使用 requestAnimationFrame 在 Canvas 中计算 FPS
如何计算画布游戏应用程序的 FPS?我看过一些例子，但没有一个使用 requestAnimationFrame，我不确定如何在那里应用他们的解决方案.这是我的代码:
How could I calculate the FPS of a canvas game application? I've seen some examples, but none of them use requestAnimationFrame, and im not sure how to apply their solutions there. This is my code:
(function(window, document, undefined){
var canvas = document.getElementById("mycanvas"),
context = canvas.getContext("2d"),
width = canvas.width,
height = canvas.height,
fps = 0,
game_running = true,
show_fps = true;
function showFPS(){
context.fillStyle = "Black";
context.font = "normal 16pt Arial";
context.fillText(fps + " fps", 10, 26);
}
function gameLoop(){
//Clear screen
context.clearRect(0, 0, width, height);
if (show_fps) showFPS();
if (game_running) requestAnimationFrame(gameLoop);
}
gameLoop();
}(this, this.document))canvas{
border: 3px solid #fd3300;
}<canvas id="mycanvas" width="300" height="150"></canvas>顺便问一下，我可以添加任何库来监控性能吗?
By the way, is there any library I could add to surpervise performance?
推荐答案
不要使用 new Date()
此 API 有几个缺陷，仅对获取当前日期 + 时间有用.不适用于测量时间跨度.
Do not use new Date()
This API has several flaws and is only useful for getting the current date + time. Not for measuring timespans.
Date-API 使用操作系统的内部时钟，该时钟不断更新并与 NTP 时间服务器同步.这意味着，这个时钟的速度/频率有时比实际时间快，有时慢 - 因此不能用于测量持续时间和帧速率.
The Date-API uses the operating system's internal clock, which is constantly updated and synchronized with NTP time servers. This means, that the speed / frequency of this clock is sometimes faster and sometimes slower than the actual time - and therefore not useable for measuring durations and framerates.
如果有人更改系统时间(手动或由于 DST)，如果单帧突然需要一个小时，您至少可以看到问题.或者是消极时期.但如果系统时钟与世界时间同步的速度快 20%，则几乎无法检测到.
If someone changes the system time (either manually or due to DST), you could at least see the problem if a single frame suddenly needed an hour. Or a negative time. But if the system clock ticks 20% faster to synchronize with world-time, it is practically impossible to detect.
此外，Date-API 非常不精确 - 通常远小于 1 毫秒.这使得它对于帧率测量尤其无用，其中一个 60Hz 帧需要约 17 毫秒.
Also, the Date-API is very imprecise - often much less than 1ms. This makes it especially useless for framerate measurements, where one 60Hz frame needs ~17ms.
Performance API 专为此类用例而设计，可等效于 new Date().只需选择其他答案之一并将 new Date() 替换为 performance.now()，就可以开始了.
The Performance API has been specificly made for such use cases and can be used equivalently to new Date(). Just take one of the other answers and replace new Date() with performance.now(), and you are ready to go.
来源:
与 Date.now() 不同的是，Performance.now() 返回的值始终以恒定速率增加，与系统时钟无关(可以手动调整或通过 NTP 等软件进行调整).否则，performance.timing.navigationStart + performance.now() 将大约等于 Date.now().
Also unlike Date.now(), the values returned by Performance.now() always increase at a constant rate, independent of the system clock (which might be adjusted manually or skewed by software like NTP). Otherwise, performance.timing.navigationStart + performance.now() will be approximately equal to Date.now().
https://developer.mozilla.org/en-US/docs/Web/API/Performance/now
对于窗户:
[时间服务] 调整本地时钟频率以使其能够收敛到正确的时间.如果本地时钟与【准确时间样本】的时间差太大，无法通过调整本地时钟来校正时钟频率，时间服务将本地时钟设置为正确的时间.
[The time service] adjusts the local clock rate to allow it to converge toward the correct time. If the time difference between the local clock and the [accurate time sample] is too large to correct by adjusting the local clock rate, the time service sets the local clock to the correct time.
https://technet.microsoft.com/en-us/library/cc773013(v=ws.10).aspx
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