Spawning Projectile

ID:2215479
 
Feb 19 2017, 3:36 pm
(See the best response by Ter13.)
Hi,

I've been having a hard time spawning a projectile exactly at the source's location. What I was trying to do is to spawn it directly at the center then make it move to the direction the source is facing. I was somehow able to get the desired result except when the source is situated between tiles.
Here's a preview:
Centered on a tile

and then the problem...


Here's how it should look like:


It's basically using its iris as a projectile.

I'm simply spawning the projectile at the source's location through:
obj/projectile
    New(shooter)
            loc = locate(shooter.x,shooter.y, shooter.z)


I know there are a lot of libraries out there that handles projectiles but I sort of find them a little bit complicated to understand at times. What I am trying to achieve is a simple system.

I would greatly appreciate it if someone could help me out with this issue.


Thanks in advance!
Feb 19 2017, 3:54 pm
Check out Absolute Positioning.

Once you install that library and link it to your project, all you need to do is:

projectile.SetCenter(source.Cx(), source.Cy(), source.z)


This makes sure the projectile is centered relative to source's bounding box no matter where they are. From there you can do whatever you want.
Feb 19 2017, 4:07 pm
Best response
To answer the question more directly:

calculate the absolute position of target:

var/ax = target.x*TILE_WIDTH + target.step_x - target.bound_x
var/ay = target.y*TILE_HEIGHT + target.step_y - target.bound_y


Calculate the relative bound width/height:

var/rw = target.bound_width - src.bound_width
var/rh = target.bound_height - src.bound_height


add half the relative bounds

var/nx = ax + rw/2
var/ny = ay + rh/2


Convert into tile-step coordinates:

var/turf/t = locate(nx/TILE_WIDTH,ny/TILE_HEIGHT,target.z)
var/sx = nx - t.x*TILE_WIDTH + src.bound_x
var/sy = ny - t.y*TILE_HEIGHT + src.bound_y


You can condense this code more too:

var/nx = target.x*TILE_WIDTH + target.step_x - target.bound_x + (target.bound_width - src.bound_width)/2
var/ny = target.y*TILE_HEIGHT + target.step_y - target.bound_y + (target.bound_height - src.bound_height)/2
var/turf/t = locate(nx/TILE_WIDTH,ny/TILE_HEIGHT,target.z)
src.Move(t,target.dir,nx-t.x*TILE_WIDTH+src.bound_x,ny-t.y*TILE_HEIGHT+src.bound_y)
Feb 19 2017, 5:31 pm
Thank you for those answers!
I was considering the Absolute Positioning library but it bugs me to try to learn the way of doing it without the lib.

I'd like to give you two a vote for the quick response but I guess I can only give it to one.

Both of the answers are absolutely helpful though.