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A Windows COM DLL Build of the gd 2.0.1 Graphics Library

This site contains information and files for  gdCOM.dll, a COM compliant dll providing the services of the gd 2.0.1 graphics library. The latest build of gdCOM is
  1. Why gdCOM - Reasons gdCOM came about
  2. How gdCOM - Examples
  3. Where gdCOM - Installation Files
  4. License Terms
  5. Miscellaneous

Why gdCOM?

Thomas Boutell's gd graphics library! An answer enough for anyone.

The gd graphics library has served as the foundation for many applications needing dynamic image creation and manipulation, especially those tied to the web. gd's standard image format prior to version 1.6 was the GIF format. Subsequently a large legal darkness descended upon the net wide use of the GIF graphics file format, as a result of the Unisys LZW compression algorithm patent. With this change, gd embraced the PNG standard (which is arguably a big step forward from GIF) as its efficient standard image format. As of gd 1.8, true colour JPEG image handlig is also suported.

All this upheaval prompted me to re-investigate the possibility of using gd in a windows environment. Primarily to solve some of the struggles I was having doing what would otherwise have been unix simple things in an IIS ASP context (sometimes I'm forced to do things the Hard way..).

Out of this, gdCOM was beaten into shape.

How gdCOM?
Essentially, gdCOM is an activeX OLE automation dll. This means that once installed, gdCOM objects can be created and used from any COM compliant container (like ASP pages or Visual Basic or anything which uses VBScript for that matter).

gdCOM is built from the latest source distributions of gd, zlib , libpng and jpeg-6b. The functions generally made available by gd in a compiled library are then wrapped in COM interface routines with conversion between the required oleautomation data types. A very minimal set of helper routines were also added, to aid in the use of file related functions from COM containers that have trouble providing file handles for gd data output.

Visual Basic Code Example:

Assuming the gdCOM component has been installed, open a new project and set the project references to include the "gdCOM 2.0.1.x Type Library". Once that is done, the Visual Basic equivalent of gd's simple C demo is as follows;

Private Sub Form_Load()

' Create a New Instance of the gdCOM object
Dim gdInstance As New gdCOM

' Define a pointer for the image Data
Dim ImagePointer As Long

' Define Variables to hold Color indexes
Dim Black As Long
Dim White As Long

' Create a New Image of a specified size

ImagePointer = gdInstance.ImageCreate(64, 64)

' Use the returned Image Pointer to define two colors

Black = gdInstance.ImageColorAllocate(ImagePointer, 0, 0, 0)
White = gdInstance.ImageColorAllocate(ImagePointer, 255, 255, 255)

' Draw a line
Call gdInstance.ImageLine(ImagePointer, 0, 0, 63, 63, White)

' Write a file using one of the "helper" routines

Call gdInstance.ImagePngHelper(ImagePointer, "test.png")

' VERY VERY Important step. Destroy the Image data held by the object

Call gdInstance.ImageDestroy(ImagePointer)

' De-allocate the gdCOM object

Set gdInstance = Nothing

End Sub
ASP Example
Again, assuming the gdCOM dll has been installed. The following ASP VBScript code replicates gd's simple C demo.

 dim OutputFilename, ImagePointer, Black, White

 set gdInstance = server.createobject("gdCOM.gdCOM.1")

 ImagePointer = gdInstance.ImageCreate(64,64)

 Black = gdInstance.ImageColorAllocate(ImagePointer,0,0,0)
 White = gdInstance.ImageColorAllocate(ImagePointer,255,255,255)

 call gdInstance.ImageLine(ImagePointer,0,0,63,63,White)

 OutputFilename = request.servervariables("APPL_PHYSICAL_PATH") + "test.png"

 call gdInstance.ImagePngHelper(ImagePointer, OutputFileName)

 call gdInstance.ImageDestroy(ImagePointer)

 set gdInstance = nothing


NOTE: If you wish to use the generated file immediately in the same ASP page that generated the image, you will need to use the direct binary data return method on your image data - as shown in the following example:


    Option Explicit

' Define an Instance Variable, Image Pointer and Color Variables

    Dim gdInstance, ImagePointer, Black, White

    ' Create a New Instance of the gdCOM Object

    Set gdInstance = Server.CreateObject("gdCOM.gdCOM.1")

' Create a New Image of the Specified Size

    ImagePointer = gdInstance.ImageCreate(64,64)

' Use the Returned Image Pointer to Allocate Two Colors

    Black = gdInstance.ImageColorAllocate(ImagePointer,0,0,0)
    White = gdInstance.ImageColorAllocate(ImagePointer,255,255,255)

' Draw a Line

    Call gdInstance.ImageLine(ImagePointer,0,0,63,63,White)

' Use the ASP Response Object to set the Content Type to PNG

    Response.ContentType = "image/PNG"

' Wrtie out the Binary PNG image directly to the HTML stream

    Response.BinaryWrite gdInstance.ImagePngBinaryData(ImagePointer)

' VERY VERY Important Step - Destroy the Image Data Held By the Object

    Call gdInstance.ImageDestroy(ImagePointer)

' Release the gdCOM Instance

    Set gdInstance = Nothing


Where gdCOM?
The latest version of gdCOM binary should be available at the Source Forge site  http:/

A complete list of the wrapped functions is provided here.

As gdCOM wraps the functionality provided by gd, the gd documentation might be worth a look see.

NOTE: Currently the gdCOM source release is available in varying degrees of quality through cvs...

Bugs? See anything strange happen? Suggestions? Help? Then try gdCOM SourceForge Pages.

License Terms
As gdCOM is a derived work from Thomas Boutell's gd.
This gdCOM page and hosting has been provided by SourceForge Logo .