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@thi.ng/shader-ast

0.2.0 • Public • Published

@thi.ng/shader-ast

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This project is part of the @thi.ng/umbrella monorepo.

About

screenshot Example shader running in plain JS & Canvas 2D context, cross-compiled JS/GLSL outputs shown on the right

Both an embedded DSL and IR format to encourage and define modular shader code directly in TypeScript and then cross-compile to different languages. Using GLSL types and semantics as starting point, the DSL is used as an assembly language to define a partially (as much as possible / feasible) type checked AST, incl. custom, user defined functions, higher-order functions, inline functions, automatic vector-scalar overrides, most of GLSL ES 3.0 built-ins, arg checking, and function return type inference.

Code generation can be done for individual expressions or entire shader programs, incl. call graph analysis and topological re-ordering of all transitively called functions (other than built-ins). Currently only GLSL & JS are supported as target (see code gen packages below), but custom code generators can be easily added. Once more details have been ironed out, we aim to support Houdini VEX (in-progress), WASM, WHLSL for WebGPU in the near future as well.

webgl/canvas2d comparison

Comparison of the raymarch shader example (link further below), cross compiled to both GLSL/WebGL and JavaScript w/ Canvas2D API and showing the difference image of both results.

VEX plane displacement

The same raymarching example compiled to Houdini VEX and used as "Point Wrangle" to displace a grid geometry (using only the depth value of the raymarching step). Larger version

Standard library of common, higher level operations

In addition to the code generation aspects, this package also provides a form of "standard library", pure functions for common shader & GPGPU use cases and which can be used as syntax sugar and / or higher level building blocks for your own shaders. So far, this includes various math utils, lighting models, fog equations, SDF primitives / operators, raymarching helpers etc. These functions are distributed in as separate package.

Benefits

  • no more copy & pasting, string interpolation / templating: use standard TS/JS tooling & full IDE integration to create shaders (e.g. docs strings, packaging, 3rd party dependencies etc.)
  • all non-builtin functions keep track of their transitive dependencies, enabling call graph analysis, dead code elimination, topologically correct code output ordering etc. - all without manual user intervention
  • improve general re-use, especially once more target codegens are available (see future goals).
  • higher-order function composition & customization (e.g. see raymarch.ts, or additive.ts)
  • cross compilation to different graphics environments
  • shader functions can be called like standard TS/JS functions (incl. automatically type checked args via TS mapped types)
  • type checking (at authoring time & compile time) and type annotations of all AST nodes catches many issues early on
  • avoids complex GLSL parsing as done by other transpilers
  • shader code will be fully minimized along with main app code in production builds as part of standard bundling processes / tool chains, no extra plugins needed
  • small run time & file size overhead (depending on output target impl)

Language specific code generators

Higher level building blocks

Prior art / influences

Future goals

See the project dashboard for current status. The TL;DR list...

  • documentation
  • struct support
  • uniform blocks
  • more code gens (JS ✅, WASM, WHLSL, OpenCL, Houdini VEX (WIP))
  • JS runtime improvements / features (non-GPU / vanilla JS shader execution)
  • Integration w/ a GLSL parser (new or existing)
  • AST transformations (optimizers, e.g. constant folding ✅)

Installation

yarn add @thi.ng/shader-ast

Dependencies

Usage examples

(Possibly non-exhaustive list, live demo links in readme's)

API

TODO - docs forthcoming

Supported types

  • float (32 bit)
  • int (signed 32bit)
  • uint (unsigned 32bit)
  • bool
  • vec2 (f32)
  • vec3 (f32)
  • vec4 (f32)
  • ivec2 (i32)
  • ivec3 (i32)
  • ivec4 (i32)
  • uvec2 (u32)
  • uvec3 (u32)
  • uvec4 (u32)
  • bvec2 (bool)
  • bvec3 (bool)
  • bvec4 (bool)
  • mat2 (2x2, f32)
  • mat3 (3x3, f32)
  • mat4 (4x4, f32)
  • sampler2D
  • sampler3D
  • samplerCube
  • sampler2DShadow
  • samplerCubeShadow
  • isampler2D
  • isampler3D
  • isamplerCube
  • usampler2D
  • usampler3D
  • usamplerCube

Operators

The following operators are all applied componentwise, take 2 arguments and support mixed vector / scalar args. One of the operands can also be a plain JS number, but not both. The resulting AST nodes will contain type hints to simplify later code generation tasks:

  • add
  • div
  • mul
  • sub

If one of the operands is a vector or matrix and the other scalar, the result will be vector/matrix.

If a plain (unwrapped) JS number value is given for one of the operands, it will be automatically wrapped in a suitable type, based on that of the other operand. E.g. In add(vec2(1), 10), the 10 will be cast to float(10). In add(ivec2(1), 10), it will be cast to int(10)...

mul has exceptional semantics for matrix * matrix, matrix * vector and vector * matrix operands (all perform correct linear algebraic multiplications). See GLSL ES language reference.

Comparison

All comparisons result in a bool term (i.e. Term<"bool">)

AST GLSL
lt <
lte <=
eq ==
neq !=
gte >=
gt >

Logic

AST GLSL
and &&
or ||
not !

Bitwise

AST GLSL
bitand &
bitor |
bitxor ^
bitnot ~

Swizzling

Only available for vector types - to extract, , optionally reordered, components and / or to expand, shorten vectors. If only one component is selected, the result will be a scalar, else a vector of the specified length.

  • $(vec3(1,2,3), "zyx") => vec3(3,2,1)

Syntax sugar for single component lookups:

  • $x(v) (same as $(v, "x"))
  • $y(v)
  • $z(v)
  • $w(v)
  • $xy(v)
  • $xyz(v)

Swizzle patterns are type checked in the editor (and at compile time), i.e.

