Arnold render settings are stored as a Video Post node. To set up the render settings programmatically you have to create a new video post instance and add it to the active render data.
The CINEMA 4D python SDK has a limitation and does not allow creating video post nodes. As a workaround C4DtoA offers a command to create the Arnold video post. The command id is 1039333.
Here's a simple example which returns the active Arnold render settings video post or creates and activates a new one if it does not exist yet:
ARNOLD_RENDERER = 1029988
ARNOLD_RENDERER_COMMAND = 1039333
def GetArnoldRenderSettings():
rdata = doc.GetActiveRenderData()
# find the active Arnold render settings
videopost = rdata.GetFirstVideoPost()
while videopost:
if videopost.GetType() == ARNOLD_RENDERER:
return videopost;
videopost = videopost.GetNext()
# create a new one when does not exist
if videopost is None:
c4d.CallCommand(ARNOLD_RENDERER_COMMAND)
videopost = rdata.GetFirstVideoPost()
while videopost:
if videopost.GetType() == ARNOLD_RENDERER:
return videopost;
videopost = videopost.GetNext()
return None
If you have the video post data you can change any render settings as you would do normally in other nodes:
# find the Arnold video post data
arnoldRenderSettings = GetArnoldRenderSettings()
if arnoldRenderSettings is None:
raise BaseException("Failed to find Arnold render settings")
# setup the settings
# see C4DtoA/res/description/ainode_options.res for the available parameter ids
# for example to change the Camera AA samples
arnoldRenderSettings[c4d.C4DAIP_OPTIONS_AA_SAMPLES] = 5
# update the scene
c4d.EventAdd()