water affecting a surface is normally a case for some fancy fluid
dynamics system such as Next Limit’s excellent set of fluid
systems, which generates fluid surfaces using particles and geometry
deformation, but even though the solution is extremely effective,
it costs money. So what free alternatives have we got?
method to create ripples on a surface would be to physically deform
the geometry itself to generate the ripples. However, manually placing
God knows how many modifiers or Space Warps, then offsetting their
animation would be a nightmarish task! So what other solutions do
scripting a deformation solution, our best bet would be material
based, either by using bump mapping, geometry displacement or displacement
mapping using an animated sequence. We can control this a lot easier
than manually editing every single ripple, and the entire effect
can be assigned to the entire surface and/or the entire scene if
needs be. Creating an individual ripple isn’t a problem –
we can simply animate an object with a ripple displacement texture
assigned to it, but to create hundreds or thousands seems like another
monstrous task. Not so. As we’re using materials, we can apply
this material to an object and then scatter it across a surface
to generate the animated map.
itself would be a simple radial gradient with a steep crest (but
only set to 50% intensity) and feathered-out tail. The lack of full
intensity allows us to use additive transparency, which will when
two waves combine, the result is a more intense wave (ie higher
displacement) at these areas.
way to create such an effect would be to use a particle system –
it has a random distribution and an object’s animation (not
material animation) can be offset to the birth of the particle.
This means that when the particle is born, the animation of the
instanced geometry for that particle begins to play. Hence, we can
set up a scale of the object with the ripple map assigned to it,
and the result would be each “ripple” (with a slight
percentage variation) starting small and growing outwards! As the
wave needs to fade out with age, using a Particle Age map to mask
the gradient out more as the particle gets older. However, Particle
Age does not work when the material is assigned to the instanced
geometry, then the particle system sourced it’s material from
the instanced geometry; it has to be directly assigned to the system
itself for it to work.
As we only
want our ripples to be applied to a surface to create our animated
texture map, we need the result of a particle hitting a surface.
For this, we can use particle spawn, namely “Spawn on Collision”.
This allows us to generate a new particle when the original collides
with a deflector Space Warp that has been assigned to the particle
system. Because we only need to see the spawned particles, we do
not need to see the original geometry type (which also has to be
instanced geometry). Therefore we can create a null object using
a Geosphere, then add a DeleteMesh modifier to remove all polygons.
Therefore when rendered (and when working in the Viewport) the original
particles will not be visible, but the spawned ones will!
We can also
create the initial splash displacement by cloning the particle system
and plane geometry and assigning a new material to the particle
system to create a small white dot when the particle is born, which
then quickly fades out. As we do not want the particle to scale
this time, we can simply remove the cloned plane’s keys and
set a size that suits us, and replace the first plane with the clone
in the new particle system’s Object Mutation Queue.
the animation out is a simple procedure. You may want to increase
the amount of particles, speed of the ripple (it is slightly slow
in the tutorial opposite to emphasise the ripple animation when
assigned to an object), turn on supersampling or increase the size
of the rendered animation to create a better quality result when
the animation is applied as a bump or displacement map.
we have it. Okay, it’s not all that effective at very close
quarters, but on a large scale, especially with animated wind methods
(see tips column) the resulting effect can be made to look quite
a Plane primitive in the top viewport and set it’s length
and width sizes to 0. Animate the length and width sizes to
600 over 100 frames. Create a new material, label it “Puddle”
and enable Face Map. Set Diffuse and Self-Illumination colours
to white, and additive transparency. Create a Mask map in the
Opacity slot and add a Particle Age map to the Mask’s
Mask slot. Set Colour 1 to a mid-grey, Colour 2 to a darker
grey and Colour 3 to black. In the Mask’s Map slot add
a Gradient Ramp map and use the settings as illustrated.
a Deflector Space Warp and set it’s Length and Width spinner
settings to 10000. Set the Bounce to 0 and increase the Friction
to 100. This will ensure that the particles do not move once
they collide with the deflector, and that the spawned particles
||Create a Geosphere
(or any other geometry – it doesn’t matter as it’s
just a placeholder to be deleted) in the top viewport and set
it’s radius to 10 with 1 segment and set the base type
to Icosa. Add a DeleteMesh modifier to the stack.
||Create a Blizzard
particle system 8000 wide by 8000 long and place it above the
Deflector (approx 1300 units). Assign the Puddles material to
it. Set up the particle system as illustrated. Bind the particle
system to the deflector. As we only want the particles to be
visible when they collide with the deflector, we enable particle
spawning on collision, and with Animation offset keying set
to Birth, the plane’s animation is offset when the deleted
Geosphere particle hits the plane!
||Copy the Puddles
material and label the new one Splash. Set the Particle Age
map’s colours to Black, Mid-Light grey, Black for colours
1,2 and 3 respectively. Set Colour 2’s age spinner to
5 and Colour 3’s to 30. Clone the Plane and Particle system
and assign the new Splash material to them. Select the new plane
and delete the keys at frames 0 and 100. Set the length and
width sizes of the new plane to 600. In the new particle system,
replace Plane01 with Plane02 in the Particle Spawn Object Mutation
the top viewport over the particle systems and set the Render
Output Size to 640x640. You may wish to enable Show Safe Frame
in the viewport’s options menu – this will help
you centre the particle systems easier.
||The generated animated
bump map has been applied to the sea’s surface. The original
scene is from a previous Q&A, in issue 24.
the resulting map does not tile or loop. However, this should be
relatively simple to sort out. By offsetting the animation in AfterFX
(or equivalent) or creating 4 copies, we can move the seam to the
centre of the frame. Cloning elements of the original animation
results in the seam being masked out. To rectify the loop problem,
a simple yet effective additive or non-additive cross fade can be
used to loop the middle part of the sequence so there are no abrupt
changes in the sequence.
You would think that binding a wind spacewarp to the particle system
wouldn’t effect the particle’s motion if it was positioned
underneath the deflector spacewarp. Unfortunately, as we’re
using particle spawn, it does, so to create an appearance of wind,
we need to animate the position, rotation of the emitter and the
amount of particles to give the impression of a wind blowing them
across the scene. This will therefore affect the spawned particles
positions at where they appear, which is the effect we are after.
As opposed to containing the initial splash and the ripple(s) in
one animated map, try splitting them into two maps, so you can use
bump mapping for the ripples and mesh displacement for the splash.
However, extra refinement of the mesh will be required to effectively
displace the geometry, or use displacement mapping.
As opposed to using one general animated map for a lot of scenes,
you will most likely find that you want the actual rain particles
to effect the splashes. In this case, you will have to create an
animated map based on the surface of the geometry and re-apply that
in a second pass render. A little extra work is involved, especially
if the geometry is deforming, but worthwhile nevertheless.
World magazine, Issue 36, March 2003.
Draper, March 2003. Reproduction without permission prohibited.