HTML5 Canvas橡皮擦工具没有透过白色

我有画布.我有涂料工具铅笔和橡皮擦.如何在不用白色覆盖(透支)的情况下擦除图纸.

这是我的代码橡皮擦用白色绘图：
http://jsfiddle.net/66z12xb0/

我在后端保存图像后绘图.

<?PHP
$images = scandir(ROOT_FS . FINISH_DRAW_PATH,1);
$imageData = $GLOBALS['HTTP_RAW_POST_DATA'];
$filteredData = substr($imageData,strpos($imageData,",") + 1);
$unencodedData = base64_decode($filteredData);

$fileName = "photo.png"; 
$fp = fopen(ROOT_FS .  SAVE_DRAW_PATH . $fileName,'wb');
fwrite($fp,$unencodedData);
fclose($fp);
?>

使用Windows照片查看器打开并查看此结果：

额外上传照片：

$("#upload_foto").click(function() {
    var data = canvas.toDataURL('image/png'); 
    var ajax = new XMLHttpRequest();
    ajax.open('POST','backend.PHP',false);
    ajax.setRequestHeader('Content-Type','application/upload');
    ajax.send(data);
}); 

<button type='button' id='upload_foto'>Upload</button>

解决方法

您使用合成创建橡皮擦的想法是个好主意.

destination-out将删除现有图纸,其中新图纸与那些现有图纸重叠.

var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var lastX;
var lastY;
var strokeColor="red";
var strokeWidth=5;
var mouseX;
var mouseY;
var canvasOffset=$("#canvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var isMouseDown=false;


function handleMouseDown(e){
  mouseX=parseInt(e.clientX-offsetX);
  mouseY=parseInt(e.clientY-offsetY);

  // Put your mousedown stuff here
  lastX=mouseX;
  lastY=mouseY;
  isMouseDown=true;
}

function handleMouseUp(e){
  mouseX=parseInt(e.clientX-offsetX);
  mouseY=parseInt(e.clientY-offsetY);

  // Put your mouseup stuff here
  isMouseDown=false;
}

function handleMouSEOut(e){
  mouseX=parseInt(e.clientX-offsetX);
  mouseY=parseInt(e.clientY-offsetY);

  // Put your mouSEOut stuff here
  isMouseDown=false;
}

function handleMouseMove(e){
  mouseX=parseInt(e.clientX-offsetX);
  mouseY=parseInt(e.clientY-offsetY);

  // Put your mousemove stuff here
  if(isMouseDown){
    ctx.beginPath();
    if(mode=="pen"){
      ctx.globalCompositeOperation="source-over";
      ctx.moveTo(lastX,lastY);
      ctx.lineTo(mouseX,mouseY);
      ctx.stroke();     
    }else{
      ctx.globalCompositeOperation="destination-out";
      ctx.arc(lastX,lastY,8,Math.PI*2,false);
      ctx.fill();
    }
    lastX=mouseX;
    lastY=mouseY;
  }
}

$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUp(e);});
$("#canvas").mouSEOut(function(e){handleMouSEOut(e);});

var mode="pen";
$("#pen").click(function(){ mode="pen"; });
$("#eraser").click(function(){ mode="eraser"; });

body{ background-color: ivory; }
canvas{border:1px solid red;}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>
<canvas id="canvas" width=300 height=300></canvas></br>
<button id="pen">Pen</button>
<button id="eraser">Eraser</button>

HTML5 Canvas橡皮擦工具没有透过白色

解决方法

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