Fossil Hybrid HR watchface code intended to be used by Gadgetbridge
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Arjan Schrijver 1a58411e8f
Allow starting watch apps from Gadgetbridge
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The Fossil Hybrid HR watches have dynamic (free-form) watchfaces since firmware version DN1.0.2.20r.v1 (official app 4.6.0). These watchfaces are built in JerryScript 2.1.0 and packed together with assets and configurations into one file.

Gadgetbridge (0.59.0 and up) uses the open source code from this repository to support these dynamic watchfaces. Due to licensing of Fossil's code, the official watchfaces cannot be redistributed. Hence the need for an open source watchface.

Note: this open source watchface is only supported by Gadgetbridge, not by the official Fossil app.


  • Daniel Dakhno, for his app SDK, which has provided tools and information necessary to analyze and build watchfaces.
  • Material Design Icons for providing an awesome repository of free icons.

Building the watchface

First make sure you have the binaries jerryscript and jerryscript-snapshot available, version 2.1.0 (other versions will not work). Also, clone the app SDK, because some of the provided tools are needed.

Pre-process your watchface with a tool like Gimp to 240x240 pixels and 2 bit (4 colors) grayscale. Then use the following command to convert your image to the RAW format used by watchfaces.

python ../Fossil-HR-SDK/tools/ -i watchface.png -o build/files/icons/background.raw -w 240 -h 240 -f raw

The same tool can be used to convert icons to the watch's format. Make sure you start with a white icon with transparent background. Then use the following command to convert your icon to the RLE format used by watchfaces.

python ../Fossil-HR-SDK/tools/ -i icon.png -o build/files/icons/icon.rle -w 24 -h 24 -f rle

Then, run the following commands in the checked out repository:

mkdir -p build/files/code/
jerry-snapshot generate -f '' open_source_watchface.js -o build/files/code/openSourceWatchface
jerry-snapshot generate -f '' widget_date.js -o build/files/code/widgetDate
jerry-snapshot generate -f '' widget_weather.js -o build/files/code/widgetWeather
jerry-snapshot generate -f '' widget_steps.js -o build/files/code/widgetSteps
jerry-snapshot generate -f '' widget_hr.js -o build/files/code/widgetHR
jerry-snapshot generate -f '' widget_battery.js -o build/files/code/widgetBattery
jerry-snapshot generate -f '' widget_calories.js -o build/files/code/widgetCalories
jerry-snapshot generate -f '' widget_2nd_tz.js -o build/files/code/widget2ndTZ
jerry-snapshot generate -f '' widget_activemins.js -o build/files/code/widgetActiveMins
jerry-snapshot generate -f '' widget_chanceofrain.js -o build/files/code/widgetChanceOfRain
jerry-snapshot generate -f '' widget_custom.js -o build/files/code/widgetCustom
python ../Fossil-HR-SDK/tools/ -i build -o open_source_watchface.wapp

Installing the watchface

Option 1:

  1. Open Gadgetbridge
  2. Tap on the "app manager" icon in the connected Fossil HR device card
  3. Tap on the round "+" button at the bottom right
  4. Select the .wapp file
  5. Enjoy the watchface on your watch!

Option 2:

  1. Share the .wapp file from another app with Gadgetbridge's "Firmware/Apps installer"
  2. Click "Install"
  3. Enjoy the watchface on your watch!

Current state and things left to do

  • Background image shows correctly
  • Hands display correct time
  • Display refresh works after leaving menu or notification
  • Notification indicator should disappear when dismissed on phone
  • Physical buttons functionality
  • Layout JSON support
  • Partial display update
  • Wrist flick functionality
  • Configurability of regular and custom functionality through config JSON
  • Suspend hands and display updating when off wrist to conserve battery power
  • Complications/widgets
    • Date / day of week
    • Weather
    • Heart rate
    • Steps count
    • Battery
    • Calories
    • Active minutes
    • 2nd timezone
    • Chance of rain
    • Custom widget (showing text from Gadgetbridge)
  • Goal rings
  • Custom images
  • Custom text

Ideas for future exploration

  • Timed backgrounds
  • Navigation instructions on watchface or widget (from OsmAnd)
  • Multiple configs (thus, watchfaces) switchable with physical button


Use reversed_watchface.js with background image reversed_watchface.raw for a fully reversed analog clock! Even the hands are running in reverse! No worries: notifications and menus are still displayed correctly.