diff --git a/app/build.gradle b/app/build.gradle
index 4828ac08aaa4f2f86a2a4f111027779f6b6b2e4b..0902d363c272349d327a0cede862bff1fd1ef421 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -1,7 +1,7 @@
 apply plugin: 'com.android.application'
 
 android {
-    compileSdkVersion 29
+    compileSdkVersion 30
     compileOptions.encoding = 'UTF-8'
 
     compileOptions {
@@ -12,7 +12,7 @@ android {
     defaultConfig {
         applicationId "foundation.e.camera"
         minSdkVersion 21
-        targetSdkVersion 29
+        targetSdkVersion 30
 
         renderscriptTargetApi 21
         //renderscriptSupportModeEnabled true // don't use support library as it bloats the APK, and we don't need pre-4.4 support
diff --git a/app/src/main/java/net/sourceforge/opencamera/MainActivity.java b/app/src/main/java/net/sourceforge/opencamera/MainActivity.java
index adf98555d7bc73f9b42fc27c32fc6bc0ca7d3875..a92a7d8972924a0a51cd4045b219efcb7d5093dd 100644
--- a/app/src/main/java/net/sourceforge/opencamera/MainActivity.java
+++ b/app/src/main/java/net/sourceforge/opencamera/MainActivity.java
@@ -651,13 +651,48 @@ public class MainActivity extends Activity {
             notificationManager.createNotificationChannel(channel);
         }
 
+        calculateNavigationGap();
+
         if( MyDebug.LOG )
             Log.d(TAG, "onCreate: total time for Activity startup: " + (System.currentTimeMillis() - debug_time));
+    }
 
+    /**
+     * if navigationMode is no gesture, then retrieve navigationBar's height & update navigation_gap
+     */
+    private void calculateNavigationGap() {
+        int resourceId = getResources().getIdentifier("config_navBarInteractionMode", "integer", "android");
+        if (resourceId > 0) {
+            int navType = getResources().getInteger(resourceId);
+            if (navType != 2) { //gesture mode = 2
+                resourceId = getResources().getIdentifier("navigation_bar_height", "dimen", "android");
+                if (resourceId > 0) {
+                    navigation_gap = getResources().getDimensionPixelSize(resourceId);
+                }
+            }
+        }
+    }
 
+    public void handleDecorFitsSystemWindows() {
+        setDecorFitsSystemWindows(!isInFullScreenMode());
     }
 
+    /**
+     * check is the preview size = maximise && is not in video mode, then return true
+     */
+    public boolean isInFullScreenMode() {
+        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
+        String preview_size = sharedPreferences.getString(PreferenceKeys.PreviewSizePreferenceKey, "preference_preview_size_display");
+        return !(preview_size.equals("preference_preview_size_wysiwyg") || preview.isVideo());
+    }
+
+    /**
+     * if sdk>=R & not in full screen, means the DecorFitsSystemWindows=true, then we can ignore navigationGap.
+     */
     public int getNavigationGap() {
+        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.R && !isInFullScreenMode()) {
+            return 0;
+        }
         return want_no_limits ? navigation_gap : 0;
     }
 
@@ -2653,6 +2688,18 @@ public class MainActivity extends Activity {
         }
     }
 
+    /**
+     * setDecorFitsSystemWindows for build >=R
+     * @return if the operation successful or not
+     */
+    public boolean setDecorFitsSystemWindows(boolean decorFitsSystemWindows) {
+        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+            getWindow().setDecorFitsSystemWindows(decorFitsSystemWindows);
+            return true;
+        }
+        return false;
+    }
+
     /** Sets the brightness level for normal operation (when camera preview is visible).
      *  If force_max is true, this always forces maximum brightness; otherwise this depends on user preference.
      */
@@ -2823,6 +2870,7 @@ public class MainActivity extends Activity {
         }
 
         setImmersiveMode(false);
+        setDecorFitsSystemWindows(true);
         camera_in_background = true;
 
