Header file for our image library

image.h

#include <memory>

#include <assert.h>
#include <android/imagedecoder.h>

// Data class for ARGB image (owns the memory associated with the image).
// 
// Note for readers: Current implementation only allows read operations but can
// be extended to support write operations by overloading `()=` operator.
class Image {
public:
    friend class ImageFactory;

    // Creating the image will allocate corresponding memory.
    Image(int width, int height, int channels, int stride) :
        width_(width),
        height_(height),
        channels_(channels),
        stride_(stride) {
        // Restricting the image to u8 datatype for this example.
        this->pixels_ = std::make_unique<uint8_t[]>(width * height * channels);
    }

    // Getter: Get pixel value of image at (x, y, c).
    uint8_t operator()(int x, int y, int c) const {
        // TODO: add assertions? (at your own risk).
        uint8_t* pixel = this->pixels_.get() + (y * stride_ + x * 4 + c);
        return *pixel;
    }

    int width() const { return this->width_; }
    int height() const { return this->height_; }
    int channels() const { return this->channels_; }
    int stride() const { return this->stride_; }

private:
    void* pixels() {
        return static_cast<void*>(this->pixels_.get());
    }

    std::unique_ptr<uint8_t[]> pixels_;
    const int width_;
    const int height_;
    const int channels_;
    const int stride_;
};


// Factory class for creating 'Image'.
class ImageFactory {
public:

    // Creates an instance of 'Image' from the file descriptor 'fd'.
    //
    // Will return 'nullptr' if it's unable to decode image successfully.
    //
    // Note for readers: If you can add abseil package to your code base, I
    // recommend changing this API to return
    // 'absl::StatusOr<std::unique_ptr<Image>>' instead. This will lead to much
    // cleaner API and improved error handling.
    static std::unique_ptr<Image> FromFd(int fd);
}