Question

我想为HTML5画布上向下移动的多个矩形设置动画。有一个类，可以通过简单地将参数传递给该类来轻松创建所需的任何矩形。问题出在类和内置方法“ requestAnimationFrame”上，我只能为单个对象设置动画：这是代码：

function resize(canvasElement) {
    window.addEventListener("resize", function () {
        canvasElement.width = window.innerWidth / 3;
        canvasElement.height = window.innerHeight * 0.9975;
    })
}
var radius = 5;
class roundRect {
    constructor(rectX, rectY, rectHeight, rectWidth, stroke, fill, c) {
        c.clearRect(rectX-100, rectY-100, rectX + 100, rectY + 100);
        c.beginPath();
        c.strokeStyle = stroke;
        c.fillStyle = fill;
        c.moveTo(rectX + rectWidth/2, rectY);
        c.arcTo(rectX + rectWidth, rectY, rectX + rectWidth, rectY + rectHeight, radius);
        c.arcTo(rectX + rectWidth, rectY + rectHeight, rectX, rectY + rectHeight, radius);
        c.arcTo(rectX, rectY + rectHeight, rectX, rectY, radius);
        c.arcTo(rectX, rectY, rectX + rectWidth / 2, rectY, radius);
        c.closePath();
        c.fill();
        c.stroke();
    }
}
var rectY = 10;
function animate() {
    new roundRect(10, rectY, 50, 7, "red", "red", ctx);
    requestAnimationFrame(animate);
    rectY++;
}
{
    var canvas = document.body.querySelector("#canvasOne");
    canvas.width = window.innerWidth / 3;
    canvas.height = window.innerHeight * 0.9975;
    resize(canvas);
    var ctx = canvas.getContext("2d");
    animate();
}

canvasOne {
    border:1px solid black;
}

<!DOCTYPE html>
<html>
<head>
    <link href="homeComing.css" rel="stylesheet" />
    <meta charset="utf-8" />
    <title></title>
</head>
<body>
    <canvas id="canvasOne"></canvas>
    <script src="homeComing.js"></script>
</body>
</html>

如果有人只编写几行代码就知道一种动画多个对象的方法，将不胜感激。预先感谢！

Answer 1

在您的课程中，您使用clearRect的方式可能会删除其他对象。
只需清除外部，然后就可以得到多个矩形。

这是一个非常简单的示例：

class roundRect {
  constructor(rectX, rectY, rectHeight, rectWidth, stroke, fill, c) {
    var radius = 5;
    c.beginPath();
    c.strokeStyle = stroke;
    c.fillStyle = fill;
    c.moveTo(rectX + rectWidth / 2, rectY);
    c.arcTo(rectX + rectWidth, rectY, rectX + rectWidth, rectY + rectHeight, radius);
    c.arcTo(rectX + rectWidth, rectY + rectHeight, rectX, rectY + rectHeight, radius);
    c.arcTo(rectX, rectY + rectHeight, rectX, rectY, radius);
    c.arcTo(rectX, rectY, rectX + rectWidth / 2, rectY, radius);
    c.closePath();
    c.fill();
    c.stroke();
  }
}

var objects = [
  {x:10, y:10, speed:{x:0, y:1},    w:50, h:7,  stroke:"red",   fill:"red"},
  {x:50, y:10, speed:{x:0.5, y:1},  w:25, h:20, stroke:"black", fill:"blue"},
  {x:190, y:10, speed:{x:-0.2, y:1}, w:20, h:18, stroke:"black", fill:"lime"}
]

function animate() {
  ctx.clearRect(0, 0, canvas.width, canvas.height);
  for (i = 0; i < objects.length; i++) { 
    var o = objects[i]
    new roundRect(o.x, o.y, o.w, o.h, o.stroke, o.fill, ctx);
    o.x += o.speed.x
    o.y += o.speed.y    
  }
  requestAnimationFrame(animate);  
}

var canvas = document.body.querySelector("#canvasOne");
canvas.width = window.innerWidth / 3;
canvas.height = window.innerHeight * 0.9975;
var ctx = canvas.getContext("2d");
animate();

<canvas id="canvasOne"></canvas>

此示例基于您的代码，但是如果您确实想用更少的代码行做更多的事情，则应该使用游戏引擎。

如何使用类和函数为html5-canvas上的多个对象设置动画？

1 个答案: