sub-pixel rendering test application

[Antoine Martin]

Follow up from #559.

The same way that #1553 provided a test application for #1309 (image depth settings), we should provide test applications for sub-pixel rendering.

[Antoine Martin]

screenshot of the new fontrendering test application

[Antoine Martin]

test app running on win32

[Antoine Martin]

r16604 adds a test application (very slow to run..), which looks like this on Linux (with or without xpra):

The right hand side shows the difference between the antialias setting shown on the left and the "NONE" setting.

So far it shows that I am unable to force sub-pixel rendering to turn on, only gray (which is the default is seems).

Interestingly, it does enable sub-pixel rendering on MS Windows where the colours are clearly visible on the deltas:

Looks like it uses more blue on the right hand side, and orange (red) on the left. So this would imply an RGB sub-pixel order which is correct. (this inverted since we XOR the two images!)
And this is confirmed by the value retrieved through the API, see Native_GUI.exe output.

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/1580