After a user requested this in the scripting forum, I put it together. Tought I might put it here for all to see.

Also check this page http://foxhound-production.com/3dgs/lazersight/lazersight.php
For a simualr particle effect used as a lazer sight.

entity* model_a;
entity* model_b;



function main
{
level_load("test_level.wmb");
wait(3);

model_a = ent_create("guard.mdl",vector(200,0,0), null);
model_b = ent_create("guard.mdl",vector(-200,0,0), null);
var var_1 = 1;
var i;
i = ent_vertices(model_a);

while(1)
{

var_1 %= i;
var_1 += 1;

particle_line(var_1);
model_a.pan += 1;
model_b.pan += 1;
wait(1);
}

}

function remove_flares()
{
my.lifespan = 0; // remove the flare particle
}

bmap beam = <beam2.tga>;
function particle_function()
{
my.bmap = beam;
my.flare = on;
my.bright = on;
my.size = 10;
my.transparent = on;
my.alpha = 50;
my.function = remove_flares;
}

var vector1[3];
var vector2[3];//local vars so this function can be ran several times at once
var dist;

FUNCTION particle_line(var_1)
{

var temp_array[3];

vec_for_vertex(vector1, model_a, var_1);//we get the vectors of the vertexs
vec_for_vertex(vector2, model_b, var_1);//same here

dist = vec_dist(vector1.x,vector2.x);//we get the distance of the vertexs
//return;
while(dist > 0)//until we are finished with this chain, NO WAIT!!!!
{
vec_set(temp,vector2.x);
vec_sub(temp,vector1.x);
vec_to_angle(temp_array,temp); // now TEMP_ARRAY looks at VECTOR2

temp.x = vector1.x + dist * cos (temp_array.pan);
temp.y = vector1.y + dist * sin (temp_array.pan);
temp.z = vector1.z + dist * tan (temp_array.tilt);//CALUCLATES THE ANGLE

effect(particle_function, 1, temp, normal);//CREATES THE PARTICLE

dist -= 1;//the higher this number the lower the quailty the particle line is, 5 is good

}
return;
}

font standard_font = "Arial",1,20; // truetype font
panel debug
{
flags = visible;
digits = 100,10,4,standard_font,1,vector1.x;
digits = 100,25,4,standard_font,1,vector1.y;
digits = 100,40,4,standard_font,1,vector1.z;

digits = 100,70,4,standard_font,1,vector2.x;
digits = 100,85,4,standard_font,1,vector2.y;
digits = 100,100,4,standard_font,1,vector2.z;
digits = 100,140,4,standard_font,1,dist;
}

you can put the my.lifespan in the partical definition itself, eliminating the function

and i thank you for the code foxhound ^^ nice of you to share it.

but if someone can post how to stretch an image between two vertices it was what i was really looking for

get the direction vector from vertex 1 to vertex 2

spawn the particals at one vertex1,
effect (function, var number, VECTOR* pos, VECTOR* speed);
in the VECTOR* speed parameter insert the direction vector you got from above.

set the particals lifespan = 0 ( or 1) mess with this depends on the distance from vert1 and vert 2

and set the particals streak flag on.


try that

if your using an animated sprite for the electric/lighting between the pod engines, you just need the distance and direction between the 2 vertexs ( of both you can find examples in the manual)

then align the sprite to the direction and scale it based on the distance ( original sprite size/ distance)

no, not stretching a particle, this is very simple that code is above, it is the contribution, what i mean is what DaBro0zar is agreeing would be good, to have a image, not particle, streched between two verteces, i already tried changing the scale_x, scale_y, and scale_z, these do not work, how can you stretch an image properly. The reason i want this so bad is it would really save on fps and it would be better for collisions, because i'm using spark effects when my saber collides...

yes, vertex attach the image ( sprite) to one vertex.
then get the vector direction from vertex 1 to vertex 2, convert that to angles
align the sprite to those angles

then getting the distance from vertex 1 to vertex 2 then scale the image( sprite) ( original hight in pixels /distance)

its no differnt then doing a vertex attachment with a model and aligning the model ( see the script exampls on acknext site) except your just adding in a scale calculation for distance

so like:
entity* player;
var create_ver;
var tilt_var;
var vertex_1 = 0; //change this to the first vertex num
var vertex_2 = 1; //change this to the second vertex num

action saber
{
vec_for_vertex (tilt_var, player, vertex_2);
my.pan = tilt_var;
my.tilt = tilt_var;
my.roll = tilt_var;
}

action player_act
{
player = me;
vec_for_vertex (create_ver, me, vertex_1);
ent_create ("sprite.tga", create_ver, saber_act);
}

not exactly in your saber action
vec_for_vertex gives a Location vector not a direction or angle vector

you subtract the FROM vector to the TO vector to get a direction vector from FROM to TO

then to convert a direction vector to pan/tilt/roll angles is done with vec_to_angle

and then if your using a sprite you will need (if i rexcall right) to add( or subtract) an 90 degree offset to the pan angle.