此代码怎么修改能让小球添加下落轨迹：
<!DOCTYPE html>
<html>
<head>
<title>自由落体运动仿真</title>
<style>
body {
background-color: #ffffcc; /* 淡黄色的颜色代码 */
}
#mycanvas {
display: block;
margin: auto;
background-color: white;
}
h1 {
font-size: 32px; /* 设置标题字体大小 */
font-weight: normal; /* 取消标题的粗体样式 */
margin-top: 20px; /* 设置标题距离顶部的距离 */
text-align: center;
}
.module {
margin-top: -200px;
}
label {
display: block;
margin-bottom: 10px;
}
input[type="number"] {
width: 50px;
margin-right: 10px;
}
</style>
</head>
<body>
<h1>基于HTML5小球自由落体运动仿真功能与实现</h1>
<canvas id="mycanvas" width="600" height="650" style="border:1px solid red;position:relative;"></canvas>
<div class="module">
<label for="elasticity">弹力：</label>
<input type="number" id="elasticity" name="elasticity" min="0" max="1" step="0.1" value="1" />
</div>
<div class="module">
<label for="speed">初始速度：</label>
<input type="number" id="speed" name="speed" min="0" max="100" step="1" value="0" />
</div>
<div class="module">
<button id="startButton">开始</button>
<button id="stopButton">停止</button>
<button id="resetButton">复位</button>
</div>
<script>
// 获取画布元素和画布上下文对象
var canvas = document.getElementById("mycanvas");
var context = canvas.getContext("2d");
var animationId = null; // 动画帧编号
// 定义物理参数
var gravity = 9.8; // 重力加速度
var airResistance = 0.1; // 空气阻力系数
// 定义小球的初始状态
var x = canvas.width/2;
var y = 0;
var radius = 20;
var speed = 0;
// 获取弹力的input元素
var elasticityInput = document.getElementById("elasticity");
var elasticity = parseFloat(elasticityInput.value);
// 获取速度的input元素
var elasticityInput = document.getElementById("elasticity");
var elasticity = parseFloat(elasticityInput.value);
// 定义允许的最小和最大弹力值
var minElasticity = parseFloat(elasticityInput.getAttribute("min"));
var maxElasticity = parseFloat(elasticityInput.getAttribute("max"));
// 更新弹力值的函数
function updateElasticity() {
// 获取当前输入框的值并转换为浮点数
var elasticityValue = parseFloat(elasticityInput.value);
// 如果值超出了允许的范围，则将其设置为最小或最大允许值
if (elasticityValue < minElasticity) {
elasticityValue = minElasticity;
} else if (elasticityValue > maxElasticity) {
elasticityValue = maxElasticity;
}
// 更新弹力值
elasticity = elasticityValue;
}
// 添加弹力值输入框的change事件监听器
elasticityInput.addEventListener("change", updateElasticity);
// 确保弹力值在页面加载时被初始化
updateElasticity();
function draw() {
// 清空画布
context.clearRect(0, 0, canvas.width, canvas.height);
// 绘制小球
context.beginPath();
context.arc(x, y, radius, 0, Math.PI*2);
context.fillStyle = "red";
context.fill();
context.closePath();
// 绘制小球速度
context.font = "16px Arial";
context.fillStyle = "black";
context.fillText("速度：" + speed.toFixed(2) + " m/s", canvas.width - 120, 30);
// 更新小球位置和速度
speed += gravity - airResistance * speed;
y += speed;
// 边界检测，如果小球碰到底部则反弹
if (y + radius > canvas.height) {
y = canvas.height - radius;
speed = -elasticity* speed;
elasticity = parseFloat(elasticityInput.value);
elasticity = parseFloat(elasticityInput.value); // 重新读取弹力值
}
// 循环调用自身
animationId = requestAnimationFrame(draw);
}
// 开始按键事件处理程序
var startButton = document.getElementById("startButton");
startButton.onclick = function() {
// 重新设置小球初始状态
x = canvas.width/2;
y = 0;
speed = 0;
// 启动动画循环
animationId = requestAnimationFrame(draw);
};
// 停止按键事件处理程序
var stopButton = document.getElementById("stopButton");
stopButton.onclick = function() {
if (animationId !== null) {
cancelAnimationFrame(animationId);
animationId = null;
}
};
// 复位按键事件处理程序
var resetButton = document.getElementById("resetButton");
resetButton.onclick = function() {
// 停止动画循环
if (animationId !== null) {
cancelAnimationFrame(animationId);
animationId = null;
}
// 将小球返回到初始位置
x = canvas.width/2;
y = 0;
speed = 0;
// 清空画布
context.clearRect(0, 0, canvas.width, canvas.height);
// 绘制小球
context.beginPath();
context.arc(x, y, radius, 0, Math.PI*2);
context.fillStyle = "red";
context.fill();
context.closePath();
};
</script>
</body>
</html>