  • $(vec2(1,2), "xyx") => ok (results in equivalent of vec3(1,2,1))
  • $(vec2(1,2), "xyz") => illegal (since z is not available in a vec2)

Array index lookups

  • index
  • indexMat

Symbol definitions / assignments

  • sym
  • arraySym
  • assign
  • input
  • output
  • uniform

Control flow

  • brk
  • cont
  • discard

If-Then-Else

  • ifThen(test, truthy, falsy)

Ternary operator

  • ternary(test, truthy, falsy)

For-loop

  • forLoop(sym, testFn, iterFn, bodyFn)

While-loop

  • whileLoop(test, body)

Built-in functions

The most common set of GLSL ES 3.0 builtins are supported. See builtins.ts for reference.

User defined functions

Functions can be created via defn and can accept 0-8 typed arguments. Functions declared in this manner can be called like any other TS/JS function and will return a function call AST node with the supplied args.

// example based on @thi.ng/shader-ast-stdlib
 
/**
 * Computes Lambert term, optionally using Half-Lambertian,
 * if `half` is true.
 *
 * https://developer.valvesoftware.com/wiki/Half_Lambert
 *
 * @param surfNormal vec3
 * @param lightDir vec3
 * @param half bool
 */
const lambert = defn(
    // return type
    "float",
    // function name
    "lambert",
    // args (incl. optional name and other opts)
    ["vec3", "vec3", "bool"],
    // function body
    (n, ldir, bidir) => {
        // pre-declare local var
        let d: FloatSym;
        // function body is array of AST nodes
        return [
            // initialize local using expr given to `sym()`
            (d = sym(dot(n, ldir))),
            // return statement
            ret(
                ternary(
                    bidir,
                    fit1101(d),
                    // also see clamp01() in stdlib
                    clamp(d, float(0), float(1))
                )
            )
        ];
    }
);

When defn is called, the function body will be checked for correct return types. Additionally a call graph for the function is generated to ensure the code generator later emits all dependent functions in the correct order.

Since defn returns a standard TS/JS function, all arguments will be automatically type checked at call sites (in TypeScript only).

Function arguments

Function argument lists are given as arrays, with each item either:

  1. an AST type string, e.g. "float"
  2. a tuple of [type, name?, opts?], e.g. ["vec2", "bar", { q: "out" }]

If no name is specified, an auto-generated one will be used. Generally, this is preferable, since these names are only used for code generation purposes and in most cases only need to be machine readable...

The body function (last arg given to defn), is called with instantiated, typed symbols representing each arg and can use any name within that function (also as shown in the above example).

See SymOpts interface in api.ts for more details about the options object...

Inline functions

If no function local variables are required and/or inlining is desired, vanilla TS/JS functions can be used to produce a partial AST, which is then inserted at the call site:

/**
 * Inline function. Computes sinc(kx).
 *
 * https://en.wikipedia.org/wiki/Sinc_function
 *
 * @param x
 * @param k
 */
const sinc = (x: FloatTerm, k: FloatTerm) =>
    div(sin(mul(x,k)), mul(x, k));

Performance tip for INLINE functions only: Since the FloatTerm type (or similarly any other XXXTerm type) refers to any expression evaluating to a "float", in some cases (like this sinc() example) it might be better to only accept FloatSym arguments, since this ensures the arg expressions are not causing duplicate evaluation. For example:

sinc(length(mul(vec3(1,2,3), 100)), float(10));

...will be expanded to:

div(
    sin(mul(length(mul(vec3(1,2,3), 100)),k)),
    mul(length(mul(vec3(1,2,3), 100)), k)
);

...which is not desirable.

If, however, the inline function asks for FloatSym args, the caller is forced to supply variables and so is also responsible to pre-define them... Alternatively, the function could be re-defined via defn to avoid such issues altogether (but then causes an additional function call at runtime - nothing comes for free!).

Global scope

Input / output variables / declarations

  • input
  • output
  • uniform

Program definition

  • program([...decls, ...functions])

Code generation

Currently, an AST can be compiled into the following languages:

GLSL (ES)

See @thi.ng/shader-ast-glsl for further details.

import { GLSLVersion, targetGLSL } from "@thi.ng/shader-ast-glsl";
 
// create codegen w/ options (defaults shown)
const glsl = targetGLSL({
    version: GLSLVersion.GLES_300,
    versionPragma: true,
    type: "fs"
});
 
console.log(glsl(lambert))

JavaScript

See @thi.ng/shader-ast-js for further details.

import { targetJS } from "@thi.ng/shader-ast-js";
 
const js = targetJS();
 
console.log(js(lambert))

Compilation & execution

AST tooling & traversal

Tree traversals

  • walk
  • allChildren
  • scopeChildren

Constant folding

Currently only works for scalars and primitive math ops:

import { constantFolding } from "@thi.ng/shader-ast";
 
const ast = mul(float(10), add(float(1), float(2)));
 
// {
//   tag: 'op2',
//   type: 'float',
//   info: undefined,
//   op: '*',
//   l: { tag: 'lit', type: 'float', info: undefined, val: 10 },
//   r: {
//     tag: 'op2',
//     type: 'float',
//     info: undefined,
//     op: '+',
//     l: { tag: 'lit', type: 'float', info: undefined, val: 1 },
//     r: { tag: 'lit', type: 'float', info: undefined, val: 2 }
//   }
// }
 
constantFolding(ast)
// { tag: 'lit', type: 'float', info: undefined, val: 30 }

Authors

  • Karsten Schmidt

License

© 2019 Karsten Schmidt // Apache Software License 2.0

install

npm i @thi.ng/shader-ast

Downloadsweekly downloads

15

version

0.2.0

license

Apache-2.0

homepage

github.com

repository

Gitgithub

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