After Effects Expressions - 02/10/2010

Simulating the effect of air currents and wind on smoke from a chimney
by using wiggle(how often, how many degrees) to add or subtract random degree amounts
from the direction propertyof a particle playground cannon.

1. Read pages 11 through 19 - pages xi through xix of the Introduction from the Marcus Geduld After Effects Expressions textbook.
2. AE Expressions: Chapter 1 - Creating Simple Expressions - we will read and study this entire chapter before spring break gets here.
   1. Pages 29-36 of the PDF cover the Write-on and the Beam effect that we did to start off the 5th week of class, the day after soup or sundae.

   2. Here is an example of the Write-on and the Beam effect as part of the Snorg Tee shirts COMP.

   3. Here is an example that shows signing your name using the WRITE-ON and the BEAM effects in combination. I signed my pineapple assignment, after the cartoon pineapple show was concluded.

3. Here is the snow falling and chimney smoke rising application we did on Wednesday, February 10th, 2010.
   1. We used the WIGGLE expression to make the smoke particle playground effect simulate being effected by wind or perhaps by gentle breezes.
   2. Watch the smoke coming out of the chimney.
   3. Recall that we held down the ALT key and clicked on the stopwatch to tell After Effects that we wanted to add an EXPRESSION to that property.
   4. The DIRECTION property for the Particle Playground effect was then controlled by the AE Expression.
   5. The smoke wiggled around due to the wiggle(0.2, 35) AE expression.
   6. Here is some information about wiggle from the Adobe After Effects CS4 help.

      wiggle(freq, amp, octaves=1, amp_mult=.5, t=time)
              
          *** FEEL FREE TO TOTALLY IGNORE the 3rd, 4th and 5th parameters. ***  
          ***        Just think of wiggle as wiggle(freq, amp).            ***
               
      wiggle(freq, amp, octaves=1, amp_mult=.5, t=time)
          
          Return type: Number or Array.         <--- *** IGNORE THIS, PLEASE!  At least until April! ***
       
          Argument type: freq, amp, octaves, amp_mult, and t are Numbers.
       
          Randomly shakes (wiggles) the value of the property.  Shake, rattle and roll!  :-)
       
          freq     value is the frequency in wiggles per second.
              
          amp      value is the amplitude in units of the property to which it is applied.
       
          octaves  is the number of octaves of noise to add together. 
                   This value controls how much detail is in the wiggle. 
                   Make this value higher than the default of 1 to include higher frequencies 
                   or lower to include amplitude harmonics in the wiggle.
         
          amp_mult is the amount that amp is multiplied by for each octave. 
                   This value controls how fast the harmonics drop off. 
                   The default is 0.5; make it closer to 1 to have the harmonics added at the same amplitude 
                   as the base frequency, or closer to 0 to add in less detail.
        
          t        is the base start time. This value defaults to the current time. 
                   Use this parameter if you want the output to be a wiggle of the property value sampled at a different time.
        
          Example: position.wiggle(5, 20, 3, .5) - note that -> position.wiggle(5, 20) would be enough!
           
                   produces about 5 wiggles per second with an average size of about 20 pixels. 
                   In addition to the main wiggle, two more levels of detailed wiggles occur with 
                   a frequency of 10 and 20 wiggles per second, and sizes of 10 and 5 pixels, respectively.
          
          FEEL FREE TO TOTALLY IGNORE the 3rd, 4th and 5th parameters.   
          Just think of wiggle as wiggle(freq, amp).  
             
          wiggle(.2, 35) was all we used and all we needed.   
             The .2 means wiggle once every 5 seconds.  
             The 35 means to wiggle as much as -35 away from the DIRECTION to as much as 35 away, which meant the smoke would
             be blowing in the wind as much as 35 degrees to the left to as much as 35 degrees to the right.
                
             If we changed the paramters to 3 and 90 for the Direction of the Cannon that was shooting out smoke effect
             from the chimney, it would be pretty funny to see.
                  
             wiggle(3, 90) means the smoke might wiggle to almost parallel to the ground as if the wind was blowing VERY HARD,
                           and then wiggle back in the totally opposite direction, and it would change directions 3 times per second!
                           
      

4. more details ...
5. will be added to this page ...
6. later on ...