Merge pull request #1616 from contour-terminal/example-cli-color-mode…

…-detection

Add example program to detect OS dark/light mode setting in the terminal

docs/vt-extensions/color-palette-update-notifications.md

@@ -38,3 +38,8 @@ The sent out DSR looks equivalent to the already above mentioned.
 This notification is not just sent when dark/light mode has been changed
 by the operating system / desktop, but also if the user explicitly changed color scheme,
 e.g. by configuration.
+
+## Example source code
+
+Please have a look at our example C++ [source code](https://github.com/contour-terminal/contour/blob/master/examples/detect-dark-light-mode.cpp)
+in order to see how to implement this in your own application.

examples/CMakeLists.txt

@@ -2,5 +2,7 @@ if(LIBTERMINAL_TESTING)
     if(UNIX)
         add_executable(watch-mouse-events watch-mouse-events.cpp)
         target_link_libraries(watch-mouse-events vtbackend)
+
+        add_executable(detect-dark-light-mode detect-dark-light-mode.cpp)
     endif()
 endif()

examples/detect-dark-light-mode.cpp

@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: Apache-2.0
+#include <csignal>
+#include <cstdlib>
+#include <iostream>
+#include <string_view>
+
+#include <termios.h>
+#include <unistd.h>
+
+using namespace std::literals;
+
+static bool processEvent(std::string_view response)
+{
+    if (response == "\033[?997;1n")
+    {
+        std::cout << "dark\n";
+        return true;
+    }
+    else if (response == "\033[?997;2n")
+    {
+        std::cout << "light\n";
+        return true;
+    }
+
+    std::cout << "unknown\n";
+    return false;
+}
+
+static bool queryDarkLightModeOnce()
+{
+    // Also send DA1 to detect end of reply, in case the terminal does not support color mode detection
+    std::cout << "\033[?996n\033[c";
+    std::cout.flush();
+
+    char buf[32];
+    size_t n = 0;
+    size_t i = 0;
+    while (i < sizeof(buf))
+    {
+        if (read(STDIN_FILENO, buf + i, 1) != 1)
+            break;
+        else if (buf[i] == 'n')
+            n = i + 1;
+        else if (buf[i] == 'c')
+        {
+            ++i;
+            break;
+        }
+        ++i;
+    }
+
+    return processEvent(std::string_view(buf, n));
+}
+
+static void signalHandler(int signo)
+{
+    std::signal(signo, SIG_DFL);
+    std::cerr << "Received signal " << signo << ", exiting...\n";
+}
+
+static void monitorDarkLightModeChanges()
+{
+    char buf[32];
+    size_t n = 0;
+    size_t i = 0;
+    while (true)
+    {
+        if (i >= sizeof(buf))
+            i = 0;
+        if (read(STDIN_FILENO, buf + i, 1) != 1)
+            break;
+        else if (buf[i] == '\033')
+        {
+            buf[0] = '\033';
+            i = 1;
+        }
+        else if (buf[i] == 'n')
+        {
+            n = i + 1;
+            auto const response = std::string_view(buf, n);
+            processEvent(response);
+        }
+        ++i;
+    }
+}
+
+int main(int argc, char* argv[])
+{
+    if (!isatty(STDIN_FILENO))
+    {
+        std::cerr << "stdin is not a terminal\n";
+        return EXIT_FAILURE;
+    }
+
+    termios oldt {};
+    termios newt {};
+    tcgetattr(STDIN_FILENO, &oldt);
+    newt = oldt;
+    newt.c_lflag &= ~(ICANON | ECHO);
+    tcsetattr(STDIN_FILENO, TCSANOW, &newt);
+
+    if (argc == 2 && (argv[1] == "-h"sv || argv[1] == "--help"sv))
+    {
+        std::cout << "Usage: " << argv[0] << " [monitor]\n";
+        return EXIT_SUCCESS;
+    }
+
+    if (!queryDarkLightModeOnce())
+        return EXIT_FAILURE;
+
+    if (argc == 2 && argv[1] == "monitor"sv)
+    {
+        struct sigaction sa;
+        sa.sa_handler = signalHandler;
+        sa.sa_flags = 0; // Explicitly don't set SA_RESTART;
+        sigemptyset(&sa.sa_mask);
+        for (int const sig: { SIGTERM, SIGINT, SIGQUIT })
+            sigaction(sig, &sa, nullptr);
+
+        std::cerr << "Monitoring dark/light mode changes, press Ctrl+C to exit...\n";
+        std::cerr << "\033[?2031h"; // Enable dark/light mode change notifications
+        std::cerr.flush();
+        monitorDarkLightModeChanges();
+        std::cerr << "\033[?2031l"; // Disable dark/light mode change notifications
+        std::cerr << "Finished monitoring dark/light mode changes\n";
+        std::cerr.flush();
+    }
+
+    // restore terminal
+    tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
+
+    return EXIT_SUCCESS;
+}