User Guide > Dynamics and Effects > nDynamics > nCloth > nCloth advanced techniques > 
Lesson 3: Wrapping the high resolution mesh and simulating the pants during animation
 
 
 

In this lesson you will:

Lesson Setup

To ensure the lesson works as described, do these steps before beginning:

  1. If you have not already done so, copy the nCloth Advanced Tutorial folder from the following location: http://www.autodesk.com/maya-advancedtechniques. Then, set the nCloth AdvancedTechniques directory as your Maya project.

    For this lesson, you need to access Maya geometry cache files in addition to the lesson scene file.

  2. Open the scene file named Character_LowRes_3.mb.

    This file can be found in the AdvancedTechniques directory that you set as your Maya project.

Wrapping the high resolution mesh

In this section of the lesson, you use a wrap deformer to create an influence object that causes the high resolution to behave like the simulated low resolution mesh. For more information, see What are deformers?.

To wrap the high resolution mesh

  1. In the scene view, show the Pants_HighRes object by selecting it in the Outliner, and then selecting Display > Show >Show Selection.

  2. -select the nCloth pants.
  3. From the Animation menu set, select Create Deformers > Wrap.

    A wrap node appears in the Attribute Editor, and a Pants_LowResBase object appears in the Outliner.

  4. In the Attribute Editor, click the wrap1 tab.
  5. In the Wrap Attributes section, turn on Exclusive Bind.

    With this turned on, each surface point (vertex) on the Pants_HighRes object is constrained or affected by the Pants_LowRes object vertices. This ensures that the Pants_HighRes object inherits the properties of the simulated nCloth pants.

  6. Hide the Pants_LowRes object, and play back the simulation.

When you play back the simulation, you notice the following:

With the high polygon count of the Pants_HighRes object, one would expect to see the simulation slow down. However, this is not the case, since the Nucleus solver is not simulating any data associated with the Pants_HighRes object. All Nucleus calculations involved in the simulation are still performed on the low resolution nCloth pants. The behavior of the Pants_HighRes object is being influenced by a new instance of the simulated nCloth pants, the Pants_LowResBase object. In the Outliner, you can see that the Pants_LowResBase object has been added to the Character_LowRes group.

The Pants_LowResBase object is the base shape for the deformation of the Pants_HighRes object, which is the wrap influence object. Like all wrap deformers, any difference in position, orientation, or shape between the base shape and the wrap influence object results in a deformation of the surface being influenced by the wrap deformer.

Simulating the nCloth pants on an animated character

In this section of the lesson, you import geometry caches for the nRigid body and nRigid shoe objects, and begin simulating the nCloth pants object while the body and shoes are animated.

Lesson setup

To ensure that this section of the lesson works as described, do these steps before beginning:

  1. If the Pants_HighRes object is visible in the scene view, hide it now, by selecting Pants_HighRes in the Outliner, and selecting Display > Hide > Hide selection.
  2. If the Pants_LowRes object is not visible in the scene, show it now, by selecting Pants_LowRes in the Outliner, and selecting Display > Show > Show Selection.

To import the geometry caches to animate the body and shoe meshes

  1. In the scene view, select the nRigid_Body object.
  2. From the Animation menu set, select Geometry Cache > Import Cache.
  3. In the Import window that appears, browse to your Maya projects folder and select Body_Animation.mc.
  4. In the scene view, select the nRigid_Shoes object.
  5. From the Animation menu set, select Geometry Cache > Import Cache.
  6. In the Import window that appears, browse to your Maya projects folder and select Shoe_Animation.mc.

You can play back the simulation to see how your nCloth pants behave when they are simulated with the animated character. However, it is difficult to closely inspect the simulation without being able to scrub the Timeline. To make it easier to identify problems in the simulation, create a cache for the nCloth pants object. For information about nCaches, see nCaching overview.

To cache the nCloth pants simulation

  1. In the scene view, select the nCloth pants.
  2. From the nDynamics menu set, select nCache > Create New Cache > .

    The Create nCache Options window appears.

