ImageView to allow users to paint on image with their finger and add a cross image on a painted area.

FingerPaintImageView.java

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.RectF;
import android.graphics.drawable.BitmapDrawable;
import android.graphics.drawable.Drawable;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.Toast;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import static android.graphics.Bitmap.Config.ARGB_8888;

public class FingerPaintImageView extends android.support.v7.widget.AppCompatImageView {

    private final String TAG = getClass().getSimpleName();
    private Bitmap mBitmap;
    private Canvas mCanvas;
    private Path mPath;
    private Paint mBitmapPaint;
    private Paint mPaint;
    private boolean placingCross = false;
    private Toast warningToast = Toast.makeText(getContext(), "You must select a shaded area", Toast.LENGTH_SHORT);
    private final int gridSpaceCount = 20;
    private Bitmap imageViewBitmap = this.getImageViewBitmapFromVector(/*this.getDrawable()*/getResources().getDrawable(R.drawable.front_bpi_man));
    private boolean crossPlaced = false;
    private float crossX;
    private float crossY;

    public FingerPaintImageView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);

        //initialise values
        mPath = new Path();
        mBitmapPaint = new Paint(Paint.DITHER_FLAG);
        mPaint = new Paint();
        mPaint.setAntiAlias(true);
        mPaint.setDither(true);
        mPaint.setColor(0xFFFF0000);
        mPaint.setStyle(Paint.Style.STROKE);
        mPaint.setStrokeJoin(Paint.Join.ROUND);
        mPaint.setStrokeCap(Paint.Cap.ROUND);
        mPaint.setStrokeWidth(20);

    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);

        mBitmap = Bitmap.createBitmap(this.getWidth(), this.getHeight(), Bitmap.Config.ARGB_8888); //changed from w and h
        mCanvas = new Canvas(mBitmap);

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
      
        //get image and scale it
        int nh = (int) ( imageViewBitmap.getHeight() * (512.0 / imageViewBitmap.getWidth()) );
        imageViewBitmap = Bitmap.createScaledBitmap(imageViewBitmap, 512, nh, true);
        //set bitmap as the imageview's bitmap
        setImageBitmap(imageViewBitmap);
    }


    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //draw the bitmap on the canvas
        canvas.drawBitmap(imageViewBitmap, getMatrix(), null);

        //do painting stuff
        if (mBitmap != null) {

            canvas.drawBitmap(mBitmap, 0, 0, mBitmapPaint);
            canvas.drawPath(mPath, mPaint); //this draws path when held down

            if (placingCross && isOnImage(mX, mY)) {
                crossPlaced = true;
                crossX = mX;
                crossY = mY;
            }
            if (crossPlaced) {
                Bitmap crossBitmap = getImageViewBitmapFromVector(getResources().getDrawable(R.drawable.cross_yellow_25px));
                int crossXCenter = crossBitmap.getWidth() / 2;
                int crossYCenter = crossBitmap.getHeight() / 2;
                canvas.drawBitmap(crossBitmap, crossX - crossXCenter, crossY - crossYCenter, null);
            }
        }
    }

    //get bitmap from vector drawable
    private Bitmap getImageViewBitmapFromVector(Drawable d) {
        try {
            Bitmap bitmap;

            bitmap = Bitmap.createBitmap(d.getIntrinsicWidth(), d.getIntrinsicHeight(), ARGB_8888);

            Canvas canvas = new Canvas(bitmap);
            d.setBounds(0, 0, canvas.getWidth(), canvas.getHeight());
            d.draw(canvas);
            return bitmap;
        } catch (OutOfMemoryError e) {
            // Handle the error
            return null;
        }
    }

    private float mX, mY;
    private static final float TOUCH_TOLERANCE = 4;
    private boolean isStarted = false;

    //handle start touch
    private void touch_start(float x, float y) {
        mPath.reset();
        if (isOnImage(x, y)) {
            if (!placingCross) {
                mPath.moveTo(x, y);
            }
            mX = x;
            mY = y;
//            Log.d(TAG, "touch_start: started on white - mX=" + mX + ", mY=" + mY);
            isStarted = true;
        }
//        Log.d(TAG, "touch_start: not started - mX=" + mX + ", mY=" + mY);
    }

    //handle moving touch
    private void touch_move(float x, float y) {

        if (isOnImage(x, y)) {
            if (!isStarted) {
                touch_start(x, y);
            }

//            Log.d(TAG, "touch_move: drawn on white - mX=" + mX + ", mY=" + mY);
            float dx = Math.abs(x - mX);
            float dy = Math.abs(y - mY);
            if (dx >= TOUCH_TOLERANCE || dy >= TOUCH_TOLERANCE) {
                if (!placingCross) {
                    mPath.quadTo(mX, mY, (x + mX) / 2, (y + mY) / 2);
                }
                mX = x;
                mY = y;
            }
        } else {
            if (isStarted) {
                touch_up();
            }
        }
    }

    //handle touch stopped
    private void touch_up() {
        if (isStarted) {
//            Log.d(TAG, "touch_up- mX=" + mX + ", mY=" + mY);
            isStarted = false;
            if (!placingCross) {
                mPath.lineTo(mX, mY);
                // commit the path to our offscreen
                mCanvas.drawPath(mPath, mPaint); //this draws the path once it is finished
            }
            // kill this so we don't double draw
            mPath.reset();
        }
    }

    //check if x,y position is on the bitmap image
    public boolean isOnImage(float x, float y) {

        int pixel = imageViewBitmap.getPixel((int) x, (int) y);

        int alphaValue = Color.alpha(pixel);

        if (placingCross) {

            int paintPixel = mBitmap.getPixel((int) x, (int) y);
            //if placing cross, check for selection of a shaded red area
            if (Color.red(paintPixel) == 255 & Color.blue(paintPixel) == 0 & Color.green(paintPixel) == 0) {
                return true;
            } else {
                if (warningToast != null) warningToast.cancel();
//                warningToast = Toast.makeText(getContext(), "You must select a shaded area", Toast.LENGTH_SHORT);
                warningToast.show();
                return false;
            }
        } else if (alphaValue > 0) {
            //if normal shading mode, just check not transparent
            return true;
        } else {
            return false;
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        //CHANGING THIS X Y MEANS THAT WHERE YOU CLICK ISN'T RIGHT, DON'T CHANGE IT HERE!
        float x = event.getX();
        float y = event.getY();

        if (x < imageViewBitmap.getWidth() && x > 0 &&
                y < imageViewBitmap.getHeight() && y > 0 &&
                x != 0.0 && y != 0.0) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:
                    touch_start(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_MOVE:
                    touch_move(x, y);
                    invalidate();
                    break;
                case MotionEvent.ACTION_UP:
                    touch_up();
                    invalidate();
                    break;
            }
            return true;
        }
        return false;
    }

    public void clear() {
        mBitmap.eraseColor(Color.TRANSPARENT);
        invalidate();
        System.gc();

        crossPlaced = false;
        crossX = 0.0f;
        crossY = 0.0f;
    }

    public void setPlacingCross(boolean placingCross) {
        this.placingCross = placingCross;
        mX = 0;
        mY = 0;
    }

}