What I expected to happen was...:
I expected it to come directly from the crosshair, as that would make the most sense to me.
What actually happened was...:
Instead, it fires above the crosshair, or shoves some of your vertical velocity into it, and ends up about 4-5 blocks above where you were aiming.
Steps to Reproduce:
1. Put a crossbow in your mainhand.
2. Put firework rockets in your offhand.
3. Load the crossbow.
4. Jump and fire while moving upwards, towards some kind of backboard that you can see the difference in where you aimed, and where it went.
Comments 8
Except I tested. I walked 20 blocks back, aimed at the block directly in front of me, the degree for looking up and down being 0.0, so when I jumped, it should've hit the 3rd block from the ground. Instead, it hit the 7th and 8th most frequently.
When you first launch the rocket, it is fired below the crosshair (although it may be hard to observe because it happens so quickly). Strangely, however, I was able to observe the same results as you did in the setup you described. It seems as though the firework launched from the crossbow takes the vertical velocity of the launcher into account, as you mentioned, which leads to the belief that it is fired above the crosshair.
Well, I did say that it could be putting the player's vertical velocity into the rocket. Strangely, I wasn't able to replicate this with arrows, though, so I think it's a rocket only issue.
Can confirm. This might be intended; projectiles are supposed to account for the velocity of the player.
Cannot confirm. The firework is launched below the crosshair, just as described in MC-137643. It can later fly above the crosshair, however.