1 L Agenda Introduction Loading models MilkShape - - PDF document

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

OpenSceneGraph Modeling

Mikael Drugge Virtual Environments Spring 2005 Based on material from http://www.openscenegraph.org/

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Agenda

• Introduction
• Loading models
• MilkShape
• Lightsources
• StateSets
• Materials
• Textures

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

Introduction

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What makes the difference...?

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What causes the difference...?

• Lightsources
• Can change e.g. the ”mood” of a scene via the lighting
• Materials
• Diffuse colour, the ”base colour”
• Specularity/hardness, making plastics, metals, etc...
• Reflections, (not in the GL pipeline, but in e.g. raytracing)
• Emission, making objects glow or shine as if by light
• Textures
• Image mapping
• Bump mapping

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Creating models

• Modeling via code
• Easy for simple models
• But, requires a fair

bit of imagination

• For example:

Sphere(0,-0.2,0,2); Sphere(1.3,1.4,0,1); Sphere(-1.3,1.4,0,1); Sphere(0,0,1.9,0.3);

What’s this?

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Creating models with modeling programs

• A number of 3D modeling tools exist...
• 3D Studio, for graphics and raytracing
• AutoCAD, for CAD applications
• Maya, for graphics and animation
• Imagine, an old Amiga raytracer
• Wingz, modeler for POVray
• MilkShape, a modeling program

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

MilkShape

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Introduction to MilkShape 3D

• A basic low-polygon modeler
• Originally designed for a game (Half-Life)
• Supports basic operations
• Select, move, rotate, scale, extrude, etc
• Low-level editing of vertices and faces
• Primitives (spheres, boxes, cylinders…)
• Skeletal animation capabilities
• Supports 37 file formats from 27 games/engines

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Introduction to MilkShape 3D

• Why have we chosen to use MilkShape?
• It is fairly intuitive to use and learn
• It’s powerful enough for this course
• Handles a lot of different formats
• Allows for 30-day free trial
• It’s fairly cheap also 

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Example screenshot of MilkShape

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The coordinate system in MilkShape

X Y Y Z Z X

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Demo of MilkShape!

• Learning by doing, so let’s create something...

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Demo of MilkShape!

• Let’s see the result in OSG...

Loading Objects 15 L

Exporting

• Autodesk 3DS
• LightWave 6.5x LWO
• Flattens all edges
• Wavefront OBJ
• Materials in an extra MTL file
• 3DS or LWO recommended

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

Loading models into OSG

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Remember this? Plugins...

OSG Scenegraph Rendering elements Tree/DAG nodes OSGDB Database loading Plug-In management OSGText Handles text, fonts, ... Plug-Ins OSGUtil Traversers Enhancements OSGSim Simulation (skybox, lights, time-of-day) OSGParticle Special effects (fire, smoke...) JPG PNG GIF ... 3DS OSG LWO ... import openscenegraph.osgDB.osgDBNamespace;

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Loading objects – code example

import openscenegraph.osgDB.osgDBNamespace; Node node =

• sgDBNamespace.readNodeFile(“somefile.lwo”);

scene.addChild(node); This will load the model into a Node Then just handle it like any other node

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What to think about for external models

• Retrieving the dimensions for the model
• Getting the BoundingSphere via node.getBound()

+ getRadius()

• E.g. for ”normalizing” the size of an unknown object

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

Lightsources

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Lights and Lightsources

• LightSource
• Extends the Group node

+ addChild() still possible

• Contains one Light

+ setLight() + getLight()

LightSource Light

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The Light

• Encapsulates OpenGL glLight() functionality
• setLightNum(), sets which GL light to operate on
• setAmbient(), ambient colour of the light
• setDiffuse(), diffuse colour component
• setSpecular(), specular component
• Example – fire in a fireplace
• setDiffuse(orange), for the primary illumination
• setAmbient(darkred), for simulating the ambient light

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The Light

• Light can be point source or spotlight
• setPosition(), positions the light
• setDirection(), aims the spotlight in the given direction
• Many functions to tweak the lighting
• setConstantAttenuation(), also Linear and Quadratic

+ Light intensity diminishes over a distance

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The Light

• More spotlight functions
• setSpotCutoff(distance)
• setSpotExponent(exp)
• (Not much documentation about

these two functions – experiment!)

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The Light – shadows?

• No shadows
• Shadows are expensive to compute
• Possible to achieve in e.g. raytracing
• OSG does not support real time shadows

+ Some engines do, however, e.g. AgentFX by Agency9

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Example

Lighting 27 L

Lightsources – example code

Light light1 = new Light(); light1.setLightNum(0); light1.setDiffuse( new Vec4fReference(1f,0f,1f, 1f)); light1.setPosition( new Vec4fReference(x, y, z, 1f)); Create a light for GL light #0 Purple light Note this!

