android: jpeg: post_processor_jpeg: Embed thumbnail into Exif metadata

Embed a Jpeg-encoded thumbnail into Exif metadata using the Thumbnailer
class that got introduced.

Introduce a helper function in Exif class for setting the thumbnail
data.

Signed-off-by: Umang Jain <email@uajain.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
[Kieran: Add todo comment, and Compression enum]
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/android/jpeg/post_processor_jpeg.h

@@ -8,12 +8,13 @@
 #define __ANDROID_POST_PROCESSOR_JPEG_H__
 
 #include "../post_processor.h"
+#include "encoder_libjpeg.h"
+#include "thumbnailer.h"
 
 #include <libcamera/geometry.h>
 
 #include "libcamera/internal/buffer.h"
 
-class Encoder;
 class CameraDevice;
 
 class PostProcessorJpeg : public PostProcessor
@@ -28,9 +29,14 @@ public:
 		    CameraMetadata *metadata) override;
 
 private:
+	void generateThumbnail(const libcamera::FrameBuffer &source,
+			       std::vector<unsigned char> *thumbnail);
+
 	CameraDevice *const cameraDevice_;
 	std::unique_ptr<Encoder> encoder_;
 	libcamera::Size streamSize_;
+	EncoderLibJpeg thumbnailEncoder_;
+	Thumbnailer thumbnailer_;
 };
 
 #endif /* __ANDROID_POST_PROCESSOR_JPEG_H__ */