/// <summary>
/// This function contains the code that controls the mouse. It decides what the
/// mouse should do based on the position of the cat: if the cat is too close,
/// it will attempt to flee. Otherwise, it will idly wander around the screen.
///
/// </summary>
private void UpdateMouse ()
{
// first, calculate how far away the mouse is from the cat, and use that
// information to decide how to behave. If they are too close, the mouse
// will switch to "active" mode - fleeing. if they are far apart, the mouse
// will switch to "idle" mode, where it roams around the screen.
// we use a hysteresis constant in the decision making process, as described
// in the accompanying doc file.
float distanceFromCat = Vector2.Distance (mousePosition, catPosition);
// the cat is a safe distance away, so the mouse should idle:
if (distanceFromCat > MouseEvadeDistance + MouseHysteresis) {
mouseState = MouseAiState.Wander;
}
// the cat is too close; the mouse should run:
else if (distanceFromCat < MouseEvadeDistance - MouseHysteresis) {
mouseState = MouseAiState.Evading;
}
// if neither of those if blocks hit, we are in the "hysteresis" range,
// and the mouse will continue doing whatever it is doing now.
// the mouse will move at a different speed depending on what state it
// is in. when idle it won't move at full speed, but when actively evading
// it will move as fast as it can. this variable is used to track which
// speed the mouse should be moving.
float currentMouseSpeed;
// the second step of the Update is to change the mouse's orientation based
// on its current state.
if (mouseState == MouseAiState.Evading) {
// If the mouse is "active," it is trying to evade the cat. The evasion
// behavior is accomplished by using the TurnToFace function to turn
// towards a point on a straight line facing away from the cat. In other
// words, if the cat is point A, and the mouse is point B, the "seek
// point" is C.
// C
// B
// A
Vector2 seekPosition = 2 * mousePosition - catPosition;
// Use the TurnToFace function, which we introduced in the AI Series 1:
// Aiming sample, to turn the mouse towards the seekPosition. Now when
// the mouse moves forward, it'll be trying to move in a straight line
// away from the cat.
mouseOrientation = TurnToFace (mousePosition, seekPosition,
mouseOrientation, MouseTurnSpeed);
// set currentMouseSpeed to MaxMouseSpeed - the mouse should run as fast
// as it can.
currentMouseSpeed = MaxMouseSpeed;
} else {
// if the mouse isn't trying to evade the cat, it should just meander
// around the screen. we'll use the Wander function, which the mouse and
// tank share, to accomplish this. mouseWanderDirection and
// mouseOrientation are passed by ref so that the wander function can
// modify them. for more information on ref parameters, see
// http://msdn2.microsoft.com/en-us/library/14akc2c7(VS.80).aspx
Wander (mousePosition, ref mouseWanderDirection, ref mouseOrientation,
MouseTurnSpeed);
// if the mouse is wandering, it should only move at 25% of its maximum
// speed.
currentMouseSpeed = .25f * MaxMouseSpeed;
}
// The final step is to move the mouse forward based on its current
// orientation. First, we construct a "heading" vector from the orientation
// angle. To do this, we'll use Cosine and Sine to tell us the x and y
// components of the heading vector. See the accompanying doc for more
// information.
Vector2 heading = new Vector2 (
(float)Math.Cos (mouseOrientation), (float)Math.Sin (mouseOrientation));
// by multiplying the heading and speed, we can get a velocity vector. the
// velocity vector is then added to the mouse's current position, moving him
// forward.
mousePosition += heading * currentMouseSpeed;
}
/// <summary>
/// This function contains the code that controls the mouse. It decides what the
/// mouse should do based on the position of the cat: if the cat is too close,
/// it will attempt to flee. Otherwise, it will idly wander around the screen.
///
/// </summary>
private void UpdateMouse()
{
// first, calculate how far away the mouse is from the cat, and use that
// information to decide how to behave. If they are too close, the mouse
// will switch to "active" mode - fleeing. if they are far apart, the mouse
// will switch to "idle" mode, where it roams around the screen.
// we use a hysteresis constant in the decision making process, as described
// in the accompanying doc file.
float distanceFromCat = Vector2.Distance(mousePosition, catPosition);
// the cat is a safe distance away, so the mouse should idle:
if (distanceFromCat > MouseEvadeDistance + MouseHysteresis)
{
mouseState = MouseAiState.Wander;
}
// the cat is too close; the mouse should run:
else if (distanceFromCat < MouseEvadeDistance - MouseHysteresis)
{
mouseState = MouseAiState.Evading;
}
// if neither of those if blocks hit, we are in the "hysteresis" range,
// and the mouse will continue doing whatever it is doing now.
// the mouse will move at a different speed depending on what state it
// is in. when idle it won't move at full speed, but when actively evading
// it will move as fast as it can. this variable is used to track which
// speed the mouse should be moving.
float currentMouseSpeed;
// the second step of the Update is to change the mouse's orientation based
// on its current state.
if (mouseState == MouseAiState.Evading)
{
// If the mouse is "active," it is trying to evade the cat. The evasion
// behavior is accomplished by using the TurnToFace function to turn
// towards a point on a straight line facing away from the cat. In other
// words, if the cat is point A, and the mouse is point B, the "seek
// point" is C.
// C
// B
// A
Vector2 seekPosition = 2 * mousePosition - catPosition;
// Use the TurnToFace function, which we introduced in the AI Series 1:
// Aiming sample, to turn the mouse towards the seekPosition. Now when
// the mouse moves forward, it'll be trying to move in a straight line
// away from the cat.
mouseOrientation = TurnToFace(mousePosition, seekPosition,
mouseOrientation, MouseTurnSpeed);
// set currentMouseSpeed to MaxMouseSpeed - the mouse should run as fast
// as it can.
currentMouseSpeed = MaxMouseSpeed;
}
else
{
// if the mouse isn't trying to evade the cat, it should just meander
// around the screen. we'll use the Wander function, which the mouse and
// tank share, to accomplish this. mouseWanderDirection and
// mouseOrientation are passed by ref so that the wander function can
// modify them. for more information on ref parameters, see
// http://msdn2.microsoft.com/en-us/library/14akc2c7(VS.80).aspx
Wander(mousePosition, ref mouseWanderDirection, ref mouseOrientation,
MouseTurnSpeed);
// if the mouse is wandering, it should only move at 25% of its maximum
// speed.
currentMouseSpeed = .25f * MaxMouseSpeed;
}
// The final step is to move the mouse forward based on its current
// orientation. First, we construct a "heading" vector from the orientation
// angle. To do this, we'll use Cosine and Sine to tell us the x and y
// components of the heading vector. See the accompanying doc for more
// information.
Vector2 heading = new Vector2(
(float)Math.Cos(mouseOrientation), (float)Math.Sin(mouseOrientation));
// by multiplying the heading and speed, we can get a velocity vector. the
// velocity vector is then added to the mouse's current position, moving him
// forward.
mousePosition += heading * currentMouseSpeed;
}
