Visibility Level Of Detail (LOD) In Game Scene
Anggota
Kelompok :
1. Claudia
Lukita. D (51415532)
2. Fadilah
Achmad. S (52415355)
3. Musthova
Noor. A (54415854)
4. Nur
Najmi Sania (55415194)
5. Saviera
Andriany (56415443)
6. Rifki Dwi Setyanto (55415962)
Kelas
: 3IA18
CHAPTER 7
Appearance of Computer Game Scene Graph
A
scene graph is a general data structure commonly used by vector-based graphics
editing applications and modern computer games, which arranges the logical and
often spatial representation of a graphical scene.
Scene
graphs are useful for modern games using 3D graphics and increasingly large
worlds or levels. In such applications, nodes in a scene graph (generally)
represent entities or objects in the scene.
For
instance, a game might define a logical relationship between a knight and a
horse so that the knight is considered an extension to the horse. The scene
graph would have a 'horse' node with a 'knight' node attached to it.
As
well as describing the logical relationship, the scene graph may also describe
the spatial relationship of the various entities: the knight moves through 3D
space as the horse moves.
In
these large applications, memory requirements are major considerations when
designing a scene graph. For this reason, many large scene graph systems use
geometry instancing to reduce memory costs and increase speed. In our example
above, each knight is a separate scene node, but the graphical representation
of the knight (made up of a 3D mesh, textures, materials and shaders) is
instanced. This means that only a single copy of the data is kept, which is
then referenced by any 'knight' nodes in the scene graph. This allows a reduced
memory budget and increased speed, since when a new knight node is created, the
appearance data does not need to be duplicated.
The
following are primary components of scene graph on games :
· Visibility
· Level
of Detail
A.
VISIBILITY
Visibility
is a measure of the distance at which an object or light can be clearly
discerned. Visibility optimization is the most effective way to gain performace
in games. There are two basic ways to do visibility optimization i.e art and
level design, technology. The games use a mix of both. Artists design game
worlds so that performance is acceptable. Many technologies have been used in
games for example 2.5D technology. Two and a half dimensional (shortened to
2.5D, known alternatively as three-quarter perspective and Pseudo-3D) is a term
used to describe either 2D graphical projections and similar techniques used to
cause images or scenes to simulate the appearance of being three-dimensional
(3D) when in fact they are not, or gameplay in an otherwise three-dimensional
video game that is restricted to a two-dimensional plane or has a virtual camera
with a fixed angle. By contrast, games using 3D computer graphics without such
restrictions are said to use true 3D.
Common
in video games, these projections have also been useful in geographic
visualization (GVIS) to help understand visual-cognitive spatial
representations or 3D visualization.
B.
LEVEL
OF DETAIL
Level
of Detail (or LOD for short) is a rather simple but efficient way of optimizing
rendering for large scenes. The basic idea is that objects that are far away
don’t have to be rendered as detailed as close objects. The following are Primary LOD selection criteria :
· Distance
or Size
· Velocity
· Eccentricity
· Depth
of Field
1.
Distance
or Size
Select resolution based upon the distance
between an element and the viewpoint,
i.e. coarser resolution for distant
geometry.
· Simple
to calculate (3-D Euclidean distance)
· Scale
dependent
· Resolution
dependent
· Field
of View dependent
2.
Size
LOD
Select
resolution based upon the projected
screen size (or area) of an element.
Objects appear smaller as they move further away.
· Requires
3-D ® 2-D projection
· Scale
invariant
· Resolution
invariant
· Field
of View invariant
Bounding
spheres or ellipsoids normally used
instead of boxes as more efficient to
calculate projected extent
3.
Eccentricity
LOD
- Resolution
is selected based upon the degree
to which an element exists in the
visual periphery, i.e. display elements that the user is looking at in high
resolution.
- Humans
can resolve less detail in their
peripheral field due to:
o
more retinal photoreceptors (rods/cones) towards fovea
o
retinal and cortical cell receptive field
sizes increases linearly with
eccentricity
o
80% of cortical cells devoted to central
10 degrees of vision
- Use
eye tracking system to track user’s gaze
or assume user looking towards center of display
4.
Velocity
LOD
- Resolution based upon the angular velocity of an element across the visual field, i.e. faster moving objects appear in lower resolution
- Humans can resolve less spatial detail in objects moving across the retina, causing objects to blur as they move/ rotate, or the user’s gaze moves
- It is believed visual information for small features are destroyed by the process of integrating stimulus energy over time
- Without eye tracking technology, assume angular velocity across display device
5.
Depth
of Field LOD
– Resolution
of element dependent upon the depth of field
focus of the user’s eyes, i.e. objects out with the fusional area appear in lower detail
– Under
binocular vision, both eyes converge on object at certain distance in order to focus retinal
image
– Objects
in front or behind this fusional area are unfocused, suffering from double images
– Must
track both eyes accurately to evaluate convergence distance.
SOURCE :
https://en.wikipedia.org/wiki/Scene_graph
https://graphics.pixar.com/library/LOD2002/2-perception.pdf
