Hi List,

Thanks, Hans, for your suggestion. In the end, I decided that I actually liked the silhouettes better than a faint version of the whole picture. Silhouettes clearly show the motion, but are far less visually distracting. In the figure below, the projectile motion’s are clear, including the cow’s constant angular velocity, but the final state still pops out.


I used “redecorated" to get the pictures with light, solid grays. Below is code for producing just the ball, if anyone wants to see the details. It includes a simple “shadow" macro that produces a shadow of any picture with an adjustable gray.

I’m having lots of metafun!
Gavin


\startMPinclusions
 picture ball;
 ball := image(
   fill fullcircle scaled 1cm
     withshademethod "circular"
     withshadecenter (.25,.25)
     withshadecolors (.8white, black);
   draw fullcircle scaled 1cm withpen pencircle scaled 0.8pt ;);
 vardef shadow(expr p, t) = 
   draw redecorated (draw p) withcolor t[background,0.8background];
 enddef; 
\stopMPinclusions

\startMPpage
 pair p;
 for i=0 upto 10:
   p := (i*cm/10, -((i-7.33)**2)*cm/7);
   shadow(ball shifted p, (i+1)/10) ;
 endfor
 draw ball shifted(1.1cm, -1.92cm) ;
\stopMPpage