gl_timer.hpp

#if RENDERER_PROFILING
	template <int N=4>
	struct TimerZone {
		int next = 0; // next timer to be used for measurement
		int count = 0; // number of timers 'buffered', ie measurement was started by result not read yet
		GLuint queries[N];
		
		TimerZone () {
			glGenQueries(N, queries);

			// could check the timer res here, but not sure what to do if it ever overflowed, just ignore since it's only for profiling anyway
			//GLint bits;
			//glGetQueryiv(GL_TIME_ELAPSED,  GL_QUERY_COUNTER_BITS, &bits);
		}
		~TimerZone () {
			glDeleteQueries(N, queries);
		}

		// always call end() after start() and never call read_seconds inbetween
		void start () {
			glBeginQuery(GL_TIME_ELAPSED, queries[next]);
		}
		void end () {
			glEndQuery(GL_TIME_ELAPSED);

			next = (next + 1) % N;
			count++;
		}

		// try to read oldest timing
		// returns false if it is still not ready to be read
		// returns true if result was ready, result in out_seconds
		// in case that a result takes so long to be readable (or you don't read them)
		//  timers will start to be reused, thus overwriting results
		//  in the case that this happend count will become larger than N and this function will return 'fake' 0 results
		bool read_seconds (float* out_seconds) {
			if (count == 0) return false;
			if (count > N) {
				// we overflowed our buffer, so this sample is overwritten, return 0 dummy value
				count--; // pop timing
				*out_seconds = 0;
				return true;
			}

			int idx = (next + N - count) % N;
			
			ZoneScoped;
			GLint avail;
			glGetQueryObjectiv(queries[idx], GL_QUERY_RESULT_AVAILABLE, &avail);
			if (avail == 0) return false;

			count--; // pop timing
			
			uint64_t elapsed_ns = 99;
			glGetQueryObjectui64v(queries[idx], GL_QUERY_RESULT, &elapsed_ns);

			*out_seconds = (float)elapsed_ns * (1.0f / NSEC);
			return true;
		}
	};

	struct TimerZoneScoped {
		TimerZone<>& zone;
		TimerZoneScoped (TimerZone<>& zone): zone{zone} {
			zone.start();
		}
		~TimerZoneScoped () {
			zone.end();
		}
	};

	#define OGL_TIMER(name) TimerZone<> name
	#define OGL_TIMER_ZONE(zone) TimerZoneScoped __scoped_glzone_##__COUNTER__(zone)
#else
	#define OGL_TIMER(name)
	#define OGL_TIMER_ZONE(zone)
#endif

// somewhere  start of frame

TimerZone<> timer_rt;

float seconds;
while (timer_rt.read_seconds(&seconds))
	histo_rt.push_timing(seconds);