How Cloth Simulation Works
Getting Started
1. Select the SubTool you would like to have the simulation run on.
2. Turn on visibility for all SubTools on that the surface needs to collide with. Hide
any that you wish to be ignored.
3. Make sure Dynamics >> Gravity is on.
4. Press Dynamics >> CollisionVolume to calculate the volume of all visible
SubTools, or Dynamics >> Recalc if already active and the scene has changed.
5. Press Dynamics >> Run Simulation.
6. You can stop at any time by clicking anywhere in the ZBrush document or
pressing the Spacebar.
Note: If a new SubTool is created or made visible you will need to press Recalc to recalculate the collision volume. To get particular effects, dummy objects can be added to your scene and
removed later.
The simulation can be stopped, allowing interaction with the object before continuing
the simulation. For example, stop the simulation by pressing Spacebar, add a mask
and then continue the simulation. Masking is respected, fixing those areas in place.
Additionally, there is the Dynamics >> On Masked option which will apply the simulation
to the masked portion, while leaving you free to move the unmasked portion. This can
allow the creation of carpet rolls, yoga mats, etc.
The simulation can also be created directly using the new Cloth sculpting brushes
or the Gizmo3D TransposeCloth brush. The TransposeCloth brush allows you to use
the Gizmo to control what’s happening without actually running the simulation. The new
sculpting brushes produce different effects as explained below.
You can even make your own brushes. Any brush can be converted to a Cloth brush
by activating the Brush >> Elasticity >> Simulation Iterations slider.
II Tips and Tricks
Storing a Morph Target
Storing a Morph Target will allow you to store the current surface area so that it will
be maintained during the simulation.
For example, load the Sim_HeadCover.zpr project from LightBox, which already has
a morph target stored.
1. Select the SubTool you would like to have the simulation run on.
2. Turn on visibility for all SubTools on that the surface needs to collide with. Hide
any that you wish to be ignored.
3. Make sure Dynamics >> Gravity is on.
4. Press Dynamics >> CollisionVolume to calculate the volume of all visible
SubTools, or Dynamics >> Recalc if already active and the scene has changed.
5. Press Dynamics >> Run Simulation.
6. You can stop at any time by clicking anywhere in the ZBrush document or
pressing the Spacebar.
Smoothing
The Smooth brush will by default contract the mesh but leave the edges unaffected.
However, you can instead use the SmoothCloth brush to allow all points of the surface
to be smoothed.
Note: The SmoothCloth brush allows this behaviour thanks to a specific modifier. To change
this, hold Shift to get the Smooth brush settings, and change the Brush >> Smooth Brush Modifiers >> Min Connected slider to 1. This allows any point of the mesh to be smoothed.
Low Resolution Meshes are key
Remember to use a low-resolution mesh for cloth. Don’t expect the simulation to
work on a mesh with five million polygons.
The idea is to create a low-resolution mesh, apply the effects and then subdivide
once you are satisfied with the cloth shape.
While keeping to as low a polygon count as possible, you will also find that denser
meshes with smaller polygons result in smaller folds. This can be useful when creating a
particular type of cloth.
To be able to work with cloth simulation while still seeing the smoothness of a
higher resolution model, use Dynamic Subdivision. In fact, this will even let you start
with a planar piece of geometry and use the Tool >> Geometry >> Dynamic Subdiv >>
Thickness slider to dynamically add depth to your flat geometry. This feature will even
work with the Dynamics >> Self Collision slider.
The Dynamics >> Max Simulation Points slider controls the higher number of
points upon which a cloth simulation can run. Any mesh with a higher polygon count
than what the slider is set to will automatically disable the dynamics. You can set higher
values but the simulation will take a lot longer to run because it has to account for so
many more points
Floor Collision
To run without interacting with the floor, turn off Dynamics >> Floor Collision. Floor
height can be adjusted using the Draw >> Elv slider. A value of -1 will automatically make
the floor grid snap to the lowest SubTool.
Deformation Animation Recording
Turning on the Tool >> Layers >> Record Deformation Animation will record the mesh
changes that occur during the simulation. This will work with either the Run Simulation
or the cloth brushes. Only changes to your mesh are recorded, so you can stop/start the
simulation and change the camera angle without it affecting the result. When you have
finished, turn the button off and you will be asked to save the recording as an MDD file.
This can be loaded back into ZBrush using the Tool >> Layers >> Import MDD button and
rendered using BPR and the TimeLine, or you can use another application that supports
MDD files.
