3D Real-time Soft Body Dynamics Demonstration Jan 20, 1999

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v. 1.0

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:

"GonaBlow"

Be sure an check out the "GonaBlow" demo. It shows what happens

when the integrator suffers from numerical instability. You can

prove this by halving the MaxStepSize in the Timing Property Dialog.

We will fix that next month.

"BoxBad"

This box is only connected along the cube edges. It is not stable in

this form. Try it out and see why.

"BoxGood"

By adding crossbeam supports, it becomes stable. This is a good example

of how to create a stable model.

"Diamond"

Another shape with pretty stiff springs. It is interesting to see how

it balances on an edge and then eventually falls. I suspect this is rounding

errors. In theory, it should balance exactly forever.

This is a pretty complex demo. Any problems or questions, email me.

The 3 files named "ListingX.txt" are the code listings that appeared in the magazine article.

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, Permidia 1 and 2 OpenGL

Drivers, Riva 128 (New Beta OGL Drivers), 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().