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

• 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

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

Node BSP, image

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

Leaf BSP, image

Solid BSP

• Expands leafs of leafy BSP to provide solid information

• Effective and elegant for techniques such as collision detection

Solid BSP, image

Solid Leafy BSP

• Simply combines leafy and solid BSPs to maintain advantages of both

Solid Leafy BSP, image

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

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

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

BSP, Collision detection

Homework

• Write code (pseudo or real) for Line-of-Sight determination

• boolean GetLOS(BSP t, point a, point b);• Complete for session 9