242-515 AGD: 10. Meshes 11

• Objectiveo to describe how shape meshes and models

can be used, with emphasis on the OBJ and MTL 3D formats

Animation and Games

Development242-515, Semester 1, 2014-2015

10. Meshes and Models

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1. Triangle Meshes2. Three Custom Meshes3. Phong and Gouraud Shading4. jME Built-in Shapes5. Using Models6. Loading Models into a Grid7. Using the Chase Camera8. The Wavefront (.obj) Format9. OBJ Cube Example10.Other Geometric Models

Overview

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• Modern hardware is optimized for triangle meshes: o polygon meshes where every polygon is a triangle

• There are three basic types of information in a triangle mesh:1. Vertices2. Edges3. Faces

1. Triangle Meshes

vertex

edgeface

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1. Vertices. Each triangle has exactly three vertices. A vertex may be shared by many triangles.

2. Edges. An edge connects two vertices. Each triangle has three edges. Usually, each edge is shared by two faces.

3. Faces. The surfaces of the triangles. Usually stored as a list of three vertices, or a list of three edges.

Triangle Mesh Information

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+X

+Z

+Y

(1,0,1)

(1,0,-1)

(-1,0,1)

(-1,0,-1)

(0,2,0)

A Pyramid

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• An indexed triangle mesh consists of a list of vertices, and a list of triangles indicies.

Indexed Triangle Mesh

+X

+Z

+Y

(1,0,1)

(1,0,-1)

(-1,0,1)

(-1,0,-1)

(0,2,0)

0 1

2

3

4

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• Each triangle is represented using three indices. • The index order is specified in terms of the front

face of the triangle. • The index order follows the right-hand rule:

o the front faces the direction of the thumbo the vertices indicies are listed in the counterclockwise

order of the fingers

Index Order and Front Faces

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• The triangle on the front of the pyramid is facing along the +z axis.

• This means that the triangle's indicies will be defined counter-clockwise as {0, 1, 4)o {1,4,0} or (4,0,1} also okay

Example

+X

+Y

0 1

4

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jME Code Fragments// Vertex positions in space Vector3f [] verts = new Vector3f[5]; verts[0] = new Vector3f(-1, 0, 1); verts[1] = new Vector3f(1, 0, 1); verts[2] = new Vector3f(1, 0, -1); verts[3] = new Vector3f(-1, 0, -1); verts[4] = new Vector3f(0, 2, 0);

// the order in which mesh should be constructed from triangles int [] indexes = {0,3,1, 1,3,2, 2,3,4, 4,3,0, 0,1,4, 4,1,2};

PyramidMesh.java

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// mesh creationMesh mesh = new Mesh();

// Setting mesh buffers // the 2nd parameter is the number of components in each value mesh.setBuffer(Type.Position, 3, BufferUtils.createFloatBuffer(verts)); mesh.setBuffer(Type.Index, 1, BufferUtils.createIntBuffer(indexes)); mesh.updateBound();

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// mesh is displayed as a white wireframe Geometry geom = new Geometry("pyramid", mesh); Material matWF = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md"); matWF.setColor("Color", ColorRGBA.White); geom.setMaterial(matWF); rootNode.attachChild(geom);

RenderState rs = matWF.getAdditionalRenderState(); rs.setWireframe(true); // activate wireframe view rs.setFaceCullMode(RenderState.FaceCullMode.Off);

cam.setLocation(new Vector3f(0.5f, 3.5f, 4)); cam.lookAt(Vector3f.ZERO, Vector3f.UNIT_Y); // look at the origin with +y-axis being up

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Execution

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2. Three Custom Meshes

solid blue

coloredverticies

lit with adirectionallight

CustomMeshes.java

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The Basic Mesh

+X

+Y

0 1

2 3

(0,0,0) (2,0,0)

(0,2,0) (2,2,0)

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Mesh mesh = new Mesh();

// Vertex positions in space Vector3f[] verts = new Vector3f[4]; verts[0] = new Vector3f(0,0,0); // can use any ordering verts[1] = new Vector3f(2,0,0); verts[2] = new Vector3f(0,2,0); verts[3] = new Vector3f(2,2,0);

// the order in which mesh should be constructed from triangles int[] indexes = {2,0,1, 1,3,2};

// setting the buffersmesh.setBuffer(Type.Position, 3, BufferUtils.createFloatBuffer(verts)); mesh.setBuffer(Type.Index, 1, BufferUtils.createIntBuffer(indexes)); mesh.updateBound();

