Update display for 4.14 kernel

[ddemidov]

Tested on the latest (2018-04-22) stretch image. It works, and is indeed able to produce grayscale images:

from time import sleep
from ev3dev2.auto import Display, Sound
from ev3dev2 import fonts

Sound().beep()

d = Display()
d.clear()
d.draw.rectangle((10,10,60,20,), fill='black')
d.draw.rectangle((10,20,60,30,), fill='gray')
d.draw.text((10,40), 'Hello1', font=fonts.load('luBS14'), fill='black')
d.draw.text((10,50), 'Hello2', font=fonts.load('luBS14'), fill='gray')
d.draw.text((10,60), 'Hello3', font=fonts.load('luBS14'))
d.update()
sleep(5)

Fixes #455

[dlech]

Hmm... we can probably get away with this since there aren't currently any other XRGB displays on ev3dev devices, but if there ever are, then they won't be usable in color.

[ddemidov]

Do you suggest to use platform here instead of bits_per_pixel?

[dlech]

I suggest using both.

elif self.var_info.bits_per_pixel == 32:
    if platform == EV3:
        grayscale
    else:
        really 32-bit

[ddemidov]

69accdf does something similar. Tested on the EV3.

[dlech]

Please only check for the special case of platform on EV3. We use 16bpp on at least 3 different devices.

[dlech]

Why is the background yellow?

[ddemidov]

Probably just a side effect of fbcat followed by convert to png. The ev3 screen looks normal, but it also could be because 'x' in 'xrgb' is in the wrong position. Since we are now using same byte for all three components, we could also put it into 'x', since it's not used anyway.

[dlech]

I have a hunch that it is because of this line:

return ((v << 24) | (v << 16) | (v << 8))

this fills XRG and leaves B as 0, which would make yellow.

[ddemidov]

b18428b results in

[WasabiFan]

I saw a comment elsewhere that this or a related fix was released already; what's the status here?

[ddemidov]

This is waiting for an approval (I think it can be merged).

[dlech]

LGTM