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-= The Scene Graph and Other jME3 Terminology
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-:revnumber: 2.0
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-:revdate: 2020/07/13
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-:keywords: spatial, node, mesh, geometry, scenegraph, rootnode
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-Before you start making games, make sure you understand general xref:tutorials:concepts/terminology.adoc[3D Graphics terminology].
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-Second, if you are a beginner, we recommend our xref:tutorials:concepts/scenegraph_for_dummies.adoc[Scene Graph for Dummies] presentation for a visual introduction to the concept of a scene graph.
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-Then continue learning about jME3 concepts here.
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-== Coordinate System
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-[.right]
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-image::tutorials:concepts/coordinate-system.png[coordinate-system.png,width="235",height="210",align="right"]
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-The jMonkeyEngine uses a right-handed coordinate system, just as OpenGL does.
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-The coordinate system consists of:
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-* The _origin_, a single central point in space.
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-** The origin point is always at coordinate zero, in Java: `new Vector3f(0,0,0)`.
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-* Three _coordinate axes_ that are mutually perpendicular, and meet in the origin.
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-** The X axis starts left and goes right.
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-** The Y axis starts below and goes up.
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-** The Z axis starts away from you, and goes towards you.
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-Every point in 3D space is uniquely defined by its X,Y,Z coordinates. The three numeric coordinates express how many "`steps`" from each of the three axes a point is. The data type for all vectors in jME3 is `com.jme3.math.Vector3f`. All vectors are relative to the described coordinate system. +
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-Example: The point `new Vector3f(3,-5,1)` is 3 steps to the right, 5 steps down, and 1 towards you.
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-[NOTE]
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-====
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-The unit of meassurement ("`one`" step) in jME3 is the *world unit*, short: wu. Typically, 1 wu is considered to be one meter. As long as you are consistant throughout your game, 1 wu can be any distance you like.
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-====
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-For your orientation:
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-* The default camera's location is `Vector3f(0.0f, 0.0f, 10.0f)`.
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-* The default camera is looking in the direction described by the (so called) negative Z unit vector `Vector3f(0.0f, 0.0f, -1.0f)`.
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-This means the player's point of view is on the positive side of the Z axis, looking back, towards the origin, down the Z axis.
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-== How to move yourself through the 3D scene
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-When you play a 3D game, you typically want to navigate the 3D scene. Note that by default, the mouse pointer is invisible, and the mouse is set up to control the camera rotation!
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-By default, jME3 uses the following common navigation inputs
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-[cols="3", options="header"]
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-|===
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-a| Game Inputs
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-a| Camera Motion
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-a| Player POV
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-a|Press the W and S keys
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-a|move the camera forward, and backward
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-a|you walk back and forth
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-a|Press the A and D keys
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-a|move the camera left and right
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-a|you step left or right
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-a|Press the Q and Y keys
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-a|move the camera up and down
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-a|you fly up and down
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-a|Move the mouse left-right
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-a|rotate the camera left/right
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-a|you look left or right
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-a|Move the mouse forwards-backwards
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-a|rotate up/down
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-a|you look at the sky or your feet
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-|===
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-These default settings are called "`WASD`" keys and "`Mouse`" Look. You can customize xref:core:input/input_handling.adoc[input handling] for your game. Sorry, but these settings work best on a QWERTY/QWERTZ keyboard.
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-== Scene Graph and RootNode
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-The _scene graph_ represents your 3D world. Objects in the jME3 scene graph are called xref:jme3/advanced/spatial.adoc[Spatial]s. Everything attached to the parent _rootNode_ is part of your scene. Your game inherits the `rootNode` object from the `SimpleApplication` class.
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-image::tutorials:concepts/scene-graph.png[scene-graph.png,width="",height="",align="center"]
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-* _Attaching_ a Spatial to the rootNode (or its child nodes) adds it to the scene;
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-* _Detaching_ a Spatial from the rootNode (or its child nodes) removes it from the scene.
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-All objects in the scene graph are in a parent-child relationship. When you transform (move, rotate, scale) one parent, all its children follow.
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-[NOTE]
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-====
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-The scene graph only manages the parent-child relationship of spatials. The actual location, rotation, or scale of an object is stored inside each Spatial.
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-====
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-== Spatials: Node vs Geometry
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-A Spatial can be transformed (in other words, it has a location, a rotation, and a scale). A Spatial can be loaded and saved as a .3jo file. There are two types of Spatials, _Node_ and _Geometry_:
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-[cols="10,45,45", options="header"]
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-|===
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-<a|
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-2+a| Spatial
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-a| Purpose:
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-2+a| A Spatial is an abstract data structure that stores transformations (translation, rotation, scale).
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-<a|
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-a| Geometry
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-a| Node
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-a| Visibility:
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-a| A visible 3-D object.
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-a| An invisible "`handle`" for a group of objects.
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-a| Purpose:
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-a| A Geometry represents the "`look`" of an object: Shape, color, texture, opacity/transparency.
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-a| A Node groups Geometries and other Nodes together: You transform a Node to affect all attached Nodes (parent-child relationship).
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-a| Content:
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-a| Transformations, mesh, material.
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-a| Transformations. No mesh, no material.
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-a| Examples:
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-a| A box, a sphere, player, a building, a piece of terrain, a vehicle, missiles, NPCs, etc…
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-a| The rootNode, the guiNode, an audioNode, a custom grouping node for a vehicle plus its passengers, etc.
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-|===
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-== How to Use This Knowledge?
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-Before you start creating your game, you should plan your scene graph: Which Nodes and Geometries will you need? Complete the xref:tutorials:beginner/beginner.adoc[Beginner tutorials] to learn how to load and create Spatials, how to lay out a scene by attaching, detaching, and transforming Spatials, and how to add interaction and effects to a game.
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-//The <<jme3#documentation-for-intermediate-users#,intermediate and advanced documentation>> gives you more details on how to put all the parts together to create an awesome 3D game in Java!
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-== See also
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-* xref:jme3/advanced/spatial.adoc[Spatial] – More details about working with Nodes and Geometries
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-* xref:jme3/advanced/traverse_scenegraph.adoc[Traverse SceneGraph] – Find any Node or Geometry in the scenegraph.
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-* xref:jme3/advanced/camera.adoc[Camera] – Learn more about the Camera in the scene.
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mitm001