More Advanced Lighting and Shading
Biography
My name is Guofu Xie. I am a second year graduate student of Institute of
Software, Chinese Academy of Sciences (ISCAS). My major is Computer
Graphics. My research focuses on rendering (e.g., Shadow, BRDF, Refraction,
Ray tracing) and modeling of material appearance. I like it and feel it very
interesting and exciting. Experience in graphics development and research is
almost 3 years. I have exceptional understanding of 2D and 3D graphics
techniques, including OpenGL, GPU (GLSL, Cg), and CUDA. My experience in
C/C++ is 5 years.
I usually take part in Open Source activities and I am vice-president of the
Open Source Association of my University. In GSoC 2008, I added HDR image
surface type into Cairo project. In University, my major is Software
Engineering. I have led some projects, for example Chinese Chess, AutoCAD
secondary development, and student management system. Now I am researching
on fast Ray Tracing, Rendering and GPU. I hope I can bring the new
development directions for Crystal Space based on my current research.
Project Details
The Lambertian and Phong model are an inadequate approximation of the
diffuse and specular component. Currently, Bidirectional reflectance
distribution model (BRDF) takes the roughness of the surface into account.
Rough surfaces can be modeled as a collection of small microfacets.
Microfacet-based BRDF models work by statistically modeling the scattering
of light from a large collection of such microfacets. The two main
components of microfacet models are an expression for the distribution of
facets and a BRDF that describes how light scatters from individual
microfacets. The Cook-Torrance model treats every facet as a perfectly
smooth mirrored reflector, while the Oren-Nayar model as a Lambertian
reflector.
Currently, Crystal Space mainly uses the Blinn-Phong shading model to
utilize direct and precomputed indirect lighting, while the model is not
inadequate surface approximation. Cook-Torrance or Oren-Nayar, which
accounts for the roughness of the surface, can represent material appearance
of the surface preferably.
In precomputation (lighter2), I will modify the function of ShadeLight in
class DirectLighting and add alternative shading models. In my
implementation, I will use some optimizations in order to efficiently
compute lighting, such as a simple expression of geometric attenuation
coefficient and an excellent approximation of Fresnel factor. In the runtime
part (shaders), I will rewrite some XML shaders about reflect, which are in
data/shader/reflect and data/shader/snippets/reflect.
About Screen Space Ambient Occlusion (SSAO), Meshula has a very good
overview in his blog. In addition, there is a project of SSAO in Second Life
of GSoC 2008. I don’t think it is difficult to implement the light
algorithm.
References
[1] M. Pharr, G. Humphreys, Physically based rendering: from theory to
implementation, Morgan Kaufman, 2004.
[2] C. Schlick, A survey of shading and reflectance models, Computer
Graphics Forum, 1994.
[3] Specular highlight, http://en.wikipedia.org/wiki/Specular_highlight
[4] Oren-Nayar model, http://en.wikipedia.org/wiki/Oren-Nayar_diffuse_model
[5] Screen Space Ambient Occlusion, http://meshula.net/wordpress/?p=145
[6] Screen Space Ambient Occlusion,
http://wiki.secondlife.com/wiki/Google_SoC_2008
--
BEST WISHES!
YOURS SINCERELY,
Guofu Xie
CG Group, State Key Laboratory of Computer Science, Institute of Software,
Chinese Academy of Sciences(ISCAS)
Tel: (+86)15810330487
Email: [email protected]
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