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Lightsources – example code

// create lightsource and set its light LightSource ls = new LightSource(); ls.setLight(light1); // turn on the lightsource ls.setLocalStateSetModes( STATEATTRIBUTEValues.ON_Val);

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Lightsources – example code

// create a “stateset” for the root node StateSet stateset = new StateSet(); root.setStateSet(stateset); // turn the lightsource on for this stateset ls.setStateSetModes(stateset, STATEATTRIBUTEValues.ON_Val); (We’ll come back to StateSets in a few slides, so don’t worry)

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Lightsources – example code

// then add the lightsource to the scene root.addChild(ls);

• Repeat the process if you need more lightsources
• You should reuse the same StateSet however
• Keep in mind you can alter light properties during run-time
• Colour, position, direction, etc...
• Turn lights on and off, etc...

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Summary – how to add a lightsource

1. Create a new LightSource 2. Create a new Light and associate with a GL light 3. Adjust the light parameters; colours, attenuation... 4. Make the lightsource use your light (via setLight()) 5. Create a stateset for the part of the scenegraph tree that should be illuminated by the lightsource 6. Turn on the lightsource in the stateset 7. Add the lightsource to the scene

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Some things to think about

• setDiffuse() may be all you need, BUT
• For materials where specularity, etc. are defined, the

lightsource needs to emit light that affects these too

• If not, the material properties will seem to have no effect
• I.e. make sure you set the colour for all components
• setDiffuse(somecolour);
• setSpecular(somecolour);
• etc...

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

StateSets

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What is a StateSet?

• It encapsulates OpenGL state modes and attributes
• Used for textures, lightsources, materials, transparency...
• E.g. specifies textures for Drawables
• Drawables can share a single StateSet
• Sharing statesets is recommended! Why?
• It minimizes state changes in the GL pipeline
• Changing the state in the pipeline is expensive!
• Thus, sharing the same StateSet is a good thing

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StateSets – example code revisited

// create a “stateset” for the root node StateSet stateset = new StateSet(); root.setStateSet(stateset); I.e. create a stateset that will apply from the root node and downwards. (The entire scene will use this stateset, meaning all of it will be illuminated by the lightsource in the example a few slides ago.)

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

Materials

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Introduction to Materials

• Not all objects are made of the same thing
• Metals, glass, plastics, wood, paper, skin, crystal...
• Different properties, depending on
• How rough/smooth the surface of the object is
• How the light refracts when hitting an object
• The colour of the object and the light
• Note!
• The theory behind all this will be presented in a future

lecture, this is mainly a primer to get you started

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Materials in OSG

• The ”Material” class
• Encapsulates OpenGL’s glMaterial state
• Usage
• Create a new Material and set its properties
• Apply the material to a StateSet via

+ stateset.setAttribute(material);

• Apply the StateSet to e.g. a Geode

+ geode.setStateSet(stateset);

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The Material class – some functions

• setDiffuse(MATERIALFace, Vec4fReference)
• setSpecular(...)
• setAmbient(...)
• setEmission(...)
• setShininess(...)
• setAlpha/setTransparency(...)

Vec4f(R, G, B, Alpha) Front and/or Back faces

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Materials – some examples and hints

• setDiffuse
• The ”base colour” of an object
• setSpecular & setShininess
• Plastics often have a white specularity, and are ”hard”, i.e.

they have a small area where this specularity occurs

• Common mistake when making metals: making them too

”hard” and white – it’s better with a softer setting and a specularity in the same nuance as the diffuse colour

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Materials – some examples and hints

• setAmbient
• Simulates the ”background noise” of all lightsources
• Instead of black ”shadows”, use the ambient colour
• setEmission
• Can make an object look like it radiates light

+ Instead of using a real lightsource – they’re expensive

• E.g. to create a torch, make the flame emissive and place a

lightsource within it, also use an ambient component

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Materials – some examples and hints

• setAlpha/setTransparency
• Sets the Alpha value of ambient, diffuse, specular and

emission colours

• setAlpha(value) = setTransparency(1 – value)
• Useful for making e.g. windows, water, holograms, etc...

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Example – creating an orange plastic ball

shape = new ShapeDrawable( new Sphere(new Vec3fReference(0f, 0f, 0f), 1f)); geode = new Geode(); stateset = new StateSet(); material = new Material(); material.setDiffuse(MATERIALFace.FRONT_AND_BACK, new Vec4fReference(1.0f, 0.5f, 0.1f, 1f)); material.setSpecular(MATERIALFace.FRONT_AND_BACK, new Vec4fReference(1.0f, 1.0f, 1.0f, 1f)); material.setShininess(MATERIALFace.FRONT_AND_BACK, 63f);

• Orange colour
• White specularity
• Make it a bit harder

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Example – creating an orange plastic ball

stateset.setAttribute(material); geode.setStateSet(stateset); geode.addDrawable(shape); ...

