.grab() that accepts a HDC, allowing for a screenshot of a specific window, rather than the entire screen.

nulano · 2024-11-02T12:47:55Z

src/display.c

@@ -331,14 +331,18 @@ PyImaging_GrabScreenWin32(PyObject *self, PyObject *args) {
    HMODULE user32;
    Func_SetThreadDpiAwarenessContext SetThreadDpiAwarenessContext_function;

-    if (!PyArg_ParseTuple(args, "|ii", &includeLayeredWindows, &all_screens)) {
+    if (!PyArg_ParseTuple(
+            args, "|ii" F_HANDLE, &includeLayeredWindows, &screens, &screen


This seems to be stealing a reference to the HDC and then deleting it, which could violate the DeleteDC documentation, https://learn.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-deletedc#remarks:

An application must not delete a DC whose handle was obtained by calling the GetDC function. Instead, it must call the ReleaseDC function to free the DC.

It would also be more intuitive to accept a HWND argument and get the HDC with the GetDC function or the GetWindowDC function (making sure to release it with ReleaseDC as stated in the documentation).

Ok, I've updated the commit to receive a HWND and use ReleaseDC.

nulano

FWIW not all windows can be captured like this. Notably, Vivaldi (my browser) only shows as a black box of the correct size, and the Windows file explorer is missing its toolbar. Other applications, e.g. PyCharm or Microsoft Spy++, are captured correctly. But I think that is just a limitation of modern Windows applications and nothing we can easily fix.

nulano · 2024-11-04T19:14:55Z

src/PIL/ImageGrab.py


 def grab(
    bbox: tuple[int, int, int, int] | None = None,
    include_layered_windows: bool = False,
    all_screens: bool = False,
    xdisplay: str | None = None,
+    handle: int | ImageWin.HWND | None = None,


Ok, I've chosen window.

nulano · 2024-11-04T19:44:17Z

src/display.c

@@ -420,7 +441,11 @@ PyImaging_GrabScreenWin32(PyObject *self, PyObject *args) {
    PyErr_SetString(PyExc_OSError, "screen grab failed");

    DeleteDC(screen_copy);
-    DeleteDC(screen);
+    if (screens == -1) {
+        ReleaseDC(wnd, screen);


You added this for the error: branch but not for the success branch.

Ok, I've updated the commit to add it or success as well.

nulano · 2024-11-04T19:47:00Z

src/display.c

@@ -351,11 +362,17 @@ PyImaging_GrabScreenWin32(PyObject *self, PyObject *args) {
        dpiAwareness = SetThreadDpiAwarenessContext_function((HANDLE)-3);


We need to match the capturing thread DPI awareness to the target window DPI awareness which can be queried with GetWindowDpiAwarenessContext (also added in Windows 10 version 1607): https://learn.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getwindowdpiawarenesscontext

Without it I get a black border around applications without native DPI scaling support (e.g. Microsoft Spy++).

Ok, I've pushed a commit.

nulano · 2024-11-04T19:52:26Z

Tests/test_imagegrab.py

+        with pytest.raises(OSError):
+            ImageGrab.grab(handle=-1)


Suggested change

with pytest.raises(OSError):

ImageGrab.grab(handle=-1)

with pytest.raises(OSError):

ImageGrab.grab(handle=-1)

with pytest.raises(OSError):

ImageGrab.grab(handle=0)

The value 0 is a special way to refer to the desktop. However, it cannot be captured in the same way as regular windows so it fails, but we can add a test for that.

Thanks. I've added a commit.

nulano · 2024-11-07T19:56:24Z

src/display.c

+                GetWindowDpiAwarenessContext_function(wnd);
+            if (dpiAwarenessContext != NULL) {
+                dpiAwareness =
+                    SetThreadDpiAwarenessContext_function(dpiAwarenessContext);


It should probably never happen that SetThreadDpiAwarenessContext is found but GetWindowDpiAwarenessContext is not.

However, if it somehow does happen, we would then use dpiAwareness before its initialized after measuring the window size. So we should ideally either fallback to PER_MONITOR_AWARE context if GetWindowDpiAwarenessContext is not found, or skip the reset a few lines later.

src/display.c

…available Co-authored-by: Ondrej Baranovič <ondreko.tiba@gmail.com>

for more information, see https://pre-commit.ci

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Fix GetWindowDpiAwarenessContext NULL check

radarhere added Windows Screen grab labels Oct 31, 2024

This was referenced Oct 31, 2024

ImageGrab.grab() doesn't ignore windows layered on top (tooltip, pop-ups, etc.) #8456

Open

Windows application screenshot #4415

Open

radarhere force-pushed the imagegrab branch 2 times, most recently from 3c59997 to 72e3f68 Compare October 31, 2024 12:38

nulano suggested changes Nov 2, 2024

View reviewed changes

radarhere force-pushed the imagegrab branch from 72e3f68 to 356c3c1 Compare November 3, 2024 12:33

radarhere changed the title ~~Allow HDC to be passed to ImageGrab.grab() on Windows~~ Allow HWND to be passed to ImageGrab.grab() on Windows Nov 4, 2024

nulano reviewed Nov 4, 2024

View reviewed changes

Allow window to be supplied for ImageGrab.grab() on Windows

607acbf

radarhere force-pushed the imagegrab branch from cfadcd7 to 607acbf Compare November 4, 2024 20:06

Test 0

28e5b92

radarhere force-pushed the imagegrab branch from 4105f0d to 30b2772 Compare November 5, 2024 03:50

Use DPI awareness from window

9622266

radarhere force-pushed the imagegrab branch from 30b2772 to 9622266 Compare November 5, 2024 07:35

Merge branch 'main' into imagegrab

f682197

nulano reviewed Nov 7, 2024

View reviewed changes

Fallback to PER_MONITOR_AWARE

7763350

nulano reviewed Nov 7, 2024

View reviewed changes

src/display.c Outdated Show resolved Hide resolved

radarhere and others added 3 commits November 8, 2024 07:45

Fallback to PER_MONITOR_AWARE if GetWindowDpiAwarenessContext is not …

a44b306

…available Co-authored-by: Ondrej Baranovič <ondreko.tiba@gmail.com>

[pre-commit.ci] auto fixes from pre-commit.com hooks

288d77e

for more information, see https://pre-commit.ci

Fix GetWindowDpiAwarenessContext NULL check

4b88670

nulano mentioned this pull request Nov 7, 2024

Fix GetWindowDpiAwarenessContext NULL check radarhere/Pillow#26

Merged

nulano and others added 3 commits November 7, 2024 22:22

Do not load GetWindowDpiAwarenessContext until its needed

a6c941a

Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>

Lint fix

acba5c4

Merge pull request #26 from nulano/imagegrab-dynamic-link

c5e89ee

Fix GetWindowDpiAwarenessContext NULL check

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Allow HWND to be passed to ImageGrab.grab() on Windows #8516

Allow HWND to be passed to ImageGrab.grab() on Windows #8516

radarhere commented Oct 31, 2024 •

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	handle: int \| ImageWin.HWND \| None = None,
	window: int \| ImageWin.HWND \| None = None,

	handle: int \| ImageWin.HWND \| None = None,
	window_handle: int \| ImageWin.HWND \| None = None,

		@@ -351,11 +362,17 @@ PyImaging_GrabScreenWin32(PyObject self, PyObject args) {
		dpiAwareness = SetThreadDpiAwarenessContext_function((HANDLE)-3);

Allow HWND to be passed to ImageGrab.grab() on Windows #8516

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Allow HWND to be passed to ImageGrab.grab() on Windows #8516

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radarhere commented Oct 31, 2024 •

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