high bit depth test application

[totaam]

For testing high bit depths.
Can probably be done easily enough using opengl.

We'll need to make sure the low bits are used so we can visually see the difference. (running the test application at normal bit depth and high bit depth)

Links:

• 10-bit color support in opengl client #1309
• wiki ImageDepth

[totaam]

r16286 adds an example based on nvidia's 30-Bit Color Technology for NVIDIA Quadro docs, which does show some color banding using a 24-bit display configuration.

[totaam]

r16301 adds a plain GTK example, which shows color banding, especially in the darker shades of grey.

It shows less banding on a 30 bit display, and identical results when running through xpra with --pixel-depth=30.
Tested OK with Linux clients, but ms windows seems to be unable to render at 30 bit. We use the exact same code to upload the "r210" pixel data, yet the result shows banding.
This may be a GTK limitation: running the examples (opengl or not) fails miserably on win32.
The type of pixel data being uploaded to the graphics card can also be inspected via logging: with -d opengl client side, or see #1309#comment:8

@maxmylin: feel free to just close.

[totaam]

2017-07-12 19:28:46: maxmylyn commented

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Closing.

Test app looks neat.

[totaam]

2017-07-13 16:26:35: antoine uploaded file color-gradient-3bpc.png (26.6 KiB)

tool shown with clipping at 3bpc

[totaam]

r16331 adds manual clipping of the bit depth we use for painting: hit any key to change it, it goes from 16 bpc down to 0 and warps.
With this change and the improvements in #1309#comment:8, it is now very easy to visually verify what bit depth is being rendered on the display (at least on Linux...) and easy to compare local and remote.

Screenshot above.