A Procedural Ocean Toolkit.pdf

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A Procedural Ocean Toolkit
M˚ rten Larsson
∗
a
Digital Domain
Jens Zalzala
†
Digital Domain
Greg Duda
‡
Digital Domain
1
Introduction
3
Shoreline
Several projects at Digital Domain have involved creating computer
generated images of an ocean surface. The most successful ap-
proach used is a well tested technique based on statistical measure-
ments of the ocean surface and an FFT based algorithm described
in [Tessendorf2002].
For a recent large project the challenge was not to render just an
ocean but to render an ocean with thousands of boats all creating
foam trails and wakes that interact with each other as well as the
ocean waves. On top of that, many shots needed a shoreline with
waves crashing onto the beach. This sketch will describe the pro-
cedural system created for generating an ocean with wakes, foam
trails and shoreline blending seamlessly with the FFT based ocean
technique.
The fully procedural shoreline setup relies on simple geometry
since crashing waves are difficult to create with only displacement
shaders and it is convenient for volumetric renders of foam and
spray.
2
Wakes and foam trails
Figure 1: Fully CG ocean.
The shoreline waves are driven by a set of points distributed around
each island or land-mass in the ocean. The points are placed us-
ing a Poisson distribution to ensure a certain distance between each
wave. All points have an automatic animation moving them from
their original position to a position on the beach. Wave geometry
is instanced on each point. The waves automatically orient them-
selves towards the shore by using a projected normal from the beach
geometry. Each wave geometry has a procedural animation of a
crashing wave timed by using the distance to shore. This anima-
tion includes the wave flattening out on the beach and moving back
into the ocean under the newer waves. Each geometry has a UV
space controlling the foam it leaves behind. These wave geometries
are then rendered with the regular ocean displacement and surface
shader. This way the ocean blends seamlessly with the shoreline
waves and even wakes from boats can mix with the crashing geom-
etry waves.
To generate the ocean surface a grid and two shaders are used (one
for displacement and one for surface shading). The ocean is ren-
dered as one continuous surface.
The entire wake system is driven by the position of the boats. Trail-
ing splines are created automatically from the boat animations. The
attributes for describing a whole spline are then stored, along with
attributes for what type of boat it is and how its foam trail is shaped,
in a point for each boat. These points are then fed to the shaders re-
sponsible for creating the ocean surface. At render time the spline
is reconstructed in the renderer and a UV space is dynamically cre-
ated that runs along the spline. Recreating the spline at render time
solves two problems. The UV spaces can have an almost infinite
precision even when the ocean is rendered with a very coarse grid.
Since the ocean often extends all the way out to the horizon, it is
important to try and keep the resolution of the grid down. The sec-
ond problem this solves is that it allows the shader to handle an
arbitrary number of overlapping UV spaces and because of that it
can handle interaction of an arbitrary number of wakes. This is also
a very important feature since the trails often overlaps when many
boats are close to each other.
Simple maps with a wake pattern are then mapped on to the UV
space and used to displace the surface before the ocean wave dis-
placement is added. An attribute on the point decides what texture
to use depending on what type of boat is making the trail. The
foam trails are generated by applying procedural noise patterns on
the same UV space. These maps and UV spaces are dragged around
automatically by the boats.
To reduce render times a LOD system is used for the UV spaces.
The curvature of the spline is used in the shader to automatically
choose between a spline, multiple line segments or just a straight
line as the basis for the UV space. This reduces render time since
the spline can be expensive to evaluate at every shader sample.
∗
e-mail:
4
Conclusion
Because it is procedural, this system has a very short setup time.
Once the points for the wakes are generated with the click of a
button and a Poisson distribution is generated automatically using
the land geometry, the ocean system is ready to render the final
image. It creates an all inclusive ocean render with all masks and
complex displacement of the ocean scape in the same render.
References
T
ESSENDORF
, J. 2002. Simulating Ocean Water. In
Course Notes
#9 (Simulating Nature: Realistic and Interactive Techniques),
SIGGRAPH 2002,
ACM Press / ACM SIGGRAPH
2006 c Copyright by Digital Domain Inc. All rights reserved.
mlarsson@d2.com
†
e-mail: jzalzala@d2.com
‡
e-mail: gduda@d2.com

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