基于canvas剪辑区域功能实现橡皮擦效果

摘要：这篇文章主要介绍了基于剪辑区域功能实现橡皮擦效果非常不错，具有参考借鉴价值，需要的朋友可以参考下这是基础结构没什么好说的下面是重点的这里有个坑要十分注意调用方法的时候，所定义的剪辑区域总是局限于期初的那个剪辑区域范围。

这篇文章主要介绍了基于canvas剪辑区域功能实现橡皮擦效果,非常不错，具有参考借鉴价值，需要的朋友可以参考下

这是基础结构 没什么好说的

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        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
                     582735936
        Draw 
        Erase 
        Eraser: 
                circle
                square
                     582735936
        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()   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