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View Full Version : Advantage of bumpmap system in XSI??


wurp
09-06-2004, 04:35 PM
Hi there

I've used XSI for quite some time now, all over I hear that "xsis bumpmap system is a bit weird but its weird for a very good reason" now my question is: what is this reason? :)

So far I havnt been able to find any reason to for example use a vector input rather than a normal color input. Mixing bumpmaps becomes hell and in general it just complicates the usage in the rendertree.

Also I want to know why when scaling the UVs in the texture editor to create a repeating texture it doesnt work for bumpmaps, why? I got it working by going into the texture projections property page and checking "Seam U" and "Seam V" but why do I have to do this only when using bump and not with for example diffuse maps??

thanks in advance

Eraq
09-06-2004, 07:18 PM
I also find bump-mapping quit weird to work with and I hope its something 3Dtutorials would cover in future versions of Adv. Rendertree videos. (prayers to mr. Saltzman )
Something that really bugs me is the way procedual bump-maps work. In other pakages its really easy to setup.

Erik

Atyss
09-06-2004, 09:17 PM
My take on the matter, and this is my very personal opinion, is that because the developers of XSI wanted to expose the mental ray mechanisms as they are. For instance, bump is really a vector process. However, I think the developers ALSO wanted to create tools to simplify the process a little bit, that is, the possibility to enable bumpmapping inside Image shaders and such.

More technically, bumpmapping is a perturbation of normals of the surface. Normals are vectors, in other words, 3 representing cartesian space coordinates. Bump change these values, wich in turn changes the shading.

Check out this page of your mr manual:
file:///C:/Softimage/XSI_4.0/Doc/mental_ray/manual/node19.html#SECTION17

Now the problem is that in XSI, to have access to this raw stuff resulted into too much way to do it, and consistency is gone, while confusion appeared. I saw in the Experience 4 book that Aaron even uses boolean shaders to drive bump. What a mess! On one hand bump mapping is very versatile, on the other hand it's, well, super versatile but not intuitive for artists.

As far as the bumpmap limitations goes I have no clue, I'm not a shader writer!


Feel free to correct me :wise:


Cheers
Bernard

Sil3
09-07-2004, 10:18 AM
However, I think the developers ALSO wanted to create tools to simplify the process a little bit, that is, the possibility to enable bumpmapping inside Image shaders and such.

If they wanted then i think they dont suceded that well, 90% of the times i dont want my color map to be the Bump map (who does?), i can use part of the color info to make a greyscale image to be my Bump starting point in Photoshop, but using a the color as only the bump??? Makes no sense to me.

wurp
09-07-2004, 10:21 AM
If they wanted then i think they dont suceded that well, 90% of the times i dont want my color map to be the Bump map (who does?), i can use part of the color info to make a greyscale image to be my Bump starting point, but using a the color as only the bump??? Makes no sense to me.

I agree 100%. I guess it can be useful for quick tests, but usually you'll want a separate bumpmap image like you said.

I really cant understand the advantage of vector inputs for bumps.

Sil3
09-07-2004, 10:23 AM
I really cant understand the advantage of vector inputs for bumps.It┤s a Highend prog, if things were so "artistic" straight forward and less technical it would be no fun :scream:

Im jk of course hehehe

thebigMuh
09-07-2004, 07:45 PM
The bumpmap system in XSI is pretty good, in theory.

Like Atyss said, bump mapping is vector business. In addition to that, however, the bump map input port doesn't expect bump basis vectors, instead, it simply replaces the surface normal with whatever you put in.

What's the difference?

If you have a color input for example on the bumpmap_generator node, then the node has to somehow calculate the effect the colors have on the final surface normal. It does that by taking the base surface normal, and then skewing it slightly, depending on the color gradients it grabs from the color input. This however means that you can only change the base surface normal. If you want to replace the surface normals with something completely different, you are stuck.

Doing this is quite easy in XSI. Here's an example with a quite sick shader tree. Using this setup I can smoothly blend between the sphere's standard surface normals and the normals of a cube by adjusting the weight in the color mixer. The geometry doesn't change, only the normals change. Try doing that with a texture map ;) I have to add that this works regardless if this is a sphere, a torus, a teapot or the famous Bunny model.

http://img23.exs.cx/img23/3589/SickBump.th.png (http://img23.exs.cx/my.php?loc=img23&image=SickBump.png)

With all that said, I have to add that the bumpmap_generator node sucks, which I think is the main problem.

Ciao, ímuh!

RayenD
09-08-2004, 12:23 AM
Hey bigMuh, did you just solve "squaring the circle" problem by accident? (call them, Nobel prize is waiting) ;).

wurp
09-08-2004, 09:19 AM
Muh.... you ARE the brainiac :)

Eraq
09-08-2004, 10:57 AM
One thing that is a puzzle to me, is how to tile procedual textures. I have a scene where I need to mix between a image texture and a procedual texture to make bumps on my surface.

Erik

wurp
09-08-2004, 11:24 AM
One thing that is a puzzle to me, is how to tile procedual textures. I have a scene where I need to mix between a image texture and a procedual texture to make bumps on my surface.

Erik

You can tile the but since they are not seamless you're gonna end up with seams all over. Instead find the parameter that controls the size of whatever procedural you're using.

Atyss
09-08-2004, 01:46 PM
Use the UV Remap function. If there is no remap available because you are using a 3D procedural, insert a texture_edit between the texture_space_generator and the shader. Note that you must uncheck the 3 wrap parameters.


Cheers
Bernard

Eraq
09-09-2004, 10:00 AM
Thanks Bernard....

It works -

I think I must one day sit down and learn a bit more about MentalRay.


Erik

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