本文实例为大家分享了JS canvas实现画板/签字板功能的具体代码,供大家参考,具体内容如下
前言
常见的电子教室里的电子黑板。
本文特点:
原生JS
封装好的模块
最简代码样例
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<!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 > </ head > < body > < canvas id = "canvas" ></ canvas > < script > let c = document.getElementById('canvas'); c.width = window.innerWidth; c.height = window.innerHeight; let ctx = c.getContext('2d'); // draw one black board ctx.fillStyle = "black"; ctx.fillRect(0,0,600,300); // 按下标记 let onoff = false, oldx = -10, oldy = -10; // 设置颜色 let linecolor = "white"; // 设置线宽 let linw = 4; // 添加鼠标事件 // 按下 c.addEventListener('mousedown', event => { onoff = true; // 位置 - 10是为了矫正位置,把绘图放在鼠标指针的顶端 oldx = event.pageX - 10; oldy = event.pageY - 10; },false); // 移动 c.addEventListener('mousemove', event => { if(onoff == true){ let newx = event.pageX - 10, newy = event.pageY - 10; // 绘图 ctx.beginPath(); ctx.moveTo(oldx,oldy); ctx.lineTo(newx,newy); ctx.strokeStyle = linecolor; ctx.lineWidth = linw; ctx.lineCap = "round"; ctx.stroke(); // 每次移动都要更新坐标位置 oldx = newx, oldy = newy; } }, true); // 弹起 c.addEventListener('mouseup', ()=> { onoff = false; },false); </ script > </ body > </ html > |
结果展示
代码讲解
思路
1、鼠标按下,开始描画。鼠标按下事件。
2、鼠标弹起,结束描画。鼠标弹起事件。
3、鼠标按下移动,路径画线。鼠标移动事件。
代码讲解
整体思路:按下鼠标,触发移动的开关,移动后开始记录线条(用移动后的坐标-移动前的坐标,然后绘线),每次移动都会更新旧坐标。松开鼠标后,释放移动开关。
1、只有在鼠标按下,才会触发移动绘图的效果,所以需要增加一个状态判断。
2、因为鼠标指针和实际位置有一个偏移量,所以在坐标定位的时候,需要增加pagex-10从而使坐标位于指针的尖端处。
3、每次移动都要更新坐标位置,用小段的线段来模拟不规则的线。
封装模块
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<canvas id= "canvas" ></canvas> <script> class Board{ constructor(canvasName = 'canvas' , data = new Map([ [ "onoff" , false ], [ "oldx" , -10], [ "oldy" , -10], [ "fillStyle" , "black" ], [ "lineColor" , "white" ], [ "lineWidth" , 4], [ "lineCap" , "round" ], [ "canvasWidth" , window.innerWidth], [ "canvasHeight" , window.innerHeight] ])){ // this.data = data; this .c = document.getElementById(canvasName); this .ctx = this .c.getContext( '2d' ); this .onoff = data.get( "onoff" ); this .oldx = data.get( "oldx" ); this .oldy = data.get( "oldy" ); this .lineColor = data.get( "lineColor" ); this .lineWidth = data.get( "lineWidth" ); this .lineCap = data.get( "lineCap" ); this .c.width = data.get( "canvasWidth" ); this .c.height = data.get( "canvasHeight" ); this .ctx.fillStyle = data.get( "fillStyle" ); this .ctx.fillRect(0,0,600,300); } eventOperation(){ // 添加鼠标事件 // 按下 this .c.addEventListener( 'mousedown' , event => { this .onoff = true ; // 位置 - 10是为了矫正位置,把绘图放在鼠标指针的顶端 this .oldx = event.pageX - 10; this .oldy = event.pageY - 10; }, false ); // 移动 this .c.addEventListener( 'mousemove' , event => { if ( this .onoff == true ){ let newx = event.pageX - 10, newy = event.pageY - 10; // 绘图 this .ctx.beginPath(); this .ctx.moveTo( this .oldx, this .oldy); this .ctx.lineTo(newx,newy); this .ctx.strokeStyle = this .lineColor; this .ctx.lineWidth = this .lineWidth; this .ctx.lineCap = this .lineCap; this .ctx.stroke(); // 每次移动都要更新坐标位置 this .oldx = newx, this .oldy = newy; } }, true ); // 弹起 this .c.addEventListener( 'mouseup' , ()=> { this .onoff = false ; }, false ); } } let board = new Board(); board.eventOperation(); </script> |
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。
原文链接:https://blog.csdn.net/u013362192/article/details/113934773