tree.cs

class treeThing {

   // tree design: all the changable variables in one place!
   struct treeStyle {

      // skipping stuff like how many branches per tree, sticks per branch..

      // sticks
      Vector2 stickAngleJagMM; // how jaggy the branches are (min-max)
      Vector2 stickLengthMM; // how long the sticks are (min-max)
      
      sprite[] sprites; // sprites to be assigned to sticks, can be assigned based on seed or using 
                        // stick's branch position to get the 'leaf' shape if you have arrange this array
                        // [0-5] small leaf > [6-10] big leaf > [11-20] small leaf, or similar
      
      // spring parameters to be assigned to sticks, from root of branch to its tip
      float springFreqRoot;
      float springFreqTip;
      float springDampRoot;
      float springDampTip;

      // branches
      Vector2 branchAngleMM; // branch angles (min-max)
      
      int maxSubBranches; // how many sub-branches can branch have?
      float subBrachChance; // chance a stick will have a sub branch growing on it (0-1)
      
   }

   class tree {
      float tSeed; // seed (0-1)
      branch[] branches;
   }

   class branch {
      float bSeed; // seed (0-1)
      float bAngle; // if you want branch to be at an angle
      stick[] sticks;
      
      void init(ref int subLeft, treeStyle style){ // subLeft is how many sub-branches this branch can have.
         
         foreach(var stick in sticks){
            stick.sAngle = style.stickAngleJagMM.lerp(stick.seed); // Vector2.lerp here is just lerp(v.x, v.y, t);
            stick.length = style.stickLengthMM.lerp(stick.seed);
            stick.posOnBranch = sticks.indexOf(stick)/(sticks.length-1);
            stick.freq = style.springFreqRoot.lerp(stick.posOnBranch);
            stick.damp = style.springDampRoot.lerp(stick.posOnBranch);
            stick.mySR.sprite = style.sprites[ style.sprites.length * stick.seed ]; // dont forget to limit this index.
            // potentially can set other properties of the sprite, like color:
            // stick.mySR.color = gradient.evaluate(stick.posOnBranch); - to get nice gradient along the branch
            
            if(subLeft>0){
               subLeft--;
               stick.subBranch = new branch(); 
               stick.subBranch.init(ref subLeft); // init the branch here, but remember
                                                  // to pass subLeft so not to run into infinite sub-branches
            }
         }
      }
      
      void updateBranch(Vector2 walkPosition, float walkAngle, float gravity, float deltaTime){
         
         // starting calculating branch
         float mass = 0; 

         foreach(var stick in sticks)
            stick.update(ref walkPosition, ref walkAngle, ref mass, gravity, deltaTime);
      }
   }

   class stick {
      float sSeed; // seed (0-1)
      float posOnBranch; // where on branch it lays (root=0, tip=1)
      Vector2 sPosition; // world position of this stick
      Vector2 velocity; // stick velocity last frame
      float sAngle; // default angle
      float length; // length, obv
      float freq, damp; // spring variables
      
      renderer mySR; // however youre rendering your stick
      
      branch subBranch; // if you want sub-branches, you'd have it here
      
      void update(ref Vector2 walkPosition, ref float walkAngle, ref float mass, float gravity, float deltaTime){
         
         mass += length;
         walkAngle += sAngle; 
         
         Vector2 stickDir = new Vector2(0,length).rotate(sAngle);
         Vector2 stickEndPos = walkPosition + stickDir + new Vector2(0, mass*gravity); // where does this stick end?
         
         // using Vector2 spring here, like this: http://allenchou.net/2015/04/game-math-numeric-springing-examples/
         sPosition = spring(
            sPosition, // current position
            stickEndPos, // target position
            ref velocity, // get and record back velocity of this stick spring 
            damp, // damping
            freq, // freq
            deltaTime
         );
         
         // this bit is important to keep sticks never change 'length'
         Vector2 newDir = sPosition - rootPos;
         sPosition = rootPos + newDir.normalized * length; // .normalized makes vector be length of 1
         
         walkPosition = sPosition;
         
         // update stick's renderer
         mySR.position = walkPosition; 
         mySR.rotation = walkAngle; // or you can just newDir.angle() or similar
         
         if(subBranch!=null){ // stick has sub-branch, lets update it recursively
            Vector2 subWalkPosition = walkPosition; // new starting position for this branch
            float subWalkAngle = sAngle + walkAngle + subBranch.bAngle; // and angle
            subBranch.updateBranch(subWalkPosition, subWalkAngle, gravity, deltaTime);
         }
      }
   }


   void init(
      treeStyle style, // contains your tree design
      float seed // main seed from which every other should be derived from (0-1)
      ){
      
      // skipping init of tree, branches, seeds, arrays, renderer here..
      
      foreach(var branch in tree.branches){
         int subLeft = style.maxSubBranches; // how many sub-branches this branch can have?
                                             // potentially. could be randomized.
         branch.bAngle = branchAngleMM.lerp(branch.bSeed);
         branch.init(ref subLeft, style);
      }
   }

   void update(
      Vector2 rootPos, // current world position
      float rootAngle, // current tree angle
      float gravity, // will be used to pull down the branches
      float deltaTime // frame duration
      ){
         
      foreach(var branch in tree.branches){
         float walkAngle = rootAngle + bAngle;
         Vector2 walkPosition = rootPos; // this can be offset using branch's seed, 
                                       // if you want several branches in an area instead of one root position
         
         branch.updateBranch(walkPosition, walkAngle, gravity, deltaTime);
      }
   }


}