canvas-renderer
v2.2.1
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HTML5 inspired canvas that can be rendered to PNG with no native dependencies.
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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
isimage/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
- 32 bit integers on the format
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.