Message: 11 Date: Thu, 30 Jan 2003 19:52:22 -0800 Subject: re: Line Tracing From: Roger Guay <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] Reply-To: [EMAIL PROTECTED]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
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