Associate material with the stateset Apply the stateset to the geode with the sphere object

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Example – a window

// you know this... shape = new ShapeDrawable( new Box(new Vec3fReference(-1f, -1f, 0f), 1f, 0.2f, 2f)); geode = new Geode(); stateset = new StateSet(); material = new Material(); // set the diffuse colour component to a lightblue nuance material.setDiffuse(MATERIALFace.FRONT_AND_BACK, new Vec4fReference(0.4f, 0.8f, 1f, 1f));

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Example – a window

stateset.setMode(GL.GL_BLEND, STATEATTRIBUTEValues.ON_Val); stateset.setRenderingHint( STATESETRenderingHint.TRANSPARENT_BIN_Val); material.setTransparency( MATERIALFace.FRONT_AND_BACK, 0.6f);

The higher the number the more transparency You need to enable blending to get transparency Set a rendering hint to use transparent bin

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Example – a window

// set properties (you know this already… ) stateset.setAttribute(material); geode.setStateSet(stateset); geode.addDrawable(shape); root.addChild(geode);

• Transparency is easy (from an API perspective),

just remember to enable the GL_BLEND mode

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Example – demo of Looks.java

Looks

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

Textures

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Introduction to Textures

• Why do we need textures?
• Difficult and expensive to model everything with polygons
• E.g. wooden surfaces, wallpapers, labels, faces, etc...
• Bumpmapping to simulate e.g. the texture of an orange
• Image maps are often cheaper in terms of computation
• (The underlying theory behind textures will be covered

in a future lecture, see this as a primer)

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Textures in OSG

• The ”Texture” class
• Encapsulates OpenGL’s texture functionality
• Texture1D/2D/3D – subclasses for 1D/2D/3D

X Y Example Texture2D

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Adding textures to PrimitiveGL.java

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Adding textures to PrimitiveGL.java

..... // define texture coordinates wrapping it around the pyramid Vec2Array texcoords = new Vec2Array(); texcoords.push_back(new Vec2fReference(0.00f, 0.00f)); // coord for v0 texcoords.push_back(new Vec2fReference(0.25f, 0.00f)); // coord for v1 texcoords.push_back(new Vec2fReference(0.50f, 0.00f)); // coord for v2 texcoords.push_back(new Vec2fReference(0.75f, 0.00f)); // coord for v3 texcoords.push_back(new Vec2fReference(0.50f, 1.00f)); // coord for v4 pyramidGeometry.setTexCoordArray(0, texcoords);

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Adding textures to PrimitiveGL.java

// create a 2D texture object Texture2D myTexture = new Texture2D(); // load an image via the plugins (e.g. JPG, GIF, TGA, etc...) Image texImage =

• sgDBNamespace.readImageFile(file);

// assign image to the texture myTexture.setImage(texImage); (The plugins should work without additional code!)

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Adding textures to PrimitiveGL.java

• Wake-up question!  What do we do next...?

StateSet stateset = new StateSet(); stateset.setTextureAttributeAndModes( 0, myTexture, STATEATTRIBUTEValues.ON_Val); ... pyramidGeode.setStateSet(stateset);

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Demo of the result

• TextureDemo.java
• Other examples
• BillboardingNode
• BillboardingTree

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Texture coordinates

• ShapeDrawables have texture coordinates defined
• I.e. create the shape and just apply the texture to it
• For a primitive GL rectangle, it’s also very simple
• An example follows...

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Texture coordinates

// a rectangle Vec2Array texcoords = new Vec2Array(); texcoords.push_back(new Vec2f(0.00f, 0.00f)); texcoords.push_back(new Vec2f(1.00f, 0.00f)); texcoords.push_back(new Vec2f(1.00f, 1.00f)); texcoords.push_back(new Vec2f(0.00f, 1.00f)); bbGeometry.setTexCoordArray(0, texcoords); 1 3 2

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

Summary

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Summary

• Introduction
• We sometimes want our virtual world to look like the real world
• Modeling objects
• Introduction to MilkShape and 3D modeling programs
• Loading the creations as nodes into OSG
• Lightsources
• How to illuminate a scene and alter its properties
• Materials
• Basic GL parameters for changing the look of objects
• Textures
• An introduction on how to use textures within OSG

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INSTITUTIONEN FÖR SYSTEMTEKNIK

LULEÅ TEKNISKA UNIVERSITET

Questions?