android/camera: Implement image flipping

We use libyuv's Mirror function to handle horizontal flip. Regarding the vertical flip, libyuv doc states that 'just set a negative height'

src/android/app/src/main/jni/camera/ndk_camera.cpp

@@ -210,8 +210,13 @@ CaptureSession::CaptureSession(ACameraManager* manager, const std::string& id) {
 #undef CAMERA_CALL
 #undef CREATE
 
-Interface::Interface(Factory& factory_, const std::string& id_, const Service::CAM::Flip& flip_)
+Interface::Interface(Factory& factory_, const std::string& id_, const Service::CAM::Flip& flip)
-    : factory(factory_), id(id_), flip(flip_) {}
+    : factory(factory_), id(id_) {
+    mirror = base_mirror =
+        flip == Service::CAM::Flip::Horizontal || flip == Service::CAM::Flip::Reverse;
+    invert = base_invert =
+        flip == Service::CAM::Flip::Vertical || flip == Service::CAM::Flip::Reverse;
+}
 
 Interface::~Interface() = default;
 
@@ -227,8 +232,11 @@ void Interface::SetResolution(const Service::CAM::Resolution& resolution_) {
     resolution = resolution_;
 }
 
-void Interface::SetFlip(Service::CAM::Flip flip_) {
+void Interface::SetFlip(Service::CAM::Flip flip) {
-    flip = flip_;
+    mirror = base_mirror ^
+             (flip == Service::CAM::Flip::Horizontal || flip == Service::CAM::Flip::Reverse);
+    invert =
+        base_invert ^ (flip == Service::CAM::Flip::Vertical || flip == Service::CAM::Flip::Reverse);
 }
 
 void Interface::SetFormat(Service::CAM::OutputFormat format_) {
@@ -265,19 +273,32 @@ std::vector<u16> Interface::ReceiveFrame() {
                       scaled_y.data(), resolution.width, scaled_u.data(), resolution.width / 4,
                       scaled_v.data(), resolution.width / 4, resolution.width, resolution.height,
                       libyuv::kFilterBilinear);
-    // TODO: Record and apply flip
+
+    if (mirror) {
+        std::vector<u8> mirrored_y(scaled_y.size());
+        std::vector<u8> mirrored_u(scaled_u.size());
+        std::vector<u8> mirrored_v(scaled_v.size());
+        libyuv::I420Mirror(scaled_y.data(), resolution.width, scaled_u.data(), resolution.width / 4,
+                           scaled_v.data(), resolution.width / 4, mirrored_y.data(),
+                           resolution.width, mirrored_u.data(), resolution.width / 4,
+                           mirrored_v.data(), resolution.width / 4, resolution.width,
+                           resolution.height);
+        scaled_y.swap(mirrored_y);
+        scaled_u.swap(mirrored_u);
+        scaled_v.swap(mirrored_v);
+    }
 
     std::vector<u16> output(resolution.width * resolution.height);
     if (format == Service::CAM::OutputFormat::RGB565) {
         libyuv::I420ToRGB565(scaled_y.data(), resolution.width, scaled_u.data(),
                              resolution.width / 4, scaled_v.data(), resolution.width / 4,
                              reinterpret_cast<u8*>(output.data()), resolution.width * 2,
-                             resolution.width, resolution.height);
+                             resolution.width, invert ? -resolution.height : resolution.height);
     } else {
         libyuv::I420ToYUY2(scaled_y.data(), resolution.width, scaled_u.data(), resolution.width / 4,
                            scaled_v.data(), resolution.width / 4,
                            reinterpret_cast<u8*>(output.data()), resolution.width * 2,
-                           resolution.width, resolution.height);
+                           resolution.width, invert ? -resolution.height : resolution.height);
     }
     return output;
 }

src/android/app/src/main/jni/camera/ndk_camera.h

@@ -37,7 +37,13 @@ private:
     std::string id;
 
     Service::CAM::Resolution resolution;
-    Service::CAM::Flip flip;
+
+    // Flipping parameters. mirror = horizontal, invert = vertical.
+    bool base_mirror{};
+    bool base_invert{};
+    bool mirror{};
+    bool invert{};
+
     Service::CAM::OutputFormat format;
     // std::vector<u16> image; // Data fetched from the frontend
     // bool opened{};          // Whether the camera was successfully opened

src/android/app/src/main/jni/camera/still_image_camera.cpp

@@ -29,7 +29,12 @@ void CleanupJNI(JNIEnv* env) {
     env->DeleteGlobalRef(s_still_image_camera_helper_class);
 }
 
-Interface::Interface(jstring path_, const Service::CAM::Flip& flip_) : path(path_), flip(flip_) {}
+Interface::Interface(jstring path_, const Service::CAM::Flip& flip) : path(path_) {
+    mirror = base_mirror =
+        flip == Service::CAM::Flip::Horizontal || flip == Service::CAM::Flip::Reverse;
+    invert = base_invert =
+        flip == Service::CAM::Flip::Vertical || flip == Service::CAM::Flip::Reverse;
+}
 
 Interface::~Interface() {
     Factory::last_path = nullptr;
@@ -70,13 +75,20 @@ void Interface::StartCapture() {
                        info.width, info.height);
     BITMAP_CALL(unlockPixels(env, bitmap));
 
+    if (mirror) {
+        std::vector<u8> mirrored(data.size());
+        libyuv::ARGBMirror(data.data(), info.stride, mirrored.data(), info.stride, info.width,
+                           info.height);
+        data.swap(mirrored);
+    }
+
     image.resize(info.height * info.width);
     if (format == Service::CAM::OutputFormat::RGB565) {
         libyuv::ARGBToRGB565(data.data(), info.stride, reinterpret_cast<u8*>(image.data()),
-                             info.width * 2, info.width, info.height);
+                             info.width * 2, info.width, invert ? -info.height : info.height);
     } else {
         libyuv::ARGBToYUY2(data.data(), info.stride, reinterpret_cast<u8*>(image.data()),
-                           info.width * 2, info.width, info.height);
+                           info.width * 2, info.width, invert ? -info.height : info.height);
     }
     opened = true;
 
@@ -87,8 +99,11 @@ void Interface::SetResolution(const Service::CAM::Resolution& resolution_) {
     resolution = resolution_;
 }
 
-void Interface::SetFlip(Service::CAM::Flip flip_) {
+void Interface::SetFlip(Service::CAM::Flip flip) {
-    flip = flip_;
+    mirror = base_mirror ^
+             (flip == Service::CAM::Flip::Horizontal || flip == Service::CAM::Flip::Reverse);
+    invert =
+        base_invert ^ (flip == Service::CAM::Flip::Vertical || flip == Service::CAM::Flip::Reverse);
 }
 
 void Interface::SetFormat(Service::CAM::OutputFormat format_) {

src/android/app/src/main/jni/camera/still_image_camera.h

@@ -31,7 +31,13 @@ public:
 private:
     jstring path;
     Service::CAM::Resolution resolution;
-    Service::CAM::Flip flip;
+
+    // Flipping parameters. mirror = horizontal, invert = vertical.
+    bool base_mirror{};
+    bool base_invert{};
+    bool mirror{};
+    bool invert{};
+
     Service::CAM::OutputFormat format;
     std::vector<u16> image; // Data fetched from the frontend
     bool opened{};          // Whether the camera was successfully opened