Computer Animation Ying Zhu Georgia State University Cloth

How to create cloth? Create an object Adjust the resolution of the mesh through subdivision The more faces on the 3D model, the better the simulation result. (However, it’s also slower.) Cloth is animated by simulating springs between vertices Under Object (F7) and “Physics buttons” panel, “Cloth” tab Press “Cloth” button

How to create cloth? Identify objects that may collide with the cloth Make these objects “collideable “ Select the object Under Object (F7) and “Physics buttons” panel, “Collision” tab Press “Collision” button Press Alt + A to start the simulation

Different types of cloth As of 2.48a, Blender has pre-defined settings for the following types of clothes Cotton Silk Rubber Denim Leather You may create your own type of cloth through the “Custom” type

Cloth parameters In the “Cloth” tab StrucStiff: overall stiffness of structure Spring Damp: Damping of cloth velocity Cloth is simulated by many springs between vertices A higher “Spring Damp” means the cloth material appears “heavier” and “smoother”, with less jiggling. BendStiff: how stiff the object when bended Air Damp: how much the cloth “flows” in the air Mass

Cloth and soft Body Soft objects with closed surface are better simulated by Soft Body

Collision parameters for cloth You can adjust the collision parameters for cloth in the “Collision” tab (next to the Cloth tab) Collision is turned on by default In most cases, you want to “Enable Self-collisions”

Collision with other objects Any object that may interact with cloth should be made “collideable” Select the object, under Object (F7) and “Physics buttons” panel, “Collision” tab (next to “Fields”), Press “Collision” button

Collision with other objects Adjust collision parameters under “Soft Body and Cloth Interaction” “Inner” and “Outer”: create a invisible “buffer zone” surrounding the object So that the cloth will not collide directly with the object mesh This is to prevent objects penetrating the cloth during the collision (due to imprecise calculation) So if you see an object penetrating the cloth, adjust its “Inner” and “Outer” values

Bake Like other physical simulations, you can bake the cloth simulation and then play it back without having to recalculate at each frame “Bake” parameters are in the “Collision” tab The bake “End” frame should be no smaller than the last frame of your cloth simulation

How to pin part of the cloth? Sometimes you want to pin certain parts of the cloth so that those parts don’t move The process Select the object Enter Edit mode Under Editing (F9) panel, “Link and Materials”, create a new vertex group, give it a meaningful name Select faces directly (or use weight paint to select faces) and then press the “Assign” button

How to pin part of the cloth? Now go to “Object”, “Physics buttons” panel, in the “Cloth” tab Press “Pinning of cloth” button Select the vertex group from the drop down menu Adjust “Pin Stiff” parameter Press Alt + A, you’ll see that the selected vertex group is now pinned

How to attach a piece of cloth to an object? Create a cloth mesh Move it closer to the object you want to attach the cloth to Make the cloth mesh a child of the target object Create a vertex group on the cloth mesh and pin it using the previously mentioned method The pinned part will be “attached” to the target object

Cloth and force fields You can use force fields to animate the cloth Particularly the “Wind” force field You may want to pin the cloth mesh first before applying the force field Otherwise the cloth may be blown away You may animate the strength of force fields by inserting key frames (or with IPO curve) Change frame number, adjust force field strength Place the mouse cursor in the “Fields” tab and press the “I” key

Apply the cloth modifier What if you just want to drape a piece of cloth over a table without animating it? Create the table object and enable “collision” for it Place a plane right above the table and enable “cloth” Increase the frame numbers (by pressing  key, don’t use Alt + A) until the cloth drapes nicely over the table Now with the cloth object selected, go to Editing panel, in “Modifiers” tab, “Apply” the Cloth modifier

Apply the cloth modifier When you apply the Cloth modifier, the cloth deformation become “fixed”

Re-enable Cloth modifier What if you want to set up a starting shape for a piece of cloth and then animate it from there? Use the previously mentioned method to fix the cloth object in a particular shape (by applying the Cloth modifier) Adjust the frame number to the starting frame of your animation Select the cloth object, go to the Cloth tab and press the “Cloth” button Now you can animate the cloth from its “starting” shape (the Cloth modifier is back on)

Smooth modifier You may want to apply a “Smooth” modifier to the cloth object But the “Smooth” modifier should be added after (below) the “Cloth” modifier

Editing cloth parameters on the fly You can let the cloth animation run in loops and adjust the cloth, collision, or force field parameters on the fly and see the changes in real-time Open a timeline window Press “Playback” and select “Continue physics” Start the animation by press the Play button in the Timeline window (not Alt + A) Adjust the parameters as the animation runs

Editing cloth parameters on the fly For example, you may want to adjust the wind strength on the fly until you find the right number This allows you to adjust parameters without having to stop and start the animation over and over again The same applies to particle systems and hair too.