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A Great Conjunction

Eugene — Sun, 27 Dec 2009 22:34:28 +0000

It’s funny what computer graphics does for me. I have noticed that it is a mental outlet so I can utilize both the artistic and technical aspects in some way. It certainly is a great deal of work however, and since I’m not in “the business” I’ve found my pursuits in the subject amorphous and without any true goals. Additionally, in taking up other things that are both artistic and technical full-time I find my mental need of the CG subject somewhat diminished.

What has of late come to the fore was a need for frivolous activities – games and the like – that are amusing but have no real application beyond enjoyment. To that end, I’ve got back in to playing Dungeons & Dragons, and have found it to be a great experience and much more fun that it was when I played so many years ago. Maybe it’s the new rules or how I have approached playing the game this time, but the game has become a strange focus of mine for some reason.

I see the need to state these things because looking at my site I see the last post was 3 months ago, and even those were just mentioning podcasts I was a part of. Be well aware though that my love of computer graphics is no less than before.

If you’re interested, the dragon illustration is by an exceptional artist by the name of Kekai Kotaki. I gather it was commissioned by Wizards Of The Coast since it graces the cover of Dungeon Magazine #168 and is astounding in the simplicity of the brush strokes and the fantastic contrast which really makes the dragon truly terrifying.

VOP COP Raster Depths

Eugene — Thu, 10 Sep 2009 22:03:53 +0000

This was an odd video to do since it seems to be a simple topic but when talking about it out loud it starts sounding complicated. I’m basically covering several sub-topics which support the overall topic. Despite the confusing ramblings in the video, what you should take away from it is that in VOP COPs, the “Raster Depth” setting can cause results to vary depending on the data generated inside.

The hip file I’m using is actually based on a workshop that used to be online (but doesn’t appear to be anymore). I used it because it had the exact components to demonstrate everything.

Also, I’m sure my friend Jason will say that he is in no way regal when it comes to compositing, but seeing what he’s been up to lately certainly indicates that he knows what he’s doing .

Sprites On Points Digital Assest

Eugene — Fri, 12 Jun 2009 20:12:39 +0000

Sprites are pretty cool, but in a clean install of Houdini you can only use them on particles using the Sprite POP. It turns out, you can add some attribute trickery to make sprites work on plain ol’ points. The cooler thing is that this Sprite SOP concept works in Houdini Escape (which doesn’t have particles). I wrote a full blown help for it too, with an icon and all – which basically copies the Sprite POP language and replaces “particles” with “points”. Yes, this has been done before. But let’s face it – that one’s old.

You can find it on my Houdini page or you can get the asset directly from here.

For those interested, here are the attributes you need to get sprites on points:

spriterot: class: point, type: float, size: 1
spritescale: class: point, type: float, size: 2
spriteuv: class: point, type: float, size: 4 (spriteuv[0] = U-offset; spriteuv[1] = V-offset; spriteuv[2] = U-scale; spriteuv[3] = V-scale)
spriteshop: class: point, type: string

Varying Materials Using A Single Shader

Eugene — Mon, 25 May 2009 03:44:22 +0000

Nothing ground breaking here, but for someone who is into neat little tricks to control shaders, I thought this was worth showing. What the video covers is a way to vary the materials on a single object using a single shader (differing from the usual method of using multiple shaders for different pieces of an object). I’ll leave it at that and let the video do the talking. I’m starting to record at my screen’s native resolution (1680 x 1050) which ups the video size but I like seeing big videos. I’m also posting these on Vimeo which I think is nice to have since you’re not always on a machine that you can download videos on.

Note: Video re-done on 5/25/2009. I thought it could be cleaner and more focused on production nuances so I re-recorded it.

Houdini And 3DConnexion Devices

Eugene — Sun, 12 Apr 2009 04:31:26 +0000

UPDATE: I thought I was doing something special and unique but it seems someone has beat me to it. Still, even with all the effort I’ve put into this (and it still not being totally usable yet), I’m finding the experience very fulfilling. When even failing is enjoyable, one must take note and realize that you must really love what you’re doing.

Yes – I have something working! Read on for the story and where I’m at:

I’ve noticed a problem with a lot of animated shorts and student work: The camera work is atrocious. It seems like all the time is spent on perfecting the modeling, animation, and shading, then in the last 10 minutes of production someone puts in a camera and animates it going to the left. Seeing this as a major issue I thought that there must be a better way to have the camera animated easily and a whole lot better. I then recalled I had a 3DConnexion SpaceNavigator that I never use because no applications I use support it. The whole line of 3DConnexion devices might be just what animators need to have better control of their camera.

The SpaceNavigator seems ideally suited to be able to control not just a camera but any object in 3 dimensions, provided that the application can see and understand the device. Unfortunately, Houdini is not one of them. So I researched it a bit and found some hope in an obscure post on the 3DConnexion forum. Someone had been able to use Python to poll data from a device using a Python module called comtypes, a COM client framework (the Windows SDK for the device is a COM dll). I tried it in Python 2.5.4 and it worked! At the time it seemed like a simple thing to add the script in Houdini and replace the trans and rotate prints to “hou.node(‘/obj/cam1′).parm(‘my param’).set(my devices param)” and get the camera to receive data from the device. Long story short – it didn’t work. Firstly, Houdini doesn’t have _ctypes.pyd which is required by the ctypes module (so I added it to Houdini x.x.x\python\lib\ which worked). Secondly, though it seemed that the device driver was being seen, an error kept posting.

