how can i learn texturing and using materials in houdini? are there any sources for learning?

Hi,

HOUDINI TUTORIALS
http://www.sidefx.com/index.php?option=com_content&task=view&id=996&Itemid=132 [sidefx.com]

what i cannot seem to found out how to do, is shade a model so as to create an alpha channel from it.

i'm sure it's so obvious that all the pros know how, and assume us rookies also should know.

LOL

for example, in the youtube houdini cg challenge alley shot, there is a space
with a parked car.

if i were to roll a ball into the space near the car, all of the models nearer the camera should create a mask to obscure the ball as it passes out of view.

i've seen the shader in the library for shadow masks… but am not sure this is what is needed as i really only want an alpha channel.

Virtually any shader(apart from those with transparencies) gives you alpha ‘for free’, so I'm unsure what you mean exactly.

Regardless, what you probably want is to render your holdback with ‘matte’ on while you're rendering your hero. This cuts out the matte object from the hero…look in the geo objects Render tab for Matte shading.

Cheers,

J.C.

i recommend a constant shader set to black, render the sequence and that should give you the mask you are looking for, if I'm understanding what you're asking for.

EDIT - if you do a test render and open it in mplay, it will render 100% black, but when you check the alpha, you'll have the black and white. You might need to separate the objects into different passes, but try it as one pass first and then divide it up as you need.

JColdrick
Virtually any shader(apart from those with transparencies) gives you alpha ‘for free’, so I'm unsure what you mean exactly.

Regardless, what you probably want is to render your holdback with ‘matte’ on while you're rendering your hero. This cuts out the matte object from the hero…look in the geo objects Render tab for Matte shading.

Cheers,

J.C.

okay, that did it!
more info:
see, i was trying to finish an entry for the houdini challenge, but ran out of time. the provided project files includes some geo rotoscoped to some alleyway footage.

the geo had the ‘phantom’ option set in the render tab. !!! after deselecting this and turning on the ‘matte’ toggle on the same tab, this rotoscoped geometry creates a very nice mask in the hero's render as it passes behind the rotoscoped geometry.

now i can render and composite my render over the provided pic sequence!

arg, 2 days too late, but whatever. i am getting that houdini is more of an on going discipline or a lifestyle.

as the phantom toggle was set on, i guess they meant for the pic seq to be mapped on to the geo, so reflections of the sequence would appear onto the cgi creation, whatever that might be.

i have yet to figure out how to project a pic sequence onto rotoscoped geometry though.

one guy's entry has a hand busting up a fence. i can guess he modeled some boards and projected the image sequence onto them as a texture.
arg. so much 2 learn.

For future reference if you want to project a texture, add a uvtextureSOP, and set the texture type to perspective from camera, then choose the camera with the browser.

Create a VEX super material inside shops, and add your file sequence to the diffuse channel via the file browser. If your matchmoving and proxy geometry is spot on, you should get a nice projected textre of the scene on your geometry.

what i cannot seem to found out how to do, is shade a model so as to create an alpha channel from it

If you need alpha masks for future compositing you can also go to Mantra node parameters and under Properties > Output add an extra image plane and set a VEX variable to Af (alpha). In render view you can check the alpha mask selecting Af in the drop-down list that usually displays C (as for color channel). The trick is to play with “objects to render” & “matte shading” parameters either with (maybe…) more mantra nodes or using Takes…

Tranguz

what i cannot seem to found out how to do, is shade a model so as to create an alpha channel from it

If you need alpha masks for future compositing you can also go to Mantra node parameters and under Properties > Output add an extra image plane and set a VEX variable to Af (alpha). In render view you can check the alpha mask selecting Af in the drop-down list that usually displays C (as for color channel). The trick is to play with “objects to render” & “matte shading” parameters either with (maybe…) more mantra nodes or using Takes…

this sounds interesting, but i cannot quite reproduce it. can anyone expand on this technique?

also,
ragupasta,
this sounds perfect! i am going to try this today. the problem is though, eventually, as in the houdini challenge hand movie, the boards of the fence get broken up. so at some point, just before the impact behind the boards, the texture must freeze and not be a projected UV.

same think on the hamster attack houdini challenge video. someone may project the asphalt onto the road model, but as it breaks up that texture must remain on the top face of each chunk of road. obviously additional materials are needed for the newly exposed interior of the road.

on the houdini challenge, alleyway project, i toyed with the idea of the background car getting crunched or dented with the new H10 cloth dent, but could not figure out how to 1st obscure the original car and 2nd map the jpeg seq onto a modeled car. now i may be able to.

as the contest is over anyway, would anyone like the project files associated and referred to here? GURUS, can i share the project files here?


alvin yap was very generous in his very very detailed breakdown
that relates to this thread:

http://www.alvinvfx.com/breakdowns_s01.html [alvinvfx.com]

after reading his tutorial, and seeing his demo reel, it looks like everything he did could be done in houdini.

Thanks for the alvinvfx link! There's some really great stuff there!