Other Things You Should Know

1. Other Things You Should Know CS 4363/6353

2. Overview • Matrix Stacks • Raytracing and NPR • Physics Engines • Common File Formats

3. 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)

4. Matrix Stack Example Camera matrix

5. Matrix Stack Example “Push” the camera matrix.Note: everything is rotated by our camera matrix… Camera matrix

6. Matrix Stack Example “Push” the translation of the sun Sun trans matrix Camera matrix

7. 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

8. Matrix Stack Example The Earth is both translated Sun trans matrix Camera matrix Note: yes, yes… I know it’s not to scale…

9. Matrix Stack Example The Earth is both translated Earth trans matrix Sun trans matrix Camera matrix

10. 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

11. Matrix Stack Example WRONG! The matrices aremultiplied TOP DOWN! Earth rot matrix Earth trans matrix Sun trans matrix Camera matrix

12. Matrix Stack Example WRONG! The matrices aremultiplied TOP DOWN! Earth trans matrix Earth rot matrix Sun trans matrix Camera matrix

13. 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

14. Matrix Stack Example What about the moon? Earth trans matrix Earth rot matrix Sun trans matrix Camera matrix

15. Matrix Stack Example Well, the moon has a translation… Moon trans matrix Earth trans matrix Earth rot matrix Sun trans matrix Camera matrix

16. 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

17. 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

18. 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

19. 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

20. Matrix Stack Example POP the Moon stuff! Earth trans matrix Earth rot matrix Sun trans matrix Camera matrix

21. Matrix Stack Example POP the Earth stuff! Earth trans matrix Earth rot matrix Sun trans matrix Camera matrix

22. Matrix Stack Example POP the Sun stuff! Sun trans matrix Camera matrix

23. Matrix Stack Example …Leaving us with just thecamera matrix. Then, we can add the spaceship matrices on top of that. Camera matrix

24. Matrix Stack Example Push the spaceship trans first! Ship trans matrix Camera matrix

25. Matrix Stack Example Then the rotation! Why? Ship rot matrix Ship trans matrix Camera matrix

26. Matrix Stack Example Now that you have your MV, draw the ship… Ship rot matrix Ship trans matrix mMV Camera matrix

27. RaYTracing • Easy to read article at http://en.wikipedia.org/wiki/Ray_tracing_(graphics) Note: there are independent reflection, refraction and shadow rays

28. Examples(again, from Wikipedia.org)

29. Examples(again, from Wikipedia.org)

30. 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

31. 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

32. 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

34. 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

35. 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

36. 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;

37. 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); }

38. 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[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(); }

39. 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)

40. 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)

41. 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 ... ...

42. 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