Gravity working oddly in keeping the character in the middle of the world

[alessa]

Hello,

I am working on an endless runner that sees a dolphin swimming on the surface level, and when the player presses up the dolphin jumps and holding the down key makes it go under water. Currently, I have almost solved the issue with the following code:

/*
*
* CONTROLS
*
* */

this.duck.body.velocity.x = this.speed*60;

if (this.cursors.up.isDown)
{
	this.duck.body.velocity.y = -200;
}
else if (this.cursors.down.isDown)
{
	this.duck.body.velocity.y = 200;
}
else {
	// set velocity to 0 when player stops pressing keys, but keep moving forward
	console.log('duck starting point: ' + this.world.centerY+50);
	console.log('duck Y: ' + this.duck.y);

	if(this.duck.y >= this.world.centerY+50){
		this.duck.body.velocity.y = -200;
	} else if(this.duck.y < this.world.centerY+50){
		this.duck.body.velocity.y = 200;
	} else {
		this.duck.body.velocity.y = 0;
	}
}

However, this doesn't look like a natural "jump", but it changes suddenly from pressed / non-pressed states. I saw the Phaser tutorial and there they check the collision with the ground to make it smoother and avoid infinite jumping capabilities. In my case, I cannot activate collision with the water, otherwise I cannot have the player go underneath it..

Any idea on how to solve this issue?