         // we disable location listening when showing settings or a dialog etc - saves battery life, also better for privacy
diff --git a/app/src/main/java/net/sourceforge/opencamera/preview/Preview.java b/app/src/main/java/net/sourceforge/opencamera/preview/Preview.java
index cb7369a69d3fa57c7fc57953c89b1f0a5fd5cd17..58bd0738efe19bf01cd22c5ee502fe05218a2f1a 100644
--- a/app/src/main/java/net/sourceforge/opencamera/preview/Preview.java
+++ b/app/src/main/java/net/sourceforge/opencamera/preview/Preview.java
@@ -1,7 +1,7 @@
 package net.sourceforge.opencamera.preview;
 
+import net.sourceforge.opencamera.MainActivity;
 import net.sourceforge.opencamera.cameracontroller.RawImage;
-//import net.sourceforge.opencamera.MainActivity;
 import net.sourceforge.opencamera.MyDebug;
 
 import foundation.e.camera.R;
@@ -3470,6 +3470,21 @@ public class Preview implements SurfaceHolder.Callback, TextureView.SurfaceTextu
         return optimalSize;
     }
 
+    private static CameraController.Size getClosestSizeForFullScreen(List<CameraController.Size> sizes, double targetRatio) {
+        if (MyDebug.LOG)
+            Log.d(TAG, "getClosestSize()");
+        CameraController.Size optimalSize = null;
+        double minDiff = Double.MIN_VALUE;
+        for (CameraController.Size size : sizes) {
+            double ratio = (double) size.width / size.height;
+            if ((ratio - targetRatio) > minDiff) {
+                optimalSize = size;
+                minDiff = ratio - targetRatio;
+            }
+        }
+        return (optimalSize != null) ? optimalSize : getClosestSize(sizes, targetRatio, null);
+    }
+
     public CameraController.Size getOptimalPreviewSize(List<CameraController.Size> sizes) {
         if (MyDebug.LOG)
             Log.d(TAG, "getOptimalPreviewSize()");
@@ -3503,6 +3518,7 @@ public class Preview implements SurfaceHolder.Callback, TextureView.SurfaceTextu
             if (MyDebug.LOG)
                 Log.d(TAG, "display_size: " + display_size.x + " x " + display_size.y);
         }
+        ((MainActivity)getContext()).handleDecorFitsSystemWindows();
         double targetRatio = calculateTargetRatioForPreview(display_size);
         int targetHeight = Math.min(display_size.y, display_size.x);
         if (targetHeight <= 0) {
@@ -3524,7 +3540,11 @@ public class Preview implements SurfaceHolder.Callback, TextureView.SurfaceTextu
             // can't find match for aspect ratio, so find closest one
             if (MyDebug.LOG)
                 Log.d(TAG, "no preview size matches the aspect ratio");
-            optimalSize = getClosestSize(sizes, targetRatio, null);
+            if (((MainActivity)getContext()).isInFullScreenMode()) {
+                optimalSize = getClosestSizeForFullScreen(sizes, targetRatio);
+            } else {
+                optimalSize = getClosestSize(sizes, targetRatio, null);
+            }
         }
         if (MyDebug.LOG) {
             Log.d(TAG, "chose optimalSize: " + optimalSize.width + " x " + optimalSize.height);
@@ -4315,12 +4335,14 @@ public class Preview implements SurfaceHolder.Callback, TextureView.SurfaceTextu
         } else {
             if (this.isOnTimer()) {
                 cancelTimer();
+                ((MainActivity)getContext()).setDecorFitsSystemWindows(true);
                 this.is_video = true;
             } else if (this.phase == PHASE_TAKING_PHOTO) {
                 // wait until photo taken
                 if (MyDebug.LOG)
                     Log.d(TAG, "wait until photo taken");
             } else {
+                ((MainActivity)getContext()).setDecorFitsSystemWindows(true);
                 this.is_video = true;
             }
         }