~~NOTOC~~

====== God Rays ======

---- dataentry extension ----
author_mail   : daniel@gamua.com Daniel Sperl
description   : Atmospheric lighting, like the typical effects you see underwater or in a forest.
compatible    : v2.2
tags          : light, god ray, sun ray
homepage_url  : https://gist.github.com/PrimaryFeather/e05a738e60c4253564d8a0f7866c5384
----

===== Overview =====

A quad that efficiently draws a 2D light ray effect on its surface. That's useful for adding atmospheric effects, like the typical effects you see
underwater or in a forest. ([[https://gist.github.com/PrimaryFeather/03de478dabd456e1985b411b8b0e22e5|Demo Source]].)

{{ :extensions:godrays.mp4?756x316 |}}

Play around with the different settings to make it suit the style you want. In addition
to the class-specific properties, you can also assign an overall color or different colors
per vertex.

Add it to a juggler or call ''advanceTime'' so that the effect
becomes animated.

<code as3>
var godRays:GodRayPlane = new GodRayPlane(320, 200);
godRays.color = 0xff8000;
godRays.speed = 0.1;  // animation speed
godRays.size = 0.1;   // number of rays ~= 1 / size
godRays.skew = 0;     // angle of rays
godRays.shear = 0;    // spread of angle
godRays.fade = 1;     // rays fade out towards the bottom
godRays.contrast = 1; // distinctiveness and brightness of the rays

addChild(godRays);
Starling.juggler.add(godRays);
</code>

<note tip>
Internally, the class creates a [[wp>Perlin noise]] texture. Each frame, only one pixel row of this texture is displayed -- stretched from top to bottom. The displayed row changes over time: this is what causes the rays to twinkle. By adjusting the texture coordinates, the angle and spread of rays can be determined.

Since most of the work is done in a shader, this effect is very lightweight and renders really fast. A ''MeshStyle'', together with a ''MeshEffect'', does the heavy lifting.
</note>
===== Changelog =====

  * //2017/10/10//: First public version
  * //2021/01/15//: Exposed 'textureOffset' property. Thanks to //aureliendc// for the pull request!

===== User Comments =====

//Feel free to edit this part of the page if you want to add information that's lacking in the above description.\\
Questions are better asked in the [[http://forum.starling-framework.org|forum]], though.//