Complete
over 2 years ago

BUG: some newer devices clear the screen on every view update. Simulator behaves differently

Some users have reported issues with my app Maze (https://apps.garmin.com/en-US/apps/3a4436a8-1126-4539-a2f2-aefb319a0ef0) and Snake (https://apps.garmin.com/en-US/apps/e443b0cc-8046-4d76-830f-e87517cf14b6), where the screen will go black after starting to play the game.

For efficiency, the screen is drawn using Dc calls, the view's onUpdate does not call the parent, and only the changed parts of the screen are redrawn: during gameplay on Maze, the previous location of the ball is blanked out, and the new location is drawn.  The event loop is run by a timer that calls Ui.requestUpdate() every 100ms.  This method has worked since I originally developed the games for my Forerunner 235.  

However, with newer devices - specifically, the Venu and the Forerunner 55 - this does not work.  For some reason, the display gets blacked out on every call to View.onUpdate. This only happens on the physical watches, not in the simulator, so I have no way to test this behaviour!I can create the undesired behaviour in the simulator by adding a call to View.onUpdate(dc) at the top of the onUpdate method in my view class.

So, here are my requests:

* please correct the behaviour on these watches

* if this behaviour was a desired change, please update your documentation to make it clear that we can no longer perform incremental updates to the screen

* please fix the simulator so that it behaves the same as these watches

* in the meantime, please tell me if there is a workaround for this issue.  I believe my code is correct since it has behaved correctly for years, and there is no detail in the documentation that says that what I'm doing is no longer possible

More details available on request - for some reason I can't add an image here.

ak6i
Parents
  • over 2 years ago

    This is well known and has been reported before and isn't a bug.  When onUpdate() is called, you want to redraw everything and not just some things. The only time you can safely update only parts of the screen is in watch faces with onPartialUpdate.  

    It's one of the things where the sim doesn't show the exact behaviour on all devices, and you just want to assume the screen is blank and you redraw everything.  

Comment
  • over 2 years ago

    This is well known and has been reported before and isn't a bug.  When onUpdate() is called, you want to redraw everything and not just some things. The only time you can safely update only parts of the screen is in watch faces with onPartialUpdate.  

    It's one of the things where the sim doesn't show the exact behaviour on all devices, and you just want to assume the screen is blank and you redraw everything.  

Children
  • over 2 years ago in reply to jim_m_58

    I have only dc calls, no layout.

    I haven't looked at using BufferedBitmap but if those render to the screen quickly, I guess it would be an option to have the onUpdate() logic first check if BufferedBitmap is present, and if so, draw to the bitmap and render that to the screen; if not, draw directly to the screen as previously.  That seems like it would be a relatively low-pain way to fix the issue without completely changing all my code, since the BufferedBitmap also provides a Dc instance.

  • over 2 years ago in reply to ak6i

    If you are using dc calls and not layouts, you actually don't need to all View.onUpdate() at all.  If you are mixing a lawout with dc calls, you need to do the View.onUpdate() before you do dc calls.  View.onUpdate() clears the screen so any dc calls before that are lost.

    The simple thing with only dc calls is to do the clear in onUpdate() and always redraw the whole screen.

    Have you looked at using buffered bitmaps to speed up your draws?

  • over 2 years ago in reply to jim_m_58

    Thanks.  I think the response could be more helpful.  Making "expected behaviour" known and understood outside of Garmin is part of good documentation.  The API docs for View.onUpdate() should contain full details of the behaviour and the expectations.  Ideally, there should also be a how-to for drawing complex graphics on screen.

    Does anyone know how to create such graphics and draw them in such a way that the full screen doesn't have to be fully redrawn every time?  

  • over 2 years ago in reply to jim_m_58

    Clearing the screen is the easy part!

    The part that I need some guidance on is how to work around the lack of ability to do an incremental update, because the graphics take literally seconds to draw. It seems like there isn’t a good universal way to do this, and that there will need to be two blocks of code: one for devices with the old behaviour; one for the newer devices that would need some kind of bitmap or buffer or something. Again, the docs aren’t that helpful here.