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/**
* get-luminosity — Determine how bright it is in your room
* Copyright © 2014 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stropts.h>
#include <linux/fb.h>
#include <errno.h>
#include <stdint.h>
#include <stdlib.h>
/* python code to generate this map:
* [c / (255 * 12.92) if c <= 255 * 0.04045 else ((c / 255 + 0.055) / (1 + 0.055)) ** 2.4 for c in range(256)]
*/
static const float LINEAR_MAP[] =
{
0.0, 0.0003035269835488375, 0.000607053967097675, 0.0009105809506465125, 0.00121410793419535, 0.0015176349177441874, 0.001821161901293025, 0.0021246888848418626, 0.0024282158683907, 0.0027317428519395377, 0.003035269835488375, 0.003346535763899161, 0.003676507324047436, 0.004024717018496307, 0.004391442037410293, 0.004776953480693729, 0.005181516702338386, 0.005605391624202723, 0.006048833022857054, 0.006512090792594475, 0.006995410187265387, 0.007499032043226175, 0.008023192985384994, 0.008568125618069307, 0.009134058702220787, 0.00972121732023785, 0.010329823029626936, 0.010960094006488246, 0.011612245179743885, 0.012286488356915872, 0.012983032342173012, 0.013702083047289686, 0.014443843596092545, 0.01520851442291271, 0.01599629336550963, 0.016807375752887384, 0.017641954488384078, 0.018500220128379697, 0.019382360956935723, 0.0202885630566524, 0.021219010376003555, 0.02217388479338738, 0.02315336617811041, 0.024157632448504756, 0.02518685962736163, 0.026241221894849898, 0.027320891639074894, 0.028426039504420793, 0.0295568344378088, 0.030713443732993635, 0.03189603307301153, 0.033104766570885055, 0.03433980680868217, 0.03560131487502034, 0.03688945040110004, 0.0382043715953465, 0.03954623527673284, 0.04091519690685319, 0.042311410620809675, 0.043735029256973465, 0.04518620438567554, 0.046665086336880095, 0.04817182422688942, 0.04970656598412723, 0.05126945837404324, 0.052860647023180246, 0.05448027644244237, 0.05612849004960009, 0.05780543019106723, 0.0595112381629812, 0.06124605423161761, 0.06301001765316767, 0.06480326669290577, 0.06662593864377289, 0.06847816984440017, 0.07036009569659588, 0.07227185068231748, 0.07421356838014963, 0.07618538148130785, 0.07818742180518633, 0.08021982031446832, 0.0822827071298148, 0.08437621154414882, 0.08650046203654976, 0.08865558628577294, 0.09084171118340768, 0.09305896284668745, 0.0953074666309647, 0.09758734714186246, 0.09989872824711389, 0.10224173308810132, 0.10461648409110419, 0.10702310297826761, 0.10946171077829933, 0.1119324278369056, 0.11443537382697373, 0.11697066775851084, 0.11953842798834562, 0.12213877222960187, 0.12477181756095049, 0.12743768043564743, 0.1301364766903643, 0.13286832155381798, 0.13563332965520566, 0.13843161503245183, 0.14126329114027164, 0.14412847085805777, 0.14702726649759498, 0.14995978981060856, 0.15292615199615017, 0.1559264637078274, 0.1589608350608804, 0.162029375639111, 0.1651321945016676, 0.16826940018969075, 0.1714411007328226, 0.17464740365558504, 0.17788841598362912, 0.18116424424986022, 0.184474994500441, 0.18782077230067787, 0.19120168274079138, 0.1946178304415758, 0.19806931955994886, 0.20155625379439707, 0.20507873639031693, 0.20863687014525575, 0.21223075741405523, 0.21586050011389926, 0.2195261997292692, 0.2232279573168085, 0.22696587351009836, 0.23074004852434915, 0.23455058216100522, 0.238397573812271, 0.24228112246555486, 0.24620132670783548, 0.25015828472995344, 0.25415209433082675, 0.2581828529215958, 0.26225065752969623, 0.26635560480286247, 0.2704977910130658, 0.27467731206038465, 