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Honours Graphics 2008

Honours Graphics 2008. Session 7. Today’s focus. Indoor environment rendering BSP and Portal techniques revisited. Indoor / urban rendering. Often makes use of BSP / PVS system Octrees and Portal systems in use as well Portals form a solution for PVS creation. BSP.

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Honours Graphics 2008

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  1. Honours Graphics 2008 Session 7

  2. Today’s focus • Indoor environment rendering • BSP and Portal techniques revisited

  3. Indoor / urban rendering • Often makes use of BSP / PVS system • Octrees and Portal systems in use as well • Portals form a solution for PVS creation

  4. BSP • Several types of BSP trees: • Node-storing BSP • Leaf-storing BSP • Solid BSP • Each BSP type has specific properties that make it more useful for certain purposes

  5. Node BSP • Original BSP tree as described by Fuchs • Chooses dividing plane from available faces in geometry. Stores dividing face in node, passes along remaining faces as appropriate • Not conducive to tasks such as collision detection as the faces on nodes have no spatial relationship • Traditionally used in software renderers as it generates the least amount of splits

  6. Node BSP, image

  7. Leaf BSP • All geometric data stored in leafs • Nodes store only dividing plane • Leafs represent cells that store all the triangles in a list • Cells are convex and it is possible to find the openings between cells (sometimes called portals) • Useful in hardware rendering and techniques such as collision detection • Portals can be used to compute PVS for BSP

  8. Leaf BSP, image

  9. Solid BSP • Expands leafs of leafy BSP to provide solid information • Effective and elegant for techniques such as collision detection

  10. Solid BSP, image

  11. Solid Leafy BSP • Simply combines leafy and solid BSPs to maintain advantages of both

  12. Solid Leafy BSP, image

  13. Portals • Either placed manually by level-designers, or automatically • Automatic placement not optimal, but useful in many cases – such as automatically creating a PVS (requires portal information) • Uses splitting nodes of BSP to determine portals automatically

  14. Portals for rendering • Many advantages: • Theoretically no overdraw (optimal for software rendering) • Allows effects such as transparency and reflection • Can cater for somewhat dynamic environments • Conceptually easy to understand • But: can have significant computational overhead with arbitrary shaped view frusta with large number of planes. • Not as good for urban scenes in general

  15. Portals for rendering, cont. • Automatic portal creation normally produces a very large set of portals • Thus typically has to rely on manually placed portals by level-designers

  16. BSP, Collision detection

  17. Homework • Write code (pseudo or real) for Line-of-Sight determination • boolean GetLOS(BSP t, point a, point b); • Complete for session 9

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