§13.1牛顿运动定律

// [From CarPhysics.cs]

// Handle car engine force

float newAccelerationForce = 0.0f;

if (Input.KeyboardUpPressed || Input.Keyboard.IsKeyDown(Keys.W) || Input.MouseLeftButtonPressed || Input.GamePadAPressed)

newAccelerationForce += MaxAccelerationPerSec;

// [etc.]

// Add acceleration force to total car force, but use the current

// car direction!

carForce += carDir * newAccelerationForce * (moveFactor * 85);// 70);//75);

// Change speed with standard formula, use acceleration as our

// force, gravity is handled below in the ApplyGravity method.

float oldSpeed = speed;

Vector3 speedChangeVector = carForce / CarMass;

// Only use the amount important for our current direction

// (slower rotation)

if (speedChangeVector.Length() > 0)

{

float speedApplyFactor = Vector3.Dot(Vector3.Normalize(speedChangeVector), carDir);

if (speedApplyFactor > 1)

speedApplyFactor = 1;

speed += speedChangeVector.Length() * speedApplyFactor;

} // if (speedChangeVector.Length)

// First handle rotations (reduce last value)

rotationChange *= 0.825f;// 75f;

// Left/right changes rotation

if (Input.KeyboardLeftPressed || Input.Keyboard.IsKeyDown(Keys.A))

rotationChange += MaxRotationPerSec * moveFactor / 2.5f;

else if (Input.KeyboardRightPressed || Input.Keyboard.IsKeyDown(Keys.D) || Input.Keyboard.IsKeyDown(Keys.E))

rotationChange -= MaxRotationPerSec * moveFactor / 2.5f;

else rotationChange = 0;

if (Input.MouseXMovement != 0)

rotationChange -= (Input.MouseXMovement / 15.0f) * MaxRotationPerSec * moveFactor;

// Rotate dir around up vector

// Interpolate rotatation amount.

virtualRotationAmount += rotationChange;

// Smooth over 200ms

float interpolatedRotationChange = (rotationChange + virtualRotationAmount) * moveFactor / 0.225f;// / 0.200f;

virtualRotationAmount -= interpolatedRotationChange;

// We can't rotate our car ourself if it is currently not on the ground

if (isCarOnGround)

carDir = Vector3.TransformNormal(carDir, Matrix.CreateFromAxisAngle(carUp, interpolatedRotationChange));

static public void TestCarPhysicsOnPlane()

{

PlaneRenderer plane = null;

TestGame.Start("TestCarPhysicsOnPlane",

delegate {

plane = new PlaneRenderer(Vector3.Zero, new Plane(new Vector3(0, 0, 1), 0), new Material("CityGround", "CityGroundNormal"), 500.0f);

// Put car on the ground and use standard direction and up vectors

RacingGame.Player.SetCarPosition( new Vector3(0, 0, 0), new Vector3(0, 1, 0), new Vector3(0, 0, 1));

},

delegate {

// Test slow computers by slowing down the framerate with Ctrl

if (Input.Keyboard.IsKeyDown(Keys.LeftControl))

Thread.Sleep(75);

Matrix carMatrix = RacingGame.Player.UpdateCarMatrixAndCamera();

// Generate shadows, just the car does shadows

ShaderEffect.shadowMapping.GenerateShadows(

delegate {

RacingGame.CarModel.GenerateShadow(carMatrix);

}

);

// Render shadows (on both the plane and the car)

ShaderEffect.shadowMapping.RenderShadows(

delegate {

RacingGame.CarModel.UseShadow(carMatrix);

plane.UseShadow(); });

BaseGame.UI.RenderGameBackground();

// Show car and ground plane

RacingGame.CarModel.RenderCar(0, Color.White, carMatrix);

plane.Render();

// Just add brake tracks (we don't render the landscape here)

RacingGame.Landscape.RenderBrakeTracks();

// Render all 3d objects

BaseGame.MeshRenderManager.Render();

// Add shadows

ShaderEffect.shadowMapping.ShowShadows();

RacingGame.Player.DisplayPhysicsValuesAndHelp();

}

);

} // TestCarPhysicsOnPlane()

// Put car 10m above the ground to test gravity and ground plane!

RacingGame.Player.SetCarPosition( new Vector3(0, 0, 10), new Vector3(0, 1, 0), new Vector3(0, 0, 1));

// Make sure we are not in free camera mode and can control the car

RacingGame.Player.FreeCamera = false;

RacingGame.Player.ZoomInTime = 0;

RacingGame.Player.SetCameraPosition(new Vector3(0, -5, 8));

/// <summary>

/// Apply gravity

/// </summary>

private void ApplyGravity()

{

// Fix car on ground float distFromGround = Vector3Helper.SignedDistanceToPlane( carPos, groundPlanePos, groundPlaneNormal);

isCarOnGround = distFromGround > -0.1f;

// Use very hard and instant gravity to fix if car is below ground!

float moveFactor = BaseGame.MoveFactorPerSecond;

float maxGravity = Gravity * moveFactor;

// Use more smooth gravity for jumping

float minGravity = -Gravity * moveFactor;

if (distFromGround > maxGravity)

{

distFromGround = maxGravity;

gravitySpeed = 0;

} // if (distFromGround)

if (distFromGround < minGravity)

{

distFromGround = minGravity;

gravitySpeed -= distFromGround;

} // if (distFromGround)

carPos.Z += distFromGround;

} // ApplyGravity()

#region Constants

/// <summary>

/// Car is 1000 kg

/// </summary>

const float CarMass = 1000;//1000.0f;

/// <summary>

///Gravity on earth is 9.81 m/s^2

/// </summary>

const float Gravity = 9.81f;

/// <summary>

/// Max speed of our car is 275 mph.

/// </summary>

//While we use mph for the display, we calculate internally with

// meters per sec since meter is the unit we use for everthing in the

// game. And it is a much nicer unit than miles or feet.

public const float MaxSpeed = 275.0f * MphToMeterPerSec;

// Convert our meter per sec to mph for display.

// 1 mile = 1.609344 kilometers</summary>>

// Each hour has 3600 seconds (60 min * 60 sec).

// 1 kilometer = 1000 meter.

public const float MeterPerSecToMph = 1.609344f * ((60.0f*60.0f)/1000.0f), MphToMeterPerSec = 1.0f / MeterPerSecToMph;

// [etc.] >