cloth-physics: A C++ repository from joeghodsi

clothSim README

Arash Ghodsi (aghodsi)
CMPS161 - Animation and Visualization
Winter 2011

clothSim Description:
Create physically based animation for a swinging hula skirt. The skirt is to be modeled as a
triangular mesh cylinder which is textured to look like a hula skirt. Each edge (including the
top-left to bottom-right diagonals) acts as a spring force on its vertices. Thus each vertex is
acted on by six spring forces (above, below, left, right, upper diagonal, and lower diagonal). The
vertices are also affected by gravity. The last force affecting the mesh is provided by an
oscillatory motion enacted on the top two rows of vertices. This force only indirectly affects
subsequent rows of vertices via the springs. The springs become looser near the bottom of the skirt
while the springs near the top are stiffer.

clothSim Solution:
I achieved all of the requirements of this project. The skirt is modeled as a triangle mesh
cylinder which is textured as a hula skirt. Each edge acts as a spring force on its vertices. Note:
I chose to use top-left to bottom-right diagonal edges.
Each vertex is affected by its six neighboring spring forces, by gravity, and by spring damping.
The only rows directly affected by the oscillatory motion are the top two rows of free-motion
vertices; all subsequent rows' vertices are affected indirectly by their spring forces. The user can
adjust the motion of the skirt by increasing or decreasing both the amplitude and frequency of the
oscillatory motion. They may also switch between a 2D swing about the z-axis or a 3D swing about
both the x-axis and z-axis, independently. You can find the controls below.
The vertex positions are determined using a system of force equations (one for each spring force,
one for gravity, one for the oscillatory motion, and one for spring damping) which are applied as
acceleration. The velocity of a given vertex is determined via Euler integration in which all of the
accelerations are summed up. The position of a given vertex is also determined via Euler integration
in which all the velocities are summed up.
Note: I used Hooke's Law to simulate the springs at each edge. Also, the spring constant, Ks,
decreased row by row toward the bottom of the skirt thus making the skirt looser near the bottom and
stiffer near the top.

To compile and run the program from the command line type:
$ make
$ clothSim
Note: The following libraries are required in order to build the sim - libglut32, libglu32 and
libopengl32

//::CONTROLS:://////////////////////////////////////////////////////////////////////////////////////
Mouse right-click: Switches in and out of wireframe rendering
Mouse click-and-hold: Rotates the camera around the skirt horizontally
1: 2D rotation
2: 3D rotation
Up and Down arrows: adjusts the amplitude up or down, respectively
Left and Right arrows: adjusts the frequency up or down, respectively
Esc: Exits the program
////////////////////////////////////////////////////////////////////////////////////////////////////

Files: main.cpp, skirt.h, skirt.cpp, quaternion.h, quaternion.cpp, Makefile, README, assets, tech_writeup.pdf

main.cpp:
Where the openGL IO occurs. Responsible for user mouse/keyboard input and displaying the skirt.

skirt.h:
Interface for the Skirt class. This class is responsible for the following:
1: Generating the skirt as a triangular mesh
2: Texturing the mesh as a hula skirt
3: Maintaining the spring force system governing the animation of the skirt
4: Animating the skirt using rotation quaternions (versors)

skirt.cpp:
Implementation for the Skirt class

quaternion.h:
Interface for the Quaternion class. This class is a wrapper class used for rotation quaternions or
versors. It can calculate the inverse, product, and sum for quaternions. It can also normalize a
quaternion and calculate slerp (spherical linear interoplation).

quaternion.cpp:
Implementation for the Quaternion class

Makefile:
The makefile used to complile this project.
To compile: at the command line type make
To run: at the command line type clothSim

README:
This file.

clothSim.exe:
A prebuilt executable

assets:
Includes the texture used, a couple variant textures, and the original source image.

tech_writeup.pdf:
A short technical paper describing the problem, my approach, and results.

joeghodsi/cloth-physics