# Other Things You Should Know - Kennesaw State University 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 Lets 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 Sun trans matrix Camera matrix Order of operations

MATRIX STACK EXAMPLE Push the translation of the sun Combine everything on the stack into one MV matrix, then draw the sun. Trans first, then camera! mMV Sun trans matrix Camera matrix MATRIX STACK EXAMPLE

The Earth is both translated Sun trans matrix Camera matrix Note: yes, yes I know its not to scale MATRIX STACK EXAMPLE The Earth is both translated Earth trans matrix Sun trans matrix Camera matrix

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 are

multiplied TOP DOWN! Earth rot matrix Earth trans matrix Sun trans matrix Camera matrix MATRIX STACK EXAMPLE WRONG! The matrices are multiplied TOP DOWN! Earth trans matrix Earth rot matrix Sun trans matrix Camera matrix

Combine everything on the stack into one MV matrix, then draw the Earth! Order MATRIX STACK EXAMPLE mMV Earth trans matrix Earth rot matrix 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 Well, the moon has a translation as well as a rotation Moon rot matrix Moon trans matrix Earth trans matrix Earth rot matrix Sun trans matrix

Camera matrix MATRIX STACK EXAMPLE Well, the moon has a translation as well as a rotation Moon trans matrix Moon rot matrix Earth trans matrix Earth rot matrix Sun trans matrix Camera matrix

Order MATRIX STACK EXAMPLE Moon trans matrix Moon rot matrix So we combine everything on the stack into one MV matrix, then draw the moon mMV Earth trans matrix Earth rot matrix Sun trans matrix

Camera matrix MATRIX STACK EXAMPLE What if we want to draw a little independent spaceship? Moon trans matrix 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 POP the Sun stuff! Sun trans matrix Camera matrix MATRIX STACK EXAMPLE Leaving us with just the camera matrix. Then, we can add the spaceship matrices on top of that.

Camera matrix MATRIX STACK EXAMPLE Push the spaceship trans first! Ship trans matrix Camera matrix MATRIX STACK EXAMPLE Then the rotation! Why? Ship rot matrix Ship trans matrix

Camera matrix MATRIX STACK EXAMPLE Now that you have your MV, draw the ship mMV Ship rot matrix Ship trans matrix 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 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 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... neSimulatorSizeInfo sizeInfo; // 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, boxSize1, boxSize1); gCubes[i]->UpdateBoundingInfo();

mass = 1.0f; gCubes[i]->SetInertiaTensor(neBoxInertiaTensor(boxSize1, boxSize1, boxSize1, 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, boxSize1, boxSize1); floor1->UpdateBoundingInfo(); pos.Set(0, 0, 0); floor1->SetPos(pos); } void display () { 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 = t.rot; cube_state = t.rot; cube_state = t.rot; cube_state = t.pos; cube_state = t.rot; cube_state = t.rot; cube_state = t.rot; cube_state = t.pos; cube_state = t.rot; cube_state = t.rot; cube_state = t.rot; cube_state = t.pos; cube_state = 0.0f; cube_state = 0.0f; cube_state = 0.0f; cube_state = 1.0f; drawCube(); } // Sphere t = sphere->GetTransform(); sphere_state = t.rot; sphere_state = t.rot; sphere_state = t.rot; sphere_state = t.pos; sphere_state = t.rot; sphere_state = t.rot; sphere_state = t.rot; sphere_state = t.pos; sphere_state = t.rot; sphere_state = t.rot; sphere_state = t.rot; sphere_state = t.pos; sphere_state = 0.0f; sphere_state = 0.0f; sphere_state = 0.0f; sphere_state = 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 Valves 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 newmtl myMat 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 equation) # size of spec (s from our lighting Tr #transparency 0.9