EagleSun nous apporta ses lumieres ainsi en ce 2004-12-31 17:12... :

>Hi yall,
>
>I'm trying to render the sun and earth... the problem is, if I set the sun
>far away properly to 149 million kilometers (scale = 1000), or even 149
>billion meters (scale = 1), the sun won't render at all, but the object
>details on earth look nice.
>
>If I try to change the scale, like setting the sun to 149 thousand
>megameters (scale = 1,000,000), the sun renders fine, but the earth details
>are bombed.
>
>I made every effort to set proper scaling on earth surface, water turbulance
>(water seems to look nice on any scale), clouds (looks nice on scale 1 thru
>100), atmosphere (looks nice on scales 1 thru 100), distance of sun
>(renders if scale is larger than 1000).
>
>Can anyone give me clues?
>
>Ideally, I would like to render the sun at 149 billion meters, and
>eventually trillions of meters for Pluto.
>
>Thanks.
>
>
>
>  
>
You hit a hardware limitation, that of the FPU that is "only" 64 bits 
(double presision). To be able to use such whide ranges, you'd need quad 
(128 bits) or octuple (256 bits) presision math, with a processor 
equiped with a FPU capable of such.
Maybe some super computer have such a beast...

The best way around that problem is to fake the scaling. Make you'r sun 
1000 tomes closer, 1000 times smaller. Have a light_source with the 
"parallel" atribute to fake the actual sun distance. For Pluto, you'd 
need to put it 1 000 000 times closer and smaller, maybe more, than it 
should. In this case, it'll look like a single pixel point at 1600*1200 
resolution.

Alain

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