Importing Tilt Brush files into Houdini

Although Tilt Brush exports FBX files with the brush stroke geometry sometimes it can be useful to get the data in the .tilt file itself. The .tilt file contains the controller positions, orientations, trigger pressure and timestamps that Tilt Brush then creates stroke geometry from. In my case I particularly wanted the timestamps, as it makes Tilt Brush a simple 6-dof capture solution.

Houdini’s python integration and the Tilt Brush Toolkit make this fairly straightforward.

First you need to get the Tilt Brush Toolkit. You can either clone the git repo or download it from github, and you need to add the Python subdirectory to your PYTHONPATH environment variable.

Now you can use a Python SOP to process the .tilt file and generate geometry. Here is the code I use:

# This code is called when instances of this SOP cook.
node = hou.pwd()
geo = node.geometry()

# Add code to modify the contents of geo.
filename = node.evalParm('filename')

from tiltbrush.tilt import Tilt
tilt = Tilt(filename)

if tilt.sketch.filename:
  filenameAttrib = geo.addAttrib(hou.attribType.Global, "filename", "")
  geo.setGlobalAttribValue(filenameAttrib, tilt.sketch.filename)

brushAttrib = geo.addAttrib(hou.attribType.Prim, "brush", 0)
colorAttrib = geo.addAttrib(hou.attribType.Prim, "Cd", (0.0, 0.0, 0.0, 0.0))
sizeAttrib = geo.addAttrib(hou.attribType.Prim, "size", 0.0)
  
time = geo.addAttrib(hou.attribType.Point, "time", 0.0)
pressure = geo.addAttrib(hou.attribType.Point, "pressure", 0.0)
orientation = geo.addAttrib(hou.attribType.Point, "orient", (0.0, 0.0, 0.0, 1.0))
poly = geo.createPolygon()

for stroke in tilt.sketch.strokes:
  poly = geo.createPolygon()
  poly.setIsClosed(False)
  for cp in stroke.controlpoints:
    point = geo.createPoint()
    point.setPosition([i / 10.0 for i in cp.position])
    point.setAttribValue(orientation, cp.orientation)
    point.setAttribValue(time, cp.extension[1] / 1000.0)
    point.setAttribValue(pressure, cp.extension[0])
    poly.addVertex(point)
  poly.setAttribValue(brushAttrib, stroke.brush_idx)
  poly.setAttribValue(colorAttrib, stroke.brush_color)
  poly.setAttribValue(sizeAttrib, stroke.brush_size)

Now you have each stroke as a curve primitive, with point attributes for position, orientation, pressure and time. The orientation is a quaternion but you can convert that into a more useful normal and up vector with an Attribute Wrangle SOP:

v@N = qrotate(@orient, {0, 0, 1 });
v@up = qrotate(@orient, {0, 1, 0});

Sweeping a line SOP along the curves will give you an approximation of the actual stroke geometry.

No Siggraph calendars for 2016

If you’re looking for Siggraph calendars for 2016 I’m afraid I haven’t had time to put them together this year.  Sorry!

Siggraph 2015 Google calendars

To add to your google calendars, cut and paste the blah@group.calendar.google.com address for the calendar into the “Add a friend’s calendar” box in the “Other calendars” list on the left side of the google calendar page.

Let me know if you see any errors.  The schedule can change, and I endeavor to update these when I see changes.

• Courses
  8l06oq1i0r1msr2hegqjgaji0o@group.calendar.google.com
    
• Papers
  899d9osiuvb9n3ke98ikvvk2r0@group.calendar.google.com
    
  (And links to the papers)
• Talks (including panels)
  55g0chci5ifmsp8crcnor3ubus@group.calendar.google.com
    
• Special events
  re6h03maiuhmlimhunl0m9p0fo@group.calendar.google.com
    
• Birds of a feather
  vaav23f89q12t1im1uoakkf1ec@group.calendar.google.com
    

Siggraph 2013 google calendars

To add to your google calendars, cut and paste the blah@group.calendar.google.com address for the calendar into the “Add a friend’s calendar” box in the “Other calendars” list on the left side of the google calendar page.

Let me know if you see any errors.  The schedule can change, and I endeavor to update these when I see changes.  Parties: I don’t get invited to them anymore as I’m nobody’s customer, so you’re on your own 😉

• Courses
  7dt1m4p5b5csqgi3m8lorogv9c@group.calendar.google.com
    
  
• Papers
  k0eohhf6ge1q4jjdedm165157s@group.calendar.google.com
    
• Talks (including panels)
  u8oideatih0joc794rur893leg@group.calendar.google.com
    
• Special events
  j9g3t3f12kmqlg2b3r96a87om0@group.calendar.google.com
    
• Birds of a feather
  880kqdmf86cd68rsvcoohp6ar8@group.calendar.google.com
    

And maybe I’ll see you all in Anaheim for beers!

Update: See this great set of links to conference content.

Comparing 160-bit hash values with SSE

I’m writing this up as it’s one of those things I was trying to do and thought I’d just be able to crib how to do it from the Internet yet a good amount of googleing turned up nothing.  So here it it for anyone else looking for the same thing.

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