Most of these parameters are mappable (ones with a connection icon beside them), meaning that you can use weight and texture maps on them to modulate their value. For more information on this, see Parameter Maps.
Controlling the Stretch with Spring Nets
Cloth deformation is controlled by a virtual “spring net.” Springs are distributed onto the cloth surface and connect the vertices of the model according to a specific rule.
There are three different types of springs that constitute the spring net, each controlling a different kind of deformation:
• Stretch springs, which connect adjacent vertices of polygons or quads. They correspond to the visible edges of the wireframe model.
• Shear springs, which connect non-adjacent vertices of the same polygon or quad.
• Bend (flex) springs, which are the same as Stretch, but connect every other vertex, skipping the adjacent ones.
This illustration shows how cloth is applied to NURBS surface objects:
Shear, Bend, and Stretch Resistance (Stiffness)
The elastic constant values associated with these springs are the Stiffness parameters found on the Cloth property page. They define how soft or rigid a fabric is, such as the difference between silk and leather.
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Most of these parameters are mappable (ones with a connection icon beside them), meaning that you can use weight and texture maps on them to modulate their value. For more information on this, see Parameter Maps. |
To help reduce that stretchy, “rubbery” look when a cloth drapes over an obstacle, use high values for all the Stiffness parameters. Low values (no resistance) allow the cloth to deform without resistance.
• Shear Resistance controls the resistance to shearing, meaning crosswise stretching, keeping as much to the original shape as possible. For high values, a Cloth’s quad remains undeformed in the simulation and the angle between two adjacent edges of the quad is near to the initial equilibrium value. For a reasonable value, make it equal to or less than the Stretch Resistance value. Try to decrease this value if the cloth’s wrinkling is too rigid.
For polygon mesh objects, the polygons are not always quad, so the shear net is not defined. What you can do to solve this is to triangulate the polygon by selecting Triangulate Polygons on the Cloth property page. The edges coming from the triangulation are then used as the shear net.
• Bend Resistance controls the resistance to bending. With low values, the cloth moves very freely like silk; with high values, the cloth appears like rigid linen or even leather. For a reasonable value, make it less than the Shear and Stretch Resistance values.
• Stretch Resistance defines the resistance to stretching as it controls the elasticity of the material. Low values allow the cloth to deform without resistance, while higher values prevent the cloth to have elasticity.
Initial Tension % gives an initial tension to the cloth by stretching or compressing the springs used to simulate the fabric. This is useful for shrinking large garments on an obstacle body in a few “pre-roll” frames.
This parameter lets the cloth act like rubber of elastic under stress. Upon release it tries to snap to a non-stretched state which is n percentage smaller as defined by this parameter. A value of 100 means the tension is as given by 100% stretching of the cloth object rest size (that is, the rest size is half the size of the initial cloth object).
You can also use negative values: for example, a value of –100 means that the tension is as given by a compression to half the cloth object rest size (that is, the rest size is a 100% stretching of the initial cloth object size).
The Stretch Limit defines the ratio of spring deformation allowed from one step to the other. A high value makes the cloth bouncier than lower values. Since numerical divergence may occur, the solver automatically increases the Iterations Per Frame value when it is needed, depending on the value you set for it.
Stretch Limit is a key factor in stabilizing the cloth simulation. Increase its value if the simulation stops running or decrease it if there seems to be instability during the simulation and play again. Values between 1 and 2.5 will probably give the best results.
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