Canvas Zoom goes to point (0,0)

问题:

I am having a problem in zooming the canvas. I have made a customized view in which I am drawing relationship diagrams now when I zoom out the canvas in goes to the position (0,0). I have seen different threads and questions but could not find appropriate answer.

What i am doing in onDraw Method is.

  canvas.scale(mScaleFactor, mScaleFactor);

I have also seen the canvas.scale(x, y, px, py) method but i do not know how to get the pivot points of x and y.

public boolean onScale(ScaleGestureDetector detector) {

mScaleFactor *= detector.getScaleFactor();
// Don't let the object get too small or too large.
mScaleFactor = Math.max(0.4f, Math.min(mScaleFactor, 5.0f));
if(mScaleFactor>=1)
   mScaleFactor=1f; 

invalidate();
return true;

}

回答1:

The pivot points are basically the point that your canvas will be transformed around, so scaling with a pivot of 0,0 makes it shrink towards that point. using the following method you can change the pivot point to wherever you want it:

canvas.scale(x, y, px, py);

Now for the new stuff: If you want your canvas to be scaled towards its centre, you will just have to know the point in the middle of your canvas:

float cX = canvas.getWidth()/2.0f; //Width/2 gives the horizontal centre
float cY = canvas.getHeight()/2.0f; //Height/2 gives the vertical centre

And then you can scale it using those coordinates:

canvas.scale(x, y, cX, cY);

回答2:

Take a look at these two answers, they describe the problem and its solutions very well.

Android Bitmap/Canvas offset after scale

Scaling image of ImageView while maintaining center point in same place