Create the Mesh

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Geometry geom = new Geometry("solid", mesh); Material mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md"); mat.setColor("Color", ColorRGBA.Blue); geom.setMaterial(mat); geom.setLocalTranslation(-2, -3, 0); rootNode.attachChild(geom);

A Solid Blue Mesh

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Mesh colMesh = mesh.clone();

Geometry colGeom = new Geometry ("colored", colMesh); Material colMat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md"); colMat.setBoolean("VertexColor", true);

// each vertex requires 4 color values (R G B A) // in the same ordering as the vertices array, verts[] float[] colorArray = {

1f, 0f, 0f, 1f, // red

0.8f, 0.2f, 1f, 1f, // purple

0.8f, 0.2f, 1f, 1f, 0f, 0f, 1f, 1f }; // blue

// Set the color buffer colMesh.setBuffer(Type.Color, 4, colorArray); colGeom.setMaterial(colMat);

:

Coloured Verticies

0 1

2 3

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// Set the color buffer colMesh.setBuffer(Type.Color, 4, colorArray); colGeom.setMaterial(colMat);

// move mesh so it doesn't overlap with the first one colGeom.setLocalTranslation(2, -3, 0); rootNode.attachChild(colGeom);

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Mesh litMesh = mesh.clone(); Geometry litGeom = new Geometry ("lit", litMesh);

Material litMat = new Material(assetManager, "Common/MatDefs/Light/Lighting.j3md"); litMat.setBoolean("UseMaterialColors", true); litMat.setColor("Diffuse", ColorRGBA.Orange); // reflection litMat.setColor("Specular", ColorRGBA.White); litMat.setFloat("Shininess", 12); litGeom.setMaterial(litMat);

:

Lit Mesh, Reflecting Orange

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// verticies require normals for Phong lighting float[] normals = {0,0,1, 0,0,1, 0,0,1, 0,0,1}; // all of them point along +z axis litMesh.setBuffer(Type.Normal, 3, BufferUtils.createFloatBuffer(normals)); litGeom.setLocalTranslation(-2, 1, 0); rootNode.attachChild(litGeom);

// add a white light to make the lit object visible DirectionalLight dl = new DirectionalLight(); dl.setDirection(new Vector3f(1, 0, -2).normalizeLocal()); dl.setColor(ColorRGBA.White);

rootNode.addLight(dl);

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Vertex Normals Diagram

+X

+Z

+Y

0 1

2 3

(0,0,0)

(0,2,0)

(2,0,0)

(2,2,0)

directionallight

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• Phong shading interpolates normals between all the shape verticies. It uses these normals to calculate the shading for every pixelo many normals are generatedo this is the default shading technique in jME

• Gouraud shading calculates the shading for each vertex, and interpolates those shading values across every pixelo this requires less computation since only vertex normals

are needed

3.3. Phong and Gouraud Shading

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• The black arrows are the vertex normals.• The blue arrows are the interpolated surface

normals.• These extra normals will make the hexagon look

smoother on screen.

Phong Shading in Action

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• Phong shading makes polygons look smoother

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4. jME Built-in Shapes

Dome (the cone and pyramid are special cases)

Torus PQTorus Surface(a NURB)

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// Sphere mesh = new Sphere(16, 16, 1.0f); // Cylinder mesh = new Cylinder(20, 50, 1, 2, true); :

Geometry geom = new Geometry("Shape", mesh); Material mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md"); mat.setColor("Color", ColorRGBA.Blue); geom.setMaterial(mat);rootNode.attachChild(geom);

RenderState rs = mat.getAdditionalRenderState(); rs.setWireframe(true); // activate wireframe view rs.setFaceCullMode(RenderState.FaceCullMode.Off);

Viewing Wireframe ShapesWireShape.java

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Dome, Cone, Pyramid

Dome mesh = new Dome(Vector3f.ZERO, 32, 32, 1f, false); // center, planes, radialSamples, radius, insideView

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Dome mesh = new Dome(Vector3f.ZERO, 2, 32, 1f, false); // cone: planes == 2 and radialSamples > 4

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Dome mesh = new Dome(Vector3f.ZERO, 2, 4, 1f, false); // pyramid: planes == 2 and radialSamples == 4

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• For more information see http://en.wikipedia.org/wiki/Torus_knot

Knotted Doughnuts (braids)

PQTorus mesh = new PQTorus(2, -3, 2, 1, 64, 64); // trefoil// (2,−3) torus knot

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PQTorus mesh = new PQTorus(3, -8, 2, 0.5f, 64, 64); // Flower torus, (3, -8) torus knot

