- Surface detail on an object is called texture
- One way to create texture is to map a pattern to a smooth surface
- After the pattern has been added, the surface still appears smooth
- Adding the pattern is basically a mapping from texture space
to object space or image space
- The pattern can be generated from digitized photographs,
synthesized using random or formal methods, or from reflections
of the environment
- These ideas were first discussed by Catmull and extended by Blinn and
Newell, and others
- A second way to create texture is to add the appearance of roughness to
a surface
- Adding roughness is a perturbation function
- The surface color can be changed by perturbing the diffuse reflection
coefficient
- The surface normal vector can be modulated (bump mapping),
or each of the normal, tangent and binormal can be altered (frame
mapping)
- These mappings apparently alter the surface geometry, but in
truth the surface remains unaltered
- A texture is implemented as a two dimensional array
(When the need to be specific exists,
assume the indices range from 0 to 63) - Given a surface
one simple way to
texture map is to use the texture color
at parameter value
- Two concerns are:
- What is the code to draw a surface?
- What if 64 steps across the surface is not a fine enough mesh?
- We'll deal with the second question here and refer to the
Surfaces section
to answer the first
- Consider mapping texture space to a convex quadralateral
(bilinear patch)
defined by corners
,
,
,
- The direct map is easy and given by simple bilinear interpolation:
given
, the point on the surface is
- This can be written as
- Or
where
and
- Let
so it is orthongonal to both and
take the inner product with V and U to determine
- In a similar manner v can be determined
Florida Tech Computer Science
William D. Shoaff
Comments to author:wds@cs.fit.edu
All contents copyright ©, William D. Shoaff
Revised: Thu Oct 24 16:06:33 EST 1996