---
title: Conventions
slug: /conventions
---

There are a few things that Excalibur does that are good to know before you start building games!

# Conventions

1. Excalibur uses a theater metaphor, for example: [[Scene|Scenes]], [[Actor|Actors]], and [Actions](/docs/actions).

2. Excalibur uses [Resources](docs/category/resources) to load external files like [images](/docs/ImageSource) and [sounds](/docs/Sound). They can also be used to load other things like data or config.

2. The negative y direction is up, and the positive y direction is down.

2. Distance units are in pixels, velocity in pixels per second, and acceleration in pixels per second per second.

3. Rotation units are in radians.

4. All elapsed times and durations in Excalibur are in milliseconds.

5. Actor z-index's follow the browser way of doing things.
   * Things with larger positive numbers are on top of lower numbers.

6. Excalibur handles offscreen draw culling for you! No need to manage that!

7. Excalibur uses pre-multiplied alphas when drawing which is important to know if you use [Material](/docs/materials)
