rendering theory & practice
DESCRIPTION
Rendering theory & practice. Introduction. We’ve looked at modelling, surfacing and animating. The final stage is rendering. This can be the most time consuming part of the process depending on the complexity of you scene. Many people underestimate the time needed But you won’t of course!. - PowerPoint PPT PresentationTRANSCRIPT
Rendering theory & practice
Introduction
We’ve looked at modelling, surfacing and animating.
The final stage is rendering. This can be the most time consuming part
of the process depending on the complexity of you scene.
Many people underestimate the time needed But you won’t of course!
Some basic things to remember
Render to frame files rather than movie files
Use file formats that use no compression or loss-less compression
Use anti-aliasing (within reason) Don’t raytrace if you can avoid it!
Simple shading
We’ve already considered this in the simplest sense: Flat, Gouraud and Phong shading
None of these consider inter-face reflections or shadows.
We need these for visual realism. For these we need global
illumination algorithms
Global illumination
This simulates the interaction of light with the entire environment rather than individual surfaces.
Light is tracked from emitters to sensors. Shadows are automatically generated, as
are interactions between surfaces. There are two common approaches: ray
tracing and radiosity Before we look at these in detail, we
should look at some general features of global illumination
Global illumination (2)
Ignoring the fact that the calculations (as we shall see later) are complex, the solution to global illumination is simple:
Start at a light source Trace every light path through the
environment it either:* hits the eye point* has its energy reduced below a threshold* travels out of the environment
A first attempt: the rendering equation
where I(x,x’) is the transport intensityg(x, x') is the visibility function(x, x') transfer emittance(x, x', x'') is the scattering term
s
xdxxIxxxxxxxgxxI ,,,,,,
Describes what happens at point x on a surface due to light travelling from it
Another attempt: surface-surface interactions
We can also model the way one surface interacts with another
This is easier to consider non-mathematically
Four different interactions:diffuse to diffusespecular to diffusediffuse to specularspecular to specular
Mechanisms of light transport
Diffuse to diffuse Specular to diffuse
Specular to specularDiffuse to specular
Mechanisms of light transport (2)
Specular-specular transfer can be calculated using ray-tracing
Diffuse-diffuse transfer can be calculated using radiosity
Specular-diffuse and diffuse-specular need a combination
We can categorise the type of transfer so that we know how to handle a given situation
Categories of light transfer
Light-Diffuse-Diffuse-Eye (LDDE) Light-Specular-Diffuse-Eye (LSDE) Light-Diffuse-Specular-Eye (LDSE) Light-Specular-Specular-Eye (LSSE) …
Examples of light transfer
Ray tracing
Initial ray
Transmitted ray
Reflected ray
Reflected ray
Transmitted ray
Eye
Initial ray
Transmitted ray Reflected ray
Including a local model
A classic ray-traced scene1
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Radiosity
This implements diffuse-diffuse transfer. Instead of following individual rays,
interaction between patches in a scene are considered.
This is different from other global illumination algorithms in two important ways:* the solution is view independent* the scene must be divided into patches
Radiosity (2)
Consider a light source as an array of emitting patches
Light is shot from these into the scene and we consider the diffuse-diffuse interaction between the light patch and the first hit patch
The energy arriving at the hit patch is then re-emitted according to the surface properties, hitting other patches…
This process iterates until there are no further significant changes in energy distribution
Radiosity example
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