基于canvas剪辑区域功能实现橡皮擦效果

时间：2021-05-22

效果如图

这是基础结构 没什么好说的

<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <title>Document</title> <style> *{padding: 0;margin: 0} a{text-decoration: none} img{border: none} ul,ol{list-style: none} br{font-size: 0;line-height: 0;font-size: 0} canvas{border: 1px solid red;background: white} body{background: gray;text-align: center} </style></head><body> <div id='controls'> Stroke color: <select id='strokeStyleSelect'> <option value='red'>red</option> <option value='green'>green</option> <option value='blue'>blue</option> <option value='orange'>orange</option> <option value='cornflowerblue'>cornflowerblue</option> <option value='goldenrod'>goldenrod</option> <option value='navy' selected>navy</option> <option value='purple'>purple</option> <option value='purple'>purple</option> </select> Fill color: <select id='fillStyleSelect'> <option value='rgba(255,0,0,0.5)'>semi-transparent red</option> <option value='green'>green</option> <option value='rgba(0,0,255,0.5)'>semi-transparent blue</option> <option value='orange'>orange</option> <option value='rgba(100,140,230,0.5)'>semi-transparent cornflowerblue</option> <option value='goldenrod' selected>goldenrod</option> <option value='navy'>navy</option> <option value='purple'>purple</option> </select> Draw <input id='drawRadio' name='drawEraserRadios' type='radio' checked/> Erase <input id='eraserRadio' name='drawEraserRadios' type='radio'/> Eraser: <select id='eraserShapeSelect'> <option value='circle'>circle</option> <option value='square'>square</option> </select> Eraser width: <select id='eraserWidthSelect'> <option value=25>25</option> <option value=50>50</option> <option value=75>75</option> <option value=100>100</option> <option value=125>125</option> <option value=150>150</option> <option value=175>175</option> <option value=200>200</option> </select> </div> <canvas id="canvas" width="950" height="600"></canvas></body></html><script src="./js/test9.js"></script>

下面是重点的js

这里有个坑要十分注意 调用clip()方法的时候，所定义的剪辑区域总是局限于期初的那个剪辑区域范围。
简单来说 clip()方法总是在上一次的剪辑区域基础上进行操作，所以说我们要把clip()方法放在save()和restore()方法中

var canvas = document.getElementById('canvas'),context = canvas.getContext('2d'),strokeStyleSelect = document.getElementById('strokeStyleSelect'), //画图的描边颜色fillStyleSelect = document.getElementById('fillStyleSelect'), //画图填充颜色drawRadio = document.getElementById('drawRadio'), //画图按钮eraserRadio = document.getElementById('eraserRadio'), //橡皮擦按钮 eraserShapeSelect = document.getElementById('eraserShapeSelect'), //橡皮擦形状eraserWidthSelect = document.getElementById('eraserWidthSelect'), //橡皮擦宽度ERASER_LINE_WIDTH = 1,drawingSurfaceImageData,lastX,lastY,mousedown = {},rubberbandRect = {},dragging = falsefunction windowToCanvas(x,y){ //这个函数的作用是捕捉鼠标点在canvas上的坐标 var bbox=canvas.getBoundingClientRect() return { x:x-bbox.left, y:y-bbox.top }}function saveDrawingSurface(){ //这个函数的作用是初始化读取画布信息并储存起来 drawingSurfaceImageData=context.getImageData(0,0,canvas.width,canvas.height)}function restoreDrawingSurface(){ //这个函数的作用是读取画布信息 context.putImageData(drawingSurfaceImageData,0,0)}function drawGrid(){ //这个函数的作用是填充进橡皮擦的剪辑区域 context.save() context.fillStyle="#fff" context.fillRect(0,0,canvas.width,canvas.height) context.restore()}function drawrubber(x,y){ context.beginPath() context.arc(x,y,eraserWidthSelect.value,0,Math.PI*2,false) context.clip()}function drawCri(x,y){ var x_width=Math.abs(x-mousedown.x) var y_width=Math.abs(y-mousedown.y) var radius=Math.sqrt(x_width*x_width+y_width*y_width) context.save() context.beginPath() context.fillStyle=fillStyleSelect.value; context.arc(mousedown.x,mousedown.y,radius,0,Math.PI*2,false) context.fill() context.restore()}canvas.onmousedown=function(e){ var loc=windowToCanvas(e.clientX,e.clientY) mousedown.x=loc.x mousedown.y=loc.y lastX=loc.x lastY=loc.y saveDrawingSurface() dragging=true}canvas.onmousemove=function(e){ if(dragging){ var loc=windowToCanvas(e.clientX,e.clientY) if(drawRadio.checked){ //如果是画图状态 // restoreDrawingSurface() drawCri(loc.x,loc.y) }else{ //如果是橡皮擦状态 context.save() drawrubber(loc.x,loc.y) drawGrid() context.restore() } }}canvas.onmouseup=function(e){ dragging=false; var loc=windowToCanvas(e.clientX,e.clientY) if(drawRadio.checked){ lastX=loc.x; lastY=loc.y; restoreDrawingSurface() drawCri(lastX,lastY) }else{ context.save() drawrubber(loc.x,loc.y) drawGrid() context.restore() }}

总结

以上所述是小编给大家介绍的基于canvas剪辑区域功能实现橡皮擦效果，希望对大家有所帮助，如果大家有任何疑问欢迎给我留言，小编会及时回复大家的！

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