Archives for: July 2009, 03

2009-07-03

Permalink 08:02:01 pm, by Olliebrown Email , 474 words, 1406 views   English (US)
Categories: GSoC 2009, Code Progress, Planning Progress

Change of Plans

A New Plan
Thanks to all who offered feedback for my previous post. With the discovery of the GSoC '08 branch for lighter2 with photon mapping plans need to change. I've been examining Greg Hoffman's changes to lighter2 to determine what work could be done and I think there's a good chunk here to constitute a project. Here's my assessment of what the branch contains:

  • There's a basic Photon Map data structure and code to emit and gather photons in a single sector.
  • This code does seem to do something but I don't think it's correct in all cases (or at least robust) yet
  • There are things missing (proper handling of materials, diffuse to diffuse light paths)
  • It's missing some options to fine tune the convergence (no max error, max recursion depth, no control over number of photons emitted)
  • Right now it's slow and has room for optimization

So, it seems given the original content of my proposal and this discovery from last summer that the new course of action should be to work on the photon mapping implementation. So, here's a basic outline of what I could do again welcoming comments:

Milestone 1: Repair

  1. Ensure the PM calculation is correct and fix where needed (such as handling LD+SE paths)

  2. Add the missing settings for controlling convergence

  3. Ensure it scales well from small test cases (like the Cornell Box) to large game levels

Milestone 2: Improve Quality

  1. Handle light traveling across portals

  2. Handle all materials properly (materials are ignored right now)

Milestone 3: Improve Speed/Features

  1. Add importance sampling to avoid redundant photon emission

  2. Move calculations to GPU (BIG speedup)

  3. Optional: Add support for 'dielectrics' (refracting materials) and caustics (via reflection and refraction)

Concerning the optional task under Milestone 2, Photon Mapping just handles caustics well (it's famous for it) and as such it would be easy to render this if the information about refraction is available in the material structure (namely index of refraction). It could make for some interesting but very specialized effects.

Time-line
I'm planning about two weeks for each milestone with an extra week for the first one just for getting out of the starting gate. Here's a rough time-line to completion of these milestones:

  • Milestone 1 (already in progress): Now - July 21st
  • Milestone 2: July 22nd - Aug 4th
  • Milestone 3: Aug 5th - Aug 18th

I want to make sure that the amount of work I'm doing is worthy of a full SoC project regardless of the time frame. I'm definitely slow getting started here and I want to ensure all involved that I will make that up as we go either by putting in extra time now or beyond the scheduled GSoC end. Therefore, I think it is best to make sure I get a project defined that is of a scope appropriate for SoC so that no one feels short changed.

OllieBrown

Info about progress on my Google Summer of Code 2009 project on Advanced Lighting & Shading in CrystalSpace.

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