"RC" <nomail@nomail> wrote in message 
news:web.49a3163629ff894ce1acfc5e0@news.povray.org...
> Hello,
>
> I know this question is going to be a head slapper but I can't seem to get 
> an
> object to increase in speed. I need this object to increase in speed every 
> x
> clock cycles, so I'm using an if statement. Problem is I can get it to 
> enter
> the 'else' section, but it never returns to my original condition after I 
> reset
> my variable counting to x (num).
>
>        #declare num = clock*60;
>        //60 being the total number of frames
>        #declare speed = clock;
>        #if (num <= 3)
>              object { Ball
>                scale 0.7
>                translate <-5.5, 0, 0>
>                translate <speed, 0, 0>
>                #declare num = num + 1;
>               }
>              #debug "speed the same\n"
>        #else
>              #declare speed = speed + 1;
>              #declare num = clock;
>              #debug"speed increased\n"
>        #end
>
> This is hurting my brain, and I know the answer is staring me down I just 
> can't
> see it. Any input? I have a feeling its related to the declare statements.
>

I think there are a few misconceptions evident from this code snippet.

The Ball object is only placed in the scene if num<=3. Else the ball is not 
added into the scene at all by this code. I suspect you need to place the 
ball object in the scene after the #if, #else, #end clause that calculates 
the distance travelled.

The comparison 'num<=3' is dodgy in a number of respects. Firstly, if you 
truly do have 60 frames then, as the frame number passes from 0 to 59, num 
will pass from 0 to 60, so won't go up in integer values. Secondly it's a 
calculated decimal value so it can't be  reliably used in this sort of 
comparison anyway (on frame 3 it may or may not be 3 to within the precision 
of the calculation). It would seem more appropriate to use the frame_number 
variable for this sort of comparison, which is an integer.

Within the #if statement, the variable 'speed' is used to translate a 
distance controlled by the clock, but this is a very small distance = 1/60 
POV-Ray units in the first 4 frames, so you may not even notice this 
distance unless your camera is really close to the ball. It'll move from 
x=-5.5 to x=-5.434 in those 4 frames.

Even if the ball appeared beyond the 4th frame (frame 3), which it doesn't 
in this code, the increase in 'speed' isn't really that at all. You're just 
adding 1 unit to the variable you've been using for distance, so it would 
jump forward during one frame transition and would then continue at the 
snails pace it was doing before. It would travel a total of 2 units in the 
60 frames, with 1 unit of that distance being added in a single step between 
frames 3 and 4.

All of the calculations you do after adding the Ball object to the scene 
have no impact at all on the Ball object., so the num=num+1 doesn't do 
anything to the ball in any of the frames.

I see Warp has given you an example using a function to calculate the X 
displacement of an object that you can then use to translate your Ball 
object while I've been writing this, which is probably all you really need, 
but I hope this explanation also helps.

Regards,
Chris B.

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