Wrong coordinates when drawing OnTouch lines on ImageView using canvas - imageview

Question

Thank you in advice for your help!
I am trying to make a simple application to draw lines on a ImageView usings OnTouch tap detection and path and bitmap painting
Tell me please where i did a mistake with the coordinates i take un OnTouch
Probably there is some commmon approache how to recalc the taked X Y coordinates
Probably i should better use some kind of different layout or OnTouch listener implementation
The image size - 1024 x 768
Android Screen 1280 x 800
The image is center loaded inside the ImageView
if i do the followings - i am getting correct drawn square with correct borders
void Button3OnClick(object sender, EventArgs eventArgs)
{
OnImageClick(50, 50, 0, 0);
OnImageClick(950, 50, 0, 0);
OnImageClick(950, 710, 0, 0);
OnImageClick(50, 710, 0, 0);
OnImageClick(40, 40, 0, 0);
DrawPolygon();
}
Why OnTouch painting gives wrong result?
Android Screenshot
Red line - the path i draw manually
Green line - the line the app draws finally
My XAML
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<Button
android:id="#+id/MyButton"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Задать Изображение" />
<Button
android:id="#+id/MyButton1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Сброс" />
<Button
android:id="#+id/MyButton2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Расчёт" />
<Button
android:id="#+id/MyButton3"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="ВЫХОД" />
<ImageView
android:src="#android:drawable/ic_menu_gallery"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:id="#+id/imageView1" />
</LinearLayout>
Here is my code
protected override void OnCreate(Bundle bundle)
{
base.OnCreate(bundle);
metrics = new DisplayMetrics();
WindowManager.DefaultDisplay.GetMetrics(metrics);
widthInDp = metrics.WidthPixels;
heightInDp = metrics.HeightPixels;
SetContentView(Resource.Layout.Main);
pointList = new List<Point>();
_imageView = FindViewById<ImageView>(Resource.Id.imageView1);
_imageView.SetOnTouchListener(this);
button = FindViewById<Button>(Resource.Id.MyButton);
button1 = FindViewById<Button>(Resource.Id.MyButton1);
button2 = FindViewById<Button>(Resource.Id.MyButton2);
button3 = FindViewById<Button>(Resource.Id.MyButton3);
button.Click += ButtonOnClick;
button1.Click += Button1OnClick;
button2.Click += Button2OnClick;
button3.Click += Button3OnClick;
}
public bool OnTouch(View v, MotionEvent e)
{
switch (e.Action)
{
case MotionEventActions.Up:
TimeSpan span = lastTouchDown - System.DateTime.Now;
float UpTouchX = e.GetX();
float UpTouchY = e.GetY();
float differenceX = Math.Abs(initialTouchX - UpTouchX);
float differenceY = Math.Abs(initialTouchY - UpTouchY);
if ((span.TotalMilliseconds < 300) && (differenceY < 10) && (differenceX < 10))
OnImageClick(UpTouchX, UpTouchY, v.MeasuredHeight, v.MeasuredWidth);
break;
case MotionEventActions.Down:
lastTouchDown = System.DateTime.Now;
initialTouchX = e.GetX();
initialTouchY = e.GetY();
break;
}
return true;
}
void OnImageClick(float x, float y, int MeasuredHeight, int MeasuredWidth)
{
int measuredHeight = MeasuredHeight;
int measuredWidth = MeasuredWidth;
Point point = new Point();
point.x = x;
point.y = y;
pointList.Add(point);
button2.Text = string.Format("Рассчёт Вершин {0}", pointList.Count);
DrawPolygon();
}
void DrawPolygon()
{
var paint = new Paint();
paint.SetARGB(255, 200, 255, 0);
paint.SetStyle(Paint.Style.Stroke );
paint.StrokeWidth = 5;
Bitmap tempBitmap = Bitmap.CreateBitmap(baseBitmap.Width, baseBitmap.Height, Bitmap.Config.Rgb565);
Canvas tempCanvas = new Canvas(tempBitmap);
tempCanvas.DrawBitmap(baseBitmap, 0, 0, null);
var path = new Path();
foreach (Point pnt in pointList)
{
if (path.IsEmpty)
path.MoveTo(pnt.x, pnt.y);
else
path.LineTo(pnt.x, pnt.y);
tempCanvas.DrawCircle(pnt.x, pnt.y, 7, paint);
}
if (!path.IsEmpty)
tempCanvas.DrawPath(path, paint);
_imageView.SetImageDrawable (new BitmapDrawable(tempBitmap));
}