canvas-实现放大镜效果

本文主要是介绍canvas-实现放大镜效果，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

canvas-实现放大镜效果目录

文章目录

前言
推荐阅读
代码展示
结果展示

前言

本文为canvas实现放大镜
逻辑简单，适合作为基础项目练手

代码展示

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>Document</title><style>body {background: rgba(100, 145, 150, 0.3);}#canvas {margin-left: 20px;margin-right: 0;margin-bottom: 20px;border: thin solid #aaaaaa;cursor: crosshair;padding: 0;}#controls {margin: 20px 0px 20px 20px;}#rubberbandDiv {position: absolute;border: 3px solid blue;cursor: crosshair;display: none;}</style>
</head>
<body><div id="controls"><input type="button" id="resetButton" value="Reset"></div><div id="rubberbandDiv"></div><canvas id="canvas" width="800" height="520">Canvas Not Support</canvas><script src="rubberband.js"></script>
</body>
</html>

/* 功能：0. 选框由css设置为标签的框线1. 根据鼠标建立选框2. 根据选框进行放大3. 在原图的基础上进行放大
*/
let canvas =document.getElementById('canvas'),context = canvas.getContext('2d'),rubberbandDiv = document.getElementById('rubberbandDiv'),resetButton = document.getElementById('resetButton'),image = new Image(),mousedown = {},rubberbandRectangle = {},dragging = false;/* Functions*/
// 弹性框的开始坐标
function rubberbandStart(x, y){mousedown.x = x,mousedown.y = y;rubberbandRectangle.left = mousedown.x,rubberbandRectangle.top = mousedown.y;moveRubberbandDiv();showRubberbandDiv();// 标记选框状态dragging = true;
}// 弹性框扩展
function rubberbandStretch(x, y){rubberbandRectangle.left = x < mousedown.x ? x : mousedown.x;rubberbandRectangle.top = y < mousedown.y ? y : mousedown.y;rubberbandRectangle.width = Math.abs(x - mousedown.x);rubberbandRectangle.height = Math.abs(y - mousedown.y);moveRubberbandDiv();resizeRubberbandDiv();
}// 弹性框结束
function rubberbandEnd() {let bbox = canvas.getBoundingClientRect();try{// 在canvas的基础上进行图像的绘制context.drawImage(canvas,rubberbandRectangle.left - bbox.left,rubberbandRectangle.top - bbox.top,rubberbandRectangle.width,rubberbandRectangle.height,0, 0, canvas.width, canvas.height);} catch(error){console.log('error');}// 绘图后重设弹性框设置resetRubberbandRectangle();// 标签的设置rubberbandDiv.style.width = 0,rubberbandDiv.style.height = 0;// 隐藏标签hideRubberbandDiv();dragging = false;
}// 移动弹性框标签的位置
function moveRubberbandDiv() {rubberbandDiv.style.top = rubberbandRectangle.top + 'px',rubberbandDiv.style.left = rubberbandRectangle.left + 'px';
}// 弹性框标签的宽高
function resizeRubberbandDiv() {rubberbandDiv.style.width = rubberbandRectangle.width + 'px',rubberbandDiv.style.height = rubberbandRectangle.height + 'px';
}// 展示弹性框标签
function showRubberbandDiv() {rubberbandDiv.style.display = 'inline';
}// 隐藏弹性框标签
function hideRubberbandDiv() {rubberbandDiv.style.display = 'none';
}// 重设弹性框
function resetRubberbandRectangle() {rubberbandRectangle = {top: 0,left: 0,width: 0,height: 0};
}// Event handlers
// 在canvas按下鼠标时，触发事件
// dom冒泡时取消，防止出现在canvas外时出现问题
canvas.onmousedown = function(e) {let x = e.clientX - 5,y = e.clientY - 5;e.preventDefault();rubberbandStart(x, y);
}// 鼠标移动时，选框开始扩展
window.onmousemove = function(event) {let x = event.clientX,y = event.clientY;event.preventDefault();if(dragging){rubberbandStretch(x, y);}
}// 放开鼠标
window.onmouseup = function(event) {event.preventDefault();rubberbandEnd();
}// 图像加载
image.onload = function() {context.drawImage(image, 0, 0, canvas.width, canvas.height);
}resetButton.onclick = function(event) {context.clearRect(0, 0, context.canvas.width,context.canvas.height);context.drawImage(image, 0, 0, canvas.width, canvas.height);
}// Initialization
image.src = 'test.jpg';