[OOP] Mother-of-all-objects with children (TList)
BlitzMax Forums/BlitzMax Programming/[OOP] Mother-of-all-objects with children (TList)
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| I am struggling with a OOP concept of father-child relations in BliztMax. All of this must be done in a OOP way. For the purpose of portability the code must be strict adhering to C#/Java conventions. The only way i think thats possible is to have a father-child relation, with one object being the father of all other objects (using a TList). Anyone who has done a bit of M$ Excel programming will know what i talk about. In Excel you instantiae an Excel Appinstance, then add worksheeets to it, and worksheets have rows, cells etc. So in a way one can trace from one worksheet to another by object model, for example to retrieve data from one sheet to another or to compare values etc etc. Basically what i want to do (for a game) is: * Instantiate a Father object which has as only a TList property. * Add all other objects to Father (ships, missiles, starfield). My problem is: i need some help on doing it. Here is a practical example: 1. Instantiate Father object. 2. Instantiate a TMain object. 3. Add the object to Father. 4. Do a TMain.GetTheShowOnTheRoad() method. The idea is then that a alien (object) can have a bullet (object), which is all ofcourse to be traced back right to Father. Also, alien could add powerup, and powerup can add defenceshield object. Ultimitley defenceshield belongs to alien. In this OOP way i could remove defenceshield then add it to player ship. You get what i mean? Does any1 have a small example for me?? I'd really appreciate your help! Is this way of doing working with father-child too complicated? I wanna make a basic framework which will bebefit in the long run. Whats your opinion? here is an example of what i try to do:
Strict
Local objStart:TMain = New TMain;
objStart.Main();
'#Region AppInstance moeder van alle Objecten
Type TAppInstance
Global AppInstance:TList;
End Type
'#EndRegion
'#Region TMain
Type TMain Extends TAppInstance
Global objGameObjectsList:TList;
Global ScreenWidth:Int;
Global ScreenHeight:Int;
Method Main()
ShowMouse();
objGameObjectsList = new TList();
Local objMain:TMain = New TMain;
Local intSterretjeTeller:Int;
Local objAlien1:TAlien = new TAlien;
objGameObjectsList.AddLast(objAlien1)
End Method
End Type
Is the above coorect to implement the M$ Excel-objectmodel idea? TIA! |
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| Type thing field parent:thing field children:tList=new tList EndType Function CreateThing(parent:thing=null) t:thing=new thing t.parent=parent if parent parent.children.addlast t endif return t EndFunction |
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| Im using the same in my current OpenGL project. Each Entity has a Parent and a Tlist of Children. That way you can find any entity through a child/parent relationship. Keep in mind though that TList does not allow Indexing like an array. so doing World.Stuffs[1].Name. will not work. You will have to create a GetChild() method that loops through the children and searches for the child you want by index or name.
Type World
global Origin:Entity '// Pointer to the very topmost Entity
Method New()
if( Origin = null ) then Origin = new Entity;
End Method
End type
type Entity
Field Parent:Entity;
Field Children:TList;
Field Name:String;
Method New()
Parent = null;
Children = new TList;
Name = "";
End Method
Function Create:Entity( parent:Entity = null, name:string = "" )
Local e:Entity = new Entity
if( parent <> null ) then
e.SetParent( parent );
end if
e.Name = name;
return e;
End Function
Method AddChild( child:Entity )
If( Not Children.Contains( child ) ) Then
child.Parent = Self;
Children.AddFirst( child );
End If
End Method
Method RemoveChild( child:Entity )
If( Children.Contains( child ) ) Then
child.Parent = null;
Children.Remove( child );
End If
End Method
Method IsChild( e:Entity )
return Children.Contains( e );
End Method
Method SetParent( p:entity )
'// we allready have a parent?
if( Parent <> null) then
Parent.RemoveChild( Self );
end if
Parent = p;
Parent.AddChild( Self );
End Method
Method GetChild:Entity( index:int )
if( index < 0 Or index >= Children.Count() ) then
'// Index is out of Bounds.
return null;
end if
return Entity( Children.ValueAtIndex( index ) );
end method
end type
local world:World = new World;
local A:Entity = Entity.Create( world.Origin, "A" );
local B:Entity = Entity.Create( A, "B" );
Local C:Entity = Entity.Create( B, "C" );
'// print Enity C's name using parent/child relationship
Print( world.Origin.GetChild(0).GetChild(0).GetChild(0).Name );
That should give you an idea of how it works with TLists. You can make it easier on yourself by using static Array's instead of TLists. It will make the Indexing easier, but extending the Array's when a new Child is added is a pain. The above should suit you fine. It is important that you dont assign a parent to an entity by simply doing :myEntity.Parent = OtherEntity; If you do this, you will not have updated the parent's child lists. So make sure you use myEntity.SetParent( .. ) method to do so. Note: there may be some small bugs, as I didnt test this code in Bmx. But the idea should work. |
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| And another thing. If you ever get to do 3D stuff and you happen to store/link your Mesh data directly to an Object of type Entity, then I would suggest to also keep a Global List of all Entities; Next to the parent/child structure. This will be needed to sort the entities' By drawing order. Just looping through them from the Origin and iterate through each child will cause problems when you are trying to render them to the screen. As some Entities way down in the chain may be required to render Before an entity somewhere High up the chain (Z-ordering and all that). But this isnt really related to your problem so i'll shut up now :) |
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| forgive me for budding in... and i'm not gonna pretend to understand exactly everything it is that you are trying to accomplish here, but from what little i did read, it appears to me that you are approaching this a lil inside out... or backend first... whatever... i would define a linked list class as a base class, then derive the game object class from that... this way, everything in the game would be capable of linking to it's parent and children automatically... if you can... take a look at pages 710 and 714 of OpenGL Game Programming by Hawkins, Aste, LaMotthe... this sort of relationship and structure is clearly explained in a few really brief paragraphs... good luck... --Mike |
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| You only to z-order your objects that have a material applied to them that uses a blend mode. |
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| I'm not sure if it's exactly what youre looking for but... http://www.blitzbasic.com/Community/posts.php?topic=59589 Maybe it'll give you an idea or 2. |
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