History: Ogre Internals Dissection FAQ

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!    answers :
!   1.  ROOT - THE OBLIGATORY CLASS/ OBJECT.
     
     
     
!!  1a. Why do I have to allocate root on heap, and not on stack ?
    That is why I do have to write
     
{CODE(wrap="1", colors="c++")}        Root *root = new Root();{CODE}
     
    and not just :
     
{CODE(wrap="1", colors="c++")}        Root root = Root();{CODE}
     
    ?
    A:
    Well, devel sindbad often holds root inside a manager class so Root gets constructed as soon as the manager is. So it actually becomes:
     
     
     
{CODE(wrap="1", colors="c++")}        class SomeManager
        {
        protected:
            Ogre::Root mOgreRoot;
        ...
        }{CODE}
     
     
     
    You might construct Root like that in your entry point Before the frame loop
    is kicked off. When using the RAII technique ( that is what this snippet does )
    you must just watch out that mOgreRoot won't be popped off from stack while the
    app is running. This is hard to do with the RAII, as with that the function
    call frames are deleted in the order opposite to how they were put onto the stack -- that
    is the 'newest ' call frame first, but when using say threading the things
    get more complicated... ( note : This is actually the same consideration as making sure you
    don't call 'delete mOgreeRootPointer' during the program's main loop.)
     
     
     
    Thus there really isn't a concrete need to manage Root using new/delete, although you can if you want.
     
!!  1b. How to create similar class with getSingleton() method ?
     
    This pattern is called Singleton :
    http://en.wikipedia.org/wiki/Singleton_pattern
     
    Deriving from Ogre::Singleton is merely a matter of doing this:
     
{CODE(wrap="1", colors="c++")}        MyAwesomeClass :: public Ogre::Singleton<MyAwesomeClass>
        {
        //code omitted - obviously
        };
     
    And in the implementation file:
     
        template<> MyAwesomeClass* Ogre::Singleton<MyAwesomeClass>::ms_Singleton = 0;{CODE}
     
    The Ogre3d's Singleton has been written by Scott Bilas, here's his blog entry
    discussing similar Singleton variant :
    http://scottbilas.com/publications/gem-singleton/ .
     
     
!!    1b2. I need more than one window for my app, can I create more than one root object for that purpose ?
     
    Two instances of root  is not possible/recommend/supported.
    (M)Ogre uses Singletons, that is one instance of the object in the same
    application context) e.g. TextureManager, MeshManager and of course
    Ogre::Root, creating  -> the second created root will "override" the first one.
     
     
!!  1b3. Can I run  Ogre3d without actually initializing root ? What functions I do have at hand then ?
     
!!  1b4. But I have read the tutorial and source SDK , the root is created nowhere    !!
     
    Most of the tutorials use the ExampleApplication framework, which does a lot of behind-the-scenes stuff, including the creation of the root.
     
!!  1c. Ogre::Root::initialise fails -- the most common causes.
     
!!  1d. Explicit 'delete root' causes application crash.
     
    The most possible cause is : your application must have had deleted root
    explictly or implicitly before your 'delete root' .
     
!!  1d2. Explicit 'root->shutdown()' causes application crash.
     
!!  1d3.Ways of properly shouting down the Ogre3d without leaking the resources.
     
!!  1e. Ogre::Root extra parametes
     
!!  1e2. Example Window without borders.
     
     
    First assign a value of "none" to misc["Border"]
    Next, make sure that when you initialise Ogre, you tell it NOT to create a default window. (pass false as the first param)
    Then, create a render window, and assign it to the "window" member variable of your application.
     
{CODE(wrap="1", colors="c++")}        // create some custom attributes for our manually created window
     
        Ogre::NameValuePairList misc;
        misc["border"] = "none";
        misc["monitorIndex"] = "0";  //I use two monitors, so I tell Ogre to draw on my main (#1) monitor
     
        // Here we tell the system not to create a default rendering window by passing 'false'
     
        mWindow = mRoot->initialise(false, "BasicTutorial7 Render Window");
     
        //now we need to create a render window manually
        //for now, the dimensions are hardcoded to MY desktop size so the window LOOKS full screen
     
        mWindow = mRoot->createRenderWindow("BasicTutorial7 Render Window",1680,1050,false, &misc ); //pass our custom attributes in "misc"{CODE}
     
!!  1f. root->showConfigDialog displays an empty window.
     
First you might not have the plugins.cfg file present in your exec's directory . The error message might be quite cryptic though -- the last message being some problems with GUI library , and the one about missing plugins.cfg is mysteriously hidden ... 
{QUOTE(replyto="Ogre.log")}./plugins.cfg not found, automatic plugin loading disabled.
*-*-* OGRE Initialising
*-*-* Version 1.9.0 (Ghadamon)
Creating resource group GUI
Added resource location './/gui' of type 'FileSystem' to resource group 'GUI' with recursive option
Added resource location './/gui/schemas' of type 'FileSystem' to resource group 'GUI' with recursive option
Creating resource group Graphics
Added resource location './/materials/RTShaderLib' of type 'FileSystem' to resource group 'Graphics' with recursive option
Added resource location './/materials/RTShaderLib/materials' of type 'FileSystem' to resource group 'Graphics' with recursive option
Added resource location './/materials/RTShaderLib/GLSL' of type 'FileSystem' to resource group 'Graphics' with recursive option
Added resource location './/materials/RTShaderLib/Cg' of type 'FileSystem' to resource group 'Graphics' with recursive option
Added resource location './/materials/scripts' of type 'FileSystem' to resource group 'Graphics' with recursive option
Added resource location './/materials/textures' of type 'FileSystem' to resource group 'Graphics' with recursive option
Added resource location './/models' of type 'FileSystem' to resource group 'Graphics' with recursive option
Creating resource group Music
Added resource location './/music' of type 'FileSystem' to resource group 'Music' with recursive option
Creating resource group Sound
Added resource location './/sounds' of type 'FileSystem' to resource group 'Sound' with recursive option
Error: Shell widget menu has zero width and/or height{QUOTE}

