Add display_gamma option for client

[Zeno-]

No description provided.

[Zeno-]

Comparisons (after adjustments to align with hardcoded light values)

hardcoded light values

8
13
21
28
37
49
57
62
70
83
102
125
157
200
255

-------------
default
-------------

gamma = 1.8
8
13
21
28
37
49
57
62
70
83
102
125
157
200
255

-------------
"Lighter"
-------------

gamma = 1.5
11
19
29
40
51
64
74
79
87
99
117
137
165
204
255

gamma = 1.3
14
25
38
50
63
77
87
92
100
111
127
145
171
208
255


gamma = 1.1
19
34
50
64
78
93
103
107
114
124
138
154
177
211
255

-------------
"Darker"
-------------
gamma = 2.2
7
10
14
18
24
33
40
43
51
65
85
111
146
194
255

gamma = 2.5
7
8
11
14
18
25
30
32
40
53
74
100
138
189
255

gamma = 3.0
7
7
9
9
11
16
18
18
24
36
57
85
125
182
255

[Calinou]

👍 I approve, good for dark screens like mine.

This could be added to the GUI (but remember that lower gamma values make stuff brighter).

[ShadowNinja]

Since there's only one global light table singleplayer servers might have the light values modified acurding to the gamma, which would be unexpected.

[Zeno-]

@ShadowNinja The comment I added about the server in the source code is misleading. The server only cares that the values are 0-15 and not what their display value (brightness) is. I'll amend the comment.

Edit: The reason I changed this from a low-priority enhancement to normal enhancement is that on my calibrated (for photography) monitors Minetest is unpleasant to play with the existing light table -- above ground at night is darker than in a cave with a single torch. If I play on my laptop it's too bright. It's not such an issue on my laptop because I simply adjust the brightness of the display, but adjusting the brightness of a calibrated monitor is not a viable solution, not to mention it's being adjusted to play a single game. All monitors have different display characteristics and I'm confident that I'm not the only one who has problems with the current light table. There is no single light table that will work on every display and be acceptable/pleasant. Adding the variance between every person's eyesight or tolerance/intolerance to brightness or perceived brightness complicates the issues even further. Therefore, allowing some adjustment (via gamma) is the most sensible approach.

[Zeno-]

commit 3d29be2