android - Define zoom/pan start position with KenBurnsView

Question

I'm working with the library KenBurnsView and I have a problem:

the overview or this nice library says the following: "Highly extensible: you can define how the rectangles to be zoomed and panned will be generated" and that's exactly what I want to do but I don't know exactly how.

I would like to be able to tell the library to zoom or pan from a specified region (a RectF I presume) of my image. I think I have to implements my own TransitionGenerator and write a custom generateNextTransition() mtehod but I don't know what to do inside.

Can anyone help me ?

Thanks. Adrian

Answer 1

You need to implement your own TransitionGenerator and override generateNextTransition() from where you must return a Transition object.

The generateNextTransition() method takes:

1. RectF drawableBounds: the bounds of the drawable that is set to the KenBurnsView;

2. RectF viewport the bounds of the KenBurnsView object.

The Transition constructor takes:

1. RectF srcRect: a subrectangle of the drawable that will fill the whole KenBurnsView when the transition starts (illustrated below):

Illustration from Wikipedia

2. RectF dstRect: a subrectangle of the drawable that will fill the whole KenBurnsView when the transition ends;

3. long duration: the duration, in milliseconds, of the transition.

4. Interpolator interpolator: an interpolator instance that will define the nature of the movement (may be an AccelerateDecelerateInterpolator, LinearInterpolator, etc.);

It might me a good idea to save dstRect to be used as srcRect in the next transition if you desire that every transition will start from the place the last transition has stopped. That's exactly what the RandomTransitionGenerator does. Keep in mind that srcRect and dstRect can have different sizes (but both should be subrectangles of drawableBounds if you want to keep the image in scene all the time). It's important that both of them have the same aspect ratio of viewport.