Object Oriented System for Scene Graph -------------------------------------- This project is a library of objects and methods used for creating 3D Scene Graphs. This tookit's foundation is supplied by OpenGL and Unix. The Objects in this library includes some basic objects for creating a scene: camera, light, attributes, transformations and some geometry objects. They can be summarized as the following class tree: Class Tree ---------- (Base classes are at the left, and derived classes are at the right.) 1.Node----------- Camera ------- Light --------TurnOff ------- DrawStyle ------- Color ------- Material ------- Transformation ------- Geometry---------------Cube ----Cylinder ----Sphere ----Triangle ----Polygon ----Line 2.GLViewer Creating a Scene Graph: ----------------------- 1.basic knowledge: The node is the basic building block used to create three-dimensional scene graph. Different type of nodes hold different information, such as a surface material, shape description, geometric transformation, light or camera. We can use a tree data structure to describe the relationships among camera, lights, and attributes. This structure is created by adding nodes as children grouping nodes. During rendering, the scene graph structure is traversed, starting from the root node, from left to right and from top to bottom. Child node inherits the transformation state of its parent. for example: Root Camera Light0 Color0 Transformation0 Object0 Transformation1 Object1 2.What's in a Node: Each node is composed of a set of data elements, known as fields, that describe the parameters of the node and some metheds to access those fields. 3.Node type Node: ----- It is the base node class which has the information and methods for creating the tree structure. The methods in the base node can also be used in its derived objects. Methods in the base node: AddChild(Node *N), adds the specified node to the beginning of the children group, note that the child added last will be rendered first. Camera ------ Camera node is derived from the base class "Node". Camera has the following Fields: Type: specifies the type of the projection is perspective or orthographic. Position: location of the camera viewpoint. default value is (0,0,0). Aimat: a point at which the camera is pointing. default value is looking down the negative z-axis. (0,0,-100) UpDirection: indicates which direction is up. Near: distance from the camera viewpoint to the near clipping plane Far: distance from the camera viewpoint to the far clipping plane Height: specifies the height of the camera view volume, this field is only useful for a orthograhic projection. Aspect: ratio of the camera viewing width to height. YAngle: specifies the vertical angle in radians of the camera view volume. Camera has the method: SetValue{v}(), SetValuev(Enum PName, float *v) SetValue(Enum PName, float v1, float v2, float v3) SetValue(Enum PName, float v) to set the value for the camera: parameter PName can be: POSITION, AIMAT, UPDIRECTION, NEAR, FAR, HEIGHT, ASPECT, YANGLE. For example: Camera *C=new Camera(ORTHO); float p[]={5, 5, 5}; C->SetValuev(POSITION, p); Note that there should be only one camera in the scene, and it should be the first child of the root. Light ----- Light node is derived from the base class "Node". Light Node has the following Fields: Position: location of the light. default value is (0,0,10,0). If the last value is 0, the light source is a directional one, and the (x,y,z) values describe its direction. Specular: specular intensity of light Ambient: ambient intensity of light SpotDirection: direction of spotlight CutOffAngle: specifies the spotlight cutoff angle On: whether the light is on, default value is false. The method for Light node: SetValue(Enum PName, Enum color) SetValue(Enum PName, float v1, float v2, float v3, float v4 ) SetValue(Enum PName, float v1, float v2, float v3) SetValue(Enum PName, float f) SetValuev(Enum PName, float *) parameter PName can be: DIFFUSE, SPECULAR, AMBIENT, POSITION, SPOTDIRECTION, DROPOFFRATE, or CUTOFFANGLE. For example: Light *L=new Light; float a[]={1.0 ,1.0, 1.0, 1.0} L->SetValuev(AMBIENT, a); TurnOn(), TurnOn the light. TurnOff ------- TurnOff node is derived from the base class "Node". This Node is to turn off the specified light. Insert this node in the scene tree structure is to bind the light on some particular objects. the following example is to bind light L to one cube: Light *L=new Light; L->TurnOn; Cube *C=new Cube; TurnOff *Off=new TurnOff(L); L->AddChild(C); C->AddChild(Off); Color ----- Color node is derived from the base class "Node". Color node includes the following fields: Color: specifies RGB color. Methods for Color node: SetValuev(float *v) SetValue(float v1, float v2, float v3) SetValue(Enum Type) The color can be set by RGE value or the name for a often used color, for example: Color *C=new Color; C->SetValue(RED); Other parameters can be: BLACK, WHITE, RED, GREEN, YELLOW, BLUE, MAGENTA, CYAN, GREY. Material -------- Material node is derived from the base class "Node". Material Node has the following Fields: Ambient: reflected color of an object in response to the ambient lighting in the scene. The default value is (0.2, 0.2, 0.2, 1.0) Specular: reflective quality of an object's highlights. The default value for this field is (0.0, 0.0, 0.0, 1.0) Diffuse: an object's base color. The default value for this field is (0.8, 0.8, 0.8, 1.0) Emission: Emissive color of material. The default value is (0.0, 0.0, 0.0, 1.0) Shininess: Degree of Shininess of an object's surface. default value is 0.0 for a diffuse surface with no shininess. Methods for Material node: SetValuev(Enum Pname, float *v) SetValue(Enum Pname, float v1, float v2, float v3, float v4) SetValue(Enum Pname, float Value) parameter PName can be: DIFFUSE, SPECULAR, AMBIENT, EMISSION, SHININESS Transformation -------------- Transformation node is derived from the base class "Node". Transformation Node has the following Fields: Translation: the translaton in x, y and z. the default value is (0.0, 0.0, 0.0) Rotation: the rotation in terms of an axis and an angle. the default value is 0.0 degree for(0.0, 0.0, 1.0) Scale: the scaling factor in x, y and z. the default value for this field is (1.0, 1.0, 1.0) Methods for Transformation node: SetValuev(Enum PName, float *, int Order); SetValue(Enum PName, float x, float y, float z, int Order); SetValue(Enum PName, float a, float x, float y, float z, int Order); parameter PName can be: TRANSLATION, ROTATION, SCALE parameter Order: specifies the order for the execution of the transformation Geometry Nodes: All Geometry nodes are derived from the class Geometry. This library provides the following simple Geometries: Cube ---- You specify the width, height, and depth; Cylinder -------- You specify the height and the radius; Sphere ------ You specify the radius; Polygon ------- You specify the vertices for the polygon and how many vertices in the polygon; Line ---- You specify the start point and the end point; Note: the geometry object allow you to set its attribute by binding attribute nodes or set its attribute directly. following is the setting methods: SetColor(Enum) SetColor(float, float, float) SetColorv(float *) SetColor(Color *) SetMaterial(Enum, float, float, float, float) SetMaterialv(Enum, float *) SetMaterial(Enum, float) SetMaterial(Material *) SetTransform(Enum, float *, int) SetTransform(Enum, float, float, float, int) SetTransform(Enum, float, float, float, float, int) SetTransform(Transformation *) SetStyle(Enum, Enum) SetStyle(Enum, float) SetStyle(DrawStyle *) for example: Material *M=new Material; . . ------>Setting M . Sphere *S=new Sphere; Sphere->SetMaterial(M); //Set M to be the Material of S GLViewer -------- GLViewer class is not a derived class of Node. After you create a whole scene tree structure, you must attach the root of the tree to a GLViewer object to show the scene. methods in GLViewer class: CreateWin(char *Name, int Width, int Height) create a window by giving the name, width and height. SetValue(Enum PName, Enum Type) set the buffer style: single buffer or double buffer. the backcolor for the window parameter for PName: BUFFER, BACKCOLOR. parameter for Type: SINGLE, DOUBLE for PName=BUFFER. BLACK, WHITE, RED, GREEN, YELLOW, BLUE, MAGENTA, CYAN, GREY for PName=BACKCOLOR Init(int argc, char **argv) Show(Node *N) N is the root for the scene graph Note: If you create more than one GLViewer object, you can open multiple windows(now you can create 3 windows in this version). Futhermore, if you attach the same root to different GLViewer you can see the same scene in different window just like the example program. If you create more than one window, you must create all of them one by one first, and call Viewer->show(root) at last. Source files: ------------- GLoo.a is the libirary. Makefile.lib is the Makefile for this library. You must include "Scene.h" in your program. Future Work ----------- 1. Add animation. 2. Add callback node for dealing with events. 3. Add detail property to make a nicer scene.