SkGifDecoder Namespace Reference

Functions
SK_API bool	IsGif (const void *, size_t)
SK_API std::unique_ptr< SkCodec >	Decode (std::unique_ptr< SkStream >, SkCodec::Result *, SkCodecs::DecodeContext=nullptr)
SK_API std::unique_ptr< SkCodec >	Decode (sk_sp< SkData >, SkCodec::Result *, SkCodecs::DecodeContext=nullptr)
constexpr SkCodecs::Decoder	Decoder ()
std::unique_ptr< SkCodec >	MakeFromStream (std::unique_ptr< SkStream > stream, SkCodec::SelectionPolicy selectionPolicy, SkCodec::Result *result)

Function Documentation

Decode() [1/2]

std::unique_ptr< SkCodec > SkGifDecoder::Decode	(	sk_sp< SkData >	data,
		SkCodec::Result *	outResult,
		SkCodecs::DecodeContext	ctx = nullptr
	)

Definition at line 1096 of file SkWuffsCodec.cpp.

                                                           {
    if (!data) {
        if (outResult) {
            *outResult = SkCodec::kInvalidInput;
        }
        return nullptr;
    }
    return Decode(SkMemoryStream::Make(std::move(data)), outResult, ctx);
}

Decode() [2/2]

std::unique_ptr< SkCodec > SkGifDecoder::Decode	(	std::unique_ptr< SkStream >	stream,
		SkCodec::Result *	outResult,
		SkCodecs::DecodeContext	ctx = nullptr
	)

Attempts to decode the given bytes as a GIF.

If the bytes are not a GIF, returns nullptr.

DecodeContext is ignored

Definition at line 1082 of file SkWuffsCodec.cpp.

                                                           {
    SkCodec::Result resultStorage;
    if (!outResult) {
        outResult = &resultStorage;
    }
    auto policy = SkCodec::SelectionPolicy::kPreferStillImage;
    if (ctx) {
        policy = *static_cast<SkCodec::SelectionPolicy*>(ctx);
    }
    return MakeFromStream(std::move(stream), policy, outResult);
}

Decoder()

constexpr SkCodecs::Decoder SkGifDecoder::Decoder ( )

inlineconstexpr

Definition at line 38 of file SkGifDecoder.h.

                                           {
    return { "gif", IsGif, Decode };
}

IsGif()

bool SkGifDecoder::IsGif	(	const void *	buf,
		size_t	bytesRead
	)

Returns true if this data claims to be a GIF image.

Definition at line 977 of file SkWuffsCodec.cpp.

                                              {
    constexpr const char* gif_ptr = "GIF8";
    constexpr size_t      gif_len = 4;
    return (bytesRead >= gif_len) && (memcmp(buf, gif_ptr, gif_len) == 0);
}

MakeFromStream()

std::unique_ptr< SkCodec > SkGifDecoder::MakeFromStream	(	std::unique_ptr< SkStream >	stream,
		SkCodec::SelectionPolicy	selectionPolicy,
		SkCodec::Result *	result
	)

Definition at line 983 of file SkWuffsCodec.cpp.

                                                                        {
    SkASSERT(result);
    if (!stream) {
        *result = SkCodec::kInvalidInput;
        return nullptr;
    }
 
    bool canSeek = stream->hasPosition() && stream->hasLength();
 
    if (selectionPolicy != SkCodec::SelectionPolicy::kPreferStillImage) {
        // Some clients (e.g. Android) need to be able to seek the stream, but may
        // not provide a seekable stream. Copy the stream to one that can seek.
        if (!canSeek) {
            auto data = SkCopyStreamToData(stream.get());
            stream = std::make_unique<SkMemoryStream>(std::move(data));
            canSeek = true;
        }
    }
 
    uint8_t               buffer[SK_WUFFS_CODEC_BUFFER_SIZE];
    wuffs_base__io_buffer iobuf =
        wuffs_base__make_io_buffer(wuffs_base__make_slice_u8(buffer, SK_WUFFS_CODEC_BUFFER_SIZE),
                                   wuffs_base__empty_io_buffer_meta());
    wuffs_base__image_config imgcfg = wuffs_base__null_image_config();
 
    // Wuffs is primarily a C library, not a C++ one. Furthermore, outside of
    // the wuffs_base__etc types, the sizeof a file format specific type like
    // GIF's wuffs_gif__decoder can vary between Wuffs versions. If p is of
    // type wuffs_gif__decoder*, then the supported API treats p as a pointer
    // to an opaque type: a private implementation detail. The API is always
    // "set_foo(p, etc)" and not "p->foo = etc".
    //
    // See https://en.wikipedia.org/wiki/Opaque_pointer#C
    //
    // Thus, we don't use C++'s new operator (which requires knowing the sizeof
    // the struct at compile time). Instead, we use sk_malloc_canfail, with
    // sizeof__wuffs_gif__decoder returning the appropriate value for the
    // (statically or dynamically) linked version of the Wuffs library.
    //
    // As a C (not C++) library, none of the Wuffs types have constructors or
    // destructors.
    //
    // In RAII style, we can still use std::unique_ptr with these pointers, but
    // we pair the pointer with sk_free instead of C++'s delete.
    void* decoder_raw = sk_malloc_canfail(sizeof__wuffs_gif__decoder());
    if (!decoder_raw) {
        *result = SkCodec::kInternalError;
        return nullptr;
    }
    std::unique_ptr<wuffs_gif__decoder, decltype(&sk_free)> decoder(
        reinterpret_cast<wuffs_gif__decoder*>(decoder_raw), &sk_free);
 
    SkCodec::Result reset_result =
        reset_and_decode_image_config(decoder.get(), &imgcfg, &iobuf, stream.get());
    if (reset_result != SkCodec::kSuccess) {
        *result = reset_result;
        return nullptr;
    }
 
    uint32_t width = imgcfg.pixcfg.width();
    uint32_t height = imgcfg.pixcfg.height();
    if ((width == 0) || (width > INT_MAX) || (height == 0) || (height > INT_MAX)) {
        *result = SkCodec::kInvalidInput;
        return nullptr;
    }
 
    uint64_t workbuf_len = decoder->workbuf_len().max_incl;
    void*    workbuf_ptr_raw = nullptr;
    if (workbuf_len) {
        workbuf_ptr_raw = workbuf_len <= SIZE_MAX ? sk_malloc_canfail(workbuf_len) : nullptr;
        if (!workbuf_ptr_raw) {
            *result = SkCodec::kInternalError;
            return nullptr;
        }
    }
    std::unique_ptr<uint8_t, decltype(&sk_free)> workbuf_ptr(
        reinterpret_cast<uint8_t*>(workbuf_ptr_raw), &sk_free);
 
    SkEncodedInfo::Color color =
        (imgcfg.pixcfg.pixel_format().repr == WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL)
            ? SkEncodedInfo::kBGRA_Color
            : SkEncodedInfo::kRGBA_Color;
 
    // In Skia's API, the alpha we calculate here and return is only for the
    // first frame.
    SkEncodedInfo::Alpha alpha = imgcfg.first_frame_is_opaque() ? SkEncodedInfo::kOpaque_Alpha
                                                                : SkEncodedInfo::kBinary_Alpha;
 
    SkEncodedInfo encodedInfo = SkEncodedInfo::Make(width, height, color, alpha, 8);
 
    *result = SkCodec::kSuccess;
    return std::unique_ptr<SkCodec>(new SkWuffsCodec(std::move(encodedInfo), std::move(stream),
                                                     canSeek,
                                                     std::move(decoder), std::move(workbuf_ptr),
                                                     workbuf_len, imgcfg, iobuf));
}