path_spline

path_spline(ENTITY, VECTOR pos, var dist)

Movement along a path. This function calculates a smooth spline curve along a closed loop path, and sets the pos vector to the calculated curve position that corresponds to the given distance on the path. This can be used for smoothly moving actors, vehicles, or cameras along a path.

Parameters:

ENTITY* - pointer to an entity attached to a path.
pos - vector to receive the calculated curve position.
dist - distance on the path to calculate the curve position for.

Returns:

Number of the node before the calculated position.

Modifies:

pos - set to a position on the spline curve.

Speed:

Medium

Remarks:

This function uses a Hermite polynomial interpolation for calculating a smooth curve that runs through all nodes of the path.
The curve connects all nodes in the order of their numbers. How they are connected through edges doesn't matter.
The dist parameter corresponds to the distances of straight lines connecting the nodes, and not to the real distance of the curve. Thus, when adding a constant speed to the dist parameter, the real speed along the curve can vary. It is the faster the more the curve deviates from the straight lines between the nodes. If this is undesired, place more nodes to avoid deviations at sharp bends in the path.
The total length of the path can be found through the path_length function.
Due to the finding of the closest node, the function is a little faster for smaller dist values. If dist exceeds the path length, it begins a new loop on the path.

Example (see also path_create):

//call camera_path(""); to let the camera run along a path in the level
function camera_path(pathname)
{
// create a dummy path entity
	me = ent_create(NULL,nullvector,NULL);
	path_set(me,pathname);
	var dist = 0;
	var vLastPos[3];
	var vDir[3];
	while(1) 
	{
// place the camera on the path
		path_spline(me,camera.x,dist);
		dist += 5*time_step;
// let the camera look ahead	
		vec_diff(vDir,camera.x,vLastPos);
		vec_to_angle(camera.pan,vDir);
		vec_set(vLastPos,camera.x);
		wait(1);
	}
}

See also:

path_create, path_scan, path_nextnode, path_setedge, path_length

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