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Managing Your Objects

Managing Your Objects. Paul Taylor 2009 Assignment Due Fri 5/6/2009. What is an Object. A Bunch of Polygons (or one), or a Sprite Each Object can have: A Translation A Rotation A Scale A Shear (not super common). Our Test Objects. A Sweet Car!. The Simplest Representation.

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Managing Your Objects

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  1. Managing Your Objects Paul Taylor 2009 Assignment Due Fri 5/6/2009

  2. What is an Object • A Bunch of Polygons (or one), or a Sprite • Each Object can have: • A Translation • A Rotation • A Scale • A Shear (not super common)

  3. Our Test Objects • A Sweet Car!

  4. The Simplest Representation • Car Body Translation, Rotation and Scale • Wheel 1 Translation, Rotation and Scale • Wheel 2 Translation, Rotation and Scale

  5. Scale Rotate Translate Scale Rotate Translate Scale Rotate Translate

  6. Using Hierarchical Objects

  7. With our Matricies Scale Rotate Translate Scale Rotate Translate Scale Rotate Translate

  8. Directed Acyclic Graphs (DAG) • Technically this is a Specialised case of a Directed Graph • The rule is there are no paths that start at a vertex and end at the same vertex (No Loops)

  9. What is the benefit? We can Reuse Objects Cars have four wheels A flock of birds may all be the same A turret may have 4 Cannons

  10. Sweet Car utilising a DAG

  11. Connecting All your Objects • We are creating a Scene Graph

  12. In effect Object Storage Looks Like Root Child 1 Child 2 Sibling 1 Sibling 2 Sibling 2 Child 1 Child 3 Sibling 2 Child 2 Sibling 2 Child 2 Sibling 1

  13. Creating Bounding Boxes BBs are typically used For Collision Detection With a Hierarchical Object generation can still be relatively simple. Outlier detection in X Y Z and –X-Y-Z directions A Bounding Sphere simply needs the most distant vertex from the Object Center More Complicated routines can be used, or you can use a Human!

  14. Constructive Geometry • Not generally used during real time renders • Consist of using Logical Operators on Polygon Objects to combine them • Intersections, Unions and Difference • A Typical Use of Constructive Geometry is in 3D Game Level creation and CAD Design

  15. Constructive Solid Geometry CSG • http://dic.academic.ru/pictures/enwiki/67/Csg_tree.png

  16. http://brlcad.org/gallery/d/242-3/csg_example.png

  17. We have our Objects Nicely packed • Why? • To Create Structures that define the 3D Worlds we are creating • Intersecting the Bounding Boxes/Spheres in the game world is much faster. • Once we know that 2 objects intersect (via BB collision) we can go deeper into the collision (If needed)

  18. Space Subdivision We have already covered BSP Trees, now we will look at 1 1/2 more Space Partitioning methods Oct-Trees KD-Trees

  19. Quad-Trees Quad Trees are the 2D baby brother of Oct Trees Computationally similar, conceptually easier Space is Divided into 4 areas If more than one object exists in a region it is again subdivided into 4 sub-regions, and so on….

  20. http://acm.pku.edu.cn/JudgeOnline/images/1610_1.jpg

  21. http://www.directionsmag.com/images/articles/spatialDBMS/quadtree.gifhttp://www.directionsmag.com/images/articles/spatialDBMS/quadtree.gif

  22. Oct-Trees • http://en.wikipedia.org/wiki/File:Octree2.png

  23. http://www.cs.ucl.ac.uk/research/equator/papers/Documents2002/Jean-Daniel_Nahmias/Massive_Model_Rendering.htmhttp://www.cs.ucl.ac.uk/research/equator/papers/Documents2002/Jean-Daniel_Nahmias/Massive_Model_Rendering.htm

  24. KD-Trees • A specialisation of Binary Trees (Similar to BSP Trees) • In a similar way to Oct Trees a KD Tree splits space in an Axis Aligned Fashion. • Different to Oct-Trees a KD Tree does not always split the world into even parts

  25. KD-Trees • http://en.wikipedia.org/wiki/Kd-tree

  26. http://www-hpcc.astro.washington.edu/old_content/papers/marios/perform/node3.htmlhttp://www-hpcc.astro.washington.edu/old_content/papers/marios/perform/node3.html

  27. What else can you do? • Oct-Trees and KD-Trees can be used for: • View Frustum Culling • Occlusion Culling • Level of Detail Detection • Spatial Indexing (Similar to a BSP Tree) • Ray Casting

  28. Bringing it all together • You organise all of your objects • Binary Tree, Object Tree, Hash Table etc • You have a method of generating Collisions • Firstly by Simplifying objects • Bounding Boxes, Spheres • Secondly by finding Collisions between objects • Oct-Trees, KD-Trees • Thirdly we can check the collision of the actual objects if required • Finally we need to do something appropriate with the collision!

  29. That’s a lot of work!

  30. Open Scene Graph (OSG) http://www.openscenegraph.org/ Multipass Object Grouping and Ordering Middleware that does Object Handling Things you could do with it: • Prototyping • Offline Rendering • A Sluggish Game

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