One of the audience offered to record the session remotely so the audio is a little scratchy, but I think it’s come across ok.

The talk covers:

• IMML
• VastScript
• Network enabled elements
• HTML interop
• Video
• Audio
• Textures
• User Profiles
• Plugins

Hopefully this is a useful primer if you are interested in developing with VastPark or are curious to know a little more about the way the system functions.

Download the PDF shown in the video here: VastPark Developer Introduction - Framework v1.3

Many months ago during May of 09, after meeting Ian Hughes at FCVW, I came across an interesting post on his blog discussing an implementation of the flocking algorithm in Unity.

I’d not heard of the term flocking or boids, so proceeded to get stuck into some research, which lead me to Conrad Parker’s page on Boids Pseudocode as well as many others who had implemented the algorithm, I figured it would be a fun little plugin to write for VastPark so gave it a try.

Implementing the algorithm

Thinking about what was required, I came up with the following as the plan for the plugin:

• Any IPositionalElement (Model, Primitive, Sound, Camera, Light, etc) would be supported
• Implement Rule 1 – “Boids try to fly towards the centre of mass of neighbouring boids”
• Implement Rule 2 – “Boids try to keep a small distance away from other objects (including other boids)”
• Implement Rule 3 – “Boids try to match velocity with near boids”
• For bonus points I’d implement “Tendency towards a particular place”, “Limiting the speed”, “Bounding the position”, “Perching” and “Scattering the flock”

In terms of the plugin this translates into these properties:

• SmallDistance
• MaxVelocity
• MinVelocity
• EnableBounds
• MaxBounds
• MinBounds
• EnablePerching
• MinPerchTime
• MaxPerchTime
• PerceivedCentre (get only)

The following callbacks:

• ElementPerched
• ElementLeftPerch

The following methods:

• SetPointOfInterest
• AddPlaceToAvoid
• AddPerch
• Scatter

The class diagrams look like this:

How does it work?

Put quite simply, the plugin works like this:

• AddElement(ImmlElement element) creates a boid instance for the positional element passed
• The plugin Update method (called once each update by the VastPark framework) proceeds to calculate the rules, one at a time for each boid to work out the new velocity and position for the element it represents
• Scatter requests made during runtime are dealt with during the next update

Downloads

Here is some sample IMML and the source code to the plugin, enjoy! Let me know if you decide to implement any of the other rules or do something cool with it

Sample IMML: flocking.imml
Source code to plugin: Plugin.Flocking.zip

Note: The source code will probably complain about some missing references. Install the Player from www.vastpark.com and link against the relevant binaries included with it.

To try drag and drop out for yourself, first download generic-drag-drop-sample.imml (right-click, save as) and open in the Player.

Next, you’ll need to expand the Items list. Do so by clicking on this icon:

By default you are presented with the list of Items of type Video and Document that the currently logged in account has access to (these can be further restricted by the hosting server’s group ACL).

In this case as we are opening the file directly, it will default to showing the most recently published Items without filtering and should look similar to this:

Click to select one of the items from the list (in my example, I’ve chosen “VastPark Logo”) and drag it onto the 3D view. The large rectangle in the centre of the screen will change colour to blue indicating it is a drop target.

Next, drop the Item onto the blue rectangle, which will cause it to change colour to green. Shortly the VastPark logo will appear on it.

How does this work?

Behind the scenes is a plugin (called MetaforikAdapter) which currently supports adapting Items of type “Document” and “Video” to a Model or Primitive element. The code to do this is quite simple.

First, reference the Plugin:

<Plugin Enabled="True" Source="http://id.vastpark.com/VastParkWS/get.vpws?name=MetaforikAdapter&amp;publisher=craigomatic&amp;domain=vastpark&amp;context=park" Name="MetaforikAdapter">
    <Element Name="InvalidRequestHandler" />
    <Parameter Key="InvalidRequestEvent" Value="InvalidRequestHandler" />    
  </Plugin>   
  
  <Script Name="InvalidRequestHandler">
    function main(obj, args)
      scene.ui:writeline('invalid request')          
    end
  </Script>

<Trigger Event="DragDrop" Target="OnDragDrop" />
<Trigger Event="DragEnter" Target="OnDragEnter" />
<Trigger Event="DragLeave" Target="OnDragLeave" />

In you script for the drop, pass the Item along with the element you want to adapt it to into the load method on the plugin. You may choose to inspect the Item before the drop to give user feedback as is done in the sample IMML.

