javascript - 无法使用 JS 在 Canvas 中移动 Arc

Question

我试图沿 x 轴移动弧，但它给出了更新函数中未定义 x 的错误。变量是否放置不当或缺少某些引用？

代码

<canvas id="myCanvas"></canvas>
<script>
    var myCanvas = document.getElementById("myCanvas");
    var c = myCanvas.getContext("2d");

    var redArc = new Circle(50, 60, 10, "red");
    var greenArc = new Circle(80, 60, 15, "green");
    var blueArc = new Circle(120, 60, 20, "blue");

    function Circle(x, y, radius, color) {
        this.x = x;
        this.y = y;
        this.radius = radius;
        this.color = color;

        this.draw = function() {
            c.beginPath();
            c.arc(this.x, this.y, this.radius, 0, Math.PI * 2);
            c.fillStyle = this.color;
            c.fill();
        }

        this.update = function() {
            redArc.x += 1;
            greenArc.x += 1;
            blueArc.x += 1;
            this.draw();
        }
        this.update();
    }        



    function animate() {
        requestAnimationFrame(animate);
        c.clearRect(0, 0, myCanvas.clientWidth, myCanvas.clientHeight);
        redArc.update();
        greenArc.update();
        blueArc.update();
    }

    animate();

我该如何修复它？有什么建议谢谢!!

Answer 1

将您的 update 方法替换为以下内容:

this.update = function() {
   this.x += 1;
   this.draw();
}

您应该使用 this.x ，而不是变量名称。

var myCanvas = document.getElementById("myCanvas");
var c = myCanvas.getContext("2d");

var redArc = new Circle(50, 60, 10, "red");
var greenArc = new Circle(80, 60, 15, "green");
var blueArc = new Circle(120, 60, 20, "blue");

function Circle(x, y, radius, color) {
   this.x = x;
   this.y = y;
   this.radius = radius;
   this.color = color;

   this.draw = function() {
      c.beginPath();
      c.arc(this.x, this.y, this.radius, 0, Math.PI * 2);
      c.fillStyle = this.color;
      c.fill();
   }

   this.update = function() {
      this.x += 1;
      this.draw();
   }

   this.update();
}

function animate() {
   c.clearRect(0, 0, myCanvas.clientWidth, myCanvas.clientHeight);
   redArc.update();
   greenArc.update();
   blueArc.update();
   requestAnimationFrame(animate);
}

animate();

<canvas id="myCanvas"></canvas>