Transfer Hi-res detail to Low-res model problem

robonilla · Talkative Joined: 07 May 2012 Posts: 25 Location: Japan

Hi guys,

I'm in need of your wisdom again!

I was trying to create a Hi-res rock generator which could export a lo-res version of the geometry and its corresponding displacement map to be used in other applications.

I found very useful topics on both here and the odforce forums, for the rock I pretty much studied and followed jwoelper's approach in here http://forums.odforce.net/index.php?/topic/10798-procedural-stonesrocks/ and it went well.

And for the bake of the displacement maps i was trying to copy what brianBurke did on his example in here http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=102853&sid=8c710daad864bc351082b6a24b6cff39

I managed to render out the maps but if you see the resulting displacement map you can clearly see UV edges, resulting on undesirable bumps on the rendered rock with the displacement map applied. Actually I wasn't able to test the sample file that I'm mimicking the approach from because of some errors, but i tried studying it and recreating what I thought I needed.

I am attaching a picture of my resulting displacement map, rendered rock with that map and my scene to see if someone can help me find what it is I am doing wrong.

Thanks in advance to you all! Any insights will be more than appreciated!

1234d · Lurker Joined: 08 Feb 2007 Posts: 4 Location: Ireland

Im looking at a similar problem and Im just wondering if you ever got to the bottom of this.

When I apply Brians setup to a simple grid with some light sculpting for displacement on it I get the attached result. As you can see in the attached pic it does work it creates a dsp map but when you crank the levels a bit it seems to have create quite a few artifacts as well. I dont know much about shading seems like there are not enough ray being generated in the shader maybe? If so how do you increase the no. of hit in the rayhit vop.
Thought it might be a sampling issue so played around with the render settings to no avail. Any help would be mucho appreciated I would really like to avoid having to jump to zbrush or mudbox to genrate the maps.
Thanks in advance.

brianBurke · Posted: Tue Oct 16, 2012 2:14 pm GMT Post subject:

seems like that problem was coming from not handling the 'zero condition' when the surfaces overlap.

here's a spruced up scene that deals with that, and also swaps a gather for the trace so that multisampling can happen as well.

-b

1234d · Lurker Joined: 08 Feb 2007 Posts: 4 Location: Ireland

Wow Thanks for taking a look a Brian. Your files are teaching me so much. Im new to the whole world of shading but I get the basic idea of tracing up the normal to generate the map. From looking through posts it seems that mantra -u does not currently support doing displacement. I did some test and it does look like the displacement is not handled correctly. In the pics with the spheres I managed to soften the edges created by the uv shell border by running the displaced pics through cops and blurring the edges which is somewhat succesful . There is still weird banding appearing on the low res object as you can see in the pics which is what I guess they mean by displacement doesnt work. I did a quick test with your older setup and you can see the banding there as well.

It seems such a pity that -u option doesnt handle displacement as it would allow you to bring in model from other package do cool houdini stuff and then output a nice map back for rendering. Especially if you have lots of variantions to iterate through.

f it really isnt possible to generate the displacement maps in houdini I guess I will have to output high and low res models and trying scripting something to either 3d coat or mudbox to generate the displacements.

You dont know if there is some way of generating clean disp maps out of Houdini per chance?

Cheers for your help

R

1234d · Lurker Joined: 08 Feb 2007 Posts: 4 Location: Ireland

sorry forgot to upload hip. the only thing added to brian file is an attempt to render a displace from a quick sculpt on a sphere which gives banding. I added a cop network to try and blur the edges of the disp map. Apologies for my awful attempt at comp but it does kind of work.

Was thinking I might take a look at Ptex in houdini and see where that takes me. From what I have quickly read you can generate a ptex file with gptex a houdini added extra. Not sure if it is possible to generate a ptex file using brians displacement shader shooting in the dark a bit but you never know. If I find anything interesting I will post it back here. It would be nice to have this in Hou.

1234d · Lurker Joined: 08 Feb 2007 Posts: 4 Location: Ireland

got dragged onto something else for a bit but just wanted to update this problem.

Looked over this problem with a mate and I think generating clean displacement maps in Houdini will not work. I think what is happening is that when baking your map the low poly geo is not being subdivided (I think of this as smoothed rather than amount of geo). When your map is reapplied at render time your renderer dices up your geo and smoothes your mesh. because your points are now in a different position you get banding. Ive attached a hip that shows what I mean replicating the issue in sop.

I dont think that Mantra currently supports unwrapping and subdivision so this is a bit of a roadblock. You can mitigate the problem by subdividing your low poly object a bit more but this kind of defeats the purpose of using a displacement map.

If I have this correct it seems a bit of a pity that Mantra doesnt support unwrapping for displacement as it would be a very nice modelling workflow, something like Transfer Maps in Maya only with all Houdinis flexibility. Assuming there was interest (its not all about fx guys Smile

I think it wouldnt be the most difficult thing for sidefx to implement either.

Im going to be back looking at this again soon currently I am going through mudbox to generate the maps which work fine but is fairly manual. Have had some success with mayas Tranfer maps but its a bit flaky at generating them in uv space. Might also take a look at zbrush as I could zscript it I think.

Again if I find anything interesting that will help in automating displacement map generation I will post it back here.