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// By Tom Smeding (2016)
// modified for new laptop (2017)
// modified for ddcutil support (2022)
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <vector>
#include <cstdlib>
#include <cstdarg>
#include <cstring>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
std::string read_process(const char *procname, const std::vector<const char*> &args) {
int pi[2];
int ret = pipe(pi);
if (ret != 0) {
perror("pipe");
exit(1);
}
pid_t pid = fork();
if (pid < 0) {
perror("fork");
exit(1);
}
if (pid == 0) {
dup2(pi[1], 1);
close(pi[0]);
close(pi[1]);
char **argv = new char*[args.size() + 2];
argv[0] = strdup(procname);
for (size_t i = 0; i < args.size(); i++) {
argv[i + 1] = strdup(args[i]);
}
argv[args.size() + 1] = nullptr;
fprintf(stderr, "procname = <%s>\n", procname);
for (size_t i = 0; i < args.size() + 2; i++) {
fprintf(stderr, "argv[%zu] = <%s>\n", i, argv[i]);
}
execvp(procname, argv);
perror("execvp");
exit(1);
}
close(pi[1]);
std::string output;
while (true) {
output.resize(output.size() + 1024);
ssize_t nr = read(pi[0], &output[output.size() - 1024], 1024);
if (nr < 0) {
if (errno == EINTR) continue;
perror("read");
exit(1);
}
if (nr == 0) break;
output.resize(output.size() - 1024 + nr);
}
close(pi[0]);
while (true) {
int status;
int ret = waitpid(pid, &status, 0);
if (ret < 0) {
if (errno == EINTR) continue;
perror("waitpid");
exit(1);
}
if (WIFEXITED(status)) break;
}
return output;
}
struct Backlight {
virtual ~Backlight() {}
virtual int increment() const = 0;
virtual bool suitable() = 0;
virtual int get_max_brightness() = 0;
virtual int get_brightness() = 0;
virtual void set_brightness(int n) = 0;
virtual void add_brightness(int n) {
n = get_brightness() + n;
if (n < 0) n = 0;
int maxval = get_max_brightness();
if (n > maxval) n = maxval;
set_brightness(n);
}
virtual int convert_absolute_brightness(int n) = 0; // to percentage
};
struct IntelBacklight : public Backlight {
private:
int read_int_file(const char *fname) {
std::ifstream f{fname};
if (!f) {
std::cerr << "Could not open brightness file" << std::endl;
exit(1);
}
int n;
f >> n;
return n;
}
public:
int increment() const { return 1000; }
bool suitable() {
struct stat st;
int ret = stat("/sys/class/backlight/intel_backlight", &st);
return ret == 0;
}
int get_max_brightness() {
return read_int_file("/sys/class/backlight/intel_backlight/max_brightness");
}
int get_brightness() {
return read_int_file("/sys/class/backlight/intel_backlight/brightness");
}
void set_brightness(int n) {
std::ofstream f{"/sys/class/backlight/intel_backlight/brightness"};
if (!f) {
std::cerr << "Could not open brightness file" << std::endl;
exit(1);
}
f << n;
}
int convert_absolute_brightness(int n) {
return n * 10;
}
};
struct DDCBacklight : public Backlight {
private:
bool have_read = false;
int brvalue, brmaxvalue;
void read_current() {
std::string output = read_process("ddcutil", {"getvcp", "-t", "10"});
std::istringstream ss{output};
std::string word;
ss >> word;
if (word != "VCP") goto format_err;
ss >> word;
if (word != "10") goto format_err;
ss >> word;
if (word != "C") goto format_err;
ss >> brvalue;
ss >> brmaxvalue;
if (!ss) goto format_err;
have_read = true;
return;
format_err:
std::cerr << "Invalid format from ddcutil" << std::endl;
exit(1);
}
public:
int increment() const { return 10; }
bool suitable() {
struct stat st;
int ret = stat("/usr/bin/ddcutil", &st);
return ret == 0;
}
int get_brightness() {
if (!have_read) read_current();
return brvalue;
}
int get_max_brightness() {
if (!have_read) read_current();
return brmaxvalue;
}
void set_brightness(int n) {
std::string argstr = std::to_string(n);
read_process("ddcutil", {"setvcp", "10", argstr.data()});
}
void add_brightness(int n) {
if (n == 0) return;
std::string absargstr = std::to_string(abs(n));
read_process("ddcutil", {"setvcp", "10", n > 0 ? "+" : "-", absargstr.data()});
}
int convert_absolute_brightness(int n) {
return n;
}
};
int main(int argc,char **argv){
uid_t uid = geteuid();
if (uid != 0) {
std::cerr << "brightness will only work with root." << std::endl;
return 1;
}
std::vector<Backlight*> instances{new IntelBacklight{}, new DDCBacklight{}};
Backlight *backlight = nullptr;
for (Backlight *b : instances) if (b->suitable()) { backlight = b; break; }
if (!backlight) {
std::cerr << "No idea how to control your monitor, sorry" << std::endl;
return 1;
}
if (argc == 1) {
std::cout << "max: " << backlight->get_max_brightness() << std::endl;
std::cout << "current: " << backlight->get_brightness() << std::endl;
} else if (argc == 2) {
if (strcmp(argv[1], "-") == 0) {
backlight->add_brightness(-backlight->increment());
} else if (strcmp(argv[1], "+") == 0) {
backlight->add_brightness(backlight->increment());
} else {
char *endp;
int n = strtol(argv[1], &endp, 10);
if (argv[1][0] == '\0' || *endp != '\0') {
std::cerr << "Invalid number '" << argv[1] << "'" << std::endl;
return 1;
}
backlight->set_brightness(backlight->convert_absolute_brightness(n));
}
}
}
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