What is fabricjs? Fabricjs front-end drawing library usage arrangement (with code)

This article brings you what is fabricjs? The usage of the fabricjs front-end drawing library is organized (with code), which has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

I have been using it for a while. Generally speaking, it is a very powerful vector drawing tool. The official documentation is also rich, but the document organization is not very good, and a small number of API designs are not consistent. It is still needed. Sort it out.

Canvas

Canvas is the most basic object. It is encapsulated for the tag and can manage all objects drawn internally.
This canvas object is not an element in the DOM. If you need to control the DOM or the corresponding context, you still need to obtain it yourself.

canvasElement = document.getElementById(canvasEle);
ctx = canvasElement.getContext("2d");

When creating a new canvas object, you can specify the width and height:

canvas = new fabric.Canvas(canvasElement, { 
            selection: false,
            width: 800,
            height:600
});

The width and height specified here will override the ones set in css. Note that this form of creating objects is basically similar in Fabric.js. The class name indicates the type of object to be created. The first parameter is the necessary data, and the second parameter is various options.

All modifications to the canvas, including adding and deleting objects, and modifying object parameters, require calling the rendering method to be displayed:

canvas.renderAll();

Basic shape

Geometric shapes such as Line, Circle, Rectangel, etc. are all basic shapes.

All basic shapes have corresponding classes, so that their position, color, size and other styles can be controlled through the properties and methods of class instances. All classes inherit from the Object class and have some public properties and methods.

Create

The following is an example of drawing a line (given two vertex coordinates):

        var line =  new fabric.Line([x1, y1, x2, y2], {
            strokeWidth: 2, //线宽
            stroke: rgba(255,0,0,0.8), //线的颜色
            selectable: false
        });
        canvas.add(line);

Example of drawing a circle (the vertex and radius are in the options), here left and top are actually (x, y), which should be borrowed from the naming in css.

        var circle =  new fabric.Circle({
            radius: 2,
            left: left,
            top: top,
            originX: 'center',
            originY: 'center',
            fill: rgba(0,200,0,0.8), 
            strokeWidth: 1,
            stroke: rgba(255,0,0,0.8),
            selectable: false
        };
        canvas.add(circle);

It can be seen from here that it is similar to creating canvas. The first parameter is specific to this class (such as the starting and ending point coordinates passed when drawing a straight line), and the second parameter is a general option. If there is no Special parameters, then the first parameter is directly the general option. All created shapes can only be displayed if they are added to the scene through the add method of canvas.

Control

left and top are properties of every Object. As for which point in the graph it refers to, the coordinates are determined by the originX and originY parameters. Determine, they are equivalent to the alignment in text editing software. originX has three optional values: left, center, right; originY also has three optional values: top, center, bottom.

Their schematic diagrams are as follows:

http://fabricjs.com/test/misc...

If you want the default origin of each object to be The center can be set like this:

fabric.Object.prototype.originX = fabric.Object.prototype.originY = 'center'

width and height are also attributes that can be directly accessed. As the name suggests, they represent length and width (all shapes have an enclosing rectangle, so you can use length and width to control the size) .

Except for the above properties that can be directly accessed, most properties need to be read and written using the get/set method. For example:

line.left = pointer.x;
line.top = pointer.y;
line.set('stroke', startColor);
line.set('height', 20);

Some articles on the Internet will write line.stroke=color, Or forms such as line.setProperty('stroke',color) are not valid and may be expressions of earlier versions.

Image

Image is similar to other shapes and is a subclass of Object. The biggest difference is that the loading of What is fabricjs? Fabricjs front-end drawing library usage arrangement (with code) files is asynchronous, so the subsequent processing of Image Operations must be completed in callbacks.

var bkImage = fabric.Image.fromURL(imgUrl,function(img) {
    canvas.add(img);
}

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