how change the alpha value of half of UIImage or UIImageView

Question

I am trying to create an animation effect where an image who's alpha value is 0.5 (approximately) at start changes to 1 gradually, but not like the conventional effect. Here is what I am looking for.

original Image.

after some time

after some more time

and at the end

So basically if the alpha value of part of the image can be reduced than I can show the animation of filling up a glass or something close to it.
I don't know if this can be done at all or if it's possible with core graphics or core animation.

P.S. They are made in photoshop.
Does anyone have any thoughts about what should be done to achieve this kind of animation?

Answer 1

I'd suggest the following:

1. Create the UIImageView that shows the image in the view.

2. Create a new UIView with a background color and transparency:

   UIView *transpView = [UIView new];
   tranpsView.alpha = 0.4;
   transpView.frame = self.view.frame;
   [self.view addSubview:transpView];
   

3. Animate the transparent view to slide upwards:

   [UIView animateWithDuration:1.0 animations:^{
       transpView.frame = CGRectOffset(transpView.frame, 0, -tranpsView.frame.size.height);
   }];
   

Don't forget to release the tranpsView after you are done. Possibly with the completed block.

To get the "glass filling up" type of animation, just change the frame of of the tranpsView accordingly. The tranpsView can be any UIView subclass (like a texture of liquid or something).

Hope that helps.!