Screen Redrawing

Former Member over 10 years ago

How much of a difference on a watch face does it make if you repaint only that portion of the screen instead of the entire screen on every update? I never see a flash, but I'm just wondering if it uses more battery to repaint the entire screen vs. just the smaller region that changed.

For example, say you have an analog watch face. If you repaint just the hands it seems like it would be more efficient, but that means drawing the hands black then drawing them again in the new location. For other watch faces trying to repaint part of the screen might take more power than just clearing and starting over.

jim_m_58 over 10 years ago

Don't forget you'll also need logic for when to draw everything vs just the hands, and when all is said and done, this adds complexity to the code, and based on your design, it might save (guessing) 1% of the battery per week. Remember, in low power the watchface only gets updated every minute.

And if you have an hours hand and a minute hand, both are moving, and need to be updated, and calling the math stuff to figure out their positions could be more "expensive" than drawing things like the hash marks for an analog watch.