The Fur Page
We have explored a technique for modeling fur quickly using
the facilities of common graphics workstations. Parameters include
hair density, length, stiffness, and color properties.
There can be a separate over and undercoat, and randomness.
Standard GL facilities are used for modeling, lighting and
rendering. Hair densities automatically compensate for
viewing distance. Gravity is approximated.
We compared four methods: single line, polyline, nurbs
curve, and nurbs surface. We found polylines produced
the best combination of speed and image quality.
On an SGI Onyx Reality Engine II with 150 MHz processors,
we can draw about 15,000 polyline hairs per second.
For further information, see ``An Interactive Fur Modeling
Technique'', by Allen Van Gelder and Jane Wilhelms, in
the Proceedings of Graphics Interface '97.
Some Sample Fur Animations
are at the bottom of this page.
Overcoat and Undercoat
This image (36 Kbytes)
shows a triangle with an overcoat and undercoat of different fur types.
Many furred animals have two or three kinds of fur of different
characteristics. We simulate this with an undercoat and overcoat
that can have different stiffness, randomness, style, amount, color, length, etc.
Hair Direction
This image (136 Kbytes)
shows hair only influenced by "weightless hair direction" (skin normals) at left,
and with 50% influence of segment direction at right. Each body segment can
have a local vector associated with it that indicates the direction in
which hair lies.
Distance-Based Culling
Hairs are minimally a pixel in width,
so we automatically draw fewer hairs at a distance.
Otherwise, the fur looks like a smooth surface.
At left, we see a furred monkey close up (271 Kbytes);
in the middle, with distance culling (57 Kbytes); and at right,
without distance culling (50 Kbytes).
Gravitational Influence
This image (90 Kbytes)
shows the influence of gravity ("floppiness") on the hairs. Each example shows
80% floppiness: the left is line fur, middle is polyline fur,
and right is nurbs curve fur.
The Four Fur Types
This image (274 Kbytes)
shows the four fur types. Upper left is straight line fur (2.6 seconds),
upper right is polyline fur (6.1 seconds), lower left is nurbs curve fur
(70.2 seconds), and
lower right is nurbs surface fur (277.5 seconds). Images were clipped from
full monkey images of about 90,000 hairs drawn in a 900x900 pixel window.
Polyline Fur at Two Distances
These images (330 Kbytes left and 459 Kbytes right)
show polyline fur with over and undercoat at mid and close ranges.
Importance of Elastic Adjustment for Fur
This image (104 Kbytes)
shows the shoulder region with fur, illustrating the importance
of correct elastic skin adjustment during motion.
When the skin isn't elastically adjusted (left), the hairs are pulled far
apart and leave gaps. When the skin is adjusted (right), the
hairs are positioned properly.
Examples of Fur Modeling
This image (210 Kbytes)
shows various monkeys with fur.
If you have patience, the image is available in a
larger version (759 Kbytes).
The upper left monkey has very random fur; the upper right has
very long fur. The middle monkey has short, dense fur. The
lower left monkey has very regular fur, and the lower right quite dense
fur.
Animations (Warning: Large!)
This animation (Quicktime, 1Mg)
shows fur changing from short and dense
to long. This is polyline fur with an over and undercoat. These
animations don't compress very well.
A larger version (Quicktime, 19 Mg!!!)
is available for those with time.
This animation (Quicktime, 10Mg!!!)
(probably not worth it) shows
fur with more randomness; it also starts short and lengthens.
A larger version (Quicktime, 31 Mg!!!)
is available for those with time.
This image (36 Kbytes)
shows a triangle with an overcoat and undercoat of different fur types.
Many furred animals have two or three kinds of fur of different
characteristics. We simulate this with an undercoat and overcoat
that can have different stiffness, randomness, style, amount, color, length, etc.
This image (136 Kbytes)
shows hair only influenced by "weightless hair direction" (skin normals) at left,
and with 50% influence of segment direction at right. Each body segment can
have a local vector associated with it that indicates the direction in
which hair lies.
Hairs are minimally a pixel in width,
so we automatically draw fewer hairs at a distance.
Otherwise, the fur looks like a smooth surface.
At left, we see a furred monkey close up (271 Kbytes);
in the middle, with distance culling (57 Kbytes); and at right,
without distance culling (50 Kbytes).
This image (90 Kbytes)
shows the influence of gravity ("floppiness") on the hairs. Each example shows
80% floppiness: the left is line fur, middle is polyline fur,
and right is nurbs curve fur.
This image (274 Kbytes)
shows the four fur types. Upper left is straight line fur (2.6 seconds),
upper right is polyline fur (6.1 seconds), lower left is nurbs curve fur
(70.2 seconds), and
lower right is nurbs surface fur (277.5 seconds). Images were clipped from
full monkey images of about 90,000 hairs drawn in a 900x900 pixel window.
These images (330 Kbytes left and 459 Kbytes right)
show polyline fur with over and undercoat at mid and close ranges.
This image (104 Kbytes)
shows the shoulder region with fur, illustrating the importance
of correct elastic skin adjustment during motion.
When the skin isn't elastically adjusted (left), the hairs are pulled far
apart and leave gaps. When the skin is adjusted (right), the
hairs are positioned properly.
This image (210 Kbytes)
shows various monkeys with fur.
If you have patience, the image is available in a
larger version (759 Kbytes).
The upper left monkey has very random fur; the upper right has
very long fur. The middle monkey has short, dense fur. The
lower left monkey has very regular fur, and the lower right quite dense
fur.