III Cloth Brushes
TransposeCloth brush
A version of the Gizmo3D which uses cloth simulation. With this you are able to use
the Gizmo3D to control what’s happening without actually running the simulation.
When scaling smaller with the TransposeCloth brush the mesh will ripple. Turn on
AllowShrink/Allow Expand (or select the standard TransPose brush) to scale normally.
Cloth Nudge
Slightly moves the surface, causing ripples.
Cloth Pull
Drags the surface. Good for controlling how the cloth drapes.
ClothInflate
Shapes the surface as if is covering a sphere.
ClothBall
Similar to Inflate, however this brush is based off the Standard brush and so will not
inflate the surface normals.
ClothFold
Scrunches slightly twists the surface for wrinkles and folds.
ClothHook
Pulls the cloth as if you have grabbed hold and dragged it.
ClothMove
A lot less simulation, giving more control to you rather than the cloth dynamics.
There will be less stretching with this brush than the Cloth Pull brush.
ClothPinch
Pulls the surface in on itself, creating a crease. Hold Alt to reverse the direction of
the crease relative to the surface..
ClothPinchTrails
Good for creating wrinkles in objects like pillows, or for wounds and scars in skin.
This brush will repeat the pinching along the path of the stroke.
ClothSlide
Lifts the surface and moves it about, creating folds as it bunches together. Hold Alt
to indent the surface.
ClothTwister
Twists the surface with circular motion. Set the Brush >> Twist >> Twist Rate slider
to a negative value to twist the opposite direction.
ClothWind
Creates an effect as if the cloth is being blown on. Useful for creating natural effects
on loose fabrics.
ClothDimple
Draws the cloth together similar to a button on a pillow.
V Dynamics Functions
The Dynamics functions are in the new Dynamics palette
Simulation Iterations
Controls the number of simulation cycles that will be used for each movement.
Higher values are more accurate but can slow down the simulation. Lower values will
result in more stretching as the simulation lacks enough time to compensate for the
change in shape. The default setting is 50.
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ZBrush 2021 - Dynamic Cloth
Strength
The cloth Strength slider affects how much the surface area is kept intact. Lower
values will mean the cloth will tend to have more stretch.
Firmness
Results from the Firmness slider - ZBrush artist Ben De Angelis
The Firmness slider affects how the surface will tend to wrinkle and fold. Lower
values will produce more folds and wrinkles. This slider can be used to simulate different
weights or types of fabric.
On Masked
Will apply the simulation to the masked portion, allowing you to move the unmasked
area. This allows for unique creations like a carpet roll, etc. If this is unpressed, the
masked portions of the mesh are ignored by the simulation and cloth brushes.
On Brushed
Will apply the simulation to the area of the brush only. This makes it possible to use
the effect on higher polygon meshes. Control the amount of fading using the Fade Border
slider.
Turn off On Brushed to have the simulation affect the whole mesh.
Fade Border
Fades the simulation effect when On Brushed is used. A higher value will give more
fading. A setting of 0 turns off fading.
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ZBrush 2021 - Dynamic Cloth
Self Collision
The object will react when it collides with itself, avoiding overlapping geometry.
A higher value will result in greater accuracy in detecting self-collision. The maximum
setting is 4 and value of 0 means self-collision is turned off.
Floor Collision
The simulation will react to the floor grid within ZBrush. Turn off to remove floor
collision. The floor height can be adjusted in the Draw palette with the Elv slider.
Allow Shrink
With this button pressed the surface will be shrunk to match all underlying surfaces.
This can add stretching to the surface. If a morph target has been stored, turning the
option off and then touching the surface will result in the mesh expanding back to its
original size, creating folds and wrinkles.
Allow Expand
Allows the mesh area to be expanded much as if using the Cloth Pull brush. If a
morph target has been stored and the mesh expansion causes stretching, turning the
option off and then touching the mesh will result in the mesh contracting back to its
original size.
Gravity
Applies gravity to all parts of the mesh equally. Working with a low-resolution mesh
with Tool >> Geometry >> Dynamic Subdiv >> Thickness offers a way for a thin surface
with variable thickness to interact with gravity.
Gravity Strength
The strength of gravity applied. Higher values will result in a faster simulation which,
depending on the Simulation Iterations setting, may result in more stretching of the mesh.
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ZBrush 2021 - Dynamic Cloth
Liquify
Changes the dynamics algorithm from cloth to liquid.
