Faking Global Illumination in Houdini with Vmantra

Image By Carlos Lemus, http://www.visualparadigms.com.

NEW!  Version 1.7 features:

• Now works with Houdini 8.X. Might not work with older versions of Houdini
• Fixed bug so that enable/disable shadow map creation toggle now works properly.
• Comp networks are now created in /img instead of /comp, so will now work in Houdini 8.X. This will DEFINITELY break versions of Houdini that are older. Just do a global search and replace in the .cmd file and change all "/img" to "/comp" and it should work if you're not getting a network created in your compositing pane.
• A new bug! If you hit "Start Over" the interface may not properly reconfigure itself. Not sure what's going on here, but I don't have time to figure it out. Just quit global.tk and restart, everything will be fine.

• Much more error checking.  If you don't have the necessary shaders or file paths are wrong, you will get a warning message.
• You can now add multiple key lights.
• Bug fix:  Dimmer slider in key lights now work.
• Shadow Maps are now created with $F in their filenames to aid multi-proc or distributed rendering.
• Interface cleaned-up.
• Buttons to turn on and off "Contribute to Specular" and "Contribute to Diffuse" settings for all global lights.
• SOP added to reference COPSII for floating-point images. (Note:  Non-square images will crash early versions of H5.5.)
  

Version 1.3 features:

• Ability to by-pass shadow map creation.

Version 1.2 features:

• De-bug mode to help track down installation problems when using this utility.

Version 1.1 features:

• Automatic detection of operating system
• Option to add all the lights at once or one at a time
• Expanded help
• Options for globally setting light resolution
• Options for globally setting Autogen setting
• Abiltiy to add a key light
• Dome object will no longer render

Here is a quick and easy way to get fairly nice global illumination style lighting using Vmantra and Houdini.   Some of the techniques were stolen/adapted from the SideEffects mailing list, and others from some of the websites below.  If you are able to create anything more beautiful than what I have come up with below, please share.  Thanks to Jens Zalzala, Carlos Lemus, and Jim Berberov for the images.
      Stomp images by Jens Zalzala
Click here to see .mov movie of above.
Click here to see .avi movie of above.

http://freespace.virgin.net/hugo.elias/radiosity/radiosity.htm - A really good explanation of Radiosity

http://www.highend3d.com/maya/tutorials/gi/ - A similar tutorial for Maya

http://www.3dluvr.com/marcosss/ - Some Arnold Renders

http://www.rendermania.com/HDRI/index.shtml

http://graphics.stanford.edu/~henrik/images/global.html - Some good Global Illumination / Radiosity Examples

http://www.artifactoryvfx.com/ - The inspiration for Globaltk -- Julian Butler's Maya Global Lighting Rig

http://www.3dluvr.com/lightengine3d/downloads/rayDiffuse/rayDiffuse1.html - Raydiffuse Homepage

http://www.lightflowtech.com/elf/ - Lightflowtech HomePage

http://www.umlaut.fr/XSI/FinalGathering.html - Mental Ray's Final Gathering Technique VS Arnold

http://www.debevec.org/HDRShop/ - HDR Shop - Great Resource for info on High Dynamic Range rendering. Also has a Houdini plug-in to allow you to create global lighting set-up from an HDR image.

Installation and Usage

Right-click and save to disc these files:

• global.tk
• global.cmd
• Simply put the two scripts provided into your common scripts directory.
• In the global.tk file, change the line:
set PATH /usr/home/etc/global.cmd
.... to the path in which you are storing the .cmd file.
• In your Houdini session, in a textport type:
tk path_to_file/global.tk (where "path_to_file" is the actual path to the file).

NOTE:  If you have added to or modified your HOUDINI_PATH, you can place the scripts in houdini/scripts/tk directory and the houdini/scripts/macro directory respectively, then you would only have to type:  tk global.tk  You still have to modify the PATH variable in the global.tk script as described above.

For further ease of use, map the launching of this utility to a hotkey:  alias F1 "tk global.tk"

