Add love.timer.getAverageDelta (issue #570) and constify love.timer.sleep

src/modules/timer/sdl/Timer.cpp

@@ -41,6 +41,7 @@ Timer::Timer()
 	: currTime(0)
 	, prevFpsUpdate(0)
 	, fps(0)
+	, averageDelta(0)
 	, fpsUpdateFrequency(1)
 	, frames(0)
 	, dt(0)
@@ -80,12 +81,13 @@ void Timer::step()
 	if (timeSinceLast > fpsUpdateFrequency)
 	{
 		fps = int((frames/timeSinceLast) + 0.5);
+		averageDelta = timeSinceLast/frames;
 		prevFpsUpdate = currTime;
 		frames = 0;
 	}
 }
 
-void Timer::sleep(double seconds)
+void Timer::sleep(double seconds) const
 {
 	if (seconds > 0)
 		delay((int)(seconds*1000));
@@ -101,6 +103,11 @@ int Timer::getFPS() const
 	return fps;
 }
 
+double Timer::getAverageDelta() const
+{
+	return averageDelta;
+}
+
 double Timer::getTime() const
 {
 	return SDL_GetTicks()/1000.0;

src/modules/timer/sdl/Timer.h

@@ -54,9 +54,10 @@ public:
 
 	const char *getName() const;
 	void step();
-	void sleep(double seconds);
+	void sleep(double seconds) const;
 	double getDelta() const;
 	int getFPS() const;
+	double getAverageDelta() const;
 	double getTime() const;
 	double getMicroTime() const;
 
@@ -69,6 +70,7 @@ private:
 
 	// Updated with a certain frequency.
 	int fps;
+	double averageDelta;
 
 	// The frequency by which to update the FPS.
 	double fpsUpdateFrequency;