XNA-如何提高精灵速度

Question

SO i'm a beginner in programming and i need help with how to make my sprites speed increase (Add a sprint feature)

i have tried myself but i failed, if someone could explain how i could do it i would be very grateful.

All i want done is if i press the right trigger on my Xbox controller while moving my left thumb stick right change the speed from 4 to 6.

This is the thing i tried , i realized this wouldn't work because it would just make the sprite move when i press he trigger.

if (pad1.Triggers.Right < 0.0f)
  position += new Vector2(-6, 0);

if (pad1.Triggers.Right >= 0.4f)
  position += new Vector2(6, 0);

I'm out of options so someone please help.

Answer 1

This is fundamentally a physics problem. Adding a constant amount to the position is only going to move the sprite more. What you're probably looking for is a way to increase the velocity over brief a period of time which is known as acceleration.

const float AccelerationForce = 0.ff;
const float MaxAccelerationForce = 0.8f;;
static readonly Vector2 MaxAcceleration
    = new Vector2(MaxAccelerationForce, MaxAccelerationForce);
static readonly Vector2 Acceleration = new Vector2(AccelerationForce, 0);
static readonly Vector2 Deceleration = new Vector2(-AccelerationForce, 0);
Vector _currentAcceleration = new Vector2(0, 0);
Vector _currentVelocity = new Vector2(0, 0);

Vector2 Clamp(Vector2 value, Vector2 min, Vector2 max)
{
    var x = MathHelper.Clamp(value.X, min.X, max.X);
    var y = MathHelper.Clamp(value.Y, min.Y, max.Y);

    return new Vector2(x, y);
}

bool RequiresAcceleration(float currentForce)
{
    return currentForce >= AccelerationForce;
}

var currentForce = GetCurrentForce();
// Calculate whether we need to accelerate or decelerated
var acceleration = RequiresAcceleration(currentForce)
                       ? Acceleration
                       : Deceleration;
var newAcceleration = _currentAcceleration + acceleration;
// acceleration is bounded MaxAcceleration > _currentAcceleration > 0
_currentAcceleration = Clamp(newAcceleration, Vector2.Zero, MaxAcceleration);

_currentVelocity += _currentAcceleration;

// Code to move the player

if (pad1.Triggers.Right < 0.0f)
  position += _currentVelocity);

if (pad1.Triggers.Right >= 0.4f)
  position -= _currentVelocity;

Answer 2

I believe this is what you are trying to achieve. Also editing a post is rather easy please edit posts rather than commenting with an update.

        if (pad1.Triggers.Right < 0)
            // This checks if left thumbstick is less than 0.
            // If it is less than zero it sets position.X += -6. 
            // If it is not less then it sets position.X += -4.
            position.X -= (pad1.ThumbSticks.Left.X < 0) ? 6 : 4;
        else if (pad1.Triggers.Right >= 0.4f) // shouldn't this be > 0.0f or > 0 ?
            // This is the same as above just in the right direction.
            position.X += (pad1.ThumbSticks.Left.X > 0) ? 6 : 4;