Lost in time and space...

       I’ve been programming games for quite some time now. Every time I build a new game, there are many elements that keeps repeating … character behaviors like movement, jumping, ducking, chasing target etc. I know there are many game development suite that comes with many built in features & defining a character & behavior is rather very easy there … But (and its an important But! ) they come at a very high price, and there’s other problem of integrating with your code.  So, I decided to build a mini-framework that would help me out with the mundane tasks (not to mention that I really got the kick out of this :) ).  Here’s a simplistic view of the design approach (not all classes are included):  


Next, I implemented XML serialization/de-serialization of above model. Here’s a Mario Character definition that worked for me:
Example 1: Mario

<?xml version="1.0" encoding="utf-8"?>
<SpriteXMLParser xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://tempuri.org/XMLSchema.xsd">
  <Identity>
    <Name>Mario</Name>
    <Group>Ram.Test</Group>
    <Version>0.0.0.1</Version>
    <Author>Ram Adhikari</Author>
    <DateOfCreation>2009-04-28</DateOfCreation>
  </Identity>
  <States startState="NORMAL">
    <State id="NORMAL">
      <!-- NOTE: State ids are case sensitive,
      Omitted other attributes because of lack of space -->
      <Draw contentPath="mario-standingImage" />
    </State>
    <State id="STANDING">
      <Draw contentPath="mario-standingImage" />
    </State>
    <State id="DUCK">
      <Draw contentPath="mario-duckImage" />
    </State>
    <State id="RAISE-HAND">
      <Draw contentPath="mario-raise-handImage" />
    </State>
    <State id="RUN1">
      <Draw contentPath="mario-running-1Image" />
    </State>
    <State id="RUN2">
      <Draw contentPath="mario-running-2Image" />
    </State>
    <State id="LEFT_RUN1">
      <Draw contentPath="mario-running-1Image" />
    </State>
    <State id="LEFT_RUN2">
      <Draw contentPath="mario-running-2Image" />
    </State>
    <State id="INVISIBLE" />
  </States>
  <Transitions>
    <Transition fromStateId="NORMAL" toStateId="STANDING" onInput="mouse.in-click" />
    <Transition fromStateId="STANDING" toStateId="NORMAL" onInput="mouse.out-click" />
    <Transition fromStateId="STANDING" toStateId="INVISIBLE" onInput="keys.Escape" />
    <Transition fromStateId="STANDING" toStateId="RUN1" onInput="keys.Right" />
    <Transition fromStateId="STANDING" toStateId="LEFT_RUN1" onInput="keys.Left" />
    <Transition fromStateId="STANDING" toStateId="DUCK" onInput="keys.Down" />
    <Transition fromStateId="STANDING" toStateId="RAISE-HAND" onInput="keys.Up" />

    <Transition fromStateId="INVISIBLE" toStateId="STANDING" onInput="keys.S" />
    <Transition fromStateId="RUN1" toStateId="NORMAL" onInput="mouse.out-click" />
    <Transition fromStateId="RUN1" toStateId="RUN2" onInput="keys.Right" />
    <Transition fromStateId="RUN1" toStateId="STANDING" onInput="keys.Left" />

    <Transition fromStateId="RUN2" toStateId="NORMAL" onInput="mouse.out-click" />
    <Transition fromStateId="RUN2" toStateId="RUN1" onInput="keys.Right" />
    <Transition fromStateId="RUN2" toStateId="STANDING" onInput="keys.Left" />

    <Transition fromStateId="LEFT_RUN1" toStateId="NORMAL" onInput="mouse.out-click" />
    <Transition fromStateId="LEFT_RUN1" toStateId="LEFT_RUN2" onInput="keys.Left" />
    <Transition fromStateId="LEFT_RUN1" toStateId="STANDING" onInput="keys.Right" />

    <Transition fromStateId="LEFT_RUN2" toStateId="NORMAL" onInput="mouse.out-click" />
    <Transition fromStateId="LEFT_RUN2" toStateId="LEFT_RUN1" onInput="keys.Left" />
    <Transition fromStateId="RUN2" toStateId="STANDING" onInput="keys.Right" />

    <Transition fromStateId="DUCK" toStateId="NORMAL" onInput="mouse.out-click" />
    <Transition fromStateId="DUCK" toStateId="STANDING" onInput="keys.Up" />

    <Transition fromStateId="RAISE-HAND" toStateId="NORMAL" onInput="mouse.out-click" />
    <Transition fromStateId="RAISE-HAND" toStateId="STANDING" onInput="keys.Down" />

  </Transitions>
</SpriteXMLParser>

Now, it will be foolish to assume that such a simple model will work for every game character definition. So, what I do is to generate the class definition of a character from the XML (this reduces a lot of effort) & do the customization. It generate the boiler code for handling input (specific to the character) & state management.

# posted by Ram Adhikari @ 4:36 AM