canvas笔记-canvas中用户与图形交互- 前端开发

运行截图如下：

点击某个圆后：

代码如下：


<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
 
<canvas id="canvas" style="border: 1px solid #aaa; display: block; margin: 50px auto;">
    当前浏览器不支持canvas
</canvas>
 
<script>
 
    let balls = [];
    let canvas = document.getElementById("canvas");
    let context = canvas.getContext("https://cdn.jxasp.com:9143/image/2d");
 
    window.onload = function(){
 
        canvas.width = 800;
        canvas.height = 800;
 
        for(let i = 0; i < 10; i++){
 
            let ball = {
                x: Math.random() * canvas.width,
                y: Math.random() * canvas.height,
                r: Math.random() * 50 + 20
            };
            balls[i] = ball;
        }
 
        draw();
        canvas.addEventListener("mouseup", detect);
    }
 
    function draw(){
 
        for(let i = 0; i < balls.length; i++){
 
            context.beginPath();
            context.arc(balls[i].x, balls[i].y, balls[i].r, 0, Math.PI * 2);
            context.fillStyle = "#058";
            context.fill();
        }
    }
 
    function detect(event){
 
        let x = event.clientX - canvas.getBoundingClientRect().left;
        let y = event.clientY - canvas.getBoundingClientRect().top;
 
        console.log("x:" + x + "  y:" + y);
 
        for(let i = 0; i < balls.length; i++){
 
            context.beginPath();
            context.arc(balls[i].x, balls[i].y, balls[i].r, 0, Math.PI * 2);
 
            if(context.isPointInPath(x, y)){
 
                context.fillStyle = "red";
                context.fill();
            }
        }
    }
 
</script>
 
</body>
</html>

这里简单说下逻辑，通过canvas.addEventListener监听鼠标弹起的事件，然后通过


let x = event.clientX - canvas.getBoundingClientRect().left;
let y = event.clientY - canvas.getBoundingClientRect().top;

获取当前再canvas中的点的坐标，每次鼠标弹起的时候就进行重绘。


if(context.isPointInPath(x, y)){
 
    context.fillStyle = "red";
    context.fill();
}

isPointInPath()方法当点位于当前路径中，则返回true，否则返回false

下面给出另外一种方法：


function mouseoverFunction(event){
 
  let mouseX = event.offsetX;
  let mouseY = event.offsetY;
 
  for(let i = 0; i < XXXXXXXObjects.length; i++){
 
    if(
      (XXXXXXXObjects[i].x <= mouseX && (XXXXXXXObjects[i].x + XXXXXXXObjects[i].width) >= mouseX) &&
      (XXXXXXXObjects[i].y <= mouseY && (XXXXXXXObjects[i].y + XXXXXXXObjects[i].height) >= mouseY)
    ){
 
      XXXXXXXObjects[i].onClicked();
    }
  }
}