parseGifInfo()

GifInfo fl::Gif::parseGifInfo ( fl::span< const fl::u8 > data, fl::string * error_message = nullptr )

static

Definition at line 29 of file gif.cpp.hpp.

                                                                                       {
    GifInfo info;
 
    // Validate input data
    if (data.empty()) {
        if (error_message) {
            *error_message = "Empty GIF data";
        }
        return info; // returns invalid info
    }
 
    // Minimum size check - GIF must have at least the header (6 bytes) + some content
    if (data.size() < 13) { // GIF header (6) + screen descriptor (7)
        if (error_message) {
            *error_message = "GIF data too small";
        }
        return info;
    }
 
    // Check GIF signature
    if (data[0] != 'G' || data[1] != 'I' || data[2] != 'F') {
        if (error_message) {
            *error_message = "Invalid GIF signature";
        }
        return info;
    }
 
    // Check version (87a or 89a)
    if (!((data[3] == '8' && data[4] == '7' && data[5] == 'a') ||
          (data[3] == '8' && data[4] == '9' && data[5] == 'a'))) {
        if (error_message) {
            *error_message = "Unsupported GIF version";
        }
        return info;
    }
 
    // Parse logical screen descriptor (starts at byte 6)
    // Width (2 bytes, little endian) at offset 6-7
    // Height (2 bytes, little endian) at offset 8-9
    fl::u16 width = data[6] | (data[7] << 8);
    fl::u16 height = data[8] | (data[9] << 8);
 
    if (width == 0 || height == 0) {
        if (error_message) {
            *error_message = "Invalid GIF dimensions";
        }
        return info;
    }
 
    // For a more complete parsing, we would need to create a temporary decoder
    // and let libnsgif parse the structure. Let's use the existing decoder briefly.
    auto decoder = fl::make_shared<fl::third_party::SoftwareGifDecoder>(PixelFormat::RGB888);
    auto stream = fl::make_shared<fl::memorybuf>(data.size());
    stream->write(data);
 
    if (decoder->begin(stream)) {
        // Now we can extract more detailed info using the decoder's methods
        info.width = decoder->getWidth();
        info.height = decoder->getHeight();
        info.frameCount = decoder->getFrameCount();
        info.loopCount = decoder->getLoopCount();
        info.isAnimated = decoder->isAnimated();
        info.bitsPerPixel = 8; // GIF is always 8 bits per pixel
        info.isValid = true;
 
        decoder->end();
    } else {
        // Fallback to basic header parsing if decoder fails
        info.width = width;
        info.height = height;
        info.frameCount = 1; // Assume static image
        info.loopCount = 0;
        info.isAnimated = false;
        info.bitsPerPixel = 8;
        info.isValid = true;
 
        if (error_message) {
            *error_message = ""; // Clear any error message for fallback case
        }
    }
 
    return info;
}

References fl::GifInfo::bitsPerPixel, fl::FL_NO_EXCEPT, fl::GifInfo::frameCount, fl::GifInfo::height, fl::height, fl::GifInfo::isAnimated, fl::GifInfo::isValid, fl::GifInfo::loopCount, fl::adl_barrier::make_shared(), fl::RGB888, fl::GifInfo::width, and fl::width.

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