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Other Things You Should KnowPowerPoint Presentation

Other Things You Should Know

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### Other Things You Should Know

CS 4363/6353

Overview

- Matrix Stacks
- Raytracing and NPR
- Physics Engines
- Common File Formats

Matrix Stacks

- Typically, matrices are stored in a stack to avoid this
- Stacks give us the ability to rotate one body around another
- Stacks are also how (character) animation is done
- Let’s say we wanted to fly through the solar system
- You still have a camera matrix
- The sun has been translated (but probably not rotated)

Matrix Stack Example

Camera matrix

Matrix Stack Example

“Push” the camera matrix.Note: everything is rotated by our camera matrix…

Camera matrix

Matrix Stack Example

“Push” the translation of the sun

Order of operations

Combine everything on the stack into one MV matrix, then drawthe sun. Trans first, then camera!

Sun trans matrix

mMV

Camera matrix

Matrix Stack Example

The Earth is both translated

Sun trans matrix

Camera matrix

Note: yes, yes… I know it’s not to scale…

Matrix Stack Example

The Earth is both translated

and rotated (in that order), so

we push those on a separate

frame…

Earth rot matrix

Earth trans matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

WRONG! The matrices aremultiplied TOP DOWN!

Earth rot matrix

Earth trans matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

WRONG! The matrices aremultiplied TOP DOWN!

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

Order

Combine everything on the

stack into one MV matrix,

then draw the Earth!

Earth trans matrix

Earth rot matrix

mMV

Sun trans matrix

Camera matrix

Matrix Stack Example

What about the moon?

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

Well, the moon has a

translation…

Moon trans matrix

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

Moon rot matrix

Well, the moon has a

translation… as well as

a rotation…

Moon trans matrix

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

Moon trans matrix

Well, the moon has a

translation… as well as

a rotation…

Moon rot matrix

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

Order

Moon trans matrix

So we combine everything

on the stack into one MV

matrix, then draw the moon

Moon rot matrix

Earth trans matrix

mMV

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

Moon trans matrix

What if we want to draw a little independent spaceship?

Moon rot matrix

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

POP the Moon stuff!

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

POP the Earth stuff!

Earth trans matrix

Earth rot matrix

Sun trans matrix

Camera matrix

Matrix Stack Example

…Leaving us with just thecamera matrix. Then, we

can add the spaceship

matrices on top of that.

Camera matrix

Matrix Stack Example

Now that you have your MV,

draw the ship…

Ship rot matrix

Ship trans matrix

mMV

Camera matrix

RaYTracing

- Easy to read article at http://en.wikipedia.org/wiki/Ray_tracing_(graphics)

Note: there are independent reflection, refraction and shadow rays

Examples(again, from Wikipedia.org)

Examples(again, from Wikipedia.org)

Raytracing

- Advantages:
- Realistic simulation of lighting
- Natural shadows
- Simple to implement (but not trivial)
- Heavily parallelizable

- Disadvantages
- Still an approximation
- not truly photorealistic
- Must limit depth

- Recursively adds up light values of rays
- Ssssssssssssslllllllllllllllloooooooooooooooowwwwwwwwwwwwww

- Still an approximation

The Uncanny Valley…

- “…holds that when human replicas look and act almost, but not perfectly, like actual human beings, it causes a response of revulsion among human observers”

Final Fantasy: The Spirits Within

http://en.wikipedia.org/wiki/Uncanny_valley

NPR(non-photorealistic Rendering)

- Stylistic
- Water color
- Impressionism

- Example: Toon Shading
- Geometry remains the same
- Shading changes

- Commonly seen in video games
- Borderlands

http://en.wikipedia.org/wiki/File:Toon_Shader.jpg

Working with Physics Engines

- There are several out there:
- Tokamak (open source, no longer maintained)
- Bullet (open source – several commercial games and movies like “2012” and “Bolt”)
- Havok (commercial – Ireland, loads of commercial games)
- PhysX (commercial – Ageia/NVDIA, CUDA, uses PPU, tons of games as well)

- Usually provide:
- Gravity
- Collision (between static and dynamic bodies)
- Soft-body physics
- Ragdoll physics
- Vehicle dynamics
- Fluid simulations
- Cloth simulations

How We use them…

- Physics engine is a black box
- We “load” the physics engine
- Tell it which objects are dynamic
- Tell it which are static
- Define parameters, such as gravity, bounce and so on

- During each frame of animation:
- Update the physics engine by a delta time
- Ask the physics engine for:
- The location of each dynamic object
- The orientation of each dynamic object

TOKAMAK Example

- Typically have a limited number of basic shapes
- Cube
- Capsule
- Sphere

- Must declare variables to hold all of the objects in your scene
#include <tokamak.h>

neSimulator* gSim = NULL; neRigidBody* gCubes[NUM_CUBES]; neRigidBody* sphere; neAnimatedBody* floor1 = NULL; neT3 t;

void setupPhysicsEngine() {

// This will define the size and shape of each cube

neGeometry* geom;

// length, width and height of the cube

neV3 boxSize1;

neV3 gravity;

neV3 pos;

float mass;

float fmass = 0.2f;

// The number of total objects the simulator has to keep track of...

neSimulatorSizeInfosizeInfo;

// Fill in the size info about the environment

sizeInfo.rigidBodiesCount = NUM_CUBES+1;

sizeInfo.animatedBodiesCount = 1;

// total number of objects

sizeInfo.geometriesCount = sizeInfo.rigidBodiesCount + sizeInfo.animatedBodiesCount;

