Light Cookies
Light cookies, also known as cookie textures, are supported by clustered lights (light_rt, light_rt_spot and env_projectedtexture). They can be used to apply a pattern to a light, controlling its shape and brightness. If you're not familiar with the concept of light cookies, imagine them like putting a piece of paper over a flashlight. If you were to cut out a shape from the paper, it would allow light to pass through, projecting a specific shape.
In Hammer, light cookies can be added to a light using the "Cookie Texture Name" and "Cookie Texture Frame" properties. When looking at lights through the Light Inspector, the texture can be set under "Pattern". For env_projectedtexture, the KeyValue is "Texture Name".
Volumetric lighting also works with light cookies.
How to use
Light cookies are textures that imitate shadows, and setting up cookie textures is as easy as setting up a texture for env_projectedtexture in vanilla Portal 2.
There are two main usages of light cookies - changing the shape of the clustered light, or replacing the dynamic shadows with an identical static image to save space in the shadow atlas.
How to make
This is a small guide that covers creation of light cookies.
Preparing the image
As mentioned above, light cookies imitate shadows. Thus, the image must contain shapes that this specific light imitates. Two easy ways to create images for light cookies are to either take a screenshot when viewing from the light itself and then heavily edit the image, or to copy the depth texture from the Clustered Light Stats and convert it to .vtf format.
Usually, light cookies are made for each light individually, but it is possible to make a commonly-shaped texture to use on multiple lights.
Converting to VTF format
After the image is created, it needs to be converted to VTF format.
Portal 2: Community Edition comes with MareTF - an open-source VTF editor. It is located in bin/win64. To convert an image into VTF, double-click maretf_gui.exe, press Create, select the cookie image, and press OK. The texture will be generated next to the original image (or in the specified output path). Copy the generated texture into a desired folder in materials (i.e. p2ce/materials/light_cookies/cookie.vtf)
Inserting into a clustered light
The last step is to put the texture into the light. There are 2 KeyValues related to light cookies - Cookie Texture Name, which is the path to the texture, and Cookie Texture Frame, which is the frame of the texture if it is animated. Simply put the path to the cookie texture in Cookie Texture Name, then recompile the map to see the changes. The cookie texture will appear for that light.
.vtf extension is not needed. The path should look like this: cookies_folder/cookie_name
env_projectedtexture entities can have .webm videos as "cookies"!
To convert .bik video format into a .webm, simply use convert_bik_to_webm.ps1 located in sdk_tools/converter.
Where to find
Officially, there are no pre-made cookies.
On the workshop, there is an addon that includes ~150 ready-to-use light cookies made by Kenney.NL and ported by Mae.
