将 HTML5 Canvas 绘图应用程序另存为 SVG 文件

Question

I'm doing a canvas drawing app and i want to be able to export the image as a svg file .I already did the function to save the image as a png file but i have some troubles with the svg part.Can you please help me? This is the html code for the save png image button:

<div class="wrapper">

    <div class="toolbar">
        <a href="#" id="save" onclick="SaveImage()">
        <img src="save.png"></a>
    </div>

<canvas id="my-canvas" width="800" height="500"></canvas>

<div id="toolbar2">
    <a id="img-file" download="image.png">
    <button onClick="download()" type="button" class="button">Save as PNG</button></a>
</div> 

And the JS:

function SaveImage(){
    var imageFile = document.getElementById("img-file");
    imageFile.setAttribute('download', 'image.png');
    imageFile.setAttribute('href', canvas.toDataURL());
}

Please help.I`m not allowed to use other js libraries.

Answer 1

You cannot convert the bitmap image of the canvas directly to SVG (except if the bitmap image like the PNG that you have tried to export is the source of a <image> element in your SVG -- but I guess that that is not the idea).

Now that this is a drawing tool, you probably maintain the state of the editor with objects and/or another data structure. With that assumption, the entire image is already represented in a structured manner. And this structure could be used for generating an SVG image. Example: a circle is drawn on the canvas with a color, size and position: {type: "circle", color: "red", x: 30, y: 56, r: 5} . This object is drawn as an arc on the canvas, but at the same time it can also be turned into a SVG <circle> element.

There are probably more libraries that can handle this for you. fabricjs could be an example. Here I link to the toSVG() function: JSDoc: Class: Canvas .