Question

我看到了this script，这是对http://www.robodesign.ro/coding/canvas-paint/20090423/

的修改

它在Fx 10中运行良好，但在Chrome中根本没有。

我通过交换offsetX和layerX摆脱了关于弃用的event.layerX / Y的Chrome警告，但它仍然没有绘制。

必须非常简单。
更新：它是 - 评论出两个context.moveTo(ev._x, ev._y);做了诀窍

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>Paint</title>
    <style type="text/css"><!--
      #container { position: relative; }
      #imageView { border: 1px solid #000; }
    --></style>
  </head>
  <body BGCOLOR="#CCFFFF"> 

    <div id="container">
      <canvas id="imageView" width="700" height="643" margin: 0 auto>
        <p>Unfortunately, your browser is currently unsupported by our web 
        application.  We are sorry for the inconvenience. Please use one of the 
        supported browsers listed below, or draw the image you want using an 
        offline tool.</p>
        <p>Supported browsers: <a href="http://www.opera.com">Opera</a>, <a 
          href="http://www.mozilla.com">Firefox</a>, <a 
          href="http://www.apple.com/safari">Safari</a>, and <a 
          href="http://www.konqueror.org">Konqueror</a>.</p>
      </canvas>
    </div>

    <script type="text/javascript">
/* © 2009 ROBO Design
 * http://www.robodesign.ro
 */

// Keep everything in anonymous function, called on window load.
if(window.addEventListener) {
window.addEventListener('load', function () {
  var canvas, context, tool;

  function init () {
    // Find the canvas element.
    canvas = document.getElementById('imageView');
    if (!canvas) {
      alert('Error: I cannot find the canvas element!');
      return;
    }

    if (!canvas.getContext) {
      alert('Error: no canvas.getContext!');
      return;
    }

    // Get the 2D canvas context.
    context = canvas.getContext('2d');
    if (!context) {
      alert('Error: failed to getContext!');
      return;
    }

    var img=new Image();
    img.onload = function(){
    context.drawImage(img,0,0);
    };
    img.src="  PainDiagram.png";

    // Pencil tool instance.
    tool = new tool_pencil();

    // Attach the mousedown, mousemove and mouseup event listeners.
    canvas.addEventListener('mousedown', ev_canvas, false);
    canvas.addEventListener('mousemove', ev_canvas, false);
    canvas.addEventListener('mouseup',   ev_canvas, false);
  }

  // This painting tool works like a drawing pencil which tracks the mouse 
  // movements.
  function tool_pencil () {
    var tool = this;
    this.started = false;

    // This is called when you start holding down the mouse button.
    // This starts the pencil drawing.
    this.mousedown = function (ev) {
        context.beginPath();
        context.lineWidth = 5;
        context.lineCap = "round";
        context.globalAlpha=0.01;
        context.shadowColor="red";
        context.shadowBlur=10;
        context.strokeStyle = "red"; // line color
        context.moveTo(ev._x, ev._y);
        tool.started = true;
    };

    // This function is called every time you move the mouse. Obviously, it only 
    // draws if the tool.started state is set to true (when you are holding down 
    // the mouse button).
    this.mousemove = function (ev) {
      if (tool.started) {
        //var p = context.getImageData(ev._x, ev._y, 1, 1).data; 
        //if(p[0]==255 && p[1]==204 && p[2]==153){
            context.moveTo(ev._x, ev._y);
            context.lineTo(ev._x, ev._y);
            context.stroke();
        //}
      }
    };

    // This is called when you release the mouse button.
    this.mouseup = function (ev) {
      if (tool.started) {
        tool.mousemove(ev);
        tool.started = false;
      }
    };
  }

  // The general-purpose event handler. This function just determines the mouse 
  // position relative to the canvas element.


  function ev_canvas (ev) {
    if (ev.offsetX || ev.offsetX == 0) { // Opera and WebKit
      ev._x = ev.offsetX;
      ev._y = ev.offsetY;
    }  
    else if (ev.layerX || ev.layerX == 0) { // Firefox
      ev._x = ev.layerX;
      ev._y = ev.layerY;
    } 

    // Call the event handler of the tool.
    var func = tool[ev.type];
    if (func) {
      func(ev);
    }
  }

  init();

}, false); }

// vim:set spell spl=en fo=wan1croql tw=80 ts=2 sw=2 sts=2 sta et ai cin fenc=utf-8 ff=unix:

    </script>
  </body>
</html>

Answer 1

从context.moveTo(ev._x, ev._y);删除行this.mousemove。

moveTo()方法创建一个新的子路径，因此您告诉画布将笔划应用于长度为零像素的路径。 Firefox显然支持这一点。有关详细信息，请参阅canvas documentation。

非常简单的Canvas绘画在Fx中不适用于Chrome

1 个答案: