Explosion Forces (repelling)

Blitz3D Forums/Blitz3D Programming/Explosion Forces (repelling)

RifRaf

(Posted 2009) [#1]

Anyone have any suggestions on the best method for appling explosion forces..

Ive already gotten the velocity mechanics in there in the most simple form possible = velocityx (vx),velocityy(vy),velocityz(vz), velocity_Decay(vd) , and gravtiy(g).

Im wondering how best to assign vx,vy,and vz from a point in 3D space (explosion). giving a Power and Radius of that explosion. so that the closer you are to the blast the more force is applied.

I dont want to use a physics lib for somthing so simple, but I want accurace velocity values to pass on to the entity.

I usually end up getting these things to work , but I can generaly assume theres much better ways (and faster) to do it, and I dont want to slow things down on this project.

Thanks in advance.

GIB3D

(Posted 2009) [#2]

Vectors and stuff maybe hehe..
http://en.wikipedia.org/wiki/Vector_space

Find the normals and somehow do something with them... I haven't figured it all out but... I'm trying.

RifRaf

(Posted 2009) [#3]

somthing that works if you are facing the explosion. but if you are not facing it, then it pulls instead of repels. what am i missing

 If distance(EntityX(t\main),EntityY(t\main),EntityZ(t\main),PickedX(),PickedY(),PickedZ()) < 30 Then  ;30 unit range
              xdist#=EntityX(t\main,1)-PickedX()
              zdist#=EntityZ(t\main,1)-PickedZ()
              ydist#=EntityY(t\main,1)-PickedY()
              dvx#=(.1-(.005 / 100.0)) * xdist  ;weird way to calc power
              dvy#=(5-(.005 / 100.0)) * ydist 
              dvz#=(.1-(.005 / 100.0)) * zdist 
              setentvelocity(t\main,dvx,dvy,dvz)

Nate the Great

(Posted 2009) [#4]

hmm... not sure what kind of physics system you are using... but simply find the dot-product in 3d as follows between the explosion and the object the explosion is repelling.

dx# = x1-x2
dy# = y1-y2
dz# = z1-z2
;dot product in 3d is as follows
dot# = dx*dx + dy*dy + dz*dz
dist# = Sqr(dot)
;do 1/dotproduct making the explosion dissipate using the inverse square
dot# = 1/dot#
;now divide distance vectors by distance and multiply by dot
dx# = (dx# / dist#) * dot
dy# = (dy# / dist#) * dot
dz# = (dz# / dist#) * dot

hope you understand the code above. I dont know how to explain it well, it just kinda works for an exponentially dissipating explosion

now just apply the vector dx,dy,dz to your physics object ( and redo it for every object in your scene within a resonable range.

RifRaf

(Posted 2009) [#5]

Thanks alot Nate, I understood it.
Wrapped it into a single call .

Function ApplyExplosionForce(ent,x2#,y2#,z2#,falloff#=.25)

x1=EntityX(ent,1)
y1=EntityY(ent,1)
z1=EntityZ(ent,1)

dx# = x1-x2
dy# = y1-y2
dz# = z1-z2

;dot product in 3d is as follows
dot# = dx*dx + dy*dy + dz*dz
dist# = Sqr(dot)

;do 1/dotproduct making the explosion dissipate using the inverse square
dot# = 1/dot#

;now divide distance vectors by distance and multiply by dot
dx# = (dx# / (dist#*falloff#)) * dot
dy# = (dy# / (dist#*falloff#)) * dot
dz# = (dz# / (dist#*falloff#)) * dot

setentvelocity(ent,dx*2500,dy*2500,dz*2500,999,1)
End Function