xcb screengrab docs and fixes

Tests/test_imagegrab.py

@@ -46,9 +46,6 @@ class TestImageGrab:
         assert isinstance(exception, IOError)
         assert str(exception).startswith("X connection failed")
 
-    @pytest.mark.skipif(
-        sys.platform not in ("win32", "darwin"), reason="requires Windows or macOS"
-    )
     def test_grabclipboard(self):
         if sys.platform == "darwin":
             subprocess.call(["screencapture", "-cx"])
@@ -62,7 +59,15 @@ $bmp = New-Object Drawing.Bitmap 200, 200
             )
             p.communicate()
         else:
-            pytest.skip("ImageGrab.grabclipboard() is macOS and Windows only")
+            exception = None
+
+            try:
+                ImageGrab.grabclipboard()
+            except IOError as e:
+                exception = e
+
+            assert isinstance(exception, IOError)
+            assert str(exception) == "ImageGrab.grabclipboard() is macOS and Windows only"
             return
 
         im = ImageGrab.grabclipboard()

docs/reference/ImageGrab.rst

@@ -11,13 +11,13 @@ or the clipboard to a PIL image memory.
 
 .. versionadded:: 1.1.3
 
-.. py:function:: PIL.ImageGrab.grab(bbox=None, include_layered_windows=False, all_screens=False)
+.. py:function:: PIL.ImageGrab.grab(bbox=None, include_layered_windows=False, all_screens=False, xdisplay=None)
 
     Take a snapshot of the screen. The pixels inside the bounding box are
     returned as an "RGB" image on Windows or "RGBA" on macOS.
     If the bounding box is omitted, the entire screen is copied.
 
-    .. versionadded:: 1.1.3 (Windows), 3.0.0 (macOS)
+    .. versionadded:: 1.1.3 (Windows), 3.0.0 (macOS), 7.0.0 (Linux (X11))
 
     :param bbox: What region to copy. Default is the entire screen.
                  Note that on Windows OS, the top-left point may be negative if ``all_screens=True`` is used.
@@ -27,6 +27,11 @@ or the clipboard to a PIL image memory.
     :param all_screens: Capture all monitors. Windows OS only.
 
         .. versionadded:: 6.2.0
+
+    :param xdisplay: X11 Display address. Pass ``None`` to grab the default system screen.
+                     Pass ``""`` to grab the default X11 screen on Windows or macOS.
+
+        .. versionadded:: 7.0.0
     :return: An image
 
 .. py:function:: PIL.ImageGrab.grabclipboard()

src/PIL/ImageGrab.py

@@ -15,10 +15,7 @@
 # See the README file for information on usage and redistribution.
 #
 
-import os
-import subprocess
 import sys
-import tempfile
 
 from . import Image
 
@@ -26,10 +23,6 @@ if sys.platform == "darwin":
     import os
     import tempfile
     import subprocess
-elif sys.platform == "win32":
-    pass
-elif not Image.core.HAVE_XCB:
-    raise ImportError("ImageGrab requires Windows, macOS, or the XCB library")
 
 
 def grab(bbox=None, include_layered_windows=False, all_screens=False, xdisplay=None):
@@ -47,7 +40,9 @@ def grab(bbox=None, include_layered_windows=False, all_screens=False, xdisplay=N
                 return im_cropped
             return im
         elif sys.platform == "win32":
-            offset, size, data = Image.core.grabscreen(include_layered_windows, all_screens)
+            offset, size, data = Image.core.grabscreen_win32(
+                include_layered_windows, all_screens
+            )
             im = Image.frombytes(
                 "RGB",
                 size,
@@ -65,7 +60,7 @@ def grab(bbox=None, include_layered_windows=False, all_screens=False, xdisplay=N
             return im
     # use xdisplay=None for default display on non-win32/macOS systems
     if not Image.core.HAVE_XCB:
-        raise AttributeError("XCB support not present")
+        raise IOError("Pillow was built without XCB support")
     size, data = Image.core.grabscreen_x11(xdisplay)
     im = Image.frombytes("RGB", size, data, "raw", "BGRX", size[0] * 4, 1)
     if bbox:
@@ -105,3 +100,5 @@ def grabclipboard():
 
             return BmpImagePlugin.DibImageFile(io.BytesIO(data))
         return data
+    else:
+        raise IOError("ImageGrab.grabclipboard() is macOS and Windows only")