Watchface: El Primero

Classic Zenith analog watchface with anti-aliasing, always-on second hand and powersafe mode.

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Powersafe mode

There are 3 operating modes for this watchface:

Active mode (10 seconds after "what's time" gesture)
- Current heart rate is shown
- Second hand is updated in 2Hz
Background mode
- Second hand is updated in 1Hz
- All data is updated once a minute, differences are re-drawn to screen buffer
Powersafe mode (activated at specific conditions)
- Second hand is not shown
- Minute hand is drawn once a minute, everything else is drawn to screen buffer
- When hour hand moves (once in 12 minutes), all data is updated, differences are re-drawn in screen buffer
- Anti-aliased custom-font hour and minute hands are replaced with vector hands

Powersafe mode is activated in a minute after entering background mode, if:

Do-not-disturb mode is on (usually it is activated in sleep mode)
Move bar is full (if you are too busy to make some steps, you don't look at watch)
Heart rate data is missing (watches are not on your hand)
Heart rate is less than 1.2x of resting heart rate (you are actually sleeping)

Technical details

There is huge full-color buffered bitmap to simplify redrawing of second hand
This buffer is also used in powersafe mode to handle minute hand updates
Elements in buffer are redrawn on-demand (background parts shaded by minute/hour hands or changed value for HR gauge)
Background actually is a custom font (it appears that font texture is stored in compressed format, because even 2bit paletted bitmaps are far bigger)
Hands are drawn from custom fonts also (60 positions for each hand are split to tiles and packed into a set of fonts to save free memory)
Fonts for hands are constantly reloading from storage while every single font is cached until next is needed; this happens every ~5 minutes in background mode and consumes lots of power, so powersafe mode uses ugly vector hands representation