Android drawing path while Zoom and Pinch

Question

I draw a bitmap and try to draw a picture on it using Canvas.for the drawing, I add it when the user draws something on the surface. I implemented a pinch of Zoom and dragged functions over the bitmap, but when the user enlarged the bitmap and drew something on it, the Path will not get a draw. I use Matrix to improve scaling and drag and drop. My problem is using Path with with Matrix.

Answer 1

This is a working example where you can see how to implement a draggable and scalable path:

Mainactivity

import android.app.Activity; import android.os.Bundle; import android.view.Window; import android.view.WindowManager; public class DrawActivity extends Activity { DrawView drawView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Set full screen view getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN); requestWindowFeature(Window.FEATURE_NO_TITLE); drawView = new DrawView(DrawActivity.this); setContentView(drawView); } } 

Drawview

 import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.util.DisplayMetrics; import android.view.Display; import android.view.MotionEvent; import android.view.ScaleGestureDetector; import android.view.View; import android.view.WindowManager; public class DrawView extends View { Context ctx; static final String TAG = "DrawView"; Paint paint = new Paint(); //These two constants specify the minimum and maximum zoom private static float MIN_ZOOM = 3f; private static float MAX_ZOOM = 10f; private float scaleFactor = 3.f; private ScaleGestureDetector detector; //These two variables keep track of the X and Y coordinate of the finger when it first //touches the screen private float startX = 0f; private float startY = 0f; //These two variables keep track of the amount we need to translate the canvas along the X //and the Y coordinate private float translateX = 0f; private float translateY = 0f; //These two variables keep track of the amount we translated the X and Y coordinates, the last time we //panned. private float previousTranslateX = 0f; private float previousTranslateY = 0f; private boolean dragged = false; // Used for set first translate to a quarter of screen private float displayWidth; private float displayHeight; public DrawView(Context context) { super(context); ctx = context; WindowManager wm = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE); Display display = wm.getDefaultDisplay(); DisplayMetrics metrics = new DisplayMetrics(); display.getMetrics(metrics); displayWidth = metrics.widthPixels; displayHeight = metrics.heightPixels; translateX = displayWidth/4; translateY = displayHeight/4; previousTranslateX = displayWidth/4; previousTranslateY = displayHeight/4; detector = new ScaleGestureDetector(context, new ScaleListener()); setFocusable(true); setFocusableInTouchMode(true); // Path color paint.setColor(Color.GRAY); paint.setAntiAlias(false); } @Override public void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.save(); //We're going to scale the X and Y coordinates by the same amount canvas.scale(scaleFactor, scaleFactor, 0, 0); //We need to divide by the scale factor here, otherwise we end up with excessive panning based on our zoom level //because the translation amount also gets scaled according to how much we've zoomed into the canvas. canvas.translate((translateX) / scaleFactor, (translateY) / scaleFactor); canvas.drawRect(0, 0, 100, 100, paint); canvas.restore(); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction() & MotionEvent.ACTION_MASK) { case MotionEvent.ACTION_DOWN: // First finger is on screen //We assign the current X and Y coordinate of the finger to startX and startY minus the previously translated //amount for each coordinates This works even when we are translating the first time because the initial //values for these two variables is zero. startX = event.getX() - previousTranslateX; startY = event.getY() - previousTranslateY; break; case MotionEvent.ACTION_MOVE: // first finger is moving on screen // update translation value to apply on Path translateX = event.getX() - startX; translateY = event.getY() - startY; break; case MotionEvent.ACTION_UP: // No more fingers on screen // All fingers went up, so let save the value of translateX and translateY into previousTranslateX and //previousTranslate previousTranslateX = translateX; previousTranslateY = translateY; break; // All touch events are sended to ScaleListener detector.onTouchEvent(event); return true; } class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener { @Override public boolean onScale(ScaleGestureDetector detector) { scaleFactor *= detector.getScaleFactor(); scaleFactor = Math.max(MIN_ZOOM, Math.min(scaleFactor, MAX_ZOOM)); invalidate(); return true; } } }