Language Syntax

File Structure

An .axsl file has the following top-level structure:

@version <number>;
@include "path/to/file.axsl";   // zero or more, must appear before globals

// Global declarations (structs, consts, uniforms, interfaces, functions)

@stage vertex   { ... }
@stage fragment { ... }
@stage geometry { ... }
@stage compute  { ... }

Comments

C-style line and block comments:

// line comment
/* block comment */

Types

All GLSL primitive and sampler types are first-class keywords in AXSL:

Scalar Types

bool, int, uint, float

Vector Types

vec2, vec3, vec4, ivec2, ivec3, ivec4, uvec2, uvec3, uvec4

Matrix Types

mat2, mat3, mat4

Sampler Types

sampler2D, samplerCube, sampler2DShadow, isampler2D, usampler2D

User-Defined Types

Any identifier token is accepted as a type name (struct names, etc.).

Built-in Variables

The following GLSL built-in variables are recognized:

Vertex Stage:

• gl_Position
• gl_PointSize
• gl_ClipDistance
• gl_VertexID
• gl_InstanceID
• gl_DrawID

Fragment Stage:

• gl_FragCoord
• gl_FrontFacing
• gl_PointCoord
• gl_FragDepth
• gl_SampleID
• gl_SamplePosition
• gl_SampleMaskIn
• gl_SampleMask

Compute Stage:

• gl_NumWorkGroups
• gl_WorkGroupSize
• gl_WorkGroupID
• gl_LocalInvocationID
• gl_GlobalInvocationID
• gl_LocalInvocationIndex

Expressions

Literals

Integer:

42
0xFF      // hexadecimal

Float:

3.14
0.        // trailing dot (abbreviation for 0.0)
1.        // abbreviation for 1.0

Boolean:

true
false

Operators

Binary:

• Arithmetic: +, -, *, /, %
• Comparison: ==, !=, <, >, <=, >=
• Logical: &&, ||
• Bitwise: &, |, ^, <<, >>

Unary Prefix:

• ! (logical not)
• ~