class hresult_exception : public std::exception {
	HRESULT hr;

public:
	hresult_exception(HRESULT hr_) : hr(hr_) {}
};

struct hresult_thrower {
	hresult_thrower& operator<<(HRESULT hr) {
		if (hr != S_OK)
			throw hresult_exception(hr);

		return *this;
	}
};

void png_encoder::save_png(std::wstring const &filename, image const &image) {
	hresult_thrower th;

	com_ptr<IWICStream> stream;
	factory->CreateStream(stream.inject());
	th << stream->InitializeFromFilename(filename.c_str(), GENERIC_WRITE);

	com_ptr<IWICBitmapEncoder> encoder;
	th << factory->CreateEncoder(GUID_ContainerFormatPng, 0, encoder.inject());
	th << encoder->Initialize(stream.get(), WICBitmapEncoderNoCache);

	com_ptr<IWICBitmapFrameEncode> bitmap_frame;
	com_ptr<IPropertyBag2> property_bag;
	th << encoder->CreateNewFrame(bitmap_frame.inject(), property_bag.inject());

	WICPixelFormatGUID formatGUID = GUID_WICPixelFormat24bppRGB;
	th << bitmap_frame->Initialize(property_bag.get());
	th << bitmap_frame->SetSize(image.width(), image.height());
	th << bitmap_frame->SetPixelFormat(&formatGUID);
	th << bitmap_frame->WritePixels(image.height(), image.stride(), image.buffer_size(), image.buffer());
	th << bitmap_frame->Commit();

	th << encoder->Commit();
}