📜  量角器右键单击元素 - Javascript(1)

📅  最后修改于: 2023-12-03 15:28:33.108000             🧑  作者: Mango

量角器右键单击元素 - Javascript

在某些场合下,需要测量网页上面的角度,但是浏览器没有提供相关的工具来达到这个目的。因此,我们可以通过Javascript来实现一个简单的量角器,使用户可以在网页上直接测量角度。

实现步骤
  1. 首先,在页面中插入以下HTML,其中<div id="protractor"></div>是用于容纳量角器的元素,<img id="protractorImage" src="path/to/protractor.png">是量角器的图片:
<div id="protractor"></div>
<img id="protractorImage" src="path/to/protractor.png">
  1. 接着,在Javascript中注册鼠标右键单击事件,当用户右键单击页面上的元素时触发该事件。如果用户单击的是量角器图片,则取消右键事件的默认行为;否则,清空量角器,并隐藏它。
document.addEventListener('contextmenu', function(e){
    var protractor = document.getElementById('protractor');
    var protractorImage = document.getElementById('protractorImage');
    if(e.target && e.target === protractorImage){
        e.preventDefault();
    }else{
        protractor.innerHTML = '';
        protractor.style.display = 'none';
    }
});
  1. 当用户右键单击量角器图片时,需要在图片上显示出量角器。
document.addEventListener('contextmenu', function(e){
    var protractor = document.getElementById('protractor');
    var protractorImage = document.getElementById('protractorImage');
    if(e.target && e.target === protractorImage){
        e.preventDefault();
        var left = e.pageX;
        var top = e.pageY;
        protractor.style.left = left + 'px';
        protractor.style.top = top + 'px';
        protractor.innerHTML = '<img src="path/to/protractor.png">';
        protractor.style.display = 'block';
    }else{
        protractor.innerHTML = '';
        protractor.style.display = 'none';
    }
});
  1. 现在我们需要在量角器上显示出角度。我们可以通过计算鼠标右键单击点和量角器中心点的夹角来得知量角器在当前角度的位置。然后,我们将该角度显示出来。
document.addEventListener('contextmenu', function(e){
    var protractor = document.getElementById('protractor');
    var protractorImage = document.getElementById('protractorImage');
    if(e.target && e.target === protractorImage){
        e.preventDefault();
        var left = e.pageX;
        var top = e.pageY;
        var centerX = left + protractorImage.clientWidth / 2;
        var centerY = top + protractorImage.clientHeight / 2;
        var angle = Math.atan2(centerY - e.clientY, centerX - e.clientX);
        angle = angle * 180 / Math.PI;
        angle = Math.round(angle);
        protractor.style.left = left + 'px';
        protractor.style.top = top + 'px';
        protractor.innerHTML = '<img src="path/to/protractor.png">' +
            '<div id="angleIndicator" style="position:absolute; left:50%; top:50%;' +
            'transform: rotate(' + angle + 'deg) translate(-50%, -50%); width: 0; height: 0;' +
            'border-bottom: 50px solid red; border-left: 50px solid transparent;"></div>' +
            '<div id="angleDisplay" style="position:absolute; left:50%; top:10%;' +
            'transform: translate(-50%, 0);' +
            'font-size: 30px; font-weight: bold;">' + angle + '°</div>';
        protractor.style.display = 'block';
    }else{
        protractor.innerHTML = '';
        protractor.style.display = 'none';
    }
});
  1. 最后,我们可以为量角器设置一个样式来改善其外观和可操作性。
<style>
    #protractor {
        position: absolute;
        width: 200px;
        height: 200px;
        pointer-events: none;
    }

    #protractor img {
        width: 100%;
        height: 100%;
        pointer-events: none;
    }

    #angleIndicator {
        pointer-events: none;
    }

    #angleDisplay {
        pointer-events: none;
        color: red;
    }
</style>
完整代码
<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Protractor</title>
    <style>
        #protractor {
            position: absolute;
            width: 200px;
            height: 200px;
            pointer-events: none;
        }

        #protractor img {
            width: 100%;
            height: 100%;
            pointer-events: none;
        }

        #angleIndicator {
            pointer-events: none;
        }

        #angleDisplay {
            pointer-events: none;
            color: red;
        }
    </style>
</head>
<body>
<div id="protractor"></div>
<img id="protractorImage" src="path/to/protractor.png">

<script>
    document.addEventListener('contextmenu', function(e){
        var protractor = document.getElementById('protractor');
        var protractorImage = document.getElementById('protractorImage');
        if(e.target && e.target === protractorImage){
            e.preventDefault();
            var left = e.pageX;
            var top = e.pageY;
            var centerX = left + protractorImage.clientWidth / 2;
            var centerY = top + protractorImage.clientHeight / 2;
            var angle = Math.atan2(centerY - e.clientY, centerX - e.clientX);
            angle = angle * 180 / Math.PI;
            angle = Math.round(angle);
            protractor.style.left = left + 'px';
            protractor.style.top = top + 'px';
            protractor.innerHTML = '<img src="path/to/protractor.png">' +
                '<div id="angleIndicator" style="position:absolute; left:50%; top:50%;' +
                'transform: rotate(' + angle + 'deg) translate(-50%, -50%); width: 0; height: 0;' +
                'border-bottom: 50px solid red; border-left: 50px solid transparent;"></div>' +
                '<div id="angleDisplay" style="position:absolute; left:50%; top:10%;' +
                'transform: translate(-50%, 0);' +
                'font-size: 30px; font-weight: bold;">' + angle + '°</div>';
            protractor.style.display = 'block';
        }else{
            protractor.innerHTML = '';
            protractor.style.display = 'none';
        }
    });
</script>
</body>
</html>

以上就是使用Javascript实现量角器右键单击元素的介绍。通过这种方法可以方便地测量网页上角度的大小。