Simplified Linux clipboard support

[stephen-huan]

According to the README,

Reading images from clipboard works only on Windows and macOS, on Linux you should read from a directory instead.

Checking the logic, there's two distinct ways manga_ocr handles clipboard:
On Wayland, the pyperclip library is used to get clipboard contents

manga-ocr/manga_ocr/run.py

Line 72 in b0cac91

pyperclip.set_clipboard("wl-clipboard")

while on Windows and MacOS it's through Pillow's PIL.ImageGrab.grabclipboard

manga-ocr/manga_ocr/run.py

Line 93 in b0cac91

img = ImageGrab.grabclipboard()

Although the documentation for grabclipboard() says

Only macOS and Windows are currently supported.

it's undocumented but the Pillow source shows that Linux support was added in 9.4.0 (using wl-paste and xclip).

Thus one can change the existing code from

manga-ocr/manga_ocr/run.py

Lines 66 to 86 in b0cac91

	if sys.platform not in ('darwin', 'win32') and write_to == 'clipboard':
	# Check if the system is using Wayland
	import os
	if os.environ.get('WAYLAND_DISPLAY'):
	# Check if the wl-clipboard package is installed
	if os.system("which wl-copy > /dev/null") == 0:
	pyperclip.set_clipboard("wl-clipboard")
	else:
	msg = 'Your session uses wayland and does not have wl-clipboard installed. ' \
	'Install wl-clipboard for write in clipboard to work.'
	raise NotImplementedError(msg)
	if read_from == 'clipboard':
	if sys.platform not in ('darwin', 'win32'):
	msg = 'Reading images from clipboard works only on macOS and Windows. ' \
	'On Linux, run "manga_ocr /path/to/screenshot/folder" to read images from a folder instead.'
	raise NotImplementedError(msg)
	from PIL import ImageGrab
	logger.info('Reading from clipboard')

to

        # if sys.platform not in ('darwin', 'win32') and write_to == 'clipboard':
        #     # Check if the system is using Wayland
        #     import os
        #     if os.environ.get('WAYLAND_DISPLAY'):
        #         # Check if the wl-clipboard package is installed
        #         if os.system("which wl-copy > /dev/null") == 0:
        #             pyperclip.set_clipboard("wl-clipboard")
        #         else:
        #             msg = 'Your session uses wayland and does not have wl-clipboard installed. ' \
        #                 'Install wl-clipboard for write in clipboard to work.'
        #             raise NotImplementedError(msg)

        if read_from == 'clipboard':

            # if sys.platform not in ('darwin', 'win32'):
            #     msg = 'Reading images from clipboard works only on macOS and Windows. ' \
            #         'On Linux, run "manga_ocr /path/to/screenshot/folder" to read images from a folder instead.'
            #     raise NotImplementedError(msg)

            from PIL import ImageGrab
            logger.info('Reading from clipboard')

and preserve support for Wayland while adding support for Linux systems running X.
This requires Pillow>=9.4.0 and pyperclip can probably be removed.
(see master...stephen-huan:manga-ocr:linux-clipboard for an implementation)

If neither wl-paste nor clip are available, the NotImplementedError should propagate through the try catch.

Note that the implementation of grabclipboard() on Linux is currently a bit wonky, see python-pillow/Pillow#7147.
In particular the current implementation will (a) generate a lot of unnecessary temporary files and (b) raise either ChildProcessError from xclip reporting Error: target image/png not available or UnidentifiedImageError from when Pillow tries to parse non-image data, e.g. plaintext when the other operating systems return None on invalid data.

It may be worthwhile to temporarily patch

            try:
                img = ImageGrab.grabclipboard()
            except OSError:
                logger.warning('Error while reading from clipboard')

to

           try:
               img = ImageGrab.grabclipboard()
           except (ChildProcessError, UnidentifiedImageError) as error:
               logger.trace(error)
           except OSError:
               logger.warning('Error while reading from clipboard')

since the default level of loguru is debug, using trace for the parse errors that occur every delay_secs prevents the user from being spammed when running with the default command manga_ocr. However, using the LOGURU_LEVEL environmental variable allows seeing every logging message, for debugging reasons.

LOGURU_LEVEL=TRACE manga_ocr

It may also be worthwhile to temporarily maintain a patched implementation of grabclipboard() from Pillow, at least until the next quarterly release of Pillow comes out (on July 1st). One should also be sure to copy the license.

[kha-white]

Thanks for letting me know about the Pillow update. I feel like it's not worth it to keep the separate patched implementation so I might just add the temporary logging patch like you proposed and use the official release.

Just one correction:

On Wayland, the pyperclip library is used to get clipboard contents

This is not exactly true, pyperclip is used only for returning the text, not for grabbing the image

[stephen-huan]

I see; I misunderstood the purpose of that code.

I also figured out that one can use clipnotify to block until the clipboard is updated, instead of polling.

Replacing

            time.sleep(delay_secs)

with

        has_clipnotify = os.system("which clipnotify > /dev/null") == 0
        ...

            # on linux with the clipnotify package
            if sys.platform == "linux" and has_clipnotify:
                # block until clipboard updates
                with subprocess.Popen(
                    ["clipnotify", "-s", "clipboard"],
                    stdout=subprocess.PIPE,
                ) as process:
                    process.stdout.read()  # type: ignore
            # poll in a platform-agonistic manner
            else:
                time.sleep(delay_secs)

is all that is necessary. The solution is Linux and X11 specific however, and requires clipnotify as a runtime dependency.

[stephen-huan]

Addressed by #44.