14

我想使用 asp.net 将多个画布保存到一个图像中。我尝试使用两幅画布，但没有保存。

帆布：

    <div style="position:relative; width:456px; padding:0px; margin:0px;">
    <canvas id="boardcanvas" width="456" height="480" style="position: absolute; left: 0;   top: -220px; z-index: 0;"></canvas>
    <canvas id="layer2" width="456" height="480" style="position: absolute;left: 0;   top:-220px; z-index: 1;"></canvas>    
   </div>


 <input type="button" id="btnSave" style="width:150px ; text-align:center;height:30px" name="btnSave" value="Save as Image!" />

查询：

<script type="text/javascript">
     // Send the canvas image to the server.
     $(function () {
         $("#btnSave").click(function () {

             can1 = document.getElementById("broadcanvas");
             ctx1 = can1.getContext("2d");
             var coll = document.getElementById("layer2");
             ctx1.drawImage(coll, 0, 0);
             var image = can1.toDataURL("image/png");   

             alert(image);
             image = image.replace('data:image/png;base64,', '');
             $.ajax({
                 type: 'POST',
                 url: 'index.aspx/UploadImage',
                 data: '{ "imageData" : "' + image + '" }',
                 contentType: 'application/json; charset=utf-8',
                 dataType: 'json',
                 success: function (msg) {
                     alert('Image saved successfully !');
                 }
             });
         });
     });
</script>

index.aspx.cs：

using System.IO;
using System.Web.Script.Services;
using System.Web.Services;

[ScriptService]
public partial class index : System.Web.UI.Page
{
    static string path = @"E:\Green\images\\";
    protected void Page_Load(object sender, EventArgs e)
    {


    }
    [WebMethod()]
    public static void UploadImage(string imageData)
    {
       string fileNameWitPath = path + DateTime.Now.ToString().Replace("/", "-").Replace(" ", "- ").Replace(":", "") + ".png";
       using (FileStream fs = new FileStream(fileNameWitPath, FileMode.Create))
        {
           using (BinaryWriter bw = new BinaryWriter(fs))
             {
                byte[] data = Convert.FromBase64String(imageData);
                bw.Write(data);
                bw.Close();
             }
         }
     }
}
4

6 回答 6

2

For the proper working of this code you have to do the below things

  1. Correct the spelling of the canvas id used in the javascript code.
  2. Change the position of the button. Currently button is under the canvas. So can't click on the button.
  3. Create directories Green and Images in E drive. It should be there E:\Green\Images

The working code is.

Javascript

<script type="text/javascript">
        // Send the canvas image to the server.
        $(function () {
            $("#btnSave").click(function () {
                can1 = document.getElementById("boardcanvas");
                ctx1 = can1.getContext("2d");
                var coll = document.getElementById("layer2");
                ctx1.drawImage(coll, 0, 0);
                var image = can1.toDataURL("image/png");

                alert(image);
                image = image.replace('data:image/png;base64,', '');
                $.ajax({
                    type: 'POST',
                    url: 'Default.aspx/UploadImage',
                    data: '{ "imageData" : "' + image + '" }',
                    contentType: 'application/json; charset=utf-8',
                    dataType: 'json',
                    success: function (msg) {
                        alert('Image saved successfully !');
                    }
                });
            });
        });
    </script>

Html code

<div style="position: relative; width: 456px; padding: 0px; margin: 0px;">
        <canvas id="boardcanvas" width="456" height="480" style="position: absolute; left: 0;
            top: -220px; z-index: 0;">
        </canvas>
        <canvas id="layer2" width="456" height="480" style="position: absolute; left: 0;
            top: -220px; z-index: 1;">
        </canvas>
    </div>
    <input type="button" id="btnSave" style="position: absolute; left: 460px; width: 150px;
        text-align: center; height: 30px; z-index: 2;" name="btnSave" value="Save as Image!" />

Asp.Net side code is OK. Please Try with the above code. Sure it will work (Don't forget to create the directory).

