offset of HitArea after zooming and scrolling - math

Question

What will be the offset of the getHitRect after zooming and scrolling. Offset of the hit area after zoom can be calculated - (event.getX() / ZoomLayout.mScaleFactor + ZoomLayout.mClipBound.left) But i have not still figured out the offset of hit area after zooming and scrolling.
public class ZoomLayout extends RelativeLayout implements OnDoubleTapListener, OnGestureListener{
//ScalingFactor i.e. Amount of Zoom
static float mScaleFactor = 1.0f;
// Maximum and Minimum Zoom
private static float MIN_ZOOM = 1.0f;
private static float MAX_ZOOM = 2.0f;
//Different Operation to be used
private final int NONE_OPERATION=0;
private final int DRAG_OPERATION=1;
private final int ZOOM_OPERATION=2;
private float mWidth= 1280;
private float mHeight=800;
// Mode to select the operation
private int mode;
//Track X and Y coordinate of the finger when it first touches the screen
private float mInitialX = 0f;
private float mInitialY = 0f;
// Track the Bound of the Image after zoom to calculate the offset
static Rect mClipBound;
// mDetector to detect the scaleGesture for the pinch Zoom
private ScaleGestureDetector mDetector;
// mDoubleTapDetector to detect the double tap
private GestureDetector mDoubleTapDetector;
//Pivot point for Scaling
static float gx=0,gy=0;
boolean mdrag=false,mZoom=false;
public ZoomLayout(Context context, AttributeSet attrs) {
super(context, attrs);
setWillNotDraw(false);
mClipBound = new Rect();
// Intialize ScaleGestureDetector
mDetector = new ScaleGestureDetector(getContext(), new ZoomListener());
mDoubleTapDetector = new GestureDetector(context,this);
mDoubleTapDetector.setOnDoubleTapListener(this);
}
public ZoomLayout(Context context) {
super(context);
setWillNotDraw(false);
mClipBound = new Rect();
// Intialize ScaleGestureDetector
mDetector = new ScaleGestureDetector(getContext(), new ZoomListener());
mDoubleTapDetector = new GestureDetector(context,this);
mDoubleTapDetector.setOnDoubleTapListener(this);
}
#Override
public boolean onTouchEvent(MotionEvent event) {
// Handles all type of motion-events possible
switch(event.getAction() ) {
case MotionEvent.ACTION_DOWN:
// Event occurs when the first finger is pressed on the Screen
Log.d("ZoomPrint", "Event: Action_Down " );
mInitialX = event.getX();
mInitialY = event.getY();
break;
case MotionEvent.ACTION_POINTER_DOWN:
//Event occurs when the second finger is pressed down
Log.d("ZoomPrint", "Event: Action_Pointer_Down " );
// If second finger is pressed on the screen with the first set the Mode to Zoom operation
mode=ZOOM_OPERATION;
break;
case MotionEvent.ACTION_POINTER_UP:
Log.d("ZoomPrint", "Event: Action_Pointer_UP " );
mdrag=true;
case MotionEvent.ACTION_UP:
//Event occurs when all the finger are taken of the screen
Log.d("ZoomPrint", "Event: Action_UP " );
//If all the fingers are taken up there will be no operation
mode = NONE_OPERATION;
mdrag=false;
break;
}
// give the event to the mDetector to get the scaling Factor
mDetector.onTouchEvent(event);
// give the event to the mDoubleTapDetector for the doubleTap
mDoubleTapDetector.onTouchEvent(event);
if(!mdrag)
invalidate();
return true;
}
#Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
onTouchEvent(ev);
return super.onInterceptTouchEvent(ev);
// return true;
}
#Override
public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
return super.invalidateChildInParent(location, dirty);
}
#Override
protected void onLayout(boolean changed, int l, int t, int r, int b)
{
int count = getChildCount();
for(int i=0;i<count;i++){
View child = getChildAt(i);
if(child.getVisibility()!=GONE){
RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams)child.getLayoutParams();
child.layout(
(int)(params.leftMargin ),
(int)(params.topMargin ),
(int)((params.leftMargin + child.getMeasuredWidth()) ),
(int)((params.topMargin + child.getMeasuredHeight()))
);
}
}
}
#Override
protected void dispatchDraw(Canvas canvas) {
//Save the canvas to set the scaling factor returned from detector
canvas.save(Canvas.MATRIX_SAVE_FLAG);
canvas.scale(mScaleFactor, mScaleFactor,gx,gy);
super.dispatchDraw(canvas);
mClipBound = canvas.getClipBounds();
canvas.restore();
}
private class ZoomListener extends ScaleGestureDetector.SimpleOnScaleGestureListener {
#Override
public boolean onScale(ScaleGestureDetector detector) {
// getting the scaleFactor from the detector
mScaleFactor *= detector.getScaleFactor(); // gives the scaling factor from the previous scaling to the current
// Log.d("ZoomPrint", "detector scaling Factor" + mScaleFactor);
gx = detector.getFocusX();
gy = detector.getFocusY();
// Limit the scale factor in the MIN and MAX bound
mScaleFactor= Math.max(Math.min(mScaleFactor, MAX_ZOOM),MIN_ZOOM);
// Log.d("ZoomPrint", "Bounded scaling Factor" + mScaleFactor);
/*//Force canvas to redraw itself only if the one event is to happen (say Zooming only ) else do not invalidate here for multi operations
As what we de for scrolling or panning will not reflect here. So we will add this in onDraw method
invalidate();*/
// Here we are only zooming so invalidate has to be done
// invalidate();
// requestLayout();
// we have handle the onScale
return true;
}
}
#Override
public boolean onDoubleTap(MotionEvent e) {
// Make the mScaleFactor to its normal value
if(mScaleFactor>1.0f)
{
mScaleFactor=1.0f;
}
// Force the canvas to redraw itself again as the changes has been occured.
invalidate();
requestLayout();
return false;
}
#Override
public boolean onDoubleTapEvent(MotionEvent e) {
// Log.d("ZoomPrint", "OnDoubleTapEvent");
return false;
}
#Override
public boolean onSingleTapConfirmed(MotionEvent e) {
// Log.d("ZoomPrint", "OnSingleTap");
return false;
}
#Override
public boolean onDown(MotionEvent e) {
// TODO Auto-generated method stub
return false;
}
#Override
public boolean onFling(MotionEvent e1, MotionEvent e2,
float velocityX, float velocityY) {
return false;
}
#Override
public void onLongPress(MotionEvent e) {
}
#Override
public boolean onScroll(MotionEvent e1, MotionEvent e2,
float distanceX, float distanceY) {
int distX= (int) distanceX, distY =(int) distanceY;
//Log.d("Print"," X " + this.mClipBound.left +" Y " + this.mClipBound.right + " b "+ this.mClipBound.bottom + " g" + this.mClipBound.top) ;
Log.d("Print", "Scroll X " + distanceX + " Y " + distanceY);
if(this.mClipBound.left<=0)
this.scrollTo(-280, 0);
else if(this.mClipBound.top<=0)
this.scrollTo(0, -250);
else if (this.mClipBound.right>=1047)
this.scrollTo(280, 0);
else if (this.mClipBound.bottom>=800)
this.scrollTo(0, 250);
else
this.scrollBy((int)distanceX,(int)distanceY);
return true;
}
#Override
public void onShowPress(MotionEvent e) {
}
#Override
public boolean onSingleTapUp(MotionEvent e) {
return false;
}

Answer 1

You need to translate the canvas during the scroll functionality. I have done it in this way in my code:
canvas.translate(getScrollX(), getScrollY());
getScrollX and Y are the amount of scroll.