  3. In the Create nCache Options window, do the following:
    • Set the Cache directory to the folder to which you want your caches saved.
    • Set the Cache Name to nCloth_PantsShape.
    • Beside File distribution, select One File.
    • Click Create.
  4. Play back the simulation.

Identifying problem areas in the simulated nCloth

When you play back the simulation, you notice the following problems with the nCloth pants object:

Dolly and tumble the scene while scrubbing the Timeline so that you can closely observe each problem area.

Editing Substeps

A useful first step to fixing simulation issues is to increase the number of Nucleus solver Substeps and Max Collision Iterations. Substeps specify the number of times per frame that the Maya Nucleus solver calculates everything involved in the simulation, from the collision detection between nCloth and passive collision objects, to the effects of Dynamic Properties attributes and the dynamic constraints. Adjusting Substeps allows you to control how the simulation time is broken up into calculation segments. Simulation quality and collision accuracy generally improve with increasing substeps values. Max Collision Iterations specify the maximum number of collision iterations per frame for this Maya Nucleus solver. A high number of Substeps or Max Collision Iterations may result in a slower solve.

Depending on the complexity of your scene, the default values of 3 Substeps and 4 Max Collision Iterations may work well when simulating a static scene in which only gravity and wind are affecting the nCloth objects. When the nCloth begins to move and self collide, higher Substeps values are required to ensure accurate collision detection, especially on fast-moving objects. Increasing Max Collision Iterations becomes important when the number of nCloth collisions increases, and when dynamic constraints are added to your object. For more information, see Substeps and Max Collision Iterations.

To edit Substeps and Max Collision Iterations

  1. In the Attribute Editor, click the nucleus1 tab.
  2. In the Solver Attributes do the following:
    • Set Substeps to 7.
    • Set Max Collision Iterations to 8.

  3. Before playing back the simulation to see the results of these new settings, delete the simulation's previous nCache, otherwise, your changes will not appear in the simulation. To delete the previous nCloth cache, select your nCloth object, and then select nCache > Delete Cache.
  4. Cache, and then play back the simulation.

When you play back the simulation, you notice that, starting at frame 1030, the polygon faces in the area of the knees look more realistic. The cloth deformation is now spread over more faces, making it look more realistic. However not all of the simulation problems were resolved. Higher Substeps and Max Collision Iterations may be required.

Because increasing Substeps and Max Collision Iterations cause the Nucleus solver to perform more calculations each simulated step, it slows down the simulation. To develop a balance between simulation quality and performance, it is useful to identify the specific areas or frames in the simulation that require higher Substeps and Max Collision Iterations. You can then animate the Substeps and Max Collision Iteration values over the duration of the simulation by setting keyframes.

To set keyframes for Substeps and Max Collision Iterations

  1. In the Timeline, go to frame 1000.
  2. In the Attribute Editor, select the nucleus1 tab.
  3. In the Solver Attributes section, do the following:
    • Set Substeps to 5.
    • -click the Substeps attribute field, and select Set Key from the context-sensitive menu.

    • Set Max Collision Iterations to 6
    • -click the Max Collision Iterations attribute field, and select Set Key from the context-sensitive menu.
  4. Continue setting keyframes in your simulation using values from the following table:
    Frame Substeps Max Collision Iterations
    1019 5 6
    1020 7 8
    1022 9 12
    1025 15 20
    1060 9 12
  5. Cache your simulation and the play it back.

Fine tuning nCloth attributes

When you play back the cache, you notice that the overall quality of the simulation has improved. However, problem areas, most notably in the waist and in the crotch, can still be observed. For example, at frame 1030, poor self collisions in the area of the crotch are resulting in undesirable polygon deformations. To improve the quality your simulation, you can to start fine tune the Dynamic Properties attributes.

