Question

I’m pretty new to manually manipulating images, so please bear with me.

I have an image that I’m allowing the user to shrink/grow and move around.

The basic behavior works perfectly. However, I need to be able to grab whatever is in the “viewport” (visible clipping region rectangle) and save it out as a separate bitmap.

Before I can do this, I need to get a fix on WHERE the image actually is and what is being displayed. This is proving more tricky than I would have imagined.

My problem is that the Matrix documentation is absurdly vague, and I’m lost as to how I can measure the coordinates and dimensions of my transformed image. As I see it, the X,Y of the image remain constant even as the user shrinks/grows it. So, even though it reports at being at 0,0 it’s displayed at (say) 100,100. And the only way I can get those coordinates is to do a fairly ugly computation (again… I’m probably not doing it the most elegant way, since geometry is not my forte).

I’m kind of hoping that I’m missing something and that there’s some way to pull the object’s auto translated coordinates and dimensions.

in an ideal world I would be able to call (pseudo) myImg.getDisplayedWidth() and myImg.getDisplayedX().

Oh, and I should add that this may all be a problem that I’m causing myself by using the center of the image as the point from which to grow/shrink. If I left the default 0,0 coordinate as the non changing point, I think the location would be correct no matter what its size was. So… maybe the answer to all this is to simply figure out my center offset and apply that to my translations?

All help greatly appreciated (and people not arbitrarily messing with my question’s title even more so!).

Answer 1

The Matrix method mapPoints(float[] dst, float[] src) can be used to get a series of translated points by applying the Matrix translation. Or in (slightly) more layman’s terms, an instance of the Matrix class contains not only the translation instruction but also convenience methods to apply the Matrix translation to a series of points.

So in your case, you just need the corners of your untranslated Bitmap (x, y, width, height) and pass the corner points into that method to get the translated points.