使用MIDP2.0开发游戏(7)设计Scheduler

王朝other·作者佚名  2006-01-10
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文章来源:J2ME开发网

Scheduler负责以固定的频率执行每一帧,所需的时钟由Clock提供,Scheduler还可以计算每帧所需时间和CPU占用率,以便可能的话动态调整任务。

以下的Scheduler的实现参考自Marshall "Game Programming Gems 3"中的C++代码:

package game.engine.core;

public class Scheduler {

// clock:

private Clock clock = new Clock();

// 启动Scheduler:

public void start() {

clock.start();

}

// 停止Scheduler:

public void stop() {

clock.stop();

}

public int getSystemTime() {

return clock.getSystemTime();

}

public int getVirtualTime() {

return clock.getVirtualTime();

}

// 执行完整的一帧:

public void executeFrame() {

System.out.println("-- start execute frame --");

clock.beginFrame();

int started = clock.getSystemTime();

// do time task:

System.out.println("doing time tasks...");

try {

Thread.sleep(500);

}catch(InterruptedException ie) {}

clock.advanceToEnd();

// do frame task:

System.out.println("doing frame tasks...");

try {

Thread.sleep(200);

}catch(InterruptedException ie) {}

// do render task:

int end = clock.getSystemTime();

int elapsed = end - started;

int frameLength = clock.getFrameEnd() - clock.getFrameStart();

System.out.println("elapsed: " + elapsed + ", frame: " + frameLength);

System.out.println("cpu usage: " + (elapsed * 100 / frameLength) + "%");

// cleanup:

System.out.println("-- end execute frame --\n");

}

public void waitUntil(int time) {

try {

while(clock.getSystemTime() Thread.sleep(1);

}

}catch(InterruptedException ie) {}

}

public static void main(String[] args) {

Scheduler scheduler = new Scheduler();

scheduler.start();

int time = 1000;

do {

scheduler.waitUntil(time);

time += 1000;

scheduler.executeFrame();

} while(scheduler.getSystemTime()<10000);

}

}

我们还没有真正的任务要执行,所以只好用两个Thread.sleep()来表示执行任务,分别是500ms和200ms,在main()方法中每1s执行一次executeFrame()方法,可以看到如下输出:

-- start execute frame --

[beginFrame] virtual time = 0, systemTime = 1002

doing time tasks...

[advanceToEnd] virtual time = 992

doing frame tasks...

elapsed: 701, frame: 992

cpu usage: 70%

-- end execute frame --

-- start execute frame --

[beginFrame] virtual time = 992, systemTime = 2003

doing time tasks...

[advanceToEnd] virtual time = 1993

doing frame tasks...

elapsed: 701, frame: 1001

cpu usage: 70%

-- end execute frame --

...

CPU使用率是70%,如果把任务时间延长大于1s,比如700ms和500ms,虚拟时间就变慢,因为CPU不能在1s内处理完任务,输出的CPU使用率100%(除了第一次计算):

-- start execute frame --

[beginFrame] virtual time = 0, systemTime = 1002

doing time tasks...

[advanceToEnd] virtual time = 992

doing frame tasks...

elapsed: 1201, frame: 992

cpu usage: 121%

-- end execute frame --

-- start execute frame --

[beginFrame] virtual time = 992, systemTime = 2203

doing time tasks...

[advanceToEnd] virtual time = 2193

doing frame tasks...

elapsed: 1202, frame: 1201

cpu usage: 100%

-- end execute frame --

-- start execute frame --

[beginFrame] virtual time = 2193, systemTime = 3415

doing time tasks...

[advanceToEnd] virtual time = 3405

doing frame tasks...

elapsed: 1202, frame: 1212

cpu usage: 99%

-- end execute frame --

...

有一些微小的误差,因为调度器自身的代码也会占用一点时间,并且currentTimeMillies()只能精确到毫秒级,不过用户是感觉不出来的,只有当CPU使用达100%时,游戏才会变慢。

待续...

 
 
 
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