canvas.js 是canvas标签的一个封装来实现图表功能的库。它大量使用方法链，就像 jQuery。

Create a new canvas like so:

c = new Canvas(document.getElementById('container'))

where container is a canvas element.

Basic Graphics

c.clear()

Fills the screen with the background color

c.arc(x, y, radius, start, end)

Draws an arc. Origin is at (x, y) with the specified radius. Start and end are radians specifying the degrees at which the arc begins and ends.

c.ellipse(x, y, radius, start, end)

Draws an ellipse. The top-left corner is at (x, y), and the ellipse has the specified width and height.

c.line(x1, y1, x2, y2)

Draws a line from (x1, y1) to (x2, y2).

c.rectangle(x, y, width, height)

Draws a rectangle. Its top-left corner is at (x, y), and the rectangle has the specified width and height. c.polygon(points...)

Draws a polygon given the vararg list of points. There must be an even number of arguments.

Bezier Curves

c.bezier(points...)

Draws one or more bezier curves given the vararg list of points. The first two points specify the start point. After that, sets of six arguments are given: the first two specify the first control point, the second two specify the second control point, and the last specifies the end point for that part of the curve. For example:

c.bezier(0, 0, 30, 20, 40, 50, 100, 100, 80, 60, 70, 90, 200, 200)

Would draw two bezier curves. The first would start at (0, 0) and end at (100, 100). It would have control points at (30, 20) and (40, 50). The second bezier curve would start at (100, 100) and end at (200, 200). It would have control points at (80, 60) and (70, 90).

Quadratic Curves

c.quadratic(points...)

Draws one or more quadratic curves given the vararg list of points. The first two points specify the start point. After that, sets of four arguments are given: the first two specify the control point and the last specifies the end point for that part of the curve. For example:

quadratic(0, 0, 30, 20, 100, 100, 80, 60, 200, 200)

Would draw two quadratic curves. The first would start at (0, 0) and end at (100, 100), with a control point at (30, 20). The second would start at (100, 100) and end at (200, 200), with a control point at (80, 60).

Images

c.image(image, x, y, width, height, sliceX, sliceY, sliceWidth, sliceHeight)

Draws an image on the canvas. Image is a DOM image element, or a string specifying where to fetch the image. x and y specify the position to draw the image. The optional arguments width and height allow for stretching/shrinking of the image drawn. The optional arguments sliceX, sliceY, sliceWidth, sliceHeight allow you to just draw a part of the specified image, which is useful for spriting.

Examples:

image(img, 0, 0)

draws the image 'img' at (0, 0).

image(img, 0, 0, 100, 50)

draws the image 'img' at (0, 0) with a width of 100 and a height of 50.

image(img, 0, 0, 100, 50, 10, 10, 15, 20)

draws a rectangular part of the image 'img', from (10, 10) with a width of 15 and a height of 20. The image is drawn on the canvas at (0, 0) with a width of 100 and a height of 50.

Styling

c.fill()

Enables fill for drawn objects

c.noFill()

Removes fill for drawn objects

c.fillStyle(style)

Sets the fill style for drawn objects. Style is a CSS string.

c.stroke()

Enables stroke for drawn objects

c.noStroke()

Removes the stroke for drawn objects

c.strokeStyle(style)

Sets the stroke style for drawn objects. Style is a CSS string. c.strokeWeight(weight)

Sets the stroke weight (i.e. thickness) for drawn objects. Weight is a number (int or float) specifying thickness.

c.fontProps(props)

Sets the font properties according to the key/values passed in by the map. Valid values include 'font', 'textAlign', and 'textBaseline'.

c.background(style)

Sets the background style. Style is a CSS string.

Other

c.run(callback)

Runs a loop, redrawing the canvas at the rate specified by framerate. At each loop iteration, the specified callback method is called, with its context being this object. If the callback returns false, the loop is broken out of.

c.framerate(fps)

Sets the framerate for redrawing when the loop in run() is active.

c.context

Provides low-level access to the canvas' Context2D object

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