Rotate PVector to a goal PVector at a linear speed - Processing Forum

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ben-cracknell

Ben Crack..

Rotate PVector to a goal PVector at a linear speed

in Programming Questions • 4 months ago

I'm having trouble figuring out the math to do this. I have a two directional (normalized) PVectors, and I need one to rotate towards the other.

I can make eased rotation work ( like in this Flash demo), but I need the rotation to happen at a fixed rate, no matter how much the angles differ.

The code that rotates with easing:

// get the angle distance between the goal and curent direction
float goalAngle = goal.heading();
float dirAngle = direction.heading();
float distance = abs(goalAngle - dirAngle);
// convert distance to a percentage to lerp (0~TWO_PI to 0~1)
float percentage = map(distance, 0, TWO_PI, 0, 1);
direction.lerp(goal, percentage);

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Replies(1)

Ben Cracknell

Ben Crack..

Re: Rotate PVector to a goal PVector at a linear speed

4 months ago

Well, I feel like an idiot:

if (difference >= 0)
direction = PVector.fromAngle(direction.heading() + TURN_SPEED);
else
direction = PVector.fromAngle(direction.heading() - TURN_SPEED);

Edit: Here is the completed code:

void update() {
// the direction will be lerped to here
PVector goal = new PVector(0, 0);
// calculate vector from input
if (upPressed)
goal.add(0, -1, 0);
if (rightPressed)
goal.add(1, 0, 0);
if (downPressed)
goal.add(0, 1, 0);
if (leftPressed)
goal.add(-1, 0, 0);
// get the angle distance between the goal and curent direction
float goalAngle = goal.heading();
float dirAngle = direction.heading();
float difference = atan2(sin(goalAngle-dirAngle), cos(goalAngle-dirAngle));
// linearly rotate towards goal
if (difference >= 0) {
if (difference > TURN_SPEED)
direction = PVector.fromAngle(direction.heading() + TURN_SPEED);
else
direction = goal;
}
if (difference < 0) {
if (difference < -TURN_SPEED)
direction = PVector.fromAngle(direction.heading() - TURN_SPEED);
else
direction = goal;
}
if (upPressed || rightPressed || downPressed || leftPressed) {
// apply direction to location
direction.normalize();
direction.mult(MOVE_SPEED);
position.add(direction);
}
}

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