How to detect Global Illumination state via Python API?

mfersaoui

Hello,

I'm developing a plugin and need to programmatically detect whether Global Illumination is enabled in the current render settings.

I've tried several approaches but none seem to work reliably. Some constants like c4d.RDATA_GI or c4d.RDATA_GLOBILLUM_ENABLE don't appear to exist, and accessing VideoPost parameters returns unexpected values.

My question is: what is the correct and recommended way to detect if Global Illumination is currently enabled? Is there a specific constant, parameter ID, or API method I should be using?

Any guidance would be greatly appreciated!

Thank you.

ferdinand

Hey @mfersaoui,

Thank you for reaching out to us. The question is a bit ambiguous. What it entails when 'Global Illumination is enabled' (or not), differs from render engine to render engine. There is neither an abstracted switch to toggle GI in all render engines, nor a flag which would signal of GI is enabled or not.

So, the first thing you would have to do, is read RDATA_RENDERENGINE and then branch of based on that. For the standard renderer, you would then check if the GI post effect is loaded and enabled. For Redshift you would get the RS post effect and then check there if has GI enabled.

You can find the post effect symbols here: VideoPost Types

Cheers,
Ferdinand

Some example code for searching the post effects in some render data.

# Get the active render data of the document.
renderData: c4d.documents.RenderData = doc.GetActiveRenderData()

# Set the active render engine to Redshift.
renderData[c4d.RDATA_RENDERENGINE] = c4d.VPrsrenderer

# Iterate over all video post effects and remove any effect not compatible with the Redshift 
# render engine and finally make sure the Redshift video post effect itself is present. We do 
# not remove the effects in place in the loop, as that would mess up the iteration because nodes
# effectively work as a linked list.
removeEffects: list[c4d.documents.BaseVideoPost] = []
foundRedshiftEffect: bool = False
for effect in mxutils.IterateTree(renderData.GetFirstVideoPost(), True):
    # This is the Redshift video post effect.
    if effect.GetType() == c4d.VPrsrenderer:
        foundRedshiftEffect = True
        continue
    # This is some effect not compatible with Redshift.
    elif not effect.RenderEngineCheck(c4d.VPrsrenderer):
        removeEffects.append(effect)

# Remove all the video post effects we marked for removal.
for effect in removeEffects:
    effect.Remove()

# And add the Redshift video post effect if it was not found yet. Note that there is no hard
# guarantee that a render engine uses the same ID for its video post effect as the render 
# engine ID (VPrsrenderer in this case). But it is a very common convention, check with your
# render engine vendor for details.
if not foundRedshiftEffect:
    redshiftEffect: c4d.documents.BaseVideoPost = mxutils.CheckType(
        c4d.documents.BaseVideoPost(c4d.VPrsrenderer))
    renderData.InsertVideoPost(redshiftEffect)

mfersaoui

@ferdinand
Hey @ferdinand,

Thank you again for the clarification — checking the Video Post list was indeed the right direction.

Just to share what worked on my side (Standard/Physical renderer), I check the presence of the GI Video Post and use its BIT_VPDISABLED state to determine whether it’s enabled.

Here’s the small helper function I’m using:

def is_gi_active(doc):
    rd = doc.GetActiveRenderData()
    if not rd:
        return False

    # GI Video Post IDs (verified on C4D 2024)
    GI_IDS = [
        1021096,    # Global Illumination Video Post (C4D 2024)
        300001038,  # VPglobalillumination (older versions)
    ]

    vp = rd.GetFirstVideoPost()
    while vp:
        if vp.GetType() in GI_IDS:
            return not vp.GetBit(c4d.BIT_VPDISABLED)
        vp = vp.GetNext()

    return False

Thanks again for your help.

Best regards,
Mustapha