Date post: | 21-Dec-2015 |
Category: |
Documents |
View: | 214 times |
Download: | 1 times |
Why?
Ray tracing has a visual signature Only models perfect
specular reflection and transmission
Interaction between diffusely reflecting surfaces Interiors, matte surfaces,
indirect lighting
Basic idea
Divide surfaces into discrete patchesObject space algorithm
Model light transfer between patches as system of linear equations
Solve matrix equation for radiosity of each patchDo it for R,G,B
Render patches as colored polygons
Simplifying assumptions
All surfaces are perfectly diffuseDoes not matter which way light
enters or leaves a surface Radiosity is constant over a patch
Radiosity Equation
Bi is radiosity of patch i energy per unit area leaving a surface patch
per unit time rate energy emitted + rate energy reflected
Ei is non-zero for emitters Ri is reflectivity of the patch
Wavelength dependent Fij is the form factor – how much light patch j
contributes to patch i Depends on geometric relationship –
distance and relative orientation
Radiosity solution
Finding form factors Hemicube method
Meshing strategies Solving set of linear equations to get
radiosity for each patch
Gathering vs. Shooting
Gathering One iteration updates a
single patch by gathering contributions from all other patches
Shooting (and sorting) Single iteration updates all
receiving patches with unshot energy
Process patches according to amount of energy they are likely to radiate
Problems
Aliasing from hemicube methodUniform pixel size
Using bilinear interpolation to reconstruct radiosity function
Using meshing of scene independent of variations in radiosity function
Hemicube aliasing
Limited resolution of the hemicube pixels
Patches of same size map to different number of cells
Meshing strategies
Discontinuity meshingCompleted before radiosity solutionPredict where discontinuities will occur
Adaptive meshingRefine a “start” mesh as the solution
progresses
Discontinuity meshing
Mesh around expected discontinuities Sharp boundaries from point
light source or object contact
Derivative discontinuities from area light sources and multi-object shadows