Houdini to Blender camera animation exporter

houdini_to_blender.py

# Houdini to Blender camera exporter thingy
# h@howiem.net / 22 Aug 2019
# 
# v1.0: hacky but seemingly working
#
# Pop this into a toolbar button's script window in Houdini
# Select a camera (or a camera switcher) and press the button
#
# A newly generated python script is now on the clipboard.
#
# Open Blender (tested w 2.79), ensure the Cycles Render mode is
# selected. (This is necessary for DoF / focus distance stuff to
# import correctly - nothing to stop you changing to a different
# renderer after the import though)
#
# In a text window, hit New and then Ctrl-V to paste the script in
#
# Rename the text block so it has ".py" on the end of its name
# Hit the Execute Script button
#
# A camera will be created and keyframes created. Should match the 
# camera from the Houdini scene perfectly.
#
# Notes:
#   - you'll need to set up the other parts of the scene, frame rate
#     and range, resolution etc.
#
#
# Todo:
#   - error checking
#   - perhaps create separate cams when a switcher is in use?

import hou

# convenience degree-to-radians factor
dtr = 3.141592654 / 180.0

theNodes = hou.selectedNodes()

h = theNodes[0]

startFrame = int(hou.playbar.playbackRange()[0])
endFrame = int(hou.playbar.playbackRange()[1])

# scale = 100.0 -oops - not implemented in this version

camNode = h
if h.type().name() == 'switcher':
    camNode = h.inputs()[h.parm("camswitch").evalAsIntAtFrame(startFrame)]

# spew out all the headery stuff first

myOutputString =                  "# script created by h's Houdini to Blender script\n\n"
myOutputString = myOutputString + "import bpy\n\n"
myOutputString = myOutputString + "# create a camera and camobject\n"
myOutputString = myOutputString + "camdata = bpy.data.cameras.new(\"theCamData\")\n"
myOutputString = myOutputString + "camobj = bpy.data.objects.new(\"theCamObj\", camdata)\n\n"

myOutputString = myOutputString + "# link into scene and make active\n"
myOutputString = myOutputString + "bpy.context.scene.objects.link(camobj)\n"
myOutputString = myOutputString + "bpy.context.scene.camera = camobj\n\n"

myOutputString = myOutputString + "bpy.data.scenes[0].update()\n\n"

myOutputString = myOutputString + "# set up camera stuff\n"
myOutputString = myOutputString + "camdata.sensor_width = " + str(camNode.parm("aperture").evalAsFloatAtFrame(startFrame)) + "\n"
myOutputString = myOutputString + "camdata.cycles.aperture_type = 'FSTOP'\n\n"

myOutputString = myOutputString + "# create some animation data for the cam (lens stuff) and the object (loc / rot)\n"
myOutputString = myOutputString + "camobj.animation_data_create()\n"
myOutputString = myOutputString + "camdata.animation_data_create()\n"
myOutputString = myOutputString + "camobj.animation_data.action = bpy.data.actions.new(name=\"camObjAction\")\n"
myOutputString = myOutputString + "camdata.animation_data.action = bpy.data.actions.new(name=\"camDataAction\")\n\n"

myOutputString = myOutputString + "################ ANIMATION DATA \n\n\n"


##############################################
#
# now do the frame by frame stuff
#

for theFrame in range (startFrame,endFrame+1):
    
    # get the info we need for this frame
    
    x = h.worldTransformAtTime(hou.frameToTime(theFrame))
    rotates = x.extractRotates('srt','xyz',hou.Vector3())
    translates = x.extractTranslates('srt')
    
    # camera-specific data gets confused by switcher objects, so find
    # the real camera object first    
    camNode = h
    if h.type().name() == 'switcher':
        camNode = h.inputs()[h.parm("camswitch").evalAsIntAtFrame(theFrame)]

    focallength = camNode.parm("focal").evalAsFloatAtFrame(theFrame)
    focusdistance = camNode.parm("focus").evalAsFloatAtFrame(theFrame)
    fstop = camNode.parm("fstop").evalAsFloatAtFrame(theFrame)
    
    ##############################
    #
    #  Apply the values
    #
    
    myOutputString = myOutputString + "camobj.location = (" + str(translates[0]) + "," + str(-translates[2]) + "," + str(translates[1]) + ")\n"
    myOutputString = myOutputString + "camobj.rotation_euler = (" + str(dtr*(90+rotates[0])) + "," + str(rotates[2]*dtr) + "," + str(rotates[1]*dtr) + ")\n"
    
    myOutputString = myOutputString + "camdata.lens = " + str(focallength) + "\n"
    myOutputString = myOutputString + "camdata.dof_distance = " + str(focusdistance) + "\n"
    myOutputString = myOutputString + "camdata.cycles.aperture_fstop = " + str(fstop) + "\n"

        
    ##############################
    #
    #  Set the keyframes
    #
    
    frameString = str(theFrame)
    
    myOutputString = myOutputString + "camobj.keyframe_insert(data_path=\"location\", index = -1, frame = " + frameString + ")\n"
    myOutputString = myOutputString + "camobj.keyframe_insert(data_path=\"rotation_euler\", index = -1, frame = " + frameString + ")\n"

    myOutputString = myOutputString + "camdata.keyframe_insert(data_path=\"lens\", index = -1, frame = " + frameString + ")\n"
    myOutputString = myOutputString + "camdata.keyframe_insert(data_path=\"dof_distance\", index = -1, frame = " + frameString + ")\n"
    myOutputString = myOutputString + "camdata.keyframe_insert(data_path=\"cycles.aperture_fstop\", index = -1, frame = " + frameString + ")\n"

    
myOutputString = myOutputString + "\n\n#### End of Data. Yay!\n"


hou.ui.copyTextToClipboard(myOutputString)