/// <summary>
/// Handles a collision between the physics object and a surface described by a surface
/// normal. The object's velocity will change such that the angle of incidence and the
/// angle of reflection are equal with respect to the surface normal. Note that this
/// method does not check whether any sort of a collision actually occurred - it trusts
/// the caller to determine that.
/// </summary>
/// <param name="physicsObject">The object whose velocity will change as a result of the
/// collision.</param>
/// <param name="surfaceNormal">The surface normal of the surface against which the object
/// collided.</param>
/// <param name="restitution">Coefficient of restitution. 1.0f means an elastic collision (no
/// energy lost), so the object will bounce back as forcefully as it went in. For 0.0f, the
/// object will effectively stop at the surface.</param>
private void HandleCollisionWithSurface(IPhysicsObject physicsObject, Vector3 surfaceNormal,
float restitution)
{
Vector3 oldVelocity = physicsObject.GetVelocity();
// Project velocity vector onto the surface normal
float v_dot_n = Vector3.Dot(oldVelocity, surfaceNormal);
// Calculate the normal force
Vector3 normalForce = -(1.0f + restitution) * v_dot_n * surfaceNormal;
// Add the normal force to the motion vector to get the new velocity
Vector3 newVelocity = oldVelocity + normalForce;
physicsObject.UpdateVelocity(newVelocity);
}
private void DoCollisionDetectionWithTerrain(IPhysicsObject physicsObject)
{
Vector3 position = physicsObject.GetPosition();
if (game.terrain.heightMapInfo.IsOnHeightmap(position))
{
float objectBottom = physicsObject.GetBoundingBox().Min.Y;
//Utility.BoundingBoxRenderer.Render(game, physicsObject.GetBoundingBox(), game.GraphicsDevice, game.worldCamera.ViewMatrix, game.worldCamera.ProjectionMatrix, Color.White);
Vector3 v = physicsObject.GetVelocity();
// In the bounding box, the bottom corners have indices 2,3,6,7. We're
// interested in checking just the collisions of the bottom corners of
// the object with the terrain.
Vector3[] corners = physicsObject.GetBoundingBox().GetCorners();
int[] bottomCorners = { 2, 3, 6, 7 };
foreach (int i in bottomCorners)
{
float terrainElevation;
Vector3 terrainNormal;
if (game.terrain.heightMapInfo.IsOnHeightmap(corners[i]))
{
game.terrain.heightMapInfo.GetHeightAndNormal(corners[i], out terrainElevation, out terrainNormal);
if (corners[i].Y <= terrainElevation)
{
HandleCollisionWithSurface(physicsObject, terrainNormal, 0.7f);
// Notify the physics object that a collision with the terrain had occurred.
physicsObject.HandleCollisionWithTerrain();
return;
}
}
}
}
}
