• Adobe After Effects Expressions

  Leaf falling expression (how do i get it to delay?)

  Posted by Simon Roberts on May 13, 2008 at 4:46 pm

  Hi

  i adapted one of Dan Ebberts tutorials to make a leaf fall from a tree. i’m really happy with it but i need it to start later than right at the beginning… and i’m having trouble doing that.

  I’ve posted the expressions below.

  i’m quite new to AE expressions… any help will probably save me hours of trying to struggle with it myself.

  Thanks

  Simon

  so this is what i have…

  there is a null layer and on the image of the leaf there are these expressions…

  The Point Effect (renamed ‘Life’)

  lmin = 1.5; //minimum particle life
  lmax = 3; //maximum particle life

  seed_random(1,true);
  life=random(lmin,lmax);
  birth=0;
  [birth,life]

  Postition

  gmin=20; //gravity
  gmax=70;
  w=20; //wind
  wdir=0; //wind direction (0 = from left)
  vmin=100; //minimum initial velocity
  vmax=300; //maximum initial velocity
  amin=30; //minimum launch angle from vertical
  amax=120; //maximum launch angle from vertical
  d=2; //drag coeffecient

  birth=effect(“life”).param(“Point”)[0];
  life=effect(“life”).param(“Point”)[1];
  origin=[position[0],position[1],position[2]];
  age=time-birth;
  seed_random(1,true);
  s=random(vmin,vmax);//initial speed
  g=random(gmin,gmax);
  v_e=this_comp.layer(“Null 1”).position.velocity_at_time(birth); //emitter velocity
  a=degrees_to_radians(random(amin,amax)); //angle from vertical
  r=degrees_to_radians(random(360)) //rotation around y axis
  x=s*Math.sin(a)*Math.cos(r);
  y=-s*Math.cos(a);
  z=s*Math.sin(a)*Math.sin(r);
  v=[x,y,z]+v_e;
  new_speed=length(v);
  unit_v=normalize(v);

  if (d>0){
  delta_p=new_speed*(1-Math.exp(-d*age))/d;
  }else{
  delta_p=age*new_speed;
  }
  delta_w=w*age;
  delta_g=g*age*age/2;

  wa=degrees_to_radians(wdir);

  origin + delta_p*unit_v + [delta_w*Math.cos(wa),0,delta_w*Math.sin(wa)] + [0,delta_g,0]

  Orientation

  rmax=0;
  rmin=-0;
  birth=effect(“life”).param(“Point”)[0];
  life=effect(“life”).param(“Point”)[1];
  age=time-birth;
  if (life==0){
  [0,0,0]
  }else{
  seed_random(birth,true);
  init_orient=random([360,360,360]);
  final_orient=(init_orient);
  init_orient +(final_orient-init_orient)*(age/life)
  }

  X Rotation

  rmax=360; //maximum rotation
  rmin=-360; //minimum rotation

  birth=effect(“life”).param(“Point”)[0];
  seed_random(1,true);
  r=random(rmin,rmax);
  life=effect(“life”).param(“Point”)[1];
  age=time-birth;
  if(life==0){
  0
  }else{
  r/life*age
  }

  Y Rotation

  rmax=360; //maximum rotation
  rmin=-360; //minimum rotation

  birth=effect(“life”).param(“Point”)[0];
  seed_random(1,true);
  r=random(rmin,rmax);
  life=effect(“life”).param(“Point”)[1];
  age=time-birth;
  if(life==0){
  0
  }else{
  r/life*age
  }

  Z Rotation

  rmax=360; //maximum rotation
  rmin=-360; //minimum rotation

  birth=effect(“life”).param(“Point”)[0];
  seed_random(1,true);
  r=random(rmin,rmax);
  life=effect(“life”).param(“Point”)[1];
  age=time-birth;
  if(life==0){
  0
  }else{
  r/life*age
  }

  Simon Roberts replied 18 years ago 2 Members · 2 Replies
• 2 Replies

• 

  Dan Ebberts

  May 13, 2008 at 8:06 pm

  I think all you need to do is change the birth variable in the point control expression and then add some code to each of the other expressions that checks to see if the current time is less than birth, in which case the expression does nothing.

  Here’s an example of a random birth expression for the point control:

  bmin = 0; // minimum birth time
  bmax = 4; // maximum birth time
  lmin = 1.5; //minimum particle life
  lmax = 3; //maximum particle life

  seed_random(1,true);
  life=random(lmin,lmax);
  birth=random(bmin,bmax);
  [birth,life]

  And here’s the z rotation expression modification to get you started:

  Z Rotation

  rmax=360; //maximum rotation
  rmin=-360; //minimum rotation

  birth=effect(“life”).param(“Point”)[0];
  seed_random(1,true);
  r=random(rmin,rmax);
  life=effect(“life”).param(“Point”)[1];
  if (time >= birth){ //***** this is new
  age=time-birth;
  if(life==0){
  0
  }else{
  r/life*age
  }
  }else{ // **** this is new
  value // **** this is new
  } // **** this is new

  Dan
• 

  Simon Roberts

  May 13, 2008 at 10:59 pm

  ah…. amazing!

  thats perfect.

  thanks very much!

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