[1.7.10] Projectile stops in mid-air?

[Ms_Raven]

I have no idea why, but I can't get any of the many projectile tutorials I've tried to work. It would always either only ever go in one direction or spawn but not move at all until hit.

 

So I gave up and de-obfuscated a mod to try to figure out just what I'm doing so wrongly compared to a finished mod that I've tried and that works, and finally found some code that's successful...at first.

 

Unfortunately, after about 2 seconds of travelling, the projectile starts slowing down exponentially for another second until it stops in mid-air... I assume it's something to do with the math, but I've always been horrible at that so I really don't know what's going on there.

 

What exactly is going on here and how can I get it to just fly straight?

 

				Vec3 vec1 = player.getLook(1);
			EntityLargeFireball fireball = new EntityLargeFireball(player.worldObj);
			fireball.setLocationAndAngles(player.posX + vec1.xCoord, player.posY + player.getEyeHeight() * 0.85,
					player.posZ + vec1.zCoord, player.rotationYaw, player.rotationPitch);
			fireball.motionX = (-MathHelper.sin(fireball.rotationYaw / 180.0F * 3.141593F)
					* MathHelper.cos(fireball.rotationPitch / 180.0F * 3.141593F));
			fireball.motionZ = (MathHelper.cos(fireball.rotationYaw / 180.0F * 3.141593F)
					* MathHelper.cos(fireball.rotationPitch / 180.0F * 3.141593F));
			fireball.motionY = (-MathHelper.sin(fireball.rotationPitch / 180.0F * 3.141593F));

			fireball.motionX *= 2.0D;
			fireball.motionY *= 2.0D;
			fireball.motionZ *= 2.0D;

[Zethariel]

Just straight? I'd look into Ghast and Blaze projectiles instead. AFAIK a large fireball is compelled to travel in a straight line by default, so you'd only need to see how a Ghast does it. I remember doing something similar in Bukkit (a fireball spell) and I don't recall any of that math present at all - just spawn the ball, apply a vector to it and go (your problem might be trynig to use motionXYZ instead of a addVector or similar method that might do the math for you).

[Ms_Raven]

That's my point, I can't figure out how to do that...

[Draco18s]

There is another set of fields called acceleration.

[coolAlias]

You're using the wrong constructor - most projectiles have a constructor that takes an EntityLivingBase, i.e. the one that is shooting the projectile, and will automatically calculate the trajectory and velocity for you. Some also have a constructor that takes the target entity which is useful for mobs shooting at players.

 

Unfortunately, EntityFireball is a bit odd in the projectile world, as Draco pointed out, but you can still use a constructor that takes more arguments for a better result. Blazes, Ghasts, etc. typically pass in the difference between the target's position and their own. From the Ghast:

double dx = this.targetedEntity.posX - this.posX;
double dy = this.targetedEntity.boundingBox.minY + (double)(this.targetedEntity.height / 2.0F) - (this.posY + (double)(this.height / 2.0F));
double dz = this.targetedEntity.posZ - this.posZ;
EntityLargeFireball entitylargefireball = new EntityLargeFireball(this.worldObj, this, dx, dy, dz);

That will create a fireball heading towards the target's current position with appropriate velocity and acceleration. Of course there are a couple extra adjustments that the ghast and such make to the position before spawning it to make sure it doesn't immediately collide with themselves, but you can see that in the code.

[Draco18s]

I also have code here for making fireballs that are shot off based on lookvec.