• Hit the help button for more instructions.
• All objects created will be prepended with "G_".
• Set the resolution of the lights.  Low resolutions like will result in fast rendering, but poor quality.  Go to about 256 to start, and up from there for better quality.
• Set the "Depth Map" paramater... near, mid or farthest.   This will require some experimentation to get right.  These settings use a different algorith to calculate shadow maps, and you should change this from default if you are getting artifacts.
• Click the "Create New Global Dome" button.  This will create a new dome to which your lights will be instanced, plus one master light and shaders.
• Position the dome in the scene so it is centered around the object you wish to render.
• Modify your dome object if you wish.  The "dome" object can be anything you want, as long as the last SOP is called "OUT."
• Change the in-line point SOP to get either randomly-coloured lights, constant coloured lights, or lights that get their colour from an image map referenced by the supplied COP network. 
• NOTE: If you are going to use a HDR (high dynamic range) image such as that produced by HDR Shop . Houdini will read in floating point images in the following formats: TIFF, Houdini5.pic or Houdini .rat. You can create floating point TIFF files using HDR Shop. Use COPs2, (the new compositor) to work with floating point images, the old one won't.
• If using an HDR image map as a base for creating lights, your best bet is to use the Lightgen plug-in by Jonathan Cohen which you can get at the HDR Shop home page. This will output a floating point tiff file in longitude map format that you can load directly into Houdini. Or you can create a new map that indicates where the lights should be placed. (The lightgen plugin available on the HDR Shop page will also output a Houdini-compatible .cmd script you can use to generate lights.)
• Load this floating point image into COPs2, then use the COPSII SOP provided by this utility in SOPs to apply the colours to your dome.
• Using group/delete SOPs, delete all the points that are below some brightness threshhold. 
• if(point("/obj/geo1/add", $PT,"Cd", 0) < .5 && point("/obj/geo1/add", $PT,"Cd", 1) < .5 && point("/obj/geo1/add", $PT,"Cd", 2) < .5, 1, 0)   (Where .5 is the minimum value you want a light attached to... remember, floating point images will contain values in excess of 1.) 
• You may still have too many points, so use a facet SOP to remove extras. Pipe the output of that to the OUT SOP.

• Click on the "Add Light to Dome" button to attach more lights to the dome object one at a time or click the "Populate Entire Dome" button to add all the lights at once.
• View through one of your lights and make sure you can see the objects you are rendering.  If you can't, adjust the near and and far clipping planes of the master light, (all other lights reference the master light).   It's probably a good idea to make the region encompassing the near and far params as tight as possible.
• Changing the values in either the master light, master shadow SHOP or master light SHOP will cause all other OBJs to update with the same values.
• Adjust the overall intensity of the light with the dimmer control in the master light, (G_light0).  Adjust shadow softness at the SHOP level.
• You can turn on or off contribution to specular or diffuse for all lights at once using the "Contr to Spec/Diff" buttons after the lights have been added.
  
• If you have made one test render, and only wish to change exposure, shadow softness, etc., then you can disable shadow map creation by clicking on the "Disable/Enable Shadow Map Creation" button. However, if you go to a different frame, the camera/lights are moving or the object deforming, you will of course have to re-create the shadow maps.
• Clicking the "Start Over" button will remove all OBJs, COPs and SHOPs prepended with "G_".
• You must use Vmantra to render your images.
• If you are using Houdini Apprentice, you will have to change the .pic extension to use the .picni extension for all shaders and lights. To do this, open a textport and type:
  opchange .pic .picni

Troubleshooting

• Fuzzy or inaccurate shadows
• Up the resolution of your lights.
• Make your dome smaller so shadow maps are more accurate... the dome should be only slightly larger than the scene.
• Change the "Depth Map" type to either closest, mid or farthest and see if it makes a difference.
• Take a look at one of the shadow maps created in the temp directory.  Can you see identifiable shapes?
• Shadow softness is turned up too high in the light SHOP.
• The volume that has to be considered when rendering the depth maps may be too high.  Change the near and far clipping planes of the lights so they just encompass the scene.
• Blocky looking shadows
• Change the shadow bias... wedge three tests: .005, .05, .5 and see if any of these improve the look. Tweak from there.
• Try changing the "Near/Mid/Far" depth map paramater.
  
• No shadows at all
• Look through one of your lights.  Can you see the object you are trying to render?  If not, change the far clipping plane until you can.
• Are there proper interfaces in all the SHOPs added by the macro?  If they don't have controls, (they are default, empty operators), then Houdini somehow can't find the necessary shaders.
• Are you using Vmantra, not old Mantra (omantra)?
  
• Script doesn't run.
• Turn on debug mode and copy and paste the commands there into a textport.  It will echo back any Houdini error messages.
  
• If you get a "no such file or directory" message in the shell, try:
• tk path_to_file/global.tk (where "path_to_file" is the actual path to your file!)
If you still get the same message, the file is not where you think it is.
• Script runs, but not everything is linked up correctly or not all the objects get added.
• There might be some funny line-breaks in the code downloaded.  Don't copy and paste text from your browser, save the files to disc directly.
• My scene seems to be lit by weirdly colored lights.
• Bypass the random_color SOP in the dome object.

Created with trans-shadow key light and one ambient	Image created with global lighting,  no ambient, no key	Image created with global lighting,  and one key light

Images by Sean Lewkiw

Robot images by Jim Berberov

Sean Lewkiw
http://www.lewkiw.com