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如何正确调整玩家精灵的速度?(基本上是一道数学题?)

angle vector math

Philipp Lenssen · 技术社区 · 14 年前

背景:我有一个鸟瞰的JavaScript游戏,玩家通过触摸一个圆来控制一艘太空船——例如,触摸圆心的左边,飞船就会向左移动,触摸右上角,飞船就会向右上角移动,等等。。。离伪操纵杆圆心越远,该方向的速度越快。但是,我并不是直接调整船的速度,而是设置一个targetSpeed.x和targetSpeed.y值,然后船将使用如下方式调整速度:

if (this.speed.x < this.targetSpeed.x) {
    this.speed.x += this.speedStep;
}
else if (this.speed.x > this.targetSpeed.x) {
    this.speed.x -= this.speedStep;
}

... y速度也是一样,speedStep是一个很小的值,可以使它更平滑,也不会太突然(船不应该从快速向左的方向转到快速向右的方向)。

2 回复 | 直到 14 年前

C. K. Young 14 年前

var xdiff = targetSpeed.x - speed.x;
var ydiff = targetSpeed.y - speed.y;
var angle = Math.atan2(ydiff, xdiff);
speed.x += speedStep * Math.cos(angle);
speed.y += speedStep * Math.sin(angle);

Christoffer Hammarström 14 年前

circleTouch == [0, 0]

在一些类似C++的伪代码中:

Scalar circleRadius = ...;
Scalar maxSpeed = ...;
Scalar acceleration = ...;

Vector calculateTargetSpeed( Vector circleTouch ) {
    Vector targetSpeed = maxSpeed * circleTouch / circleRadius;

    return targetSpeed;
}

Vector calculateNewSpeed( Vector currentSpeed, Vector targetSpeed ) {
    Vector speedDiff = targetSpeed - currentSpeed;

    Vector newSpeed = currentSpeed + acceleration * normalized(speedDiff);

    return newSpeed;
}

// Divide v by its length to get normalized vector (length 1) with same x/y ratio
Vector normalized( Vector v ) {
    return v / length(v);
}

// Pythagoras for the length of v
Scalar length( Vector v ) {
    Scalar length = sqrt(v.x * v.x + v.y * v.y); // or preferably hypot(v.x, v.y)

    return length;
}