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• jME's built-in shapes come with pre-calculated normals, which can be displayed visually with the ShowNormals.j3md material definition.o a color gradient is calculated from the model's surface

normals. o no need for lights in the scene

Shapes and Normals

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public void simpleInitApp() { Cylinder mesh = new Cylinder(20, 50, 1, 2, true); Geometry geom = new Geometry("Shape", mesh); Material mat = new Material(assetManager,

"Common/MatDefs/Misc/ShowNormals.j3md"); geom.setMaterial(mat); geom.rotate(FastMath.HALF_PI, 0, 0); rootNode.attachChild(geom);}

Viewing a Cylinder's Normals

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• There are many free 3D models available onlineo e.g. at http://archive3d.net/,

http://sketchup.google.com/3dwarehouse/o see the list of websites at

http://www.hongkiat.com/blog/ 60-excellent-free-3d-model-websites/

• There are many 3D model formats:o e.g. 3D Studio (.3ds), Blender (.blend), Wavefront (.obj)o see the list at

http://edutechwiki.unige.ch/en/3D_file_format

5. Using Models

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• Blender (http://www.blender.org/)o extremely powerful, free, open source 3D modellero a confusing GUI which keeps being changedo use it to import models, and export them in a different

format

• 3DViewer (http://www.xs4all.nl/~karelse/3DViewer/)o very simple, free 3D viewer which is useful for checking

models

3D Tools

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• jME can load models in two formats:o Wavefront .obj formato Ogre XML

• I'll use .obj since it's a simple format, and is supported by most (all) 3D modeling tools.o the format is text-based, and is easy to edit manually

(see later)

• Blender can export Ogre XML files, but it requires the installation of a plugino details at http://jmonkeyengine.org/wiki/doku.php/

jme3:advanced:3d_models

3D Formats in jME

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• jME can also save Spatial nodes as .j3o binary files, which can be loaded later.o details at http://jmonkeyengine.org/wiki/doku.php/

jme3:advanced:save_and_load

• .j3o files can be viewed and edited by the jME SDK

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6. Loading Models into a Grid

GridZoneLoad.java

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The Grid Zone

+X

+Z

+Y

1 unit

1 unit

1 unit

0.1 unit

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// globals private static final float STEP = 0.1f; // space between grid lines private static final float WIDTH = 1.0f; // extent along +axis of grid and box

public void simpleInitApp() { addZone(1.2f,3.2f); // (Y,Z) camera position

// load the model Spatial model = assetManager.loadModel( "Models/Teapot/Teapot.obj"); rootNode.attachChild(model); } // end of simpleInitApp()

Partial CodeGridZoneLoad.java

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private void addZone(float y, float z) { viewPort.setBackgroundColor(ColorRGBA.DarkGray);

cam.setLocation(new Vector3f(0,y,z)); cam.lookAt(Vector3f.ZERO, Vector3f.UNIT_Y); // look at the origin with +y-axis being up

// grid-based floor int numLines = (int)((WIDTH/STEP)*2 + 1); addWireShape(new Grid(numLines, numLines, STEP), ColorRGBA.White).center();

// axes arrows addArrow(Vector3f.UNIT_X, ColorRGBA.Red); addArrow(Vector3f.UNIT_Y, ColorRGBA.Green); addArrow(Vector3f.UNIT_Z, ColorRGBA.Blue);

addBox(WIDTH); // wireframe box :

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// white light aimed down in front-left quadrant DirectionalLight dl1 = new DirectionalLight(); dl1.setDirection(new Vector3f(-1, -1, 1).normalizeLocal()); dl1.setColor( ColorRGBA.White); rootNode.addLight(dl1);

// white light aimed down in back-right quadrant DirectionalLight dl2 = new DirectionalLight(); dl2.setDirection(new Vector3f(1, -1, -1).normalizeLocal()); dl2.setColor( ColorRGBA.White); rootNode.addLight(dl2);

} // end of addZone()

xz

y

xz

y

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private void addArrow(Vector3f dir, ColorRGBA color) { Arrow arrow = new Arrow(dir); arrow.setLineWidth(3); // make arrow thicker addWireShape(arrow, color); } // end of addArrow()

private void addBox(float size) // a wireframe box { Geometry g = addWireShape( new WireBox(size, size/2, size), ColorRGBA.Yellow); g.setLocalTranslation( new Vector3f(0, size/2, 0)); }

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private Geometry addWireShape(Mesh shape, ColorRGBA color) // add a colored wireframe version of shape to the scene { Geometry g = new Geometry("shape", shape); Material mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md"); mat.getAdditionalRenderState().setWireframe(true); mat.setColor("Color", color); g.setMaterial(mat); rootNode.attachChild(g); return g; } // end of addWireShape()

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• The imported shape may be too large, translated a long way from the origin, or rotated incorrectly.