When fine adjusting nCloth attributes, such as Dynamic Properties attributes, it is useful to create a duplicate of the nCloth mesh at different frames of your simulation. When you play back the simulation, you can then compare your currently simulated nCloth against the duplicate mesh and evaluate:

To help solve the problems in the crotch area, you can increase Bend Resistance so that the edges of the polygons better retain their shape. For more information, see Bend Resistance.

To create a duplicate mesh and edit Bend Resistance

  1. In the Timeline, go to frame 1030.
  2. In the scene view, select the nCloth pants and select Edit > Duplicate.
  3. In the Outliner, select Pants_LowRes1 and in the scene view, move the mesh object to the right of your character.

  4. In the Attribute Editor, click the nCloth_PantsShape tab.
  5. In the Dynamics Properties section, set Bend Resistance to 5.

  6. Cache simulation and play it back.

When you play back the simulation, you notice that the cloth is bending more realistically in the crotch area. In the Timeline go to frame 1030, and compare your simulated nCloth to the duplicate mesh. Dolly and tumble the scene so that you can closely observe the problem area.

Editing Quality Settings and resolving interpenetrations

When you play back the simulation and compare the problem areas with duplicate meshes, you notice that the problem areas between frame 1030 and 1035 still persist.

Another way to improve simulation quality is to edit the Self Collision Flag and Quality Settings attributes, which affect the nCloth components' collisions and self collisions. By default, Self Collision Flag is set to VertexFace, which means that the nCloth object's vertices and faces collide with each other. Setting Self Collision Flag to Full Surface sets all of the object components (vertices, edges, and faces) to participate in self collisions. When simulating a low resolution mesh, increasing the number of potential self collision areas of the nCloth object is important because of the mesh’s low vertex, edge, and face count. Setting Self Collision Flag to Full Surface on high resolution nCloth meshes increases simulation time. This is less of an issue with low resolution meshes, which makes this alternative much more appealing for iterative simulation tests. For more information, see Collisions.

To edit the Self Collision Flag attribute

  1. In the Timeline, go to frame 1033.
  2. In the scene view, select the nCloth pants and select Edit > Duplicate.
  3. In the Outliner, select Pants_LowRes2 and in the scene view, move the mesh object to the left of your character.

  4. In the Attribute Editor, click the nCloth_PantsShape tab.
  5. In the Collisions section, set Self Collision Flag to Full Surface.

After initial fine adjustments to Self Collision attribute, you edit the Quality Settings to improve collisions and self collisions in the simulation. This will resolve any remaining interpenetrations between the nCloth pants object and the nRigid shoes. You can also increase Thickness or create a Thickness Map to improve collision detection.

To edit the Quality Settings

  1. In the Attribute Editor, select the nCloth_PantsShape tab.
  2. In the Quality Settings section, do the following:
    • Make sure Max Iterations is set to 10000.
    • Turn on Trapped Check.
    • Turn on Self Trapped Check.

  3. Cache the simulation and then play it back.

In the Timeline, go to frame 1033, and compare your simulated nCloth to the duplicate mesh. Dolly and tumble the scene so that you can closely observe the problem area.

Comparing the wrapped nCloth simulation with the simulated high resolution mesh

To complete the attribute adjustments of the nCloth pants object, you compare the wrapped nCloth simulation to the reference character object (the original simulated high resolution mesh).

To compare the low and high resolution nCloth meshes

  1. Hide the Pants_LowRes object, selecting it in the Outliner, and then selecting Display > Hide > Hide Selection.
  2. Show the Pants_HighRes object by selecting it in the Outliner, and then selecting Display > Show >Show Selection.
  3. Using the Displays Layers Editor, turn on Visible to display the Reference_Character object in the scene view.
  4. Scrub through the Timeline to compare how nCloth meshes behave in the animation. Dolly and tumble the scene so that you can closely observe the problem area.

Observations

When you play back or scrub the simulation, you notice the following:

To force the pant legs of the nCloth pants to simulate in the same way as the pants legs on the reference character object, adjust the Friction attribute.

Please send us your comment about this page