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DHTML Target

From OpenLaszlo

This is a working page of issues for the DHTML target.

Contents

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Definition Issues

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Media

The OpenLaszlo platform accepts Flash (swf) files at both compile-time and runtime. Flash files are used to present vector graphics, authored animations, and to wrap video and audio files.

The Flash file format satisfies these requirements:

  • Designer-friendly authoring tool
  • Stroked and filled paths
  • Linear and radial gradients
  • Lossy and lossless images
  • Hairlines
  • Multiframe animation
  • Synchronized audio

We need to decide which of these features are supported in OpenLaszlo:DHTML. In particular, hairlines and stretchy gradients are common design features; are they supported in DHTML?

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Proxied Mode

Does OpenLaszlo:DHTML support proxied mode?

  • XMLHTTPRequest security schemes may require server proxying
    • Can be worked around with JASON, a <script> tag can load from anywhere



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Implementation Issues

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Prototype Chain

IE does not support prototype chaining. There is no @__proto__@, and there is no @constructor@ for @super@. We need to figure out how to compile classes and constructors for this platform.

This has been solved by using Douglas Crockford's strategy for implementing class-based inheritance in JavaScript.

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Views

Each view V compiles to a <div>, that contains V's child views.

Issues:

  • Is clip=false possible? Does this require layers?
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Layout

Views can be positioned using CSS position: absolute; margin-left: x; margin-top: y.

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Animation

  • A global variable stores a list of animation records.
  • LzNode.animate() adds a record to this list.
  • When an animation is added to the list and it was empty, call doAnimations().
  • doAnimations() steps through the animation list, executing animations and removing animations which have expired. If the list is empty when it ends, it invokes setTimeout(doAnimations, xxx).
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Media Requests

DOM manipulation of the background property of a view's style.

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Data Requests

HTTPDataRequest.

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Data Binding

This is requires:

  • A runtime XML DOM representation
  • An XPath implementation that executes against that DOM
  • A procedural interface for instantiating views

All of these seem easy.

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Constraints

Use the existing compiler mechanism to build dependency functions for constraints, and port the event notification mechanism.

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CSS

How should we use browser CSS support - clientside/serverside, roll our own, browser/DHTML or a combination the two?

Notes on FlashMX CSS support - Example of CSS in Flash

  • RUNTIME SUPPORT
    • multiple CSS styles can apply to different parts of text
    • CSS can be external or programmatically generated
    • only applies to HTML text in TextFields - p, b, li, a, a:link, a:hover, a:active, user-defined tags, classes
  • COMPONENT SUPPORT
    • v2 Components can use styles to adjust colors and text
    • the following components are styleable - Alert, DataGrid, List, Menu, SimpleButton, TextArea, TextInput, Tree
  • NOTES
    • CSS is not supported in Flash Lite
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Performance Issues

  • What is the performance of a page that contains large number of absolutely positioned divs?
  • What is startup time for an application that links in a large runtime library?
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