于 2013-08-08T12:57:14.357 回答
1

这里的问题是您正在使用var collin的画布drawImage()。您应该改用它的上下文。这是修复：

can1 = document.getElementById("broadcanvas");
ctx1 = can1.getContext("2d");
var coll = document.getElementById("layer2");
var ctx2 = coll.getContext("2d");
ctx1.drawImage(ctx2, 0, 0);
var image = can1.toDataURL("image/png");
于 2013-08-06T03:47:14.400 回答
1

看起来您只将一张图像（“broadcanvas”）转换为数据 url。尝试这个：

var image = ctx1.toDataURL("image/png");

不相似的变量命名会帮助您更快地发现这一点。

于 2012-09-23T00:24:23.233 回答
0

这是我做的一个技巧，我在确保所有图像都已加载且可用时遇到了很多问题。

创建图像后，立即使用onload事件来跟踪图像是否可以使用。我发现使用类似以下代码的东西会产生奇迹（未经测试，主要用作一般参考）：

//I set to the window event to make sure it stays available. This is handy in many applications that may need to wait.
window.image1 = document.getElementById('img1');
window.image2 = document.getElementById('img2');
window.canv1 = document.getElementById('canv1');
window.canv2 = document.getElementById('canv2');
window.ctx1 = window.canv1.getContext('2d');
window.ctx2 = window.canv2.getContext('2d');
window.imagesLoaded = 0; 

//load the images
window.image1.onload = function(){
  window.imagesLoaded++;
}
window.image2.onload = function(){
  window.imagesLoaded++;
}

//function to handle them all loading
function loaded(){
  if(window.imagesLoaded==2){

    //draw initial images
    ctx1.drawImage(image1,0,0);
    ctx2.drawImage(image2,0,0);

    //at this point you should have 2 canvas's with 2 different images, 
    //now as I understand it you want to save them both to one canvas. 
    //So first grab a new canvas element.
    var newImg1 = window.canv1.toDataURL('image/png');
    var newImg2 = window.canv2.toDataURL('image/png');
    window.canv3 = document.getElementById('canv3');
    window.ctx3 = window.canv3.getContext('2d');

    //this is the tricky part, side by side, 
    //overlapping or top/bottom by manipulating the x,y. 
    //I just make a general example here.
    ctx3.drawImage(newImg1,0,0);
    ctx3.drawImage(newImg2,10,10);

    //finally create the new image as an image, 
    //you can do whatever you need with this
    var newImg3 = window.canv3.toDataURL('image/png');
  }else{
    //set a timeout to retry this function if the images were not ready
    setTimeout(function(){
      loaded();
    },100);
  }
}
loaded();

在这个例子中我可能过度使用了窗口对象，很可能只需要在“imagesLoaded”变量上使用它来确保我可以看到它的更新，但是这样就不需要将参数传递给函数。

于 2013-08-12T20:04:35.287 回答
0

当asp.Net和基本上所有服务器端库通常可以利用操作系统上的图像处理库（在Linux中，如GD、GD2、ImageMagick等）。

是为了避免将两个不同的文件上传到服务器吗？因为使用这种方法，您只会节省 HTTP 事务，而不必节省带宽。

只是一个想法，因为它听起来不像客户端固有的任何需要在这里完成的事情。那可能只是因为您的示例被精简了。

于 2013-08-08T15:57:50.503 回答
0

这是一个工作示例：

<!DOCTYPE html>
<html>
<body>

<p>Image to use:</p>
<img id="scream" src="http://www.w3schools.com/tags/img_the_scream.jpg" alt="The Scream" width="220" height="277">

<p>Canvas:</p>
<canvas id="myCanvas" width="250" height="300" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

<p> Canvas2: </p>
<canvas id="myCanvas2" width="250" height="300" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>

<script>

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");

var img=document.getElementById("scream");
ctx.drawImage(img,30,5);
ctx.drawImage(img,5,30);

var c2=document.getElementById("myCanvas2");

var ctx2=c2.getContext("2d");


ctx2.drawImage(c,0,0)
ctx2.drawImage(img,-10,50);


var image = c2.toDataURL("image/png"); 
console.log(image);

image = image.replace('data:image/png;base64,', '');
console.log(image);

</script>

</body>
</html>

这是一个带有工作示例的小提琴：小提琴

于 2013-07-26T13:11:27.357 回答