canvas-renderer

canvas-renderer

HTML5 inspired canvas implemented in Node.js for rendering PNG images.

• Render simple polygons as PNG with no native dependencies like PhantomJS.
• The library does not run in the browser.
• This is not an attempt to implement the complete HTML5 CanvasRenderingContext2D interface. See the supported methods below.
• The performance has not been in focus. If performance is important in your project, consider using a native backed canvas implementation.

Sample

Install the canvas-renderer NPM package.

npm install canvas-renderer

The following example renders two triangles to test.png.

const fs = require("fs");
const canvasRenderer = require("canvas-renderer");

var canvas = canvasRenderer.createCanvas(100, 100);

var ctx = canvas.getContext("2d");

ctx.fillStyle = "#ff0000";
ctx.beginPath();
ctx.moveTo(10, 10);
ctx.lineTo(90, 10);
ctx.lineTo(10, 90);
ctx.fill();

ctx.fillStyle = "#0000ff";
ctx.beginPath();
ctx.moveTo(90, 90);
ctx.lineTo(90, 50);
ctx.lineTo(50, 90);
ctx.fill();

var testpng = fs.createWriteStream("test.png");
testpng.write(canvas.toPng());
testpng.close();

API

To create an instance of Canvas, use the createCanvas(width, height) method that is exposed by the module. Use the getContext() method on the canvas to get a CanvasContext object.

Canvas

Properties

• width (integer)

  The width of the canvas in pixels.

• height (integer)

  The height of the canvas in pixels.

• backColor (color)

  Specifies the background color. See fillStyle below for allowed values. Default is transparent.

Methods

• toPng([keywords])

  Renders the canvas as a PNG data stream and returns it as a Buffer. keywords is an optional dictionary defining the keywords to be written to the PNG stream. See https://www.w3.org/TR/PNG/#11keywords.

• getContext()

  Gets a CanvasContext object for drawing on this canvas.

• toDataURL([type], [encoderOptions])

  Renders the canvas as a dataURI. Note that the two parameters are currently ignored since the only supported type is image/png.

CanvasContext

Properties

• fillStyle (color)

  Specifies the fill color that is used when the fill() method is called. Allowed values are:

  • 32 bit integers on the format 0xRRGGBBAA
  • string "transparent"
  • strings on the format "#2c4" (#RGB)
  • strings on the format "#2c4f" (#RGBA)
  • strings on the format "#22cc44" (#RRGGBB)
  • strings on the format "#22cc44ff" (#RRGGBBAA)
  • strings on the format "rgb(255, 124, 22)"
  • strings on the format "rgb(255, 124, 22, 0.5)"
  • strings on the format "rgb(255, 124, 22, 50%)"
  • strings on the format "rgba(255, 124, 22, 0.5)"
  • strings on the format "rgba(255, 124, 22, 50%)"
  • strings on the format "rgb(23%, 45%, 75%)"
  • strings on the format "rgb(23%, 45%, 75%, 0.5)"
  • strings on the format "rgb(23%, 45%, 75%, 50%)"
  • strings on the format "rgba(23%, 45%, 75%, 0.5)"
  • strings on the format "rgba(23%, 45%, 75%, 50%)"
  • strings on the format "hsl(134, 50%, 50%)"
  • strings on the format "hsl(134, 50%, 50%, 0.5)"
  • strings on the format "hsl(134, 50%, 50%, 50%)"
  • strings on the format "hsla(134, 50%, 50%, 0.5)"
  • strings on the format "hsla(134, 50%, 50%, 50%)"
  • strings on the format "hwb(134, 50%, 50%)"
  • strings on the format "hwb(134, 50%, 50%, 0.5)"
  • strings on the format "hwb(134, 50%, 50%, 50%)"
  • named colors listed in CSS Color Module Level 4

Paths

• beginPath()

  Removes all existing subpaths and begins a new path.

• moveTo(x, y)

  Begins a new subpath by moving the cursor to the specified position.

• lineTo(x, y)

  Inserts an edge between the last and specified position.

• arc(x, y, radius, startAngle, endAngle, [anticlockwise])

  Adds an arc to the current subpath. See MDN for details.

• closePath()

  Starts a new subpath that begins in the same point as the start and end point of the previous one.

Rendering

• clearRect(x, y, width, height)

  Fills the specified rectangle with fully transparent black without affecting the current paths.

• fill([windingRule])

  Fills the defined paths. windingRule defines the winding rule to be used for determining which areas are covered by the current path. Valid values are "evenodd" and "nonzero". Default is "nonzero".

• fillRect(x, y, width, height)

  Fills the specified rectangle without affecting the current paths.

Operations

• save()

  Saves the current transformation and fill style to a stack. The state can be restored using restore().

• restore()

  Restores the last state saved by save() and removes the state from the state stack.

Transformation

• resetTransform()

• rotate(angle)

• scale(x, y)

• setTransform(a, b, c, d, e, f)

• transform(a, b, c, d, e, f)

• translate(x, y)

License

canvas-renderer is released under the MIT license.