gistfile1.go

package spectrum

import (
	"testing"
	"time"
)

const (
	second = 1e9
	ms = 1e6
)

type FpsCounter struct {
	// The channel on which timings are sent from client code
	Timings chan<- int64
	
	// Client code receives fps values from this channel
	Fps <-chan float

	// Same as Timings but the end we use
	timings <-chan int64

	timeInterval int64

	// Same as Fps but the end we use
	fps chan<- float

	// The ticker that triggers the calculation of average fps
	ticker <-chan int64
}

func NewFpsCounter(timeInterval int64) *FpsCounter {

	timings := make(chan int64)
	fps := make(chan float)

	fpsCounter := &FpsCounter{timings, fps, timings, timeInterval, fps, time.Tick(timeInterval)}

	var (
		sum, numSamples int64
		lastFps float
	)
	
	// Non-blocking fps stream
	go func() {
		for {
			fpsCounter.fps <- lastFps
		}
	}()

	// Wait for timings and calculate the sum
	go func() {
		for t := range timings {
			sum += t
			numSamples++
		}
	}()

	// Calculate average fps and reset variables every tick
	go func() {
		for {
			<-fpsCounter.ticker

			if numSamples > 0 {
				avgTime := sum / numSamples
				lastFps = 1 / (float(avgTime) / second)
			}

			sum, numSamples = 0, 0
		}
	}()

	return fpsCounter
}

// Helper for TestFpsCounter
func loopFor(timeInterval int64, block func(elapsedTime int64)) {
	var elapsedTime int64
	startTime := time.Nanoseconds()
	for elapsedTime < timeInterval {
		block(elapsedTime)
		elapsedTime = time.Nanoseconds() - startTime
	}
}

func TestFpsCounter(t *testing.T) {
	// Collect timings every second
	var timeInterval int64 = 1 * second
	// Create a new FpsCounter service with the given timeInterval
	fpsCounter := NewFpsCounter(timeInterval)

	// Simulate a three seconds emulator loop
	loopFor(3 * second, func(elapsedTime int64) {

		fpsCounter.Timings <- 20 * ms // Send a dummy time of
					      // 20ms (50 fps)

		fps := <-fpsCounter.Fps // Receive fps from the
					// FpsCounter service

		// After 2 seconds average fps should be 50
		if elapsedTime > 2 * second {
			if fps != 50 {
				t.Errorf("fps should be 50 but got %f", fps)
			}
		}
	})
}