gdimage

Yet Another GD Graphics Library Wrapper For Node.JS

This software wraps popular LibGD graphics library into Node.JS module which helps interpreting graphics inside Node.JS. Rather than writing dozens of native codes, this software uses ffi to wrap libgd api methods into JavaScript functions.

Usage

gdimage requires ref and node-ffi which are native modules, so you need a C++ compiler (gcc, llvm, msvc etc.) before installing it.

Also, GD native library is required. In Linux / OSX, you can install it with a package manager

npm install gdimage
(sudo) apt-get install libgd3 # in debian/ubuntu 
(sudo) yum install gd # in fedora/centos 
brew install gd # in osx 

In Windows, you need to download and install libgd manually, see Gd for Windows

Usage example:

var gd = require('gdimage');
 
var image = gd.create(200, 100);
var white = image.allocateColor('#ffffff'),
    red = image.allocateColor('#ff0000');
 
image.fill(0, 0, 200, 100, white);
image.line(0, 0, 200, 100, red, true);
 
var buf = image.encode('png');
require('fs').writeFileSync('out.png', buf);

API Reference

function create

function create(width:int, height:int, trueColor:boolean = true): GDImage

Creates a new GDImage instance.

When trueColor set to true, the image is in TrueColor mode, the total color count is unlimited.

Parameters:

• width the image width, in pixels
• height the image height, in pixels
• trueColor whether TrueColor mode is enabled, default to true.

Returns:

a new GDImage instance

function decode

function decode(buf:Buffer, format:string = 'auto'): GDImage

Decodes a image file content into a GDImage instance.

Parameters:

• buf a buffer that contains file content.
• format a string or mime type denoting the format of the image. The format name is case insensitive. When set to 'auto', the file format is guessed by the file head. Supported image formats are:
  • bmp image/bmp application/x-ms-bmp application/x-bmp
  • jpg jpe jpeg jfif jfi jif image/jpeg
  • gif image/gif
  • png image/png
  • tiff tif image/tiff

Returns:

a GDImage instance, which maybe TrueColor or not, depending on the file format.

function trueColor

function trueColor(r, g, b, a): Color
function trueColor(rgb:string): Color
function trueColor(rgba:string): Color

Resolves a 32 bit RGBA true color. trueColor accepts several types of arguments:

• gd.trueColor('#RRGGBB'), where 'RRGGBB' is hex color codes. For Example #FF0000 denotes red
• gd.trueColor('#RRGGBBAA')
• gd.trueColor(r, g, b), where r, g, b are digits between 0 ~ 255
• gd.trueColor(r, g, b, a), where a is a number between 0 and 1

So gd.trueColor('#ff00ff') is equivalent to gd.trueColor('#ff00ffff'), as well as gd.trueColor(255, 0, 255, 1)

class GDImage

A GDImage object wraps a native libgd image instance, and wraps several native methods into javascript functions which helps us working with it. Methods and fields available are as follows.

int GDImage::width, int GDImage::height

the width and height of the image, in pixels.

GDIMage::toTrueColor

function toTrueColor(): GDImage

Converts a platte image to true color. Calling this on a true color image has no effects.

Returns the GDImage itself.

GDImage::destroy

function destroy()

Destroys the image, frees memories and resources. A GDImage must be freed manually to prevent memory leak.

GDImage::allocateColor

function allocateColor(r, g, b, a): Color

Allocates a color in the color space. image.allocateColor accepts same arguments as gd.trueColor.

If the image is in true color mode, image.allocateColor acts like gd.trueColor.

If the image is in platte mode, for example it is decoded from a PNG8 or GIF file, the color allocation may fail because the color platte cannot have more colors. To prevent the potential failure, you can

• convert the image to true color mode by calling image.toTrueColor().
• find a closest color from the platte by calling image.getClosestColor(rgba)
• use image.resolveColor(rgba)

GDImage::getColor

Gets an existing color from the color space. If none matching, an exception is thrown.

image.getColor accepts same arguments as gd.trueColor.

Not that image.GetColor acts like gd.trueColor in true color mode, it will never fail.

GDImage::getClosestColor

Gets an existing color closest to the rgba value from the color space.

image.getClosestColor accepts same arguments as gd.trueColor.

Not that image.GetColor acts like gd.trueColor in true color mode, it will never fail.

GDImage::resolveColor

This method will always return a color instance. First it tries to find a matching color, if none matching, it tries to allocate a new color. If both failed, it returns a closest color from the color space.

Not that image.GetColor acts like gd.trueColor in true color mode, it will never fail.

GDImage::scale

function scale(new_width:int, new_height:int, auto_destroy:boolean = false): GDImage

Scales the image into new size. If auto_destroy is set to true, the current image is destroyed after the it is scaled.

Returns a new GDImage created.

GDImage::rotate

function rotate(angle:float, bg_color:Color = null, auto_close:boolean = false): GDImage

Rotates the image clockwise. angle shold be between 0~360. When angle is not 90 180 270, the bg_color is used to fill the empty.

Returns a new GDImage created.

GDImage::line

function line(x1:int, y1:int, x2:int, y2:int, color:Color, anti_aliased:boolean = false): GDImage

Draws a solid line from (x1, y1) to (x2, y2). If anti_aliased is set to true, anti-aliasing is enabled

Returns the GDImage itself.

GDImage::text

function text(str:string, x:int, y:int, size:double, color:Color, angle:float = 0, font:string = "arial"): Array.<number>

Writes text with true type font, returns a rect which wraps the text. Only true type fonts are supported.

Parameters:

• str text to write
• x y start coordinate of the baseline
• size text size in dots/pixels
• color foreground color
• angle angle of baseline, in degrees
• font name/path of font, such as arial times courier, or Symbol.ttf, or /System/Library/Fonts/Symbol.ttf etc. You can supply multi names with ;

Returns an array of 4 digits denoting an rectangle of the bounds: [x, y, w, h]

Find out system font names:

In Windows, check C:\WINDOWS\FONTS C:\WINNT\FONTS for files named *.ttf. In Unix/Linux, check /usr/share/fonts/TrueType /usr/lib/X11/fonts etc. In Mac/OSX, check /Library/Fonts /System/Library/Fonts.

Note that modern os uses ttc file format which is not supported by libgd. If you want to use some fonts that the os does not supply, you should download and install the font files in ttf format or put them in your project directory and specify the font path as below.

Use Your custom font paths:

To use custom font paths, you can supply an environment variable with the paths, separated with : or;

# in posix shell: 
GDFONTPATH="/Users/kyrios.li/fonts:/Library/Fonts" node start
 
# in windows cmd: 
set GDFONTPATH="C:\\Users\\kyrios.li\\fonts;C:\\Windows\\Fonts"

Or just set the font path in node.js:

process.env.GDFONTPATH = require('path').resolve(__dirname, 'fonts') + ':/Library/Fonts';

GDImage::encode

function encode(format:string, auto_close:boolean = false): Buffer

Encodes the image into image file content. Supported formats are:

• bmp
• png
• jpg jpeg
• gif
• tiff
• Webp