基於canvas剪輯區域功能實現橡皮擦效果

前端愛好者發表於2018-11-25
Canvas

這篇文章主要介紹了基於canvas剪輯區域功能實現橡皮擦效果,非常不錯，具有參考借鑑價值，需要的朋友可以參考下

這是基礎結構 沒什麼好說的

?<!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>      582735936
        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>      582735936
        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>

下面是重點的js

這裡有個坑要十分注意 呼叫clip()方法的時候，所定義的剪輯區域總是侷限於期初的那個剪輯區域範圍。

簡單來說 clip()方法總是在上一次的剪輯區域基礎上進行操作，所以說我們要把clip()方法放在save()和restore()方法中

var canvas = document.getElementById(`canvas`),
context = canvas.getContext(`2d`),
strokeStyleSelect = document.getElementById(`strokeStyleSelect`),  //畫圖的描邊顏色
fillStyleSelect = document.getElementById(`fillStyleSelect`),    //畫圖填充顏色
drawRadio = document.getElementById(`drawRadio`),          //畫圖按鈕
eraserRadio = document.getElementById(`eraserRadio`),       //橡皮擦按鈕 
eraserShapeSelect = document.getElementById(`eraserShapeSelect`), //橡皮擦形狀
eraserWidthSelect = document.getElementById(`eraserWidthSelect`), //橡皮擦寬度
ERASER_LINE_WIDTH = 1,
drawingSurfaceImageData,
lastX,
lastY,
mousedown = {},
rubberbandRect = {},
dragging = false
function windowToCanvas(x,y){ //這個函式的作用是捕捉滑鼠點在canvas上的座標
  var bbox=canvas.getBoundingClientRect()
  return {
    x:x-bbox.left,
    y:y-bbox.top
  }
}
function saveDrawingSurface(){  //這個函式的作用是初始化讀取畫布資訊並儲存起來
  drawingSurfaceImageData=context.getImageData(0,0,canvas.width,canvas.height)
}
function restoreDrawingSurface(){ //這個函式的作用是讀取畫布資訊
  context.putImageData(drawingSurfaceImageData,0,0)
}
function drawGrid(){ //這個函式的作用是填充進橡皮擦的剪輯區域
  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()   582735936
}
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){ //如果是畫圖狀態
      // 
      restoreDrawingSurface()
      drawCri(loc.x,loc.y)
    }else{ //如果是橡皮擦狀態
      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()
  }
}

總結

以上所述是小編給大家介紹的基於canvas剪輯區域功能實現橡皮擦效果，希望對大家有所幫助

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