Re: [Visualpython-users] disconnect between curve position and color

[Bruce S. <bas...@un...>]

This looks like a bug to me, and I'll try to see whether it can be fixed 
(assuming it's a bug, not a feature!). Here is a workaround, though it is a 
workaround that will do the wrong thing in the future if the bug is fixed:

    trail.color[:-1] = trail.color[1:]  # move the colors down one slot to 
compensate
    trail.pos = trail.pos[1:]  # delete first slot in the position list

Bruce Sherwood

At 02:20 PM 02/07/01 -0700, Bruce Peterson wrote:
>The VPython documentation discusses using the curve object to
>create trails for moving objects. The curve can also be used to record
>the history of an intrinsic parameter (such as temperature represented
>by object color) with code like:
>         obj.pos=newpos
>         obj.color=newcolor
>         trail.append(pos=newpos, color=newcolor)
>However if an abbreviated history is desired then the code
>         obj.pos=newpos
>         obj.color=newcolor
>         trail.append(pos=newpos, color=newcolor)
>         if len(trail.pos)>maxlen:
>                 trail.pos=trail.pos[1:]
>
>correctly truncates the curve length but incorrectly truncates the color.
>Internally the curve object appears to implement:
>
>                 if len(self.color)>len(self.pos):
>                         self.color=self.color[0:len(self.pos)-1]
>
>Is there any known way around this so that colors remain correctly associated
>with position?
>
>BTW storing position and color in a seperate list and replacing the entire
>list on each iteration rapidly goes into memory management meltdown - it
>works for small examples but rapidly dies with larger examples.
>
>
>Bruce Peterson
>Terastat, Inc
>Information Access Systems
>Voice (425) 466 7344
>Fax (206) 350 3685
>
>
>
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