5 5a 5b 2 3 1 4 3 front 2 4 front 5a back 1 5b

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Unformatted text preview: r half-space for a polygon can back face cull. ● Always drawing the opposite side of the viewer first Lecture 9 19/10/2007 In what order will the faces be drawn? 5 5a 5b 2 3 1 4 3 front 2 4 front 5a back 1 5b Displaying a BSP tree : Front to Back ● The back-to-front rendering will result in a lot of over drawing again ● Front-to-back traversal is more efficient (Chen and Gordon, 1991) ○ Record which region has been filled in already ○ Terminate when all regions of the screen is filled in Lecture 9 19/10/2007 * Displaying a BSP tree : Front to Back (2) •To hold data on filled in pixels, use Active Edge Table •Recording the pixels not filled in yet for each scan line Lecture 9 19/10/2007 * BSP Tree: Discussions ● A lot of computation required at start. ○ Need to produce a well balanced tree ○ Intersecting polygon splitting may also be costly ● Cheap to check visibility once tree is set up ● Efficient when objects don’t change very often in the scene. 5 2 1 3 5 back 4 back 3 front 1 back 2 4 Alternate formulatio n starting at 5 BSP Tree: Discussions (2) ● Good to combine with Z-buffer ● Render the static objects first (front-to-back) with the Z-buffer on, ● And then the dynamic objects (doors, characters) 19/10/2007 Ex. Architectural scenes Here there can be an enormous amount of occlusion Lecture 9 19/10/2007 * Portal Culling D Model scene as a graph: • Nodes: Cells (or rooms) • Edges: Portals (or doors) B E A C F G Graph gives us: • Potentially visible set 1.Render the room 2.If portal to the next room is visible, render the connected room in the portal region 3.Repeat the process along the scene graph A B C D E 19/10/2007 * Object space and Image space classification: ● Object space techniques: applied before...
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This document was uploaded on 03/26/2014.

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