<Script Name="OnDragDrop">
    function main(obj, args)            
      --args.data contains the Item which was dragged in
      
      --load returns a controller object
      c = metaforikadapter:load(args.data, obj)      
    
      scene.ui:writeline('item name: '..c.item.name)
      scene.ui:writeline('id: '..c.id)
      scene.ui:writeline('is first: '..tostring(c.isfirst))
      scene.ui:writeline('is last: '..tostring(c.islast))
      scene.ui:writeline('total pages: '..tostring(c.pages))
      scene.ui:writeline('current page: '..tostring(c.currentpage))
    end
</Script>
  
<Script Name="OnDragEnter">
    function main(obj, args)
        scene.ui:writeline('drag enter on: '..obj.name..' of type: '..args.data.assets[0].type)     
    end
</Script>
  
<Script Name="OnDragLeave">
    function main(obj, args)
      scene.ui:writeline('drag leave on: '..obj.name)
    end
</Script>

Working with elements other than Document or Video

One thing to be aware of is that you don’t necessarily have to use the MetaforikAdapter plugin to benefit from drag and drop. If you want to allow for models or sounds to be dropped in, you can use the item.updateuri as the source for the element and add it into the scene, like this:

<Script Name="OnDragDrop">
    function main(obj, args)    
      item = args.data
      if(item.assets[0].type == 'Model') then       
          m = model()
          m.source = args.data.updateuri
      
          scene:add(m)     
      end
    end
</Script>

Final Note

That’s really all there is to it, you may want to craft different UI depending on the state of the controller properties in the MetaforikAdapter plugin sample, ie: to handle a multi-page document differently to a video or single page document, or in the model example to only allow certain users to drop models into a specific region of your space.

If you haven’t already read the original article and are interested in how it works, be sure to have a read before continuing.

Define Element

The Define element is a declarative way of expressing a variable in IMML. It’s equivalent to doing element:set(‘variableName’, variableValue) but doesn’t require interpretation via the scripting engine which results in much better performance. It’s also a much nicer way to store global variables as they can be placed in more a easily identifiable location in the IMML rather than being buried within a script.

My Define in the sample looks similar to this (truncated for brevity):

<!--Use any Yahoo stock codes in the below define to control the stocks being generated and updated-->
 <Define Key="stocks" Value="IPL.AX,VIL.AX,FMG.AX,RIO.AX,BHP.AX,BOQ.AX" />

To change the ticker to show different stocks, replace any of the entries in the Value of the Define with the appropriate Yahoo ticker code for the relevant stock.

Tooltip Plugin

Note: To use the Tooltip plugin, you’ll need to be running either the most recent Player snapshot or version 0.98+ as it uses the Handle property that was added recently to the IRenderEngine interface.

The tooltip concept has been around for quite a while and is used by just about every modern desktop application. Ever wondered what that big red button does and hovered your mouse to find out? If yes, you’ve seen a tooltip. This plugin extends the concept to allow developers to associate a tip with an element in world.

To do so is quite simple, the following functions are provided with the plugin:

int Add(string text, ImmlElement element)
void Remove(int id)
void SetText(int id, string text)

To make use of these, I’ve added 2 lines to _updateStock in the UpdateStocks script:

--update the volume tooltip	
id = lastTradeVisual:get('tooltipId')
tooltipplugin:settext(id, 'Volume: '..volume)

…and 3 lines to _generateStock in the GenerateStocks script:

--store a define value on the last trade to represent volume for the tooltip
lastTradePrim:set('volume', volume)
id = tooltipplugin:add('Volume: '..volume, lastTradePrim)
lastTradePrim:set('tooltipId', id)

The end result still looks similar to before, but we now get tooltips when hovering:

Download the updated IMML here: stock-ticker.imml

Here’s a teaser:

Vastpark Facial Expressions Demo from VastPark on Vimeo.

Virtual Worlds Down Under – Part 4 of 4 – Masterclass 2 from VastPark on Vimeo.