node-pngjs-draw

Adds basic drawing functionnalities to pngjs node module.

Install

$ npm install --save pngjs-draw

Example

var fs = require('fs');
var drawing = require('pngjs-draw');
var png = drawing(require('pngjs').PNG);

fs.createReadStream("blue.png")
  .pipe(new png({ filterType: 4 }))
  .on('parsed', function() {
    // Draws a pixel with transparent green
    this.drawPixel(150,200, this.colors.black())

    // Draws a line with transparent red
    this.drawLine(0,0,200,200, this.colors.red(50))

    // Draws a rectangle with transparent black
    this.fillRect(150,150,75,20, this.colors.black(100))

    // Draws a filled rectangle with transparent white
    this.fillRect(50,50,100,100, this.colors.white(100))

    // Draws a text with custom color
    this.drawText(20,20, "Hello world !", this.colors.new(255,100,10))

    // Writes file
    this.pack().pipe(fs.createWriteStream('blue.out.png'));
  });

Documentation

PNG.prototype.drawPixel

Draws the pixel at the given coordinates with the given color.

• {int} x The x coordinate of the pixel
• {int} y The y coordinate of the pixel
• {Array(byte)} color The color used to paint the pixel

PNG.prototype.drawLine

Draws a line beetween two points with the given color.

• {int} x0 The x coordinate of the start
• {int} y0 The y coordinate of the start
• {int} x1 The x coordinate of the end
• {int} y1 The y coordinate of the end
• {Array(byte)} color The color used to paint the line

PNG.prototype.drawRect

Draws a stroked rectangle with the given color.

• {int} x The top left x coordinate of the rectangle
• {int} y The top left y coordinate of the rectangle
• {int} width The width of the rectangle
• {int} height The height of the rectangle
• {Array(byte)} color The color used to paint strokes of the rectangle

PNG.prototype.fillRect

Draws a filled rectangle with the given color.

• {int} x The top left x coordinate of the rectangle
• {int} y The top left y coordinate of the rectangle
• {int} width The width of the rectangle
• {int} height The height of the rectangle
• {Array(byte)} color The color used to fill the rectangle

PNG.prototype.drawText

Draw a text to the image.

• {int} x The top left x coordinate of the string
• {int} y The top left y coordinate of the string
• {string} text The string value
• {Array(byte)} color The color used used as foreground
• {Object} font The font used to render the string (optional)
• {Object} text The string value

return {int} The length in pixel of the rendered string

PNG.prototype.measureString

Measure the rendered text length with the given font.

• {string} text The string value
• {Array(byte)} color The color used used as foreground
• {Object} font The font used to render the string (optional)

return {int} The length in pixel of the rendered string

Creating colors

[<R>,<G>,<B>,<A>]

A color is a javascript array containing Red/Green/Blue/Alpha byte components.

PNG.prototype.colors.new = function(r,g,b,a)

The new method generates an array with the provided components.

Default values :

• r: 0
• g: 0
• b: 0
• a: 255

PNG.prototype.colors.red = function(a)
PNG.prototype.colors.greed = function(a)
PNG.prototype.colors.blue = function(a)
PNG.prototype.colors.black = function(a)
PNG.prototype.colors.white = function(a)

Helper methods for creating base colors are also available.

Custom fonts

In order to use a custom font, you must first generate a font module from an image presenting all the supported characters.

For more details, take a look at these files :

• build-font.js
• fonts/*
• custom-font/*

Roadmap / Ideas

• More shapes (circles, polygons)
• Rotations
• Multi-lines texts

Copyright and license

MIT © Aloïs Deniel