ID2D1Bitmap 到 Wic 与 Alpha 但不是 PNG

Question

我正在保存 Direct2D 设备上下文的位图。我的目标是保持 32 位（带 alpha 的 RGB）但没有 PNG，我宁愿有 32 位位图。

我正在使用这个功能：

HRESULT SaveBitmapToStream(
    _In_ CComPtr<ID2D1Bitmap1> d2dBitmap,
    _In_ CComPtr<IWICImagingFactory2> wicFactory2,
    _In_ CComPtr<ID2D1DeviceContext> d2dContext,
    _In_ REFGUID wicFormat,
    _In_ IStream* stream
)
{
    // Create and initialize WIC Bitmap Encoder.
    CComPtr<IWICBitmapEncoder> wicBitmapEncoder;
    auto hr =
        wicFactory2->CreateEncoder(
            wicFormat,
            nullptr,    // No preferred codec vendor.
            &wicBitmapEncoder
        );

    hr =
        wicBitmapEncoder->Initialize(
            stream,
            WICBitmapEncoderNoCache
        );

// Create and initialize WIC Frame Encoder.
    CComPtr<IWICBitmapFrameEncode> wicFrameEncode;
    hr =
        wicBitmapEncoder->CreateNewFrame(
            &wicFrameEncode,
            nullptr     // No encoder options.
        );

    if (FAILED(hr))
        return hr;
    hr = 
        wicFrameEncode->Initialize(nullptr);
    if (FAILED(hr))
        return hr;

// Retrieve D2D Device.
    CComPtr<ID2D1Device> d2dDevice;
    if (!d2dContext)
        return E_FAIL;
    d2dContext->GetDevice(&d2dDevice);

    // Create IWICImageEncoder.
    CComPtr<IWICImageEncoder> imageEncoder;
    hr = 
        wicFactory2->CreateImageEncoder(
            d2dDevice,
            &imageEncoder
        );
    if (FAILED(hr))
        return hr;

    hr =        
        imageEncoder->WriteFrame(
            d2dBitmap,  wicFrameEncode,
            nullptr     // Use default WICImageParameter options.
        );
    if (FAILED(hr))
        return hr;

    hr = wicFrameEncode->Commit();

    if (FAILED(hr))
        return hr;

    hr = wicBitmapEncoder->Commit();

    if (FAILED(hr))
        return hr;
// Flush all memory buffers to the next-level storage object.
    hr =
        stream->Commit(STGC_DEFAULT);

    return hr;

}

问题是，当我传递 GUID_ContainerFormatBmp 时，生成的位图没有 alpha。我必须放 GUID_ContainerFormatPng，但这会压缩我不想要的图像，这是用于视频渲染，我不想进行任何压缩。

有没有办法以 32 位格式而不是压缩格式获取 Direct2D 上下文的捕获？

Answer 1

native BMP codec 支持属性、EnableV5Header32bppBGRA 类型 VT_BOOL:

Specifies whether to allow encoding data in the GUID_WICPixelFormat32bppBGRA pixel format. If this option is set to VARIANT_TRUE, the BMP will be written out with a BITMAPV5HEADER header. The default value is VARIANT_FALSE.

Note for 16-bit and 32-bit Windows BMP files, the BMP codec ignores any alpha channel, as many legacy image files contain invalid data in this extra channel. Starting with Windows 8, 32-bit Windows BMP files written using the BITMAPV5HEADER with valid alpha channel content are read as WICPixelFormat32bppBGRA

ID2D1Bitmap 到 Wic 与 Alpha 但不是 PNG

ID2D1Bitmap to Wic with Alpha but not PNG

c++

winapi

direct2d