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.

Hello,

I'm encountering an issue with transparency when drawing a MultipassBitmap over a background in a custom GeUserArea. The transparent areas appear black unless I save the bitmap before drawing it.

Code Snippet:

// ARGBfbuf is a Float32 image buffer with ARGB data
// w = width, h = height

auto Bmp = MultipassBitmap::Alloc(w, h, COLORMODE::ARGBf);
if (!Bmp)
{
    // Handle allocation failure
    return;
}
Bmp->SetColorProfile(ColorProfile::GetDefaultSRGB());

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

// Add root alpha channel to the MultipassBitmap
auto rootAlpha = Bmp->AddAlpha(nullptr, COLORMODE::GRAYf);
if (!rootAlpha)
{
    // Handle error
    return;
}
// Set parameters for the root alpha
rootAlpha->SetParameter(MPBTYPE_NAME, "rootAlpha");
rootAlpha->SetParameter(MPBTYPE_SAVE, FALSE);
rootAlpha->SetParameter(MPBTYPE_SHOW, TRUE);

auto layer = Bmp->GetLayerNum(0);
if (!layer)
{
    // Handle error
    return;
}

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

// Add alpha channel to the layer
auto alpha = layer->AddAlpha(nullptr, COLORMODE::GRAYf);
if (!alpha)
{
    // Handle error
    return;
}

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

for (Int32 y = 0; y < h; ++y)
{
    Float32* ptr = ARGBfbuf + (y * w * 4);

    // Copy image line to the layer
    layer->SetPixelCnt(0, y, w, reinterpret_cast<UChar*>(ptr), COLORBYTES_ARGBf, COLORMODE::ARGBf, PIXELCNT_0);

    // Copy alpha line to the alpha layer
    alpha->SetPixelCnt(0, y, w, reinterpret_cast<UChar*>(ptr), COLORBYTES_ARGBf, COLORMODE::GRAYf, PIXELCNT_0);
}

// In the GeUserArea render function:

// Draw background image
DrawBitmap(Background, 0, 0, GetWidth(), GetHeight(),
           0, 0, Background->GetBw(), Background->GetBh(),
           BMP_NORMAL);

// Draw bitmap with transparency
DrawBitmap(Bmp, 0, 0, GetWidth(), GetHeight(),
           0, 0, Bmp->GetBw(), Bmp->GetBh(),
           BMP_NORMAL | BMP_APPLY_COLORPROFILE | BMP_TRANSPARENTALPHA);

Issue:

Transparent areas (where alpha = 0.0f) appear black instead of showing the background.
Workaround:

Saving the bitmap before drawing fixes the issue:

// Save and delete the file
String path = GeGetStartupWritePath() + "/temp.tga";
Bmp->Save(path, FILTER_TGA, nullptr, SAVEBIT_ALPHA);
GeFKill(path);

// Then draw as before
DrawBitmap(Bmp, ...);

Additional Information:

• I tried using BaseBitmap instead of MultipassBitmap, but BaseBitmap does not support floating-point color modes (COLORMODE::ARGBf), which I need for my application.
• Even when using BaseBitmap and saving the image, the transparency issue persists.

Questions:

1. Why does saving the MultipassBitmap make the transparency work?
2. How can I achieve proper transparency without saving the bitmap?
3. Is there a way to handle floating-point ARGB data with transparency using BaseBitmap, or is MultipassBitmap the only option?
4. Do the SetParameter calls on the Bmp, Layer, root alpha, and alpha layers have any effect on this issue, and am I using them correctly?

Any insights or solutions would be greatly appreciated!