Implementation of ImageFactory in image library

image.cc

#include "image.h"

#include <android/imagedecoder.h>

static std::unique_ptr<Image> ImageFactory::FromFd(int fd) {
    // First create decoder from fd.
    AImageDecoder* decoder;
    int result = AImageDecoder_createFromFd(fd, &decoder);
    if (result != ANDROID_IMAGE_DECODER_SUCCESS) {
        // More info: https://developer.android.com/ndk/reference/group/image-decoder#aimagedecoder_createfromfd
        // Not a good idea to opaquely consume the error, it'd be a good idea to
        // use StatusOr from abseil package: https://abseil.io/
        return nullptr;
    }

    // Lambda for cleaning up the decoder when exiting.
    auto decoder_cleanup = [&decoder] () {
        AImageDecoder_delete(decoder);
    };

    const AImageDecoderHeaderInfo* header_info = AImageDecoder_getHeaderInfo(decoder);
    int bitmap_format = AImageDecoderHeaderInfo_getAndroidBitmapFormat(header_info);
    // This is just for example. I don't want to handle other cases in this
    // example, but that should be easy enough to do.
    if (bitmap_format != ANDROID_BITMAP_FORMAT_RGBA_8888) {
        decoder_cleanup();
        return nullptr;
    }
    constexpr int kChannels = 4;
    int width = AImageDecoderHeaderInfo_getWidth(header_info);
    int height = AImageDecoderHeaderInfo_getHeight(header_info);

    size_t stride = AImageDecoder_getMinimumStride(decoder);
    std::unique_ptr<Image> image_ptr = std::make_unique<Image>(
        width, height, kChannels, stride);

    size_t size = width * height * kChannels;
    int decode_result = AImageDecoder_decodeImage(
        decoder, image_ptr->pixels(), stride, size);
    if (decode_result != ANDROID_IMAGE_DECODER_SUCCESS) {
        decoder_cleanup();
        return nullptr;
    }

    decoder_cleanup();
    return image_ptr;
}