2 * @brief X11環境 (の中でもmaid-x11を必要とする特殊な環境)でガンマ値を調整する
6 * Important note about "colors"
8 * The "TERM_*" color definitions list the "composition" of each
9 * "Angband color" in terms of "quarters" of each of the three color
10 * components (Red, Green, Blue), for example, TERM_UMBER is defined
11 * as 2/4 Red, 1/4 Green, 0/4 Blue.
13 * The following info is from "Torbjorn Lindgren" (see "main-xaw.c").
15 * These values are NOT gamma-corrected. On most machines (with the
16 * Macintosh being an important exception), you must "gamma-correct"
17 * the given values, that is, "correct for the intrinsic non-linearity
18 * of the phosphor", by converting the given intensity levels based
19 * on the "gamma" of the target screen, which is usually 1.7 (or 1.5).
21 * The actual formula for conversion is unknown to me at this time,
22 * but you can use the table below for the most common gamma values.
24 * So, on most machines, simply convert the values based on the "gamma"
25 * of the target screen, which is usually in the range 1.5 to 1.7, and
26 * usually is closest to 1.7. The converted value for each of the five
27 * different "quarter" values is given below:
29 * Given Gamma 1.0 Gamma 1.5 Gamma 1.7 Hex 1.7
30 * ----- ---- ---- ---- ---
31 * 0/4 0.00 0.00 0.00 #00
32 * 1/4 0.25 0.27 0.28 #47
33 * 2/4 0.50 0.55 0.56 #8f
34 * 3/4 0.75 0.82 0.84 #d7
35 * 4/4 1.00 1.00 1.00 #ff
37 * Note that some machines (i.e. most IBM machines) are limited to a
38 * hard-coded set of colors, and so the information above is useless.
40 * Also, some machines are limited to a pre-determined set of colors,
41 * for example, the IBM can only display 16 colors, and only 14 of
42 * those colors resemble colors used by Angband, and then only when
43 * you ignore the fact that "Slate" and "cyan" are not really matches,
44 * so on the IBM, we use "orange" for both "Umber", and "Light Umber"
45 * in addition to the obvious "Orange", since by combining all of the
46 * "indeterminate" colors into a single color, the rest of the colors
47 * are left with "meaningful" values.
50 #include "system/angband.h"
51 #include "main/x11-gamma-builder.h"
53 /* Table of gamma values */
54 byte gamma_table[256];
56 /* Table of ln(x/256) * 256 for x going from 0 -> 255 */
57 static s16b gamma_helper[256] =
59 0,-1420,-1242,-1138,-1065,-1007,-961,-921,-887,-857,-830,-806,-783,-762,-744,-726,
60 -710,-694,-679,-666,-652,-640,-628,-617,-606,-596,-586,-576,-567,-577,-549,-541,
61 -532,-525,-517,-509,-502,-495,-488,-482,-475,-469,-463,-457,-451,-455,-439,-434,
62 -429,-423,-418,-413,-408,-403,-398,-394,-389,-385,-380,-376,-371,-367,-363,-359,
63 -355,-351,-347,-343,-339,-336,-332,-328,-325,-321,-318,-314,-311,-308,-304,-301,
64 -298,-295,-291,-288,-285,-282,-279,-276,-273,-271,-268,-265,-262,-259,-257,-254,
65 -251,-248,-246,-243,-241,-238,-236,-233,-231,-228,-226,-223,-221,-219,-216,-214,
66 -212,-209,-207,-205,-203,-200,-198,-196,-194,-192,-190,-188,-186,-184,-182,-180,
67 -178,-176,-174,-172,-170,-168,-166,-164,-162,-160,-158,-156,-155,-153,-151,-149,
68 -147,-146,-144,-142,-140,-139,-137,-135,-134,-132,-130,-128,-127,-125,-124,-122,
69 -120,-119,-117,-116,-114,-112,-111,-109,-108,-106,-105,-103,-102,-100,-99,-97,
70 -96,-95,-93,-92,-90,-89,-87,-86,-85,-83,-82,-80,-79,-78,-76,-75,
71 -74,-72,-71,-70,-68,-67,-66,-65,-63,-62,-61,-59,-58,-57,-56,-54,
72 -53,-52,-51,-50,-48,-47,-46,-45,-44,-42,-41,-40,-39,-38,-37,-35,
73 -34,-33,-32,-31,-30,-29,-27,-26,-25,-24,-23,-22,-21,-20,-19,-18,
74 -17,-16,-14,-13,-12,-11,-10,-9,-8,-7,-6,-5,-4,-3,-2,-1
78 * Build the gamma table so that floating point isn't needed.
80 * Note gamma goes from 0->256. The old value of 100 is now 128.
82 void build_gamma_table(int gamma)
85 gamma_table[255] = 255;
86 for (int i = 1; i < 255; i++)
89 * Initialise the Taylor series
91 * value and diff have been scaled by 256
94 long value = 256 * 256;
95 long diff = ((long)gamma_helper[i]) * (gamma - 256);
104 * Use the following identiy to calculate the gamma table.
105 * exp(x) = 1 + x + x^2/2 + x^3/(2*3) + x^4/(2*3*4) +...
107 * n is the current term number.
109 * The gamma_helper array contains a table of
111 * This is used because a^b = exp(b*ln(a))
117 * Note that everything is scaled by 256 for accuracy,
118 * plus another factor of 256 for the final result to
119 * be from 0-255. Thus gamma_helper[] * gamma must be
120 * divided by 256*256 each itteration, to get back to
121 * the original power series.
123 diff = (((diff / 256) * gamma_helper[i]) * (gamma - 256)) / (256 * n);
127 * Store the value in the table so that the
128 * floating point pow function isn't needed .
130 gamma_table[i] = ((long)(value / 256) * i) / 256;