TIEA311 Tietokonegrafiikan perusteet kevät 2017

Transcription

1 TIEA311 Tietokonegrafiikan perusteet kevät 2017 ( Principles of Computer Graphics Spring 2017) Copyright and Fair Use Notice: The lecture videos of this course are made available for registered students only. Please, do not redistribute them for other purposes. Use of auxiliary copyrighted material (academic papers, industrial standards, web pages, videos, and other materials) as a part of this lecture is intended to happen under academic fair use to illustrate key points of the subject matter. The lecturer may be contacted for take-down requests or other copyright concerns ( paavo.j.nieminen@jyu.fi).

2 TIEA311 Tietokonegrafiikan perusteet kevät 2017 ( Principles of Computer Graphics Spring 2017) Adapted from: Wojciech Matusik, and Frédo Durand: Computer Graphics. Fall Massachusetts Institute of Technology: MIT OpenCourseWare, License: Creative Commons BY-NC-SA Original license terms apply. Re-arrangement and new content copyright 2017 by Paavo Nieminen and Jarno Kansanaho Frontpage of the local course version, held during Spring 2017 at the Faculty of Information technology, University of Jyväskylä: nieminen/tgp17/

3 TIEA311 - Local plan for today Today (Thu, Feb 2, 2017) in Mattilanniemi... Corrections to the previous lecture talk (slides are not replicated here we just discuss the previous ones about homogeneous coordinates, homogenization, and perspective in 2D and 3D). Continue with the MIT OCW slides about hierarchical models Leave that story to whichever cliffhanger happens when we go to break. Have a break to get coffee, air, walk abouts, or whatever breaks are necessary. Take a deep breath Discuss Assignment 1, with C++, if lecture room technology allows

4 6.837 Computer Graphics Hierarchical Modeling Wojciech Matusik, MIT EECS Some slides from BarbCutler & Jaakko Lehtinen Image courtesy of BrokenSphere on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 1 1

5 Hierarchical Modeling Triangles, parametric curves and surfaces are the building blocks from which more complex real-world objects are modeled. Hierarchical modeling creates complex realworld objects by combining simple primitive shapes into more complex aggregate objects. Image courtesy of Nostalgic dave on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 21

6 Hierarchical models Image courtesy of David Bařina, Kamil Dudka, Jakub Filák, Lukáš Hefka on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 22

7 Hierarchical models Image courtesy of David Bařina, Kamil Dudka, Jakub Filák, Lukáš Hefka on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 23

8 Hierarchical models Image courtesy of David Bařina, Kamil Dudka, Jakub Filák, Lukáš Hefka on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 24

9 Hierarchical models Image courtesy of David Bařina, Kamil Dudka, Jakub Filák, Lukáš Hefka on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 25

10 Hierarchical models Image courtesy of David Bařina, Kamil Dudka, Jakub Filák, Lukáš Hefka on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 26

11 Hierarchical models Image courtesy of David Bařina, Kamil Dudka, Jakub Filák, Lukáš Hefka on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see 27

12 Hierarchical ing of Objects The scene graph represents the logical organization of scene scene chair table ground table fruits Durand 28

13 Scene Graph Convenient Data structure for scene representation Geometry (meshes, etc.) Transformations Materials, color Multiple instances Basic idea: Hierarchical Tree Useful for manipulation/animation Also for articulated figures Useful for rendering, too Ray tracing acceleration, occlusion culling But note that two things that are close to each other in the tree are NOT necessarily spatially near each other Image courtesy of David Bařina, Kamil Dudka, Jakub Filák, Lukáš Hefka on Wikimedia Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see This image is in the public domain. Source: Wikimedia Commons. 29

14 Scene Graph Representation Basic idea: Tree Comprised of several node types Shape: 3D geometric objects Transform: Affect current transformation Property: Color, texture : Collection of subgraphs C++ implementation base class Object children, parent derived classes for each node type (group, transform) 30

15 Scene Graph Representation In fact, generalization of a tree: Directed Acyclic Graph (DAG) Means a node can have multiple parents, but cycles are not allowed Why? Allows multiple instantiations Reuse complex hierarchies many times in the scene using different transformations (example: a tree) Of course, if you only want to reuse meshes, just load the mesh once and make several geometry nodes point to the same data Trsfrm Trsfrm Trsfrm Trsfrm 31

16 Simple Example with s { numobjects 3 { numobjects 3 Box { <BOX PARAMS> } Box { <BOX PARAMS> } Box { <BOX PARAMS> } } { numobjects 2 { Box { <BOX PARAMS> } Box { <BOX PARAMS> } Box { <BOX PARAMS> } } { Box { <BOX PARAMS> } Sphere { <SPHERE PARAMS> } Sphere { <SPHERE PARAMS> } } } Plane { <PLANE PARAMS> } } Text format is fictitious, better to use XML in real applications Durand 32

17 Simple Example with s { numobjects 3 { numobjects 3 Box { <BOX PARAMS> } Box { <BOX PARAMS> } Box { <BOX PARAMS> } } { numobjects 2 { Box { <BOX PARAMS> } Box { <BOX PARAMS> } Box { <BOX PARAMS> } } { Box { <BOX PARAMS> } Sphere { <SPHERE PARAMS> } Sphere { <SPHERE PARAMS> } } } Plane { <PLANE PARAMS> } } Here we have only simple shapes, but easy to add a Mesh node whose parameters specify an.obj to load (say) Durand 34

