[android-developers] Drawing

I'm using the following  type of code to  do panning and zooming  on my own extension of an  ImageView

    setBackgroundColor(Color.BLACK);

matrix.postScale(newfactor , newfactor , mid.x , mid.y);

setImageMatrix(matrix);

Now I want to be able to draw lines on top of this image = = matrix

currently I'm using

mPaint.setColor(Color.BLUE);

canvas.drawLine(pointA.x, pointA.y, pointB.x, pointB.y, mPaint);

However this won't show  up,

so my question is   How can I draw a line to the matrix  variable used for zooming and panning ?

Also I'm looking for  tutorials on  LayerDrawable if you know of any

Thanks in advance