3D Real-time Soft Body Friction Demonstration July, 1999

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v. 1.0 With Friction

This is a quick demonstration to show how the Coulomb method

of dry friction can be applied to a dynamic simulation.

The demo is built on the same soft body code from earlier in

the year. However, there have been some key changes.

1. A contact model has been added. This required changing

the particle structure so models from the previous version will

not work. I create the cube and diamond for this demo. The

contact model checks to see if distance from the particle to the

contact surface is below the contactEpsilon threshold (currently 0.01f).

If so, the particle is marked and the contact normal is saved.

2. Friction force is added via the Coulomb model during

ComputeForces. If the relative velocity is greater then the

threshold STATIC_THRESHOLD, the kinetic friction is applied.

Otherwise, static friction is used.

Notes:

In order to see the friction force in action, world damping

has been reduced. You can toggle friction on and off to

see how it halts the object (F key or Menu switch).

Obviously particles are not the best thing for showing off

friction. Friction works better on rigid bodies with larger

masses. I will address this next month when I start building

a Billiards simulation with rigid spheres.

In the meantime, you can play with the coefficients and

contact model. Switch integrators and see the effects.

If you are ambitions, add this into the cloth demo from

a few months ago to the sphere collision routines.

Also think about creating a list of contacts and storing

friction coefficients with the contact. I wanted to do

it that way but ran out of time.

Next month, the app will have a totally different look.

Much more like a production game with less MFC style stuff.

Brush up on your billiards...

Jeff

v. 1.0 Jan 1999

This program simulates soft body dynamics of a particle system

with particles connected with springs.

This program is fairly complicated. In order to show off the

features I wanted to demonstrate, I needed to create quite a

number of functions and UI. I appologize for all the extra junk

but it was as clear as I could make it in the time allowed.

All the major functions for the actual dynamic simulation are in

the files: PhysEnv.h and PhysEnv.cpp. Some of the timing

and display code is in OGLView.h and OGLView.cpp. Most of

the UI is passed through MainFrm.cpp to OGLView.

All of the simulation constants can be set through the

Simulation Properties dialog. Any changes to the spring constants

are applied to all springs in the simulation. There is currently

no way to change the settings for an individual spring.

You can load in one of the pre-made simulations or create a

new one by loading in an OBJ. The OBJ needs to be scaled

within a +-5 unit cube world so it fits within the world boundaries.

An OBJ file loads as a point cloud. You then can connect the dots

by selecting vertices two at a time. Press "ENTER" to connect the

points with a spring. The normal length of the spring is the distance

at the time of spring creation.

You can select one or two vertices and apply an user force to

the selected vertex/vertices. Once selected, a user force is

applied with the arrow keys for X-axis and Z-axis and HOME/END

applies the force to the Y-axis. The magnitude of the user force

is set in the sim properties dialog.

You can also click and drag the LMB to apply a force in the local

X and Y axis. The mousespring force is set in the sim properties

dialog. The force will apply to the one or two vertices selected.

Demos:

Jeff Lander

jeffl@darwin3d.com

www.darwin3d.com/gamedev.htm

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I compiled the code with Visual C++ 6.0. It has been tested

with Microsoft OpenGL, SGI OpenGL for Windows, Permidia 1 and 2 OpenGL

Drivers, Riva 128, TNT, TNT2, AccelGalaxy,

and Symetra Ultra FX Pro.

It should run on any OpenGL fully complient driver. This

DOES NOT include the mini-QuakeGL driver for 3DFX. 3DFX

OpenGL does not support OpenGL in a window so will not work

with this application.

Also, depending on how well GLlines are drawn on your system, the

sim should run too fast, too slow, or just right. I try to lock

it to the clock except to set the timesteps. If it is strange,

adjust COGLView::RunSim().