So more research was needed. I thought maybe using the old comtypes (v 0.2.1) with the script from the 3DConnection post was the issue, so I upgraded to comtypes 0.6.0. But if you read the post, only 0.2.1 works with the script. More research… then after getting the script to work with 0.6.0, I still got the same error.

So off to odforce I went (to cry for help) which got me thinking more but all of those avenues were dead ends. Then – you guessed it – more research. Which lead me to figure out what was wrong. My comtypes module in Houdini wasn’t compiled! I had no .pyc or .pyo files anywhere! And that was it, after I compiled everything using the Python compileall module in Houdini itself it all worked out. Now I can get Houdini’s command window to print the data from the device just fine. The next step is to see if it’s feasible to get this data into Houdini beyond printing to a window, but that is for another day (and another post) mainly because some quick tests cause Houdini to freeze up when I try to use the data to send to a parameter.

Here’s a quick look:

Houdini Using A 3DConnexion Device Via Python from Geneome on Vimeo.

There are some 32/64-bit issues. The _ctypes.pyd that comes with Python only seems to be compiled for 32-bit machines. So unless I compile my own 64-bit _cytpes.pyd, this only works with a 32-bit Houdini. You can use a 64 bit _ctypes, which works with Houdini 10 64 bit but you need to use a different ctypes module version (1.0.2). As we are using a COM dll to poll data, this is a Windows only method. I need to look at the 3DConnexion SDK for Linux to see if Linux is in the cards through this or some other method.

(See the follow-up here.)

Houdini Occlusion Asset

Eugene — Sun, 04 Jan 2009 21:21:26 +0000

I’ve received a few requests for an asset of the occlusion inline VOP I used for the occlusion video so I thought I would put one together. I call it “Occlusion 2″ mainly because it’s the second occlusion VEX function. The occlusion VOP that comes with Houdini is actually the first function which gives you occluded irradiance which is a bit different from the occlusion we’re typically used to. I bet Houdini will eventually have this second function added in VOP form, but until then you can add it with this asset.

I put a help section in the asset, though as it’s not working right now, I’ll say that there is an added output called occlusion which is basically 1-coverage. Using this removes the need for the later subtraction step I note in the video. If you would like to see the help you can right click on the VOP, go to Type Properties, then go to the Help tab.

You can find the asset here (also linked to on the tutorial page).

v1: Initial Release

Houdini BRDF Asset

Eugene — Mon, 15 Dec 2008 03:04:04 +0000

I’m not sure why illuminance loops fascinate me so. It could be because I never had access to such a cool feature or maybe it leads me to re-visit classic bi-directional reflectance functions (I like the math). Whatever the reason, I decided to create a brdf VOP digital asset so you don’t need to type a lot to get the functions I describe in Part 3 of the Image Plane tutorial series. What’s interesting is that Peter Bowmar has created an asset for this already, but I wanted to learn how to make a digital asset. The interesting is that I didn’t look a Peter’s asset at all so I went about writing the code for it in my own way. It turns out we did it quite different.

One issue that arose though is that the help file and built-in Houdini icons don’t work as described in the Custom VOPs tutorial, so though the help file is written in the asset it doesn’t work right and there are no icons (at least the one I wanted to use). Another issue is that Houdini (at least in 9.5) has the limitation that you can’t get illuminance loop derived image planes from area lights.

You can find the asset here (also linked to on the tutorial page).

v1: Initial Release
v2: Adding a parameter to rough now works. The fix causes the rough not to be hidden when diffuse is used, but it doesn’t case any harm keeping it unhidden.
v3: Added string input parameter so you could select the BRDF type after promoting the inputs.

Image Planes Part 4 (Object IDs)

Eugene — Thu, 20 Nov 2008 04:00:25 +0000

Didn’t think the image plane series was complete enough so I tacked on this little diddy. I covers how to get object (or primitive) ids using image planes in Houdini and what you can do with them in the compositor using the lumakey COP. The compositor part I learned from SYmek, who I feel is an integral part of the Houdini community (and who I had an argument with about points on the Sunflow forum a while back ).

Image Planes Part 3 (Light Export)

Eugene — Tue, 18 Nov 2008 15:24:57 +0000

I’m fairly pleased with this video only because I learned a lot on my way to get this worked out. Well, I learned a lot of mistakes one could make with Houdini’s VEX like what you shouldn’t put in illuminance loops. I felt obliged to do this video since in the very first video I mentioned that I would talk about light export in the image planes. What this covers is how to get planes/passes for each light in the scene. You can find the video as well as the final hipnc file here. The final hipnc file has specular components added which I didn’t cover in the video since the technique to get the diffuse planes is so similar.

Image Planes Part 2 (An Occlusion Plane)

Eugene — Mon, 13 Oct 2008 02:39:44 +0000

Okay, so I went a bit off the track on this one. It’s loosely an image plane video and more of a “how to do an occlusion pass inside a shader then put it in a plane” video. So I’m not sure if I should keep it under the “image plane” heading or create some new one. Either way, this topic was a weird one I was wrestling so I did a lot of forum searches and made lots of mistakes (basically writing my VEX poorly). So I thought I would at least show my results so people could see what I found. What’s made this more interesting is looking into the different occlusion functions and trying to figure out why they differ and what they really give you.

Edit: In this video I use a subtract node to subtract the occlusion output from a constant float (1). Houdini user Jason M. pointed out that I could have used the compliment VOP instead which does the same thing in one node rather than the two I used. So remember that the compliment VOP is around!