Transparency Issue with MultipassBitmap in GeUserArea

[T1001]

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!