CODEWITHSUNDEEP
c++mathinterpolation
Lenny White
Lenny White

Reputation: 452

How to linearly interpolate to destination that is not constant

If I want to linearly interpolate from point A (source) to point B (destination) on a 2d plane I could do it like this. Vector2 here is a struct consisting of x and y floats.

 Vector2 Interpolate(Vector2 source, Vector2 destination, float delta) {
      return source+(destination-source)*delta;
 }

 void OnEachUpdate() {
   delta += 0.05f;
   delta = max(delta, 1.0f);
   currentVector = Interpolate(source, destination, delta);
 }

This way I can interpolate from source to destination with a given delta. However what if I have destination vector that is not constant? Say the user can change the destination by pointing a mouse cursor on a 2d plane. An object should linearly interpolate to the destination vector.

I could do something like this but it's not a linear interpolation, but more like sigmoidal, which is not what I want.

 delta = 0.05f;
 currentVector += Interpolate(currentVector, destination, delta);

Upvotes: 1

Views: 410

Answers (1)

HolyBlackCat
HolyBlackCat

Reputation: 96166

Since you said you want to keep the speed constant, I assume you want this:

float speed = whatever;
float delta_x = target_x - current_x;
float delta_y = target_y - current_y;
float dist_sqr = delta_x*delta_x + delta_y*delta_y;
if (dist_sqr <= speed*speed)
{
    // The destination is reached.
    current_x = target_x;
    current_y = target_y;
}
else
{
    float dist = std::sqrt(dist_sqr);
    current_x += delta_x / dist * speed;
    current_y += delta_y / dist * speed;
}

Upvotes: 1

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