0.2788942634768104, 0.2831487404299921, 0.2874408377269175, 0.29177064981753587, 0.2961382707983211, 0.3005437944157765, 0.3049873140698863, 0.30946892281750854, 0.31398871337571754, 0.31854677812509186, 0.32314320911295075, 0.3277780980565422, 0.33245153634617935, 0.33716361504833037, 0.3419144249086609, 0.3467040563550296, 0.35153259950043936, 0.3564001441459435, 0.3613067797835095, 0.3662525955988395, 0.3712376804741491, 0.3762621229909065, 0.38132601143253014, 0.386429433787049, 0.39157247774972326, 0.39675523072562685, 0.4019777798321958, 0.4072402119017367, 0.41254261348390375, 0.4178850708481375, 0.4232676699860717, 0.4286904966139066, 0.43415363617474895, 0.4396571738409188, 0.44520119451622786, 0.45078578283822346, 0.45641102318040466, 0.4620769996544071, 0.467783796112159, 0.47353149614800955, 0.4793201831008268, 0.4851499400560704, 0.4910208498478356, 0.4969329950608704, 0.5028864580325687, 0.5088813208549338, 0.5149176653765214, 0.5209955732043543, 0.5271151257058131, 0.5332764040105052, 0.5394794890121072, 0.5457244613701866, 0.5520114015120001, 0.5583403896342679, 0.5647115057049292, 0.5711248294648731, 0.5775804404296506, 0.5840784178911641, 0.5906188409193369, 0.5972017883637634, 0.6038273388553378, 0.6104955708078648, 0.6172065624196511, 0.6239603916750761, 0.6307571363461468, 0.6375968739940326, 0.6444796819705821, 0.6514056374198242, 0.6583748172794485, 0.665387298282272, 0.6724431569576875, 0.6795424696330938, 0.6866853124353135, 0.6938717612919899, 0.7011018919329731, 0.7083757798916868, 0.7156935005064807, 0.7230551289219693, 0.7304607400903537, 0.7379104087727308, 0.7454042095403874, 0.7529422167760779, 0.7605245046752924, 0.768151147247507, 0.7758222183174236, 0.7835377915261935, 0.7912979403326302, 0.799102738014409, 0.8069522576692516, 0.8148465722161012, 0.8227857543962835, 0.8307698767746546, 0.83879901174074, 0.846873231509858, 0.8549926081242338, 0.8631572134541023, 0.8713671191987972, 0.8796223968878317, 0.8879231178819663, 0.8962693533742664, 0.9046611743911496, 0.9130986517934192, 0.9215818562772946, 0.9301108583754237, 0.938685728457888, 0.9473065367331999, 0.9559733532492861, 0.9646862478944651, 0.9734452903984125, 0.9822505503331171, 0.9911020971138298, 1.0
};
#define linearise(value, ch) (LINEAR_MAP[(value >> (8 * ch)) & 255])
int main()
{
auto struct fb_var_screeninfo var_info;
long width;
long height;
long y;
auto int fd;
auto const char* restrict mem;
register float grand_sum = 0;
float inv_width;
if (fd = open("/dev/fb0", O_RDONLY), fd == -1)
return perror("get-luminosity::framebuffer: open: /dev/fb0"), close(fd), 1;
if (ioctl(fd, (unsigned long)FBIOGET_VSCREENINFO, &var_info))
return perror("get-luminosity::framebuffer: ioctl"), close(fd), 1;
width = var_info.xres;
height = var_info.yres;
inv_width = 1.f / (float)width;
mem = mmap(NULL, (size_t)(width * height * 4), PROT_READ, MAP_SHARED, fd, (off_t)0);
if (mem == MAP_FAILED)
return perror("get-luminosity::framebuffer: mmap"), close(fd), 1;
for (y = 0; y < height; y++)
{
register const int32_t* restrict linemem = (const int32_t*)(mem + y * width * 4);
register const int32_t* restrict end = linemem + width;
float sum = 0;
while (linemem != end)
{
int32_t value = *linemem++;
sum += linearise(value, 0) + linearise(value, 1) + linearise(value, 2);
}
grand_sum += (float)sum * inv_width;
}
grand_sum /= (float)(height * 3);
fprintf(stderr, "%lf\n", (double)grand_sum);
fflush(stdout);
close(fd);
return 0;
}
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