The World map shows what areas of the Earth are in daylight, which are at night and in twilight. Use the slider to interactively set the time and date and visualize the changing of the seasons and the length of the day. The widget shows live data on your homescreen and is designed to be very battery friendly.
This is an open source port of Day & Night Map and Widget available on Google Play.
Day & Night Map and Widget is integrated in SunLocator, an app to predict the sun's position in multiple ways (Augmented Reality, Map, 3D Terrain simulation). Available on Google Play.
The Renderscript file daynightscript.rs handles the rendering of the map's shadows on a pixel by pixel basis, depicting regions with night, civil dawn/dusk, nautical dawn/dusk and astronomical dawn/dusk. Mercator projection of the map makes it straightforward to calculate which pixel is which longitude/latitude.
Calculation is based on Grena, 2012 - Five new algorithms for the computation of sun position from 2010 to 2110 algorithms with modifications.
Renderscript allows running computational intensive tasks in parallel using GPUs and multi-core CPUs. This lets the app calculate the sun elevation at every pixel of the map (800x400 px) very fast while allowing interactively changing the time/date.
Note: RenderScript is deprecated starting in Android 12. See here. I still have not got around to migrate it to Vulkan, as suggested in the linked article.
The app itself is quite straightforward. PhotoView is used to allow a tiny bit of panning/zooming the map. The widget is implemented in DayNightWidget.java.
