Line Tracing

[Jim Hurley]

>
>Message: 11
>Date: Thu, 30 Jan 2003 19:52:22 -0800
>Subject: re: Line Tracing
>From: Roger Guay <rogerguay at centurytel.net>
>To: use-revolution at lists.runrev.com
>Reply-To: use-revolution at lists.runrev.com
>
>Thanks to Gary Rathbone and Jim Hurley for their suggestions, but the
>Lockscreen property does not work, and although Jim's script is very
>clever, it results in a very choppy motion compared to repeatedly
>setting the loc of an object via an equation of motion (such as a
>projectile.)  Any other ideas?
>
>Thanks, Roger


Roger,

I'm not sure why the motion should be choppy for you. Runs very 
smoothly on my older Mac Powerbook (233 Mhz). You might try "set the 
grid to false". And I'm not sure what you mean by "setting the loc of 
an object via an  equation of motion." Actually that is  sort of what 
I did, using a  finite difference solution of the differential 
equation of motion. Perhaps you mean using the solution of the 
differential equation,  simply  incrementing the observation point. 
But that shouldn't in any way  affect the speed or choppyness.

If, as Sarah suggested, you only want to see the finished product of 
the motion, the resulting trajectory and not its evolution in time, 
you should try vector graphics.  The script  below bounces a ball 
across the  screen using a graphic line tool:

on mouseUp
   put the width of this stack into w
   put 1 into vx
   put 4 into vy
   put 0 into x
   put 200 into y
   put .1 into gravity
   set the style of the templateGraphic  to "line" -- Polygon closes 
the end points
   create graphic  "aGraphic"
   put "" into gPoints
   --lock screen
   put the tick into startTime
   repeat until x > w
     set the loc of button "ball" to x,y
     put  round(x +vx) &comma &round(y - vy)& return after gPoints
     set points of graphic "aGraphic" to gPoints -- Try moving this 
line outside the repeat loop
     add vx to x
     add -vy to y
     subtract gravity from vy
     if y > 200 then
       add gravity  to vy
       multiply vy by -1
     end if
   end repeat
   --set points of graphic "aGraphic" to gPoints
  -- unlock screen
   choose the browse tool
   put the ticks - starttime
end mouseUp


If you run this as is, it will produce the *evolving* path of the 
button "ball." It actually runs more slowly than the pencil tool 
(1000 ticks for graphic tool, 600 ticks for the pencil on my 
machine.) A second problem is that it evolves more and more  slowly 
as it moves across the screen. You have to successively create a 
larger and larger list of points, about a  thousand  at the end, and 
redraw this graphic at  each step.

But if you comment out the  "set points" *within* the repeat loop and 
instead "set points" *outside* the repeat loop, it is blazingly fast, 
just 39 ticks. (See the commented lines above. Also  lock and unlock 
the screen.) Most of the time  is taken creating the graphic points 
and very little drawing the result.

(Shameless plug. This is all much easier in Turtle Graphics. See 
RunRev web site.)

http://www.runrev.com/revolution/education/usercontributions.html


Jim