Flag Physics

Cloth Physics

Flag/misc - https://www.youtube.com/watch?v=kjOq8OB_3AQ

This tutorial shows how to turn a plane into a cloth and allow a wind actor to effect it. I have managed to replicate this process albeit with some changes due to an issue I encountered when importing an FBX import from 3dsmax.

This tutorial briefly shows Unreal 4s ability to distinguish separate elements of an imported FBX file. Within a single mesh. In the tutorial the flag and pole both have their own individual material slots respectively to put different textures in. However, for reasons I can’t explain the FBX I exported from 3dsMax did not distinguish between the flag and the pole when imported into UE. This not only gives me a single material slot but also means I cannot select the what should be 2 parts individually, meaning that the cloth modifier and cloth paint process would affect both the flag and the pole. I attempted to resolve the issue by attaching polys orders and grouping them in different orders and configurations, however nothing worked. The best I could do was import the model as a single FBX that when imported into UE would split into 2 different meshes. Due to the simplicity of the model this was not a big issue but with something more complicated it would mean I would have to stick the individual parts of the model together by hand back where they should be, which would be time consuming and potentially result in undesirable differences from the original model.

This issue only seems to effect skeletal meshes as there is an option to combine meshes when creating a static mesh. As a static mesh cannot be converted into a skeletal one this issue may raise its head in a more troublesome manner when importing a complex model that requires a skeletal mesh, such as a character model. A workaround of this issue would to be to unwrap every element of a model under a single unwrap, but this will mean I would not be able to properly adjust material properties individually. If my character wore armour and had a cape all modifications of the texture then the properties of the armour and the cape would be the same if I adjusted them within Unreal 4.

Otherwise this method is pretty simple to execute and highly customisable. The plane must be of a high poly count as the engine uses them as reference to move them individually to create the realistic cloth physics. As is the case of all polygon counts being smart about how many are used in different instances is key to creating a more optimised game. If the object is small, it will need less as there is less surface area to move around and if the cloth is in the background then players will likely not notice if the cloth movement is not finely detailed. I also imagine this technique uses CPU and/or GPU resources to simulate the physics, so this is something that will potentially result in performance loss.