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This chapter will teach you about writing custom shaders in the Shader monad.

The shader monad is a state monad in which you build custom shader code which will then be parsed into actual code. When writing shaders, it is recommended to do the following imports:

import Prelude()
import Mischief.Materials

Prelude needs to be hidden, as shader code uses its own definition of primitive types and operations. See for instance, Float vs Float and + vs. +.

When working with shaders, there are 3 primitive types:

• Int
• Uint
• Float

Each can be built with a literal. For instance, this is a shader that returns 5:

five :: Shader a Int
five = pure 5

There are vecs of between 2 and 4 elements. Each size having its own constructor: vec2, vec3, vec4.

foo :: Vec3 Float
foo = vec3 3.4 0.1 (-5)

There are also arrays, which can be of vecs or primitives.

bar :: Array (Vec2 Uint)
bar = array [vec2 5 0, vec2 1 4, vec2 10 3]

Arrays can be indexed into using !!:

let x = bar !! 2

Finally, there are matrices:

baz :: Mat 2 3
baz = mat (vec3 5 0 4, vec3 1 1 1)

You can cast between different primitive types, or between vecs of the same size, using cast.

Algebric operators are defined using a convention inspired by Linear.

Two elements of the same type can be multiplied using *.

let a :: Float = 2 * 3

A scalar (left) can be multiplied with a vector (right) using *^, and vice versa for ^*.

let a :: Vec2 Float = 2 *^ vec2 5 2

A matrix (left) can be multiplied with a vector (right) using !*^, or with a scalar (right) using !*. Vice versa for ^*! and *!.

The same goes for other operators, such as /, +, -, %.

Shader functions are defined according to the [wgpu standard](https:/www.w3.orgTRWGSL] in Mischief.Shader.Functions.

If a function you need isn't yet defined by Mischief, you can bind it yourself using unsafeCall. For instance, assuming atan2 wasn't defined, you could call it like this:

let x :: Vec2 Float = vec2 5 2
let y :: Vec2 Float = vec2 1 2
let z :: Vec2 Float = unsafeCall "atan2" [Param x, Param y]

But be careful! This removes all typechecking. If you call a function with the wrong parameters it will panic.