18 Adding Attributes (Material, etc.) 35 { numobjects 3 Material { <BLUE> } { numobjects 3 Box { <BOX PARAMS> } Box { <BOX PARAMS> } Box { <BOX PARAMS> } } { numobjects 2 Material { <BROWN> } { Box { <BOX PARAMS> } Box { <BOX PARAMS> } Box { <BOX PARAMS> } } { Material { <GREEN> } Box { <BOX PARAMS> } Material { <RED> } Sphere { <SPHERE PARAMS> } Material { <ORANGE> } Sphere { <SPHERE PARAMS> } } } Material { <BLACK> } Plane { <PLANE PARAMS> } }

19 Adding Transformations 36

20 Questions? 37

21 Scene Graph Traversal 38 Depth first recursion Visit node, then visit subtrees (top to bottom, left to right) When visiting a geometry node: Draw it! How to handle transformations? Remember, transformations are always specified in coordinate system of the parent

22 Scene Graph Traversal 39 How to handle transformations? Traversal algorithm keeps a transformation state S (a 4x4 matrix) from world coordinates Initialized to identity in the beginning Geometry nodes always drawn using current S When visiting a transformation node T: multiply current state S with T, then visit child nodes Has the effect that nodes below will have new transformation When all children have been visited, undo the effect of T!

23 Traversal Example 43 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit)

24 Traversal Example 44 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = I

25 Traversal Example 45 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1

26 Traversal Example 46 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1

27 Traversal Example 47 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1 T2

28 Traversal Example 48 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1 T2

29 Traversal Example 49 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1 T2

30 Traversal Example 50 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1

31 Traversal Example 51 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1 R1

32 Traversal Example 52 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1 R1

33 Traversal Example 53 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1 R1

34 Traversal Example 54 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1

35 Traversal Example 55 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1

36 Traversal Example 56 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = I

37 Traversal Example 57 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = R2

38 Traversal Example 58 Root Translate T1 Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = R2

39 Traversal Example Root Translate T1 Rotate R2 (table, fruits) Translate T2 Rotate R1 (chair, legs)... (tabletop, legs) (basket, fruit) S = R2 59

40 Traversal Example Translate T1 Root At each node, the current object-to-world transformation is the matrix product of all transformations found on the way from the node to the root. Rotate R2 (table, fruits) (chair, legs) Translate T2 Rotate R1 (tabletop, legs) (basket, fruit) S = T1R1 60

41 TIEA311 - Cliffhanger! So... what is a good way to handle this traversal especially undoing previous transformations? How is this related to the OpenGL specification and the codes that draw the triangles of the OBJ file (or the Utah Teapot) in our Assignment 0? Next lecture continues, again, right from these thoughts, with minimal recap be prepared! Now: We have an all-important break, letting our brains cool down a bit. After the break: Connection between theory, practice, and learning. Concrete C++ coding, if Santa has brought us Visual Studio in the lecture hall.

42 TIEA311 - Local situation Observations from computer classes and the unofficial IRC-chat IRCnet irc.cc.tut.fi allows us to connect; Linkki Jyväskylä ry has how-to guides; running screen and irssi on our university servers is standard practice): WOW, do we have a heterogeneous group working on homogeneous coordinates (joke, joke, so we don t get all gloomy about this! No need to be gloomy!) This is no surprise more like an everyday thing. Do not stress out! We will adapt the course requirements to match our needs. The needs? (1) Everyone learns important stuff on his/her own current level, moving towards being an IT pro. (2) Everyone learns the basics / fundamentals / principles of computer graphics, too (but then again, it is only one application among so many in IT).

43 TIEA311 - What it means to adapt If we need to extend deadlines, we do. If we need to leave out Assignments from our local requirements, we do. If we need to define grade 1/5 as partial implementation wrt to an original Assignment, we do. If someone feels that the course is progressing too slowly, you are free to move on to the next Assignment! The MIT OCW total material covers a full semester course... do as much as you can in the 135 hours allocated for this 5 ECTS version. Also, try helping your coursemates; that will teach you not only the stuff but the important skill of explaining stuff to others. Also, whatever you personally had to do in order to discover something, might be suitable for some other person, too! I can only offer my own perspective (and that is always projected to a lower dimension... joke. funny.)

44 TIEA311 - Words of advice, midcourse You can. There is nothing wrong with your brain. Never say I don t have the brain for this. You do have! Never think it is wasted time to feel the pain of not yet understanding, if you are focused in trying to understand You must understand your question before there is any chance to understand an answer. Otherwise you just hear or see a meaningless fact that passes by. You cannot suddenly appear at the top of a mountain you climb step by step! People who climb to Mount Everest must first climb other mountains; Before the top of Mt. Everest they need to spend time to acclimatize or they die. I honestly think that the solution to most problems I ve seen so far on this course instance is: Slow down. Breathe. Forget that there is a deadline and focus on understanding, right in the current moment.

45 TIEA311 - Words of a wiser man This course is not a math course far from it! But we are dealing with math kinda stuff, so let me cite Sheldon Axler from his Preface to the Student in his wonderful book Linear Algebra Done Right : You cannot expect to read mathematics the way you read a novel. If you zip through a page in less than an hour, you are probably going too fast. When you encounter the phrase as you should verify, you should indeed do the verification, which will usually require some writing on your part. When steps are left out, you need to supply the missing pieces. You should ponder and internalize each definition. For each theorem, you should seek examples to show why each hypothesis is necessary.

46 TIEA311 - Dive! This said... let s look at the Assignments. [live, on-screen, thanking Santa (and our IT support, naturally)]