Reflection

Features you'd like to see in future versions, gripes, ideas..
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AdamB
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Re: Reflection

Post by AdamB » Wed Jul 02, 2008 7:12 pm

marchab wrote:Oh, I must say I'm a bit confused now as to how to name the material files.
Do we need 2 or 3 files; mytextur.jpg, mytextur_ulvmap.jpg, mytextur_specmap.jpg?
You need 2 files. Either mytextur.jpg & mytextur_specmap.jpg OR mytextur.jpg & mytextur_uvlmap.jpg (NB spelling, its "uvlmap")

The first form gives you just control of the amount of reflection.

The second form gives you control of surface normal, amount of reflection and Fresnel.
marchab wrote:I am surprised to see that the skybox reflects alright but not the objects of the model.
The glass on top of the base box, which is the same as the one on the front side, does not reflect the stone podium on it.
I must be missing something, no?
OK, long-ish answer coming up..

If LightUp was a full raytracer it would trace the rays off every surface to find out what was reflected. However, this is slow. To get around this, LightUp caches what is visible at key points around the your model and when it needs to know what's reflected at a point on a surface it queries the nearest cache to get an approximation of the reflection.

Some important things flow from this.

First, while the reflections give a good sense that a surface is shiny and what its reflecting, the reflections you get will generally not be exact. If you want exact reflections, use a raytracer and wait 10 minutes a frame. :-)

Second, LightUp has to find the best cache to use. For groups and component instances, it does this by finding the closest IrrCache object you've placed in the scene, if there are none it uses the skybox. For 'free geometry' not in any group or component instance it always uses the skybox as a cache for reflections.

A common technique for using reflections in LightUp, is to embed a IrrCache at the center of a group/component so that it will cache the surroundings and give a reasonable stab at rendering the reflected environment.

So in answer to your question, you have some 'free geometry' and LightUp is simply using the skybox as a cache. If you put the geometry in a group and add a IrrCache you'll get something that shows the stone podium however your results will depend on how you group things and place IrrCaches.

The broad message is that reflections in LightUp are meant to give a sense of materials in the model and not some light simulation.

Hope that helps,
Adam
Developer of LightUp http://www.light-up.co.uk

marchab
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Re: Reflection

Post by marchab » Wed Jul 02, 2008 9:18 pm

Thanks a lot for the explanations.
AdamB wrote: If you put the geometry in a group and add a IrrCache you'll get something that shows the stone podium however your results will depend on how you group things and place IrrCaches.
I'll give it a try. So I have to put an IrrCache in the group containing the reflective material, right ?
The broad message is that reflections in LightUp are meant to give a sense of materials in the model and not some light simulation.
Fair enough.
I do prefer the LU "tour" method over the raytracers one frame shot.
Mario C, SketchUp & LightUp trainer, Mac & pc

marchab
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Re: Reflection

Post by marchab » Tue Jul 08, 2008 4:47 pm

One more thing about Skybox; such a nice feature :)
It looks like the image files should not have accent in their names.
Mario C, SketchUp & LightUp trainer, Mac & pc

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