• In that case, add code to simpleInitApp() like:

o model.scale(0.01f); // 100 times smaller

o model.rotate(0, (float)Math.toRadians(90), 0); // rotate 90 degrees around the y-axis

o model.setLocalTranslation( new Vector3f(-2, 0, 0)); // move 2 units left along the x-axis

Adjusting the Model

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• The loaded bus.obj model is too large:o Spatial model = assetManager.loadModel( "models/bus.obj");

o bus.obj is in the local models/ directory

• I worked out the size problem by using the camera keys and mouse to move about:o the WASDQZ keys to zoom in/out

and translate left/right/up/down.o the mouse to rotate left/right/up/down

Bus Example

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• Original viewof the bus:

• After zooming out a lot (it's a seat inside thebus):

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• bus.obj in 3DViewer (to check the model):

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• Modified jME code:Spatial model = assetManager.loadModel("models/bus.obj");model.scale(0.005f); model.setLocalTranslation( new Vector3f(0, 0.2f, 0));

200x smallerthen movedup 0.2f units:

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Spatial model = assetManager.loadModel( "Models/HoverTank/Tank2.mesh.xml");model.scale(0.1f);model.rotate(0, -(float)Math.toRadians(90), 0);

HoverTank

10x smallerthen rotated-90 degreesaround they-axis:

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• A drawback of the default camera (a FlyByCamera object) is that rotation is around the camera's position.

• For model viewing, it is often better to rotate around the model.

• This is possible by using a ChaseCamera object insteado this kind of camera can rotate around a specified Spatialo it will also automatically follow the Spatal if it moves (i.e.

it chases the model)

7. Using the Chase Camera

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Rotating Around the HoverTank

ViewHoverTank.java

rotate left and up by dragging the mouse

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public void simpleInitApp() { Node tank = (Node) assetManager.loadModel( "Models/HoverTank/Tank2.mesh.xml"); rootNode.attachChild(tank);

// replace FlyByCamera by ChaseCamera flyCam.setEnabled(false); ChaseCamera chaseCam = new ChaseCamera(cam, tank, inputManager); // camera follows the tank and // can turn around it by dragging the mouse chaseCam.setSmoothMotion(true); chaseCam.setMaxDistance(100000); chaseCam.setMinVerticalRotation(-FastMath.PI / 2); :

Partial Code

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// white light from above Vector3f lightDir = new Vector3f(-1, -1, 1).normalize(); DirectionalLight dl1 = new DirectionalLight(); dl1.setColor(ColorRGBA.White); dl1.setDirection(lightDir); rootNode.addLight(dl1);

// orange light from below Vector3f lightDir2 = new Vector3f(1, 1, -1).normalize(); DirectionalLight dl2 = new DirectionalLight(); dl2.setColor(ColorRGBA.Orange); dl2.setDirection(lightDir2); rootNode.addLight(dl2);

} // end of simpleInitApp()

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• Most models are made up of triangles. • Each triangle is called a face.

• Each face is defined using verticeso a face may also have normals and texture coordinates

• Faces can be grouped together, and different groups can be assigned materials made from ambient, diffuse, and specular colors, and textures.

• • The material information is stored in a separate

MTL text file.

8. The Wavefront (.obj) Format

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• There are three types of basic OBJ statements: o for defining shapeo for groupingo for materials (most of these operations are located in

the separate .mtl file)

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• Vertex position:v float float float

• each "v" line has an index, starting from 1

• A normal:vn float float float

• each "vn" line has an index, starting from 1

• 2D or 3D texture coordinate:vt float float [float]

• each "vt" line has an index, startiong from 1

Defining Shape

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• A face (in terms of vertex indicies)f int int int

• A face (uses vertex and texture indicies)f int/int int/int int/int

• A face (uses vertex, texture and normal indicies):f int/int/int int/int/int int/int/int

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• g name • Faces ("f" lines) defined after a "g" line will belong

to the group called “name”.

• Named groups are a useful way of referring to a collection of faces for assigning materials or textures.

Grouping

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• mltlib filename• The MTL file named in the “mltlib” statement will

contain material definitions used in the rest of the OBJ file.