// total number of collisions possible n*(n-1)/2

sizeInfo.overlappedPairsCount = sizeInfo.geometriesCount*(sizeInfo.geometriesCount-1)/2;

sizeInfo.rigidParticleCount = 0;

sizeInfo.constraintsCount = 0;

sizeInfo.terrainNodesStartCount = 0;

gravity.Set(0.0f, -3.0f, 0.0f);

gSim = neSimulator::CreateSimulator(sizeInfo, NULL, &gravity);

// Setup a box - using loop

for (int i = 0; i < NUM_CUBES; i++) {

gCubes[i] = gSim->CreateRigidBody();

// Get the geometry object from the cube

geom = gCubes[i]->AddGeometry();

boxSize1.Set(1.0f, 1.0f, 1.0f);

geom->SetBoxSize(boxSize1[0], boxSize1[1], boxSize1[2]);

gCubes[i]->UpdateBoundingInfo();

mass = 1.0f;

gCubes[i]->SetInertiaTensor(neBoxInertiaTensor(boxSize1[0], boxSize1[1], boxSize1[2], mass));

gCubes[i]->SetMass(mass);

pos.Set(i%10-5, i/10+0.5, -30);

gCubes[i]->SetPos(pos);

}

// Create the sphere

sphere = gSim->CreateRigidBody();

geom = sphere->AddGeometry();

geom->SetSphereDiameter(2);

sphere->UpdateBoundingInfo();

sphere->SetInertiaTensor(neSphereInertiaTensor(2, fmass));

sphere->SetMass(fmass);

pos.Set(0, 1, -4);

sphere->SetPos(pos);

sphere->SetAngularDamping(0.01f);

// Create the floor

floor1 = gSim->CreateAnimatedBody();

geom = floor1->AddGeometry();

boxSize1.Set(100, 0.001, 100);

geom->SetBoxSize(boxSize1[0], boxSize1[1], boxSize1[2]);

floor1->UpdateBoundingInfo();

pos.Set(0, 0, 0);

floor1->SetPos(pos);

}

degree += 0.1f;

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

gSim->Advance(0.015);

//Cubes

for (int i = 0; i < NUM_CUBES; i++) {

t = gCubes[i]->GetTransform();

cube_state[0][0] = t.rot[0][0]; cube_state[1][0] = t.rot[1][0]; cube_state[2][0] = t.rot[2][0]; cube_state[3][0] = t.pos[0];

cube_state[0][1] = t.rot[0][1]; cube_state[1][1] = t.rot[1][1]; cube_state[2][1] = t.rot[2][1]; cube_state[3][1] = t.pos[1];

cube_state[0][2] = t.rot[0][2]; cube_state[1][2] = t.rot[1][2]; cube_state[2][2] = t.rot[2][2]; cube_state[3][2] = t.pos[2];

cube_state[0][3] = 0.0f; cube_state[1][3] = 0.0f; cube_state[2][3] = 0.0f; cube_state[3][3] = 1.0f;

drawCube(…);

}

// Sphere

t = sphere->GetTransform();

sphere_state[0][0] = t.rot[0][0]; sphere_state[1][0] = t.rot[1][0]; sphere_state[2][0] = t.rot[2][0]; sphere_state[3][0] = t.pos[0];

sphere_state[0][1] = t.rot[0][1]; sphere_state[1][1] = t.rot[1][1]; sphere_state[2][1] = t.rot[2][1]; sphere_state[3][1] = t.pos[1];

sphere_state[0][2] = t.rot[0][2]; sphere_state[1][2] = t.rot[1][2]; sphere_state[2][2] = t.rot[2][2]; sphere_state[3][2] = t.pos[2];

sphere_state[0][3] = 0.0f; sphere_state[1][3] = 0.0f; sphere_state[2][3] = 0.0f; sphere_state[3][3] = 1.0f;

drawSphere(…);

glutSwapBuffers();

glutPostRedisplay();

}

Common File Formats

- .3ds – AutoDesk 3DS Max (legacy)
- .blend - Blender
- .c4d – Cinema 4D
- .dae – COLLADA (xml)
- .fbx – AutoDesk
- .lwo – LightWave Object
- .ma/.mb – AutoDesk Maya
- .max – AutoDesk 3DS Max
- .md2/.md3 – Quake 2/Quake 3
- .pov – POV ray file
- .skp – Google Sketchup
- .sldasm – SolidWorlds Assembly
- .smd – Valve’s format
- .u3D – Universal 3D (3D Industry Consortium - xml)

The .OBJ file FOrmat

- Also called WaveFront OBJ
- Text-based
- Easy to work with and widely accepted
- File specifies:
- Position of each vertex
- UVs of each vertex
- Normals of each vertex
- List of faces (triangles)

Example(http://en.wikipedia.org/wiki/Wavefront_.obj_file)

# List of Vertices, with (x,y,z[,w]) coordinates, w is optional.

v 0.123 0.234 0.345 1.0

v ...

...

# Texture coordinates, in (u,v[,w]) coordinates, w is optional.

vt 0.500 -1.352 [0.234]

vt ...

...

# Normals in (x,y,z) form; normals might not be unit.

vn 0.707 0.000 0.707

vn ...

...

# Face Definitions (see below)

f 1 2 3 # Vertices only

f 3/1 4/2 5/3 # Vertices/Texture coords

f 6/4/1 3/5/3 7/6/5 # Vertices/Textures/Normals

f ...

...

Other Options

- Smooth shading
- s 1 – smoothing is true
- s off – no smoothing

- Materials may be put into a separate .mtl file
- newmtlmyMat
- Ka 1.000 1.000 1.000 #ambient white
- Kd 1.000 1.000 1.000 #diffuse white
- Ks 0.000 0.000 0.000 #specular off
- Ns 50.000 # size of spec (s from our lighting equation)
- Tr 0.9 #transparency

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