基于canvas剪辑区域功能实现橡皮擦效果

效果如图

这是基础结构 没什么好说的

  
  
  
  
  


    

        Stroke color: 
                 red
                 green
                 blue
                 orange
                 cornflowerblue
                 goldenrod
                 navy
                 purple
                 purple
               
        Fill color: 
                 semi-transparent red
                 green
                 semi-transparent blue
                 orange
                 semi-transparent cornflowerblue
                 goldenrod
                 navy
                 purple
               
        Draw 
        Erase 
        Eraser: 
                circle
                square
               
        Eraser width: 
                25
                50
                75
                100
                125
                150
                175
                200
               
       
  

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 = false
function 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！