How to change an object's speed, but not direction

[ylluminarious]

How do you change the speed of an object in phaser without changing its direction?  For example, I have a ball that collides against a moving platform.  I want the ball to change direction, but not gain any additional speed from the collision against a moving side of the platform. Up to now I have had to take the sign of the velocities of the object and then reapply a constant value speed to it on collision, but that seems quite wrong for a library as robust as Phaser is.

 

How do you modify speed and direction independently outside of velocity?

[Qqwy]

I don't know if there is a better way, but what I usually do is to have a predefined speed, then look at the angle of the object, and apply something like:

 

object.velocity.x += speed * Math.sin(object.angle);

object.velocity.y += speed * Math.cos(object.angle);

 

There also seems to be (at least in Arcade physics) a body.velocityFromAngle() method, which seems to more or less do something similar. and might be what you need.

[ylluminate]

That's unfortunate.  I have done it similar to @Qqwy, for example, I would take the `Math.sign(object.body.velocity.x)` and then assign the speed manually to that while reassigning the direction (`sign`). While it works, it seems that there should be a more direct way to modify just speed of the direction vectors without these extra steps.

 

Here's an example of when I used it in `game.physics.arcade.collide`:

 

game.physics.arcade.collide(object1, object2, function () {  direction_x = Math.sign(object1.body.velocity.x);  direction_y = Math.sign(object1.body.velocity.y);  object1.body.velocity.x = OBJECT1_VELOCITY * direction_x; //Where OBJECT1_VELOCITY is a constant  object1.body.velocity.y = OBJECT1_VELOCITY * direction_y;});

 

Obviously the example is for a very simple motion that does not take into consideration angles, etc, but it works in my case. I too was hoping to see other input that would show a clearer way to just modify speed while retaining the other vector data of the velocity. I can't imagine phaser not having this and that we're just missing something relatively simple in the library...