So how are 3D graphics painted?
The example teapot shown below is a typical polygon object.
Polygon objects are constructed out of multi-sided shapes
(polygons), called faces. The computer can calculate how shapes
react to light. Generally, objects that have curved surfaces
need to be made up of lots of faces in order that they not
look like they are facetted. The more faces, the more calculations
the computer must perform.
Why a teapot?
Back in 1974, one of the pioneers of computer graphics, Martin
Newell, had been told that he didn't have interesting enough
computer "models". His wife Sandy suggested that
he model a teapot they had purchased from a department store
in Salt Lake City. While it may not have been the first actual
3D model, it has passed on into technology folk law as such.
 |
Image 1 shows the teapot object in what is called a "wire-frame"
view. It does look like it's made out of wire. Note that there
are some areas of the teapot where you can see through to the
neck of the spout and the bottom of the handle.
The reason you can see only these areas through the object is
because the faces that make up the object are only one-sided.
there is no "back" 3D modellers talk about the visible
side as being the "normal" side. So you can
think of faces as being polygons with direction.
In Image two comes the clever part where the 3D software paints
in all the faces. The wire-frame object now looks solid. Note
that because there is no "back" to the faces, you
can see straight through the top of the rim.
Solid objects are all fine and good, but in order to look like
real objects their surfaces need to be able to exhib complicated
properties. In 3D modelling this is done my applying maps. Maps
can be photographs of real surfaces, they can be procural maps,
which are computer generated patterns. Modern 3D programmes
don't just deal with one layer of mapping either. You can apply
different maps for different surface properties.
For example, the above teapot has a diffuse colour map that
gives it a clay colour. There is a bump map, which gives the
appearance of chips and dents in the surface. There is also
a specularity map that indicates which parts are more reflective.
Before image four we have only altered the teapot.
If we also alter the light source, we make make the image
look more realistic. The final image uses a number of omni
lights (they illuminate in all directions like the sun. There
is also a directional light that is assigned to cast the strong
shadows.
Lighting 3D models has been designed using
photographic and filmic conventions, so lighting 3D scenes
is very much like being a lighting technician or cinematographer.
It is a complex business that many consider to be a sperate
art in itself.
|
