/// <summary>
/// Evalute sphere physics, generate new velocities based on collisions, and update
/// sphere positions
/// </summary>
protected void UpdateSpheres(GameTime gameTime)
{
Vector3 gravity = Vector3.UnitY * -4.0f;
float shakeForce = 1.0f;
// Tilt limit
const float limit = 0.85f;
// Tilt offset that determines where 'flat'
const float tiltoffset = 0.76f;
double accelReadingZ;
double accelReadingY;
float elapsedGameTime = (float)gameTime.ElapsedGameTime.TotalSeconds;
// Read the current state of the accelerometer
Vector3 currentAccelerometerReading = Accelerometer.GetState().Acceleration;
// We need to reverse the accelerometer reading for the y axis depending on orientation
if (Window.CurrentOrientation == DisplayOrientation.LandscapeLeft)
{
currentAccelerometerReading.Y = -currentAccelerometerReading.Y;
}
// Compute accelerometer magnitude
Vector3 accelMag = Vector3.Zero;
accelMag = currentAccelerometerReading;
float newMag = accelMag.Length();
// Detect a shake gesture. Search for a peak that is > 1.3f in magnitude.
if (accelhistory[1] > 1.3f && accelhistory[0] < accelhistory[1] && accelhistory[1] > newMag)
{
// Compute shake force
shakeForce += 10.0f * (accelhistory[1] - 1.3f) / 3.5f;
}
// MRU cache for accelerometer magnitudes
accelhistory[0] = accelhistory[1];
accelhistory[1] = newMag;
// Read accelerometer Z and Y, which will be used for modifying gravity
accelReadingZ = currentAccelerometerReading.Z;
accelReadingY = currentAccelerometerReading.Y;
// Limit the rotation based on accelerometer
float rotateX = Math.Max(Math.Min((float)-(accelReadingZ + tiltoffset), limit), -limit);
float rotateY = Math.Max(Math.Min((float)accelReadingY, limit), -limit);
// Rotate gravity vector based on accelerometer input
Matrix rotationToBeDone = Matrix.CreateRotationX(rotateX * MathHelper.PiOver2);
Matrix rotationToBeDone2 = Matrix.CreateRotationZ(rotateY * MathHelper.PiOver2);
gravity = Vector3.Transform(gravity, rotationToBeDone);
gravity = Vector3.Transform(gravity, rotationToBeDone2);
// Update positions, add air friction and gravity
for (int i = 0; i < numSpheres; i++)
{
Sphere mySphere = spheres[i];
mySphere.Position += mySphere.Velocity * elapsedGameTime * 0.99f;
// Apply accelleration due to gravity
mySphere.Velocity += gravity * elapsedGameTime;
}
// Resolve sphere-sphere collisions
for (int i = 0; i < numSpheres; i++)
{
for (int j = i + 1; j < numSpheres; j++)
{
SphereCollisionImplicit(spheres[i], spheres[j]);
}
}
// Resolve collisions with floor
for (int i = 0; i < numSpheres; i++)
{
Sphere mySphere = spheres[i];
if (mySphere.Position.Y < floorPlaneHeight + mySphere.Radius)
{
// subtract out pre-accelerated gravity first
mySphere.Velocity -= gravity * elapsedGameTime;
// apply shake force
if (shakeForce > 1.0f)
{
// Add some upward momentum
mySphere.Velocity.Y += 0.1f;
// Compute current speed
float speed = mySphere.Velocity.Length();
// Limit new speed
float speedadjust = speed;
speedadjust = Math.Min(speed, 4.0f);
speedadjust = Math.Max(speed, 2.0f);
// normalize
mySphere.Velocity *= 1.0f / speed;
// accellerate based on shake force
mySphere.Velocity *= speedadjust * shakeForce;
}
mySphere.Position.Y = floorPlaneHeight + mySphere.Radius;
if (mySphere.Velocity.Y < 0)
{
// Determine "complete rest"
if (mySphere.Velocity.Y > (gravity.Y * elapsedGameTime * 2.0f) &&
mySphere.Velocity.LengthSquared() < (0.5 * 0.5))
{
mySphere.Velocity.Y = 0.0f;
}
else // Otherwise, bounce.
{
mySphere.Velocity.Y = -mySphere.Velocity.Y * collisionDamping;
}
}
}
// Resolves collisions with walls
if (mySphere.Position.X < -worldSize + mySphere.Radius)
{
mySphere.Position.X = -worldSize + mySphere.Radius;
if (mySphere.Velocity.X < 0)
{
mySphere.Velocity.X = -mySphere.Velocity.X * collisionDamping;
}
}
if (mySphere.Position.X > worldSize - mySphere.Radius)
{
mySphere.Position.X = worldSize - mySphere.Radius;
if (mySphere.Velocity.X > 0)
{
mySphere.Velocity.X = -mySphere.Velocity.X * collisionDamping;
}
}
if (mySphere.Position.Z < -worldSize + mySphere.Radius)
{
mySphere.Position.Z = -worldSize + mySphere.Radius;
if (mySphere.Velocity.Z < 0)
{
mySphere.Velocity.Z = -mySphere.Velocity.Z * collisionDamping;
}
}
if (mySphere.Position.Z > worldSize - mySphere.Radius)
{
mySphere.Position.Z = worldSize - mySphere.Radius;
if (mySphere.Velocity.Z > 0)
{
mySphere.Velocity.Z = -mySphere.Velocity.Z * collisionDamping;
}
}
}
}
