个回答

• sdwsq

  2016-12-15 13:50:16

  var cw = Math.min(800,$(window).width()-20);

  var ch = cw;

  
  

  var canvas = document.getElementById("canvas");

  var ctx = canvas.getContext("2d");

  var inmove=false;

  var lastLoc={x:0,y:0}

  var lastlinewidth=-1;

  
  

  var lastTime=0;

  canvas.width = cw;

  canvas.height = ch;

  
  

  drawback();

  
  

  
  

  //鼠标和canvas互动的必要函数

  function windowto(x,y){

  var boxx=canvas.getBoundingClientRect()

  return {x:Math.round(x-boxx.left), y:Math.round(y-boxx.top)}

  }

  
  

  $("#clear").click(function(){

  ctx.clearRect(0,0,cw,ch)

  drawback();

  })

  
  

  function begin(point){

  inmove=true;

  lastLoc=windowto(point.x,point.y)

  lastTime=new Date().getTime();

  }

  
  

  function end(){

  inmove=false

  }

  
  

  canvas.onmousedown=function(e){

  e.preventDefault()

  begin({x:e.clientX,y:e.clientY})

  }

  
  

  canvas.onmouseup=function(e){

  e.preventDefault()

  end()

  }

  canvas.onmouseout=function(e){

  e.preventDefault()

  end()

  }

  
  

  canvas.onmousemove=function(e){

  e.preventDefault()

  if(inmove){

  move({x:e.clientX,y:e.clientY})

  }

  }

  
  

  canvas.addEventListener('touchstart',function(e){

  e.preventDefault()

  touch=e.touches[0]

  begin({x:touch.pageX,Y:touch.pageY})

  })

  
  

  canvas.addEventListener('touchmove',function(e){

  e.preventDefault()

  if(inmove){

  touch=e.touches[0]

  move({x:touch.pageX , y:touch.pageY})

  }

  })

  
  

  canvas.addEventListener('touchend',function(e){

  e.preventDefault()

  end()

  })

  
  

  
  

  function calelinewidth(t,s){

  var v=s/t;

  var resultLinewidth;

  if(v<=0.1)

  resultLinewidth=30

  else if(v>=10)

  resultLinewidth=1

  else

  resultLinewidth=30-(v-0.1)/(10-0.1)*(30-1)

  if(lastlinewidth==-1)

  return resultLinewidth

  return lastlinewidth*2/3+resultLinewidth*1/3

  }

  function move(point){

  var curLoc=windowto(point.x,point.y)

  var curtime=new Date().getTime()

  var s=calc(lastLoc,curLoc)

  var t=curtime-lastTime;

  var linewidth=calelinewidth(t,s);

  ctx.beginPath()

  ctx.moveTo(lastLoc.x,lastLoc.y)

  ctx.lineTo(curLoc.x,curLoc.y)

  ctx.strokeStyle="black"

  ctx.lineWidth=linewidth

  ctx.lineCap="round"

  ctx.lineJoin="round"

  ctx.stroke();

  lastLoc=curLoc;

  lastTime=curtime;

  lastlinewidth=linewidth;

  }

  
  

  
  

  
  

  function calc(loc1,loc2){

  return Math.sqrt((loc1.x-loc2.x)*(loc1.x-loc2.x)+(loc1.y-loc2.y)*(loc1.y-loc2.y))

  }

  
  

  function drawback() {

  ctx.save()

  ctx.strokeStyle = "brown"

  
  

  ctx.beginPath()

  ctx.moveTo(3, 3)

  ctx.lineTo(cw - 3, 3)

  ctx.lineTo(cw - 3, ch - 3)

  ctx.lineTo(3, ch - 3)

  ctx.closePath()

  
  

  ctx.lineWidth = 6

  ctx.stroke()

  
  

  ctx.beginPath()

  ctx.setLineDash([10, 10]);

  ctx.moveTo(0, 0);

  ctx.lineTo(cw, ch);

  
  

  ctx.moveTo(cw, 0);

  ctx.lineTo(0, ch);

  
  

  ctx.moveTo(cw / 2, 0)

  ctx.lineTo(cw / 2, ch)

  
  

  ctx.moveTo(0, ch / 2)

  ctx.lineTo(cw, ch / 2)

  
  

  ctx.lineWidth = 1;

  ctx.stroke()

  ctx.restore()

  }

  
  

  0