visualpython-users

[Visualpython-users] Visual 3.2.4

[Bruce S. <Bru...@nc...>]

Version 3.2.4 now available at vpython.org (and SourceForge) fixes the 
following errors:
1) curve now always plots final point (so there isn't a gap at the end),
2) diff_angle(a,b) is 0 if either a.mag or b.mag is 0 instead of pi/2 
(one could argue that it should be an error, or NaN, "not a number", but 
making the result zero is consistent with norm(vector(0,0,0)) is also zero),
3) frame documentation changed to explain that frame.objects list only 
visible objects,
4) makes display.exit = 0 again work (only a single graphics window 
closes when you click its close box).

The gap at the end of a curve only showed up with curves longer than 
1024 points. For such curves, Visual uses only every Nth point to 
display the curve, up to a total of 1024 displayed points. The bug was 
that the last of these selected points wasn't always the last point in 
the full curve, creating a gap at the end of the displayed object.

Bruce Sherwood

Re: [Visualpython-users] Visual 3.2.4

[Jeremy S. <rez...@ma...>]

I'm working on a program that draws a continuous curve, and when the  
number of points on that curve exceeds 1024, a new curve is drawn at  
the end of the old curve.

How many 1024-point curves can visual python manage before crashing?

-Jeremy S.



On Dec 19, 2005, at 2:01 PM, Bruce Sherwood wrote:

> curve now always plots final point (so there isn't a gap at the end),
>
> The gap at the end of a curve only showed up with curves longer  
> than 1024 points. For such curves, Visual uses only every Nth point  
> to display the curve, up to a total of 1024 displayed points. The  
> bug was that the last of these selected points wasn't always the  
> last point in the full curve, creating a gap at the end of the  
> displayed object.
>
> Bruce Sherwood

Re: [Visualpython-users] Visual 3.2.4

[Jonathan B. <jbr...@ea...>]

On Mon, 2005-12-19 at 18:48 -0500, Jeremy Sachs wrote:
> I'm working on a program that draws a continuous curve, and when the  
> number of points on that curve exceeds 1024, a new curve is drawn at  
> the end of the old curve.
> 
> How many 1024-point curves can visual python manage before crashing?

Here goes a long answer to a simple question...

It should go until you run out of physical RAM.  For N points, the
maximum memory usage is 2*3*sizeof(double)*2*N, or 48 bytes per point,
but it can be as few as 24 bytes per point.

Curve objects preallocate storage for up to 2x the total number of
points in order to make curve.append() work fast.  When using .append(),
the total allocated storage is approximated by min( 256, 2^X) for
incrementally increasing values of X (it is actually slightly more than
this).  If you precalculate the curve's pos or color array rather than
simply append() to it, the storage will be enough for exactly 2x the
size of the initial array (doubling as needed for subsequent appends).
You don't normally see this extra allocation since curve.pos is actually
a slice into the real pos array.

For your usage pattern, the extra space will be small, and total storage
will be a pinch larger than 24 bytes per point.  There's also some
per-object overhead which should be pretty small compared to the storage
required for the points themselves.  Therefore, per-object memory usage
should be about 24-25K per 1024-point curve segment.

As far as rendering goes, curves with zero radius (the default) are
rendered much much faster than thick curves.

HTH,
-Jonathan