Issue Retrieving Alpha Layer from a Layer in MultipassBitmap

T1001

Hello,

I'm experiencing an issue with the Cinema 4D SDK when working with layers and alpha layers in MultipassBitmap objects. Specifically, after adding an alpha layer to a layer within a MultipassBitmap, I'm unable to retrieve it using the available functions.

Here's a simple code snippet demonstrating the problem:

// Allocate a MultipassBitmap
AutoFree<MultipassBitmap> bmp = MultipassBitmap::Alloc(800, 600, COLORMODE::ARGBf);
if (!bmp) return;

// Set parameters for the MultipassBitmap
bmp->SetParameter(MPBTYPE_NAME, "bitmap");
bmp->SetParameter(MPBTYPE_SAVE, TRUE);
bmp->SetParameter(MPBTYPE_SHOW, TRUE);

// Get the first layer of the MultipassBitmap
// The first layer is automatically created at the [bmp] allocation time
MultipassBitmap* layer = bmp->GetLayerNum(0);
if (!layer) return;

// Set parameters for the layer
layer->SetParameter(MPBTYPE_NAME, "layer0");
layer->SetParameter(MPBTYPE_SAVE, TRUE);
layer->SetParameter(MPBTYPE_SHOW, TRUE);

// Get the initial alpha layer count
Int32 cn = layer->GetAlphaLayerCount(); // Returns 0 as expected

// Add an alpha channel to the layer
MultipassBitmap* alpha = layer->AddAlpha(nullptr, COLORMODE::GRAYf);
if (!alpha) return;

// Set parameters for the alpha layer
alpha->SetParameter(MPBTYPE_NAME, "alpha0");
alpha->SetParameter(MPBTYPE_SAVE, TRUE);
alpha->SetParameter(MPBTYPE_SHOW, TRUE);

// Get the updated alpha layer count
cn = layer->GetAlphaLayerCount(); // Now returns 1, which is correct

// Attempt to get the alpha layer
MultipassBitmap* tmpAlpha = layer->GetAlphaLayerNum(0); // Returns null pointer unexpectedly

if (!tmpAlpha)
{
    // tmpAlpha is null, even though we just added an alpha layer
    // This is unexpected behavior
}
else
{
    // Proceed with tmpAlpha
}

Issue:

After adding an alpha layer to bitmap layer, layer->GetAlphaLayerCount() correctly returns 1.
However, when I call layer->GetAlphaLayerNum(0), it returns a null pointer.
It seems that GetAlphaLayerNum() does not retrieve the alpha layer from within the layer, or perhaps I'm using it incorrectly.

Questions:

How can I retrieve the alpha layer that I've added to a layer within a MultipassBitmap?
Is there a specific function to access alpha layers within layers of a MultipassBitmap?
Am I missing any steps or using the functions incorrectly in this context?

Additional Information

I'm using Cinema 4D SDK version [2024].
The AddAlpha method seems to work correctly, as the layer count increases after calling it.
The documentation isn't clear on how to retrieve alpha layers from layers within a MultipassBitmap.

Any insights or solutions would be greatly appreciated!

Thank you in advance for your assistance.