I have a spline. I want to move an object along that spline, and have it
motion-blur as it moves. It seems that I can only feed the spline "clock",
or else the blur doesn't show up. I want to control it with another value,
that doesn't increase constantly like clock, say with autoclck.mcr, but it
doesn't blur! What can I do?

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"Tony[B]" <ben### [at] panamac-comnet> wrote in message
news:39f27d6f@news.povray.org...
> I have a spline. I want to move an object along that spline, and have it
> motion-blur as it moves. It seems that I can only feed the spline "clock",
> or else the blur doesn't show up. I want to control it with another value,
> that doesn't increase constantly like clock, say with autoclck.mcr, but it
> doesn't blur! What can I do?

Try putting it all within the motion_blur {} statement.  Seems you can't access
external variables, so that should do okay.  Not sure about whether everything
will need to be in there or just the final #declare, been a while since I was
trying it myself.

Bob

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In article <39f27d6f@news.povray.org>, "Tony[B]" 
<ben### [at] panamac-comnet> wrote:

> I have a spline. I want to move an object along that spline, and have it
> motion-blur as it moves. It seems that I can only feed the spline "clock",
> or else the blur doesn't show up. I want to control it with another value,
> that doesn't increase constantly like clock, say with autoclck.mcr, but it
> doesn't blur! What can I do?

As long as the value you give to the spline is calculated using the 
"clock" value within the motion_blur block, it should work. I don't know 
how the AutoClock macros are doing things, but I don't see how they 
wouldn't work.
For example: this will work:
motion_blur {
    #declare Val = sqr(sin(clock));
    object {MyObject translate MySpline(Val)}
}

But this will not blur with movement along the spline:
#declare Val = sqr(sin(clock));
motion_blur {
    object {MyObject translate MySpline(Val)}
}

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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> But this will not blur with movement along the spline:
> #declare Val = sqr(sin(clock));
> motion_blur {
>     object {MyObject translate MySpline(Val)}
> }

Why? Can't this be fixed?

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In article <39f33152@news.povray.org>, "Tony[B]" 
<ben### [at] panamac-comnet> wrote:

> Why?

Because motion_blur works by parsing the block multiple times, changing 
the clock variable slightly each time. If a variable is declared outside 
that block, it is parsed once and the result fed into the block. Since 
this value doesn't rely on the blurred clock, all the copies of whatever 
is affected by the blur are exactly the same.


> Can't this be fixed?

Probably...but only by parsing the entire scene file multiple times. And 
this would probably eliminate the possibility of having separate 
motion_blur blocks with different quality levels, would make parsing 
much slower, would require rewriting a large portion of the existing 
motion blur code, would be more difficult to implement, and finally, 
isn't really something that *should* be "fixed". The way it is is(don't 
you just *love* English?) far more flexible, it gives you much more 
control of what actually goes on. If you want something animated but not 
blurred, no problem: just save the clock value in a variable outside the 
motion_blur block.

Sorry, but it isn't a bug, just a misunderstanding on your part.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

<><

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Oh... :( OK

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