# Background

The background node acts as a catch-all for input events. Any input event that isn't captured by another interactive element is processed by this node.

To add a background to your scene, add a `Sprite` node as the first child of the `scene` node, name it "background", make sure the `Offset/Centered` property is not checked and add the `globals/background.gd` script.

This enables you to use `Area2D` nodes for your items, which lets you draw one or more `CollisionPolygon2D` child nodes to capture input, using only editor tools for the drawing. You can also add `Sprite` nodes as children of the `Area2D` item node if your items are not part of the background image.

*Important note:* Having children on the background is possible, but discouraged. Usually there is a way of having them parallel to the background in the node tree, and not much testing has been put into children of the background. Please open an issue on GitHub if you find an insurmountable problem!

### Parallax

To create an illusion of perspective in a 2D game, a technique called parallax scrolling effect can be used. This effect is achieved by adding one or more additional background layers, which are moved at a different speed than the foreground when the camera pans.

To implement a [ParallaxBackground](http://docs.godotengine.org/en/3.0/classes/class_parallaxbackground.html) in Escoria, a `Sprite` with the `globals/background.gd` script must be used for the foreground, as described in the previous section. Since the camera limits are calculated from the size of the `Sprite` texture, the image used must cover the visible space of the room, with transparent regions where the parallax layers will be visible.

Each layer must have a `Sprite` child node with the `Offset/Centered` property unchecked, and the parallax image must either be larger than the foreground or be repeated using the `Motion/Mirroring` property of the `ParallaxLayer` node to counter the `Motion/Scale` property, which is used to control how fast the layer scrolls. Remember to adjust the `Transform/Position` property of the `ParallaxLayer` to make sure that the layer covers the left and upper edges of the viewport when the scene is played.

Note: When using `camera_set_zoom` or `camera_set_zoom_height` in combination with parallax backgrounds, the `ParallaxBackground`'s `Scroll/Ignore Camera Zoom` property should be turned off so that the parallax layers do not move when zooming.