|
|
@@ -0,0 +1,155 @@
|
|
|
+= The Scene Graph and Other jME3 Terminology
|
|
|
+:revnumber: 2.0
|
|
|
+:revdate: 2020/07/13
|
|
|
+:keywords: spatial, node, mesh, geometry, scenegraph, rootnode
|
|
|
+
|
|
|
+
|
|
|
+Before you start making games, make sure you understand general xref:tutorials:concepts/terminology.adoc[3D Graphics terminology].
|
|
|
+
|
|
|
+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.
|
|
|
+
|
|
|
+Then continue learning about jME3 concepts here.
|
|
|
+
|
|
|
+
|
|
|
+== Coordinate System
|
|
|
+
|
|
|
+[.right]
|
|
|
+image::tutorials:concepts/coordinate-system.png[coordinate-system.png,width="235",height="210",align="right"]
|
|
|
+
|
|
|
+
|
|
|
+The jMonkeyEngine uses a right-handed coordinate system, just as OpenGL does.
|
|
|
+
|
|
|
+The coordinate system consists of:
|
|
|
+
|
|
|
+* The _origin_, a single central point in space.
|
|
|
+** The origin point is always at coordinate zero, in Java: `new Vector3f(0,0,0)`.
|
|
|
+
|
|
|
+* Three _coordinate axes_ that are mutually perpendicular, and meet in the origin.
|
|
|
+** The X axis starts left and goes right.
|
|
|
+** The Y axis starts below and goes up.
|
|
|
+** The Z axis starts away from you, and goes towards you.
|
|
|
+
|
|
|
+
|
|
|
+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. +
|
|
|
+Example: The point `new Vector3f(3,-5,1)` is 3 steps to the right, 5 steps down, and 1 towards you.
|
|
|
+
|
|
|
+
|
|
|
+[NOTE]
|
|
|
+====
|
|
|
+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.
|
|
|
+====
|
|
|
+
|
|
|
+
|
|
|
+For your orientation:
|
|
|
+
|
|
|
+* The default camera's location is `Vector3f(0.0f, 0.0f, 10.0f)`.
|
|
|
+* The default camera is looking in the direction described by the (so called) negative Z unit vector `Vector3f(0.0f, 0.0f, -1.0f)`.
|
|
|
+
|
|
|
+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.
|
|
|
+
|
|
|
+
|
|
|
+== How to move yourself through the 3D scene
|
|
|
+
|
|
|
+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!
|
|
|
+
|
|
|
+By default, jME3 uses the following common navigation inputs
|
|
|
+[cols="3", options="header"]
|
|
|
+|===
|
|
|
+
|
|
|
+a| Game Inputs
|
|
|
+a| Camera Motion
|
|
|
+a| Player POV
|
|
|
+
|
|
|
+a|Press the W and S keys
|
|
|
+a|move the camera forward, and backward
|
|
|
+a|you walk back and forth
|
|
|
+
|
|
|
+a|Press the A and D keys
|
|
|
+a|move the camera left and right
|
|
|
+a|you step left or right
|
|
|
+
|
|
|
+a|Press the Q and Y keys
|
|
|
+a|move the camera up and down
|
|
|
+a|you fly up and down
|
|
|
+
|
|
|
+a|Move the mouse left-right
|
|
|
+a|rotate the camera left/right
|
|
|
+a|you look left or right
|
|
|
+
|
|
|
+a|Move the mouse forwards-backwards
|
|
|
+a|rotate up/down
|
|
|
+a|you look at the sky or your feet
|
|
|
+
|
|
|
+|===
|
|
|
+
|
|
|
+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.
|
|
|
+
|
|
|
+
|
|
|
+== Scene Graph and RootNode
|
|
|
+
|
|
|
+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.
|
|
|
+
|
|
|
+
|
|
|
+image::tutorials:concepts/scene-graph.png[scene-graph.png,width="",height="",align="center"]
|
|
|
+
|
|
|
+
|
|
|
+* _Attaching_ a Spatial to the rootNode (or its child nodes) adds it to the scene;
|
|
|
+* _Detaching_ a Spatial from the rootNode (or its child nodes) removes it from the scene.
|
|
|
+
|
|
|
+All objects in the scene graph are in a parent-child relationship. When you transform (move, rotate, scale) one parent, all its children follow.
|
|
|
+
|
|
|
+
|
|
|
+[NOTE]
|
|
|
+====
|
|
|
+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.
|
|
|
+====
|
|
|
+
|
|
|
+
|
|
|
+
|
|
|
+== Spatials: Node vs Geometry
|
|
|
+
|
|
|
+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_:
|
|
|
+[cols="10,45,45", options="header"]
|
|
|
+|===
|
|
|
+
|
|
|
+<a|
|
|
|
+2+a| Spatial
|
|
|
+
|
|
|
+a| Purpose:
|
|
|
+2+a| A Spatial is an abstract data structure that stores transformations (translation, rotation, scale).
|
|
|
+
|
|
|
+<a|
|
|
|
+a| Geometry
|
|
|
+a| Node
|
|
|
+
|
|
|
+a| Visibility:
|
|
|
+a| A visible 3-D object.
|
|
|
+a| An invisible "`handle`" for a group of objects.
|
|
|
+
|
|
|
+a| Purpose:
|
|
|
+a| A Geometry represents the "`look`" of an object: Shape, color, texture, opacity/transparency.
|
|
|
+a| A Node groups Geometries and other Nodes together: You transform a Node to affect all attached Nodes (parent-child relationship).
|
|
|
+
|
|
|
+a| Content:
|
|
|
+a| Transformations, mesh, material.
|
|
|
+a| Transformations. No mesh, no material.
|
|
|
+
|
|
|
+a| Examples:
|
|
|
+a| A box, a sphere, player, a building, a piece of terrain, a vehicle, missiles, NPCs, etc…
|
|
|
+a| The rootNode, the guiNode, an audioNode, a custom grouping node for a vehicle plus its passengers, etc.
|
|
|
+
|
|
|
+|===
|
|
|
+
|
|
|
+
|
|
|
+== How to Use This Knowledge?
|
|
|
+
|
|
|
+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.
|
|
|
+
|
|
|
+//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!
|
|
|
+
|
|
|
+
|
|
|
+== See also
|
|
|
+
|
|
|
+* xref:jme3/advanced/spatial.adoc[Spatial] – More details about working with Nodes and Geometries
|
|
|
+* xref:jme3/advanced/traverse_scenegraph.adoc[Traverse SceneGraph] – Find any Node or Geometry in the scenegraph.
|
|
|
+* xref:jme3/advanced/camera.adoc[Camera] – Learn more about the Camera in the scene.
|
mitm001