support 16-bit depth

[totaam]

Issue migrated from trac ticket # 1315

component: server | priority: minor | resolution: fixed

2016-09-20 08:05:54: antoine created the issue

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Similar to #909 but using less bits per pixel.

Not much to be gained from using 16-bit colour instead of 24 bits per pixel.
Most libraries will convert to 24-bit internally and very few encoders support 16-bit - apparently, libvpx does.
I guess some very specific applications might benefit on very bandwidth constrained links. Or some application may just require those modes?

We could at least handle this a little bit more gracefully than we do now and convert to 24-bit rather than just failing:

Traceback (most recent call last):
  File "/usr/lib64/python2.7/site-packages/xpra/x11/gtk2/window_damage.py", line 171, in get_image
    shm_image = shm.get_image(handle.get_pixmap(), x, y, width, height)
  File "xpra/x11/bindings/ximage.pyx", line 561, in xpra.x11.bindings.ximage.XShmWrapper.get_image (xpra/x11/bindings/ximage.c:7071)
    imageWrapper.set_image(self.image)
  File "xpra/x11/bindings/ximage.pyx", line 267, in xpra.x11.bindings.ximage.XImageWrapper.set_image (xpra/x11/bindings/ximage.c:2404)
    raise Exception("invalid image depth: %i bpp" % self.depth)
Exception: invalid image depth: 16 bpp

Note: we cannot support 8-bit colour depth (or less) in seamless mode as the X11 server then disables compositing.

[totaam]

2017-02-19 16:03:03: antoine changed status from new to closed

[totaam]

2017-02-19 16:03:03: antoine set resolution to fixed

[totaam]

2017-02-19 16:03:03: antoine changed title from support lower bit depths to support 16-bit depth

[totaam]

2017-02-19 16:03:03: antoine commented

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r15120 adds support for 16-bit display servers, we convert the pixels to RGB(X) before encoding, only png and rgb encodings are supported in this mode. (and scrolling detection).

8-bit depth (#1445) would be more interesting to support, but it is also harder to implement.

[totaam]

2017-02-20 09:08:48: antoine commented

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Testing different bit depths is now much easier in r15124, see [r15124](.. commit d013136), see [ImageDepth](r15124](..-commit-d013136fcbd922903e05aa2c2c8e7a615843e8d9), see [../wiki/ImageDepth).