Stupid WheeledVehicle tricks

Stupid WheeledVehicle Tricks!

Here's a couple code snipplets that should answer some questions that keep popping up in the fourms and on IRC.

Drive on walls! Or, Mommy! My vehicle has sticky wheels!

In wheeledVehicle.cc, WheeledVehicle::updateForces, look for:

// Sum up spring and wheel torque forces
   for (Wheel* wheel = mWheel; wheel < wend; wheel++)  {
      if (!wheel->tire || !wheel->spring)
         continue;

      F32 Fy = 0;
      if (wheel->surface.contact) {

Change it to this:

// Add for "surfacegravity"
   Point3F surfaceGravity(0, 0, 0);

   // Sum up spring and wheel torque forces
   for (Wheel* wheel = mWheel; wheel < wend; wheel++)  {
      if (!wheel->tire || !wheel->spring)
         continue;

      F32 Fy = 0;
      if (wheel->surface.contact) {

		 // Ok, we're calculating a weird gravity
		 surfaceGravity += wheel->surface.normal;

Next, look for this:

// If we've added anything other than gravity, then we're no
   // longer at rest. Could test this a little more efficiently...
   if (mRigid.atRest && (mRigid.force.len() || mRigid.torque.len()))
      mRigid.atRest = false;

   mRigid.force += Point3F(0, 0, sWheeledVehicleGravity * mRigid.mass);

Change it to this:

surfaceGravity.normalize();
     surfaceGravity *= (mRigid.mass * sWheeledVehicleGravity);
     mRigid.force += surfaceGravity;

For extra credit, wrap this calculation with a chcek for a datablock flag, or a per object flag that will allow for normal gravity, and drive on wall gravity.



Next, very cheesy two wheeled vehicles:

This basically add's a gyroscopic force to allow vehicles to remain upright. It acts kinda like one of those clowns that you can punch over and over again, but it still
manages to upright itself.

In wheeledVehicle.cc, WheeledVehicle::updateForces, look for:

// Jet Force
   if (mJetting)
      mRigid.force += by * mDataBlock->jetForce;

Add this after it:

// Roll torque
	mRigid.torque += by * mSteering.x * mDataBlock->leanForce; // 1250
	// Gyro force
	F32 upCo = mDot(bx, Point3F(0, 0, 1));
	F32 yAngVel = mDot(by, mRigid.angVelocity);
	mRigid.torque += (by * mDataBlock->gyroForce * upCo) - (mDataBlock->gyroForceDampen * yAngVel * by); // 500

Now, we have to add a few datablock parameters:

Add these three lines to the private section of WheeledVehicleData in WheeledVehicle.h

F32 leanForce;						// Amount of lean to apply when turning
	F32 gyroForce;						// Amount of force to apply to upright the vehicle
	F32 gyroForceDampen;				// Dampen the spring force

Add these three lines to WheeledVehicleData::WheeledVehicleData()

gyroForce = 1600;
	gyroForceDampen = 500;
	leanForce = 1250;

Add these three lines to WheeledVehicleData::initPersistFields()

addField("leanForce", TypeF32, Offset(leanForce, WheeledVehicleData));
	addField("gyroForce", TypeF32, Offset(gyroForce, WheeledVehicleData));
	addField("gyroForceDampen", TypeF32, Offset(gyroForceDampen, WheeledVehicleData));

These three to WheeledVehicleData::packData

stream->write(leanForce);
	stream->write(gyroForce);
	stream->write(gyroForceDampen);

Finally, these three to WheeledVehicleData::unpackData

stream->read(&leanForce);
	stream->read(&gyroForce);
	stream->read(&gyroForceDampen);

Oh yeah, you need a small script change to make sure the wheels are setup right:

In car.cs replace onAdd with the following:

function WheeledVehicleData::onAdd(%this,%obj)
{
   // Setup the car with some defaults tires & springs
   for (%i = %obj.getWheelCount() - 1; %i >= 0; %i--) {
      %obj.setWheelTire(%i,DefaultCarTire);
      %obj.setWheelSpring(%i,DefaultCarSpring);
      %obj.setWheelPowered(%i,false);
   }
   
   // Steer front tires
   %obj.setWheelSteering(0,1);
//   %obj.setWheelSteering(1,1);

   // Only power the two rear wheels...
   %obj.setWheelPowered(1,true);
//   %obj.setWheelPowered(3,true);
}