XML 3D - BTS530/630 Project

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Programmers

Mark Paruzel
Yi Shen

Canvas Object

History

Canvas elements simplify the drawing of custom pixels to the screen as well as the modification of these pixels in real-time. There have been numerous requests for a canvas tag inside HTML documents which provided custom draw ability inside XUL (A Cross-Platform drawing management library). Unfortunately, XUL is client side based which only allows the modification of web pages from the user’s endpoint. The Canvas Tag was originally developed in order to create modifications to the browser from the server end. An on-screen Canvas object is basically a wrapper around the XUL engine that allows the visual manipulation of pixels on the webpage.

Objective

The objective of Canvas was to provide a drawing interface inside the HTML document which website designers could use to create interactive content. It also allows the designers of the webpage to change the Canvas object on the fly using JavaScript or Python. The Canvas tag exposes the functionality of XUL with added security and safeguards to prevent damage to the client's computer.

XML 2D/3D Addition to Canvas

Rationale

The basis of the Canvas tag is to provide immediate drawing to the screen. The drawing can consist of regular 2D pixel manipulations as well as a proposed 3D model manipulation. In addition, it will provide a safe and simple application programming interface (API) to the OpenGL Layer. The OpenGL Layer is a library that handles the math required for 3D transformations. Unfortunately, OpenGL has the power to talk directly to the hardware therefore allowing direct manipulation of the hardware or possibly potential damage. Consequently, the OpenGL Layer will not be included in this project due to its complex nature and constant upkeep. In addition, the OpenGL API is extremely low-level and may be confusing when exposed to the internet.

However, the first step in creating a 2D/3D Canvas element is to use a custom XML tag to specify the 2D/3D objects on the screen as well as the drawing area available. In this case, the developer will be able to create 2D and 3D objects on the client's screen as well as provide logic to modify these objects in real-time. By using the Document Object Model (DOM) to interpret the XML language and retrieve the attributes of the objects, this causes the objects to be presented for modification purposes.

The Document Object Model

The Document Object Model is an API that allows for the interpretation of HTML and XML documents. It provides a structural representation of the document, which enables for easy modification and visual representation of the webpage. In essence, it connects the markup languages to structural code inside the browser. The DOM is contained in a tree structure that allows for easy search and retrieval of HTML and XML tags and their properties. This technology allows the Canvas tags to be read and retrieved in an efficient manner.

Use of XML 2D/3D

The project consists of several iteration focusing primarily on the implementation of HTML that allow access to the 2D drawing functionality. Eventually, the functionality will extent into the 3D world once the canvas API supports it. These 3D Tags will be based upon the syntax of its counterpart, the 2D Canvas tags. Essentially, the syntax for the 2D tags will be similar to the following:

<canvas>
 -- draw a square on the screen
 <rectangle width="4" height="10" />
</canvas>

The syntax of these tags will be intuitive and flexible enough to be implemented along side regular HTML code. The initial iterations will focus only on the implementation of the 2D tags which will tie into the existing 2D drawing code. This will essentially allow a developer to use the Canvas capabilities without writing large amounts of complex JavaScript code. In addition to tags that allow simple drawing, there will be group modifier tags that will be able to change a series of tags at the same time. For example, grouping a bunch of lines together would allow for group modifications rather then modifying each line separately. 

<canvas>
 -- either with an explicit 2D matrix
 <transform position="m1..m9">
  <line startposition="5, 10" endposition="40, 70" />
  <line startposition="15, 30" endposition="50, 40" />
  <line startposition="25, 60" endposition="60, 10" />
 </transform>
</canvas>

Eventually, this functionality will be applied to the 3D world and will assist in the transformation, scaling, and rotation or 3D objects on the screen. It will provide a larger flexibility aspect to the markup language.

These are the basic principles that govern 2D and 3D controls over an object. An object can be anything from a simple primitive such as a line or circle to a complex 3D Mesh that can be downloaded from the internet or from the client's computer. Furthermore, the eventual incorporation of 3D into the Canvas framework will allow this API to become robust as it advances.

Use of XML in JavaScript

In order to draw the objects onto the screen, JavaScript will be used to call functions inside the core of Firefox. The API will be written to allow programmers to not only access the various attributes of the objects but also to mitigate complexity. The webpage will initiate a call to our JavaScript functions, that will start the drawingcode.

Tag Reference

This is a tentative List and will change in time (Last Updated Feb 16, 2007):

Iterations & Progress

Link to The Test Page is available here.

Completed Iterations

  • Iteration 0: Fix Tag Compatibility (Completed: Dec 20, 2006)
    • Write DOM Parsing Code
    • Create Wiki site to detail out the Tags
    • Write JavaScript code to manage and Draw the Tags
  • Iteration 1: Fix Tag Compatibility (Completed: Jan 27, 2007)
    • Restructure the parsing Code to Accept Tags without an Ending Tag
    • Write a Test for the above task
    • Rewrite Tag parsing Code
    • Write Test for the Tag Parsing Code
    • Update the Wiki with new content
    • Issue: A temporary fix to the first task was to serve the page as XHTML (Cludgy!?)
  • Iteration 2: Create New 2D Tags (Completed: Feb 9, 2007)
    • Line Tag
      • Create <Line> Tag
      • Write Test for the Line Tag
    • Arc Tag
      • Create <Arc> Tag
      • Write Test for the Arc Tag
    • Circle Tag
      • Create <Circle> Tag
      • Write Test for the Circle Tag
    • Rectangle Tag
      • Create <Rectangle> Tag
      • Write Test for the Rectangle Tag
    • Image Tag
      • Create <Image> Tag
      • Write Test for the Image Tag
    • Update Wiki Site to reflect Above Changes
  • Iteration 3: Enhancing the DOM Parsing Code (Completed: Mar 1, 2007)
    • Refactor the DOM Parsing code to use DOM rather then Objects in memory
    • Write a test for the above task
    • Research into DOM events which are fired when changes are made
    • Write a test for the above task
    • Update Wiki Site to reflect Above Changes

Incomplete Iterations

  • Iteration 4: Create Grouping Tags (Currently Being Worked On...)
    • Scale Tag
      • Create <Scale> Tag
      • Write Test for the Scale Tag
    • Rotate Tag
      • Create <Rotate> Tag
      • Write Test for the Rotate Tag
    • Transform Tag
      • Create <Transform> Tag
      • Write Test for Transform Tag
    • Update Wiki Site to reflect Above Changes

Possible Ideas For Future Iterations

  • Iteration 5?: Extending 2D Functionality to Join 2D Primitives
    • Create <path> Grouping Tag to create line Joins
    • Create <curve> Tag for different types of curves
    • Update Wiki Site to reflect Above Changes

SVN Repository

  • svn://zenit.senecac.on.ca/bts630_071r7

References Used

Mozilla Wiki Main Page
Official Canvas 3D Wiki
Canvas 2D Reference
Canvas 3D Reference

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