1 KIPA Game Engine Seminars Jonathan Blow Ajou University December 4, 2002 Day 8

2 Small issues left over from yesterday Discuss cross-platformness of Keyboard::event Why I converted the 5km map example to centimeters Memory allocation and “block loading” –Why block loading is kind of funny

3 Filter bandwidth When talking about the frame-time independent filters, I have been speaking of decay rate and not filter bandwidth When a question was asked in terms of bandwidth, it made me wonder why I do this Answer: it has to do with uniform vs nonuniform sampling

4 Event Queues Show example of a big networking switch like we discussed yesterday –Interesting structure where things can be sent noncentralized, but must be received centralized An indicator that the structure should be questioned? Example of in-game object destroy/create, hide/unhide –Another reason to perhaps want that history query feature

5 Mesh Load/Save Looking through the code for the triangle strip mesh

6 Why the Tcp_Connection class Interface with Web services, etc

7 Looking at the network protocol code… We talked about UDP vs TCP kinds of things, but never looked at the various classes –Talk about the prevent-a-copy trick for wrapped_send() that I don’t actually do yet –Two-level structure of Net_Manager::* and Network::*

8 Rendering

9 BRDF Rendering (Show demo again) Discussion of the basic idea Two reasons to do this: –Better simulation of the real world –Data-driven shaders

10 BRDFs: Acquiring the data Gonioreflectometer measurements Virtual gonioreflectometer –Raytracer and some microgeometry Analytic function –Ward model

11 The Singular Value Decomposition (SVD) Factor A into VSW* –V and W are unitary –S is diagonal, positive entries on diagonal, highest magnitude first Same as weighted sum of vectors

12 Using the SVD on BRDF data Our starting matrix is 4D, not 2D Our V, W are 2D matrices These matrices can be stored as texture maps, and multiplied together –Just 2 texture units per piece of the approximation The parameterization of V and W are determined by the initial parameterization of A

13 SVD cost SVD is very expensive so we can use an approximation instead Kautz and McCool use the “Normalized Decomposition” (ND)

14 Dynamic Range on conventional hardware? Need to compute Vs k W* and store that in the frame buffer –Clamping in texture units causes problems! s too high? –So we need to scale the s values to the range [0, 1] Then we suffer a lot of banding in the texture units –This scaling needs to be the same for all objects in the scene One bright object makes the darker objects suffer

15 Solved on newer cards Radeon 9700, Geforce 5 FX Linear-light frame buffer (gamma = 1), floating point pixels, exponentiate pixels when it’s time to page flip –or let the CLUT / RAMDAC do the right thing Still not perfect –Limited handling of fp pixels is available (no antialiasing, alpha blending)

16 Why shaders are not cool A shader is treated as a monolithic program Can only call subroutines within that program (no subroutines until pixel shader 2.0) There can be a combinatoric explosion of shaders based on what you want to do –Example of different BRDF parameterizations