If you have none plugins.cfg create one ; at least should be there :
{QUOTE(replyto="plugins.cfg")}# Define plugin folder
 PluginFolder=/usr/lib/OGRE{QUOTE}

and if you have there a file say RenderSystem_GL.so ( or with longer multiply extensions [ as on Unixes* ] ) just paste the filename there: 

{QUOTE(replyto="plugins.cfg")}Plugin=RenderSystem_GL{QUOTE}

When everythings fine you should see in the Ogre.log ( or any other file you log into ) as well in terminal ( iff called from terminal ) : 
{QUOTE(replyto="Ogre.log")}16:16:19: Loading library /usr/lib/OGRE/RenderSystem_GL
16:16:19: Installing plugin: GL RenderSystem
16:16:19: OpenGL Rendering Subsystem created.
16:16:19: Plugin successfully installed{QUOTE}

!! 1g. What are Root's important containers I would have to modify through it's methods ?  ( 
!! Diagram and Schemes. 

!! 1g. How the life cycle of handling FrameListeners look like ? ( Diagram or Scheme ) 

{IMG(src="tiki-download_file.php?fileId=2201&amp;display",button="y",height="80%",width="80%")}{IMG}

!   2. RESOURCES, MATERIALS, AND RESOURCES' MANAGMENT

!!  2a. Do I need to use the Resource, ResouceManagers schemes ?
!!  2a2. Can I make my game without this mechanism ?
     
!!  2b. Why does my object display as white (or black) in Ogre?
!!  2b2. Why does my resource creation or load fail in strange ways?
!!  2b3. What is the Ogre::Resource's typical lifecycle ( diagram or scheme ) ?
     {IMG(src="tiki-download_file.php?fileId=2200&amp;display")}{IMG}
!!  2b4. What are usual methods of managing this lifecycle ?
See the Legend in the picture above ... 
!!  2b5. Why is OgreCore.zip missing?
     
!!  2c. Why it only service small part of assets' types needed to create game (e.g. no music , sound files , no third party data ).
!!  2c2. How do I extend that mechanism for all assets in my game ?
!!  2c3. How do I write my own Resource type ?
!!  2c4. How do I write my own Resource manager ?

!   3.  SCENEMANAGERS AND SCENENODES
!!  3a. Is it necessary to use them in my game ? 
The scene manager is the primary part of ogre that deals with rendering the user's scene. It handles the creation and destruction of most classes (cameras, lights, renderables, etc). While it's possible to access Ogre's lower level render systems directly, that's not really recommended and isn't documented.
SceneNodes are needed because they hold the transform data for objects, are used for visibility culling and are the way that the scene manager knows which objects to render (anything that isn't attached to a scene node isn't part of the scene, so won't be drawn).
Well, mostly. Certain things don't need scene nodes. In Ogre 1.9 and below, cameras, static geometry and lights don't need scene nodes. They are still part of the scene manager though. In Ogre 2.0, things are a little different. Cameras get added to the root scene node automatically. Static geometry is done with static scene nodes and static entities. I think lights work the same though (not sure).

!!  3b. How it generally work  ? 
!!  3b2. There seems to be very little transformations types, why so ? 
It depends on what you exactly mean by transform types. In the 3D computer graphics special kind of transformations is studied with a special care -- Affine_transformation [http://en.wikipedia.org/wiki/Affine_transformation|http://en.wikipedia.org/wiki/Affine_transformation] , that is most of the "most necessary" operations are derived from it, also from almost two decades the graphical PC hardware is geared toward the fastest processing of that family of operations. 
As to Ogre3d: It supports translation, scale and orientation in the transform of a scene node. The only other transform type that other engines might typically support is skew. Ogre doesn't support skew itself, but it can be done inside of a vertex shader. 3 out of 4 isn't really "very little".

!!  3b3. What is the order of visiting the SceneNodes tree graph ? Where does it happen in code ? 
!!  3c. Can I have more than one Entiety to a SceneNode attached ? 

You can have as many renderable objects of any type attached to one scene node. They will all share the same local origin however, as things like entities have no concept of world transforms, the scene node does that for them.

!!  3d. Can I create cycles in the Ogre3d graph ? 

The Ogre scene manager uses a directed acyclic tree.

!!  3e. Can I prevent from inheriting any property from parent to child ? 

The node class has setInheritOrientation() and setInheritScale() methods. These let you enable or disable inheriting those two properties from a parent node. There is no direct position equivalent (you can just use a second scene node instead).

!!  3e2. I have two nodes which ain't parent/child related yet I would like two of them to share one of the properties. 

If a parent-child relation is no option for you, then you are stuck with handling it yourself by either:

a) Keeping track of all changes of the node you want to follow yourself

b) Using an Ogre::Node::Listener that you can attach to the node you want to track (the "parent") and the once an update event is fired, you update the tracking ("child") node as well:

API: Ogre::Scenenode::setListener()
API: Ogre::Node::Listener::nodeUpated()


!!  3f. When I attach / detach a node then the Ogre3d seems to have delays. Why is it so ? Can I improve that ?