From 6b302374a9835e4735fbab03c10af675d4b55280 Mon Sep 17 00:00:00 2001
From: Bob Polis <rpb.polis@avans.nl>
Date: Mon, 26 Oct 2020 20:51:31 +0100
Subject: [PATCH] removed timer implementation, replaced with thread and
 nanosleep to drive frame rate

---
 Makefile |  2 +-
 main.cpp | 54 +++++++++++++++++++++++++-----------------------------
 2 files changed, 26 insertions(+), 30 deletions(-)

diff --git a/Makefile b/Makefile
index 58f5e96..807570a 100644
--- a/Makefile
+++ b/Makefile
@@ -27,7 +27,7 @@ else
 	CXXFLAGS += -D NDEBUG -O3
 endif
 
-LDLIBS := -lm -lpthread -lscgui -lSDL2 -lcairo -lscerror -lrt
+LDLIBS := -lm -lpthread -lscgui -lSDL2 -lcairo -lscerror
 
 .PHONY: all clean install
 
diff --git a/main.cpp b/main.cpp
index ac24167..1f47603 100644
--- a/main.cpp
+++ b/main.cpp
@@ -14,17 +14,21 @@
 #include <libscgui.hpp>
 #include <unistd.h>
 #include <cairo/cairo.h>
-#include <signal.h>
 #include <time.h>
 #include <libscerror.hpp>
+#include <cmath>
+#include <thread>
 
 const int WIDTH {700};
 const int HEIGHT {700};
+constexpr double FPS {50.0};
+constexpr int nanosecs {static_cast<int>(round(1000000000.0 / FPS))};
 
 sc::gui::Window* main_window {nullptr};
 sc::gui::Image* main_image {nullptr};
 cairo_t* cr {nullptr};
-bool timer_expired {true};
+bool expired {true};
+bool should_run {true};
 
 void print_help() {
     std::cout << "usage: screensaver [-h|--version]\n";
@@ -36,9 +40,15 @@ void print_version() {
     std::cout << "screensaver version 1.0\n";
 }
 
-void timer_signal_handler(int /*sig*/, siginfo_t* /*si*/, void* /*uc*/) {
-    // timer_t* tmr {si->si_value.sival_ptr};
-    timer_expired = true;
+void update_frame() {
+    while (should_run) {
+        expired = true;
+
+        struct timespec delay;
+        delay.tv_sec = 0;
+        delay.tv_nsec = nanosecs;
+        nanosleep(&delay, nullptr);
+    }
 }
 
 void draw() {
@@ -49,8 +59,8 @@ void draw() {
     static double r = 0;
     static double dr = 0.01;
 
-    if (timer_expired) {
-        timer_expired = false;
+    if (expired) {
+        expired = false;
         sc::gui::ImageLock lock {*main_image};
 
         // white background
@@ -86,7 +96,8 @@ void draw() {
         if (x < 300) dx = 1;
         if (y < 300) dy = 1;
         r += dr;
-        if (r > 1) r = 0;
+        if (r > 1) dr = -0.01;
+        if (r < 0) dr = 0.01;
     }
 }
 
@@ -128,27 +139,6 @@ int main(int argc, const char * argv[]) {
         //     }
         // }
 
-        // install timer signal handler
-        struct sigaction sa;
-        sa.sa_flags = SA_SIGINFO;
-        sa.sa_sigaction = timer_signal_handler;
-        sigemptyset(&sa.sa_mask);
-        throw_if_min1(sigaction(SIGRTMAX, &sa, nullptr));
-
-        // setup repeating timer with 100 ms interval
-        timer_t timer;
-        struct sigevent sev;
-        sev.sigev_notify = SIGEV_SIGNAL;
-        sev.sigev_signo = SIGRTMAX;
-        sev.sigev_value.sival_ptr = &timer;
-        struct itimerspec ts;
-        ts.it_interval.tv_sec = 0;
-        ts.it_interval.tv_nsec = 25000000;
-        ts.it_value.tv_sec = 0;
-        ts.it_value.tv_nsec = 1;
-        throw_if_min1(timer_create(CLOCK_REALTIME, &sev, &timer));
-        throw_if_min1(timer_settime(timer, 0, &ts, nullptr));
-
         // RAII instances
         sc::gui::SDLWrapper sdl2;
         sc::gui::SDLImageWrapper sdl_image;
@@ -168,12 +158,18 @@ int main(int argc, const char * argv[]) {
                                                                  CAIRO_FORMAT_RGB24, s->w, s->h, s->pitch)};
         cr = cairo_create(cs);
 
+        // setup thread which periodically sets 'expired'
+        std::thread frame_timer {update_frame};
+
         sc::gui::app().add_run_loop_action(draw);
         sc::gui::app().run();
 
         cairo_surface_destroy(cs);
         cairo_destroy(cr);
 
+        should_run = false;
+        frame_timer.join();
+
     } catch (const std::exception& ex) {
         std::cerr << "screensaver: " << ex.what() << '\n';
         return EXIT_FAILURE;