Note that some variation in the mesh is necessary for this mode to function, which
means that a perfectly flat plane will not respond.
Set Direction
By default, gravity is from the top of ZBrush window to the bottom. You can set a
new direction relative to the model. Simply rotate your model so that the desired direction
goes from the top of the ZBrush canvas to the bottom. Now click Set Direction to store
that angle. From then on, gravity will take place in the desired direction relative to the
model, no matter how you rotate the model on the canvas.
Inflate
The simulation will expand the mesh area. Polygons are moved outwards in the
direction they are facing. The Inflate Amount slider sets the speed of the simulation. XYZ
buttons will restrict the simulation to any of the axes. For example, to only inflate along
the Z axis, press X and Y to turn them off. You will notice the X and Y will be greyed out
while the Z will still be white.
Inflate Amount
The speed at which the mesh will expand when the Inflate option is turned on.
Deflate
The simulation will shrink the mesh area. Polygons are moved backwards from the
way they are facing. The Deflate Amount slider sets the speed of the simulation. XYZ
buttons will restrict the simulation to any of the axes. For example, to only deflate along
the Z axis, press X and Y to turn them off. You will notice the X and Y will be greyed out
while the Z will still be white.
Deflate Amount
The speed at which the mesh will expand when the Deflate option is turned on.
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ZBrush 2021 - Dynamic Cloth
Expand
Expand will grow the surface area, rippling it. Points are moved away from each
other in all directions.
Expand Amount
The speed at which the mesh will grow when the Expand option is turned on.
Contract
The simulation will shrink the mesh area. Points are moved towards each other from
all directions. The Contract Amount slider sets the speed of the simulation.
Contract Amount
The speed at which the mesh will shrink when the Contract option is turned on.
CollisionVolume
Calculate the Collision Volume. If this switch is not active the simulation will not react
to anything in your scene.
Recalc
Press the Recalc button whenever you have changed anything in your scene. This
applies to turning SubTool visibility on or off, as well as moving or adding SubTools. If you
turn off or delete a SubTool without pressing Recalc then the simulation will still react as
if it was there.
Resolution
Controls the smoothness of the collision volume. A low value, such as 128, will give
a very “blocky” result.
Higher values are best.
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ZBrush 2021 - Dynamic Cloth
Inflate
The Collision Volume Inflate slider controls the amount the collision volume is
“inflated”, so that the cloth reacts a bit above the surface. For tighter clothing, reduce
this slider.
Run Simulation
Runs the cloth Simulation. Click anywhere on the document background or press the
Spacebar to stop the simulation. You can then mask any areas you want to keep as they
are before pressing the button again to continue the simulation.
Max Simulation Points
Controls the number of points above which the simulation will be disabled. The slider
value is in 1000’s, so the default value of 250 is for a mesh of 250,000 points. Trying
to run a cloth simulation on a mesh with density higher than this will not work. You use
this slider to raise the threshold but you may not get the results you want without also
changing the Simulation Iterations and Gravity Strength sliders. Cloth Simulations work
best on low polygon meshes. You can use Dynamic Subdiv to show a high-resolution
preview and then apply the subdivisions after you have the effect you want.
VI Cloth Simulation Examples
The following project files can be loaded from LightBox and are a good way of
exploring cloth simulation.
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ZBrush 2021 - Dynamic Cloth
Sim_Gravity01.zpr
Running the simulation with this project demonstrates dynamic surface collision.
1. Press Dynamics >> CollisionVolume or Recalc.
2. Press Run Simulation to view the simulation.
3. Click the left mouse button or press Spacebar at any time to abort the simulation.
Sim_PlaneInRing.zpr
This project demonstrates the brush-based cloth simulation.
1. Press Dynamics >> CollisionVolume or Recalc.
2. Press B-C-K to select the ClothHook brush.
3. Set brush size to approximately 300.
4. Turn off Dynamics>>On Brushed.
5. Click on the plane and pass it through the ring.
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ZBrush 2021 - Dynamic Cloth
Sim_HeadCover.zpr
This project demonstrates cloth simulation and dynamic surface collision using the
TransposeCloth Gizmo3D.
1. Press Dynamics >> CollisionVolume or Recalc.
2. Press B-T-C to select the TransposeCloth gizmo.
3. Use the Gizmo to move the hemisphere and have it conform to the shape of
the head.
Experiment with different settings for the Dynamics >> Simulation Iterations slider
to see how it affects the result.
