How to Turn On Cosinus Shaders with Iris or OptiFine

Cosinus is a shader pack, so it needs a shader loader such as Iris or OptiFine. Once the loader works, switching Cosinus on takes about a minute.

Put the pack where the loader can find it

1. Launch Minecraft once with your shader loader installed. This creates a shaderpacks folder inside your .minecraft directory.

2. Open Options > Video Settings > Shader Packs.

3. Click Open Shader Pack Folder. This opens the shaderpacks folder directly.

4. Drop the Cosinus Shaders file into that folder. Leave it zipped unless your loader asks otherwise.

5. Return to the game. The pack should now appear in the shader list.

Activate it and check that it works

1. Click Cosinus Shaders in the list to select it.

2. Click Apply or Done, depending on your loader.

3. Load a world.

The pack keeps the simple look of vanilla blocks and lighting. If it is working, you will see the familiar landscape with wavy, warped screen effects based on cosine functions laid over it. If nothing looks different, reopen the Shader Packs menu and make sure Cosinus is highlighted, not "Off" or "(internal)".

If the pack does not show up at all, check that you placed it in shaderpacks and not resourcepacks. The two folders are easy to mix up, and Cosinus will only load from the shader folder.