All geometry is in homogeneous coordinates (`geometry/Vec3`):
line through two points = cross product, intersection of two lines = cross product.
Infinite points are handled without special cases.
## Languages
English (default), Bulgarian, French, German and Spanish. The language is changed from a menu in the toolbar and does not depend on the device language (`AppCompatDelegate.setApplicationLocales`).
The selection is saved; on Android 13+, the language can also be changed from the app's system settings.
## Structure
- `geometry/` – Vec3, Projective, Homography (pure Java, no Android)
- `view/` – GeometryView (base class: dragging, drawing lines) and the four scenes
- `MainActivity` – tabs (TabLayout), tooltip, numeric information, "Reset" button