As part of the process of creating a 3D
scene, we are building up a model of
The geometry of those objects
The relationship of those objects to each other
The relationship of the objects to the camera.
However, in order to turn this scene into a
useable image, we must go through a
The aim of rendering is to view objects as
Not polymeshes, wireframes, or any other of
the representations we have discussed.
Requires several steps
Identify which surfaces are visible
Project surfaces onto the 2D viewing plane
Shade surfaces appropriately
Convert from mathematical representation into
RENDERING – TWO FLAVOURS
Depending on the intended application,
rendering can have one of two flavours.
Movies, static scenes
In both cases, the end goal is the same.
Turn the mathematical representations of a 3D scene
into something pretty.
For real-time scenarios, trade-offs are
Scenes must be rendered quickly enough for
the human eye to be fooled
Around 30 frames per second
Trade off is between photorealism and speed of
Can use tricks to ‘fool’ viewers.
As time goes by, this trade-off becomes
Computers get faster, our eyes don’t.
NON REAL-TIME RENDERING
For non-interactive media, time is not important.
We can spent many more seconds rendering an image
because we have no throughput to reach.
Each frame may take minutes/hours to render.
Played back at 25-30 frames per second.
Like old fashioned cartoon animations.
RENDERING - LIGHT
Simply assigning a colour to a surface
gives an unrealistic appearance.
The interaction of light with objects is one of
the primary mechanisms for achieving
Light interaction is complex
Texture of surfaces
RENDERING - LIGHT
The appearance of an object depends on:
The type of light source
Distance to the light source
Orientation of the object relative to the light source
Surface properties of the object
Determines the nature of light interaction
Repeat for all light sources.
Lots of processing.
RENDERING - LIGHT
In non real-time situations, we can precisely
model the physics of light interaction.
Such as with ray-tracing
For real-time situations, an approximation will
As long as it looks good.
There are several kinds of light sources
that are used in 3D modelling.
Point light sources
Ambient light sources
Directional light sources
They are all used to give differing
‘textures’ of light and shadow.
Choosing the right kind and number of light
sources an important part of good scene
LIGHT SOURCES - AMBIENT
Ambient light is the general background
All objects reflect light to some degree
Light can reach parts of a room/scene that are in no
direct line of light.
Illumination is constant on all surfaces
Regardless of position or orientation
Light is uniform across a scene.
LIGHT SOURCES - DIRECTIONAL
Directional light sources emit light
strongly in a particular direction.
Like the sun
Objects in the line of light more brightly
illuminated than other objects.
Light is uniformly provided in a fixed
Light source is assumed to be very far
No need to deal with light distance
Objects at the back of a scene lit to the
same degree as objects at the front
Provided they are directly in the path of light.
LIGHT SOURCES - POINT
Point light sources have
They emit light equally in all directions.
Like a lightbulb.
Light strength attenuates
Gets weaker with distance
Gradients of illumination across a surface
Can be moved around with a scene.
LIGHT SOURCES - SPOTLIGHT
Very similar to a point light source
Difference is that spotlight source does not
radiate in all directions.
Direction of light can be varied within a scene.
This distinguishes it from directional light.
Light attenuates with distance.
This also distinguishes it from directional light.
The surface of an object represents the next
implication for light interaction.
They can glow in the dark
The colour of the surface determines the level of
Black absorbs all visible spectrums
White reflects all visible spectrums.
Coloured surfaces vary depending on colour.
Reflect some wavelengths
Wavelength interaction with colours a matter of
Reflection can be either
Reflects like a mirror
Light gets reflected at angles
Angle of reflection
Ever tried shooting a laser pointer at a mirror?
It’s like that
Reflects at many angles at once
Diffuse reflection is the primary way in which we can see
Reflection is dependant upon
The arrangements of facets on a surface
The roughness of the surface
The orientation of the surface
The absorbption of the surface.
Light can also be refracted
As light moves from one medium to another, the path
of the light bends.
Mechanics of this are not trivial
Sometimes, objects transmit light through
Such objects can be transparent (like glass) or
Transparent objects refract light passing through.
White light through a prism
Translucent objects diffuse the light that passes
Two approaches used to render light
Local reflection models
Everything floats in ‘dark space’
Only one reflection of light considered
Global reflection models
Light reflects off of objects which reflect onto other objects
Very costly to render
Not yet perfected
One aspect of rendering is the interaction
of light upon surfaces.
This can be
Issue complicated by the physics of light
Different kinds of lights
Lighting is an important part of rendering
believable 3D scenes.