Tree collision

This is a frequently asked question. The most popular answer is some derivative of the reference manual's topic, "Setting Up Tree Collisions." That works just fine, and potentially gives every tree its own collider.

My cheapo computer has a cheapo video card in it, and I keep it that way so I am forced to optimize my games for those who also have lousy video cards. It occurred to me that my FPS game's flying protagonist can really only hit the nearest tree, so giving every tree a collider means physics processing for every tree but one has no return on investment. Why not move one efficient capsule collider to the nearest tree in case I smack into it? A built-in array and a little math in a short script sped up my FPS dramatically compared to painting trees on my terrain with one probably unused capsule collider each. I got rid of the capsule collider in my prototype tree and supplied the original colliderless tree to the terrain tool for painting onto my terrain. I attached the following script "sctTerrain" to the terrain object named "Terrain." I added a capsule object to the scene having a capsule collider and a kinematic rigidbody (recommended by Unity if I am going to move my collider around a lot). I sized the capsule by hand to appropriately match the prototype tree, the top branches of which I can fly through without dying. The capsule has its mesh renderer turned off so it is invisible but still solid. I named the capsule "Tree" so if I fly into the capsule I can report, "Tree got you." If my script can't find any trees AND cannot find the capsule object, it destroys itself at Start() because it is unneeded. Otherwise it places the capsule to surround the nearest tree trunk and scales it to match the tree's height less the sparse top branches. This math-based technique for colliding with trees is fast, and I recommend it:

 #pragma strict
 #pragma downcast
 
 private var paryTrees : TreeInstance[];
 private var pvecTerrainPosition : Vector3;
 private var pvecTerrainSize : Vector3;
 private var pgobTreeCollide : GameObject;
 private var pvecCollideScale : Vector3;
 private var pbooCollideWithTrees : boolean = false;
 
 function Start(){
 
     // Get the terrain's position
     pvecTerrainPosition = Terrain.activeTerrain.transform.position;
 
     // Get the terrain's size from the terrain data
     pvecTerrainSize = Terrain.activeTerrain.terrainData.size;
     // Get the tree instances
     paryTrees = Terrain.activeTerrain.terrainData.treeInstances;
     
     // Get the invisible capsule having the capsule collider that makes the nearest tree solid
     pgobTreeCollide = GameObject.Find("Tree");        // This is a capsule having a capsule collider, but when the flier hits it we want it to be reported that the flier hit a tree.
     
     // Are there trees and a tree collider?
     if ((pgobTreeCollide != null) && (paryTrees.length > 0)){
         // Set a flag to make this script useful
         pbooCollideWithTrees = true;
         // Get the original local scale of the capsule.  This is manually matched to the scale of the prototype of the tree.
         pvecCollideScale = pgobTreeCollide.transform.localScale;
     }
     // No need to use this script
     else {Destroy(this);}
 }
 
 function Update () {
     var L : int;
     var triTree : TreeInstance;
     var vecFlier : Vector3 = sctFly.svecXYZ;        // My protagonist's position, passed by a static variable in a script called sctFly.
     var fltProximity : float;
     var fltNearest : float = 9999.9999;                // Farther, to start, than is possible in my game.
     var vec3 : Vector3;
     var vecTree : Vector3;
     var intNearestPntr : int;
     
     // Test the flag
     if (pbooCollideWithTrees == true){
         // Find the nearest tree to the flier
         for (L = 0; L < paryTrees.length; L++){
             // Get the tree instance
             triTree = paryTrees[L];
             // Get the normalized tree position
             vecTree = triTree.position;
             // Get the world coordinates of the tree position
             vec3 = (Vector3.Scale(pvecTerrainSize, vecTree) + pvecTerrainPosition);
             // Calculate the proximity
             fltProximity = Vector3.Distance(vecFlier, vec3);
             // Nearest so far?
             if (fltProximity < fltNearest){
                 // Remember the nearest
                 fltNearest = fltProximity;
                 // Remember the index
                 intNearestPntr = L;
             }
         }
         // Get the closest tree
         triTree = paryTrees[intNearestPntr];
         // Get the normalized tree position of the closest tree
         vecTree = triTree.position;
         // Get the world coordinates of the tree position
         vec3 = (Vector3.Scale(pvecTerrainSize, vecTree) + pvecTerrainPosition);
         // Scale the capsule having the capsule collider that represents a solid tree
         pgobTreeCollide.transform.localScale = (pvecCollideScale * triTree.heightScale);
         // Add some height to position the capsule correctly on the tree
         vec3.y += pgobTreeCollide.transform.localScale.y;
         // Position the capsule having the capsule collider at the nearest tree
         pgobTreeCollide.transform.position = vec3;
     }
 }

By the way, speaking of optimization, I've got my "Billboard start" setting for trees at 16, very close. It is more disconcerting to see trees change from billboards to meshes at a distance-- unless it is a huge distance that slows my system down a LOT-- than it is to see flat trees up close. Close-up tree billboards look fine, and the transition to meshes is almost unnoticeable as I fly past. Even from high above them, when you'd think they'd look like foreshortened plane segments, billboard trees look good. Somebody at Unity was thinking! Thanks, Loren