Double tapping zoom animation flicker sometimes. about tileview

I've run into similar issue with my app and the problem is that TileView (or actually it's parent ZoomPanLayout) triggers a fling gesture even if the distance between two motion events is very small, thus causing some unwanted scrolling. This can be found in ZoomPanLayout.java around line 760 - performFling().

[moagrius]

@redred77 sorry I didn't notice this issue when it was created. i did see the notification when onder7973 replied. My guess is that you're seeing artifacts as new samples and tile sets are rendered before the previous have been cleaned up. I'd suggest turning transtions off and setting all detail levels to the same sample image (just to test, not as a fix). If you don't see the flicker after that, it's probably as I guessed. If not, post back and I'll dig in a little more.

@onder7973 I think redred77 is experiencing something different. I think you're describing a pinch gesture that results in a small fling? LMK if that's not right. Otherwise, if you'd like to modify ZoomPanLayout to have a minimum distance reached before a fling is invoked, feel free to fork and issue a pull request. As long as existing API doesn't break, the code is legible, consistent with existing patterns, and performs reasonably, I'll generally accept pull requests that expand the usability of the widget.

That said, if you don't have the time or inclination to do it, I might add it if/when I get some appreciable free time, or if several users request it as well.

Thanks for your input.

@moagrius my comment was based on redred77's details:

"When I double tap, view scales to that position smoothly but sometimes it flickers."

that seemed very familiar to me as to what I noticed when double tapping the view. If you actually do the double tap pretty quickly it does fling the view and then scrolls/zooms based on doubletap gesture, which may look like flickering. Plus I can confirm that adding a min distance prevents this (I have a code in place that works). I'll see if I can fork it as I am normally using SVN with my projects, not Git.

[moagrius]

cool

[kwent]

Changing the MINIMUM_VELOCITY constant from 50 to something like 500 is an easy way to fix the flickering without removing the fling Method.

50 as a default seems way too small I believe as it triggers with double taps.

[moagrius]

I'm open to both approaches. If no one provides a reasonable fork in the next couple weeks, I'll do a patch myself.

[redred77]

I read all comments and could find the problem.
I think adjusting MINIMUM_VELOCITY is not the solution for inner problem.
The point is, fling scroll and double tap scrolling can occur simultaneously.
I think to stop fling before start double tap scrolling is more reasonable.

if (determineIfQualifiedDoubleTap()) {
scroller.forceFinished(true); // to stop fling
saveHistoricalScale();
saveDoubleTapHistory();
...

I am not sure if it is consistent and working well with all existing sources but it works well on my project.

[moagrius]

thanks @redred77 - I've included your patch in the latest commit.