Bevy uses a right-handed Y-up coordinate system.
Bevy uses the same coordinate system for 3D, 2D, and UI, for consistency.
It is easiest to explain in terms of 2D:
- The X axis goes from left to right (+X points right).
- The Y axis goes from bottom to top (+Y points up).
- The Z axis goes from far to near (+Z points towards you, out of the screen).
- For 2D, the origin (X=0.0; Y=0.0) is at the center of the screen by default.
- For UI, the origin is at the bottom left corner.
When you are working with 2D sprites, you can put the background on Z=0.0, and place other sprites at increasing positive Z coordinates to layer them on top.
In 3D, the axes are oriented the same way.
This is a right-handed coordinate system. You can use the fingers of your right hand to visualize the 3 axes: thumb=X, index=Y, middle=Z.
It is the same as Godot, Maya, and OpenGL. Compared to Unity, the Z axis is inverted.
(graphic modifed and used with permission; original by @FreyaHolmer)
Note: In Bevy, the Y axis always points UP.
This may feel unintuitive when working with UI (as it is the opposite from web pages), or if you are used to working with 2D libraries where the Y axis points down.
Also beware of a common pitfall when working in 2D: the camera must be positioned at a far away Z coordinate (=999.9 by default), or you might not be able to see your sprites!