• usemtl name • All subsequent faces after this line will be

rendered with the named material, until the next “usemtl” line.

Material Use Statements

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• Ambient RGB color:Ka r g b

• Diffuse RGB:Kd r g b

• Specular color: Ks r g b

• Transparency:d alpha Tr alpha

The MTL File Format

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• Shininess:Ns s

• Illumination mode:illum n

• If n == 1 then no specular highlights are used• If n == 2 then use “Ks” value for the highlights• if n == 0 then all lighting is disabled

• Texture filename:map_Ka filename

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• A cube was exported from Blender as the OBJ file blenderCube.objo a MTL file was created automatically, called

blenderCube.mtl

9. OBJ Cube Example

in Blender

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# Blender v2.62 (sub 0) OBJ File: ''# www.blender.orgmtllib blenderCube.mtlo Cubev 1.000000 -1.000000 -1.000000 // 1v 1.000000 -1.000000 1.000000 // 2v -1.000000 -1.000000 1.000000 // 3v -1.000000 -1.000000 -1.000000 // 4v 1.000000 1.000000 -0.999999 // 5v 0.999999 1.000000 1.000001 // 6v -1.000000 1.000000 1.000000 // 7v -1.000000 1.000000 -1.000000 // 8

vn 0.000000 -1.000000 0.000000 // 1vn 0.000000 1.000000 0.000000 // 2vn 1.000000 0.000000 0.000000 // 3vn -0.000000 -0.000000 1.000000 // 4vn -1.000000 -0.000000 -0.000000 // 5vn 0.000000 0.000000 -1.000000 // 6g Cube_Cube_Materialusemtl Material :

The OBJ file

only 6 normals(1 per face)

blenderCube.obj

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s offf 1//1 2//1 3//1f 1//1 3//1 4//1f 5//2 8//2 7//2f 5//2 7//2 6//2f 1//3 5//3 6//3f 1//3 6//3 2//3f 2//4 6//4 7//4f 2//4 7//4 3//4f 3//5 7//5 8//5f 3//5 8//5 4//5f 5//6 1//6 4//6f 5//6 4//6 8//6

each face is defined using3 vertices and 1 normal;no tex coords used

12 faces (even though thecube only has 6 sides)

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4

OBJ Cube Diagram

+X

+Z

+Y

(1,-1,1)

(1,-1,-1)

(-1,1,1)

1

23

5

(-1,-1,1)

(1,1,-1)

67

(-1,1,-1)8

53

2

6

4

1

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A Cube Side Has 2 Faces

+X

+Z

+Y

(1,-1,1)

(1,1,1)(-1,1,1)

23(-1,-1,1)

67

4

f 2//4 6//4 7//4f 2//4 7//4 3//4

uses the right hand ruleto define the front face

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# Blender MTL File: ''# Material Count: 1newmtl MaterialNs 96.078431Ka 0.000000 0.000000 0.000000 // no ambientKd 0.640000 0.640000 0.640000 // grayKs 0.500000 0.500000 0.500000Ni 1.000000 // no refractiond 1.000000 // no transparencyillum 2 // use Ks for highlights

The MTL File blenderCube.mtl

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Spatial model = assetManager.loadModel("models/blenderCube.obj");model.scale(0.5f);

Loaded by jME

Cube's sidesare scaled to0.5 units

GridZoneLoad.java

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• It's easy to modify the MTL file:Kd 0.54 0.89 0.63 // jade (see Part 9, sec 6.1)

Modifying the Material

Cube's diffusereflection isnow jade

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• The OBJ format is fully explained at:o http://local.wasp.uwa.edu.au/~pbourke/dataformats/obj/

• The MTL format:o http://local.wasp.uwa.edu.au/~pbourke/dataformats/mtl/

Full OBJ and MTL Details

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• The use of meshes composed of verticies, faces, edges, and normals is the standard way of creating models in computer graphics.

• There are other approaches, such as:o Constructive Solid Geometry (CSG)o Metaballs

10. Other Geometric Models

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• CSG builds a shape using Boolean operators (union, difference, intersection) on primitive shapes (cubes, spheres, etc)o available in the Unreal engine

Constructive Solid Geometry (CSG)

union:cube + sphere

difference: cube - sphere

intersection: cube ∩ sphere

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• Used to model organic shapes and fluids. • A ball has a fuzzy region around it. • When two ball come near to each other, their

fuzzy regions start merging.

Metaballs

the red and blue metaballs come together