added support for android to crop image to preview.

android/src/main/java/com/lwansbrough/RCTCamera/MutableImage.java

@@ -76,6 +76,19 @@ public class MutableImage {
         }
     }
 
+    public void cropToPreview(float xPercentage, float yPercentage) throws ImageMutationFailedException {
+        int width = this.currentRepresentation.getWidth();
+        int height = this.currentRepresentation.getHeight();
+
+        int x = (int) Math.round(height * xPercentage);
+        int y = (int) Math.round(width * yPercentage);
+
+        int cropWidth = width - (y*2);
+        int cropHeight =  height - (x*2);
+
+        this.currentRepresentation = Bitmap.createBitmap(this.currentRepresentation, y, x, cropWidth, cropHeight);
+    }
+
     //see http://www.impulseadventure.com/photo/exif-orientation.html
     private void rotate(int exifOrientation) throws ImageMutationFailedException {
         final Matrix bitmapMatrix = new Matrix();

android/src/main/java/com/lwansbrough/RCTCamera/RCTCamera.java

@@ -4,6 +4,7 @@
 
 package com.lwansbrough.RCTCamera;
 
+import android.graphics.drawable.GradientDrawable;
 import android.hardware.Camera;
 import android.media.CamcorderProfile;
 import android.util.Log;
@@ -73,6 +74,22 @@ public class RCTCamera {
         return cameraInfo.previewHeight;
     }
 
+    public float getPreviewPaddingHeight(int type) {
+        CameraInfoWrapper cameraInfo = _cameraInfos.get(type);
+        if (null == cameraInfo) {
+            return 0;
+        }
+        return cameraInfo.previewPaddingHeight;
+    }
+
+    public float getPreviewPaddingWidth(int type) {
+        CameraInfoWrapper cameraInfo = _cameraInfos.get(type);
+        if (null == cameraInfo) {
+            return 0;
+        }
+        return cameraInfo.previewPaddingWidth;
+    }
+
     public Camera.Size getBestSize(List<Camera.Size> supportedSizes, int maxWidth, int maxHeight) {
         Camera.Size bestSize = null;
         for (Camera.Size size : supportedSizes) {
@@ -418,6 +435,16 @@ public class RCTCamera {
         }
     }
 
+    public void setPreviewPadding(int type, float width, float height) {
+        CameraInfoWrapper cameraInfo = _cameraInfos.get(type);
+        if (cameraInfo == null) {
+            return;
+        }
+
+        cameraInfo.previewPaddingWidth = Math.abs(width);
+        cameraInfo.previewPaddingHeight = Math.abs(height);
+    }
+
     private RCTCamera(int deviceOrientation) {
         _cameras = new HashMap<>();
         _cameraInfos = new HashMap<>();
@@ -448,6 +475,9 @@ public class RCTCamera {
         public int rotation = 0;
         public int previewWidth = -1;
         public int previewHeight = -1;
+        public int previewHeight = -1;
+        public float previewPaddingHeight = -1;
+        public float previewPaddingWidth = -1;
 
         public CameraInfoWrapper(Camera.CameraInfo info) {
             this.info = info;

android/src/main/java/com/lwansbrough/RCTCamera/RCTCameraModule.java

@@ -580,6 +580,17 @@ public class RCTCameraModule extends ReactContextBaseJavaModule
             }
         }
 
+        try {
+            int type = options.getInt("type");
+            float paddingWidth = RCTCamera.getInstance().getPreviewPaddingWidth(type);
+            float paddingHeight = RCTCamera.getInstance().getPreviewPaddingHeight(type);
+
+            mutableImage.cropToPreview(paddingWidth, paddingHeight);
+        }
+         catch (MutableImage.ImageMutationFailedException e) {
+             promise.reject("Error cropping image to preview", e);
+         }
+
         boolean shouldMirror = options.hasKey("mirrorImage") && options.getBoolean("mirrorImage");
         if (shouldMirror) {
             try {

android/src/main/java/com/lwansbrough/RCTCamera/RCTCameraView.java

@@ -6,6 +6,7 @@ package com.lwansbrough.RCTCamera;
 
 import android.content.Context;
 import android.hardware.SensorManager;
+import android.util.Log;
 import android.view.OrientationEventListener;
 import android.view.ViewGroup;
 import android.view.WindowManager;
@@ -180,6 +181,11 @@ public class RCTCameraView extends ViewGroup {
         int viewFinderPaddingX = (int) ((width - viewfinderWidth) / 2);
         int viewFinderPaddingY = (int) ((height - viewfinderHeight) / 2);
 
+        float paddingXPercentage = (float)viewFinderPaddingX / (float)viewfinderWidth;
+        float paddingYPercentage = (float)viewFinderPaddingY / (float)viewfinderHeight;
+
+        RCTCamera.getInstance().setPreviewPadding(_viewFinder.getCameraType(), paddingXPercentage, paddingYPercentage);
+
         this._viewFinder.layout(viewFinderPaddingX, viewFinderPaddingY, viewFinderPaddingX + viewfinderWidth, viewFinderPaddingY + viewfinderHeight);
         this.postInvalidate(this.getLeft(), this.getTop(), this.getRight(), this.getBottom());
     }

android/src/main/java/com/lwansbrough/RCTCamera/RCTCameraViewFinder.java

@@ -83,6 +83,10 @@ class RCTCameraViewFinder extends TextureView implements TextureView.SurfaceText
     public void onSurfaceTextureUpdated(SurfaceTexture surface) {
     }
 
+    public int getCameraType() {
+        return _cameraType;
+    }
+
     public double getRatio() {
         int width = RCTCamera.getInstance().getPreviewWidth(this._cameraType);
         int height = RCTCamera.getInstance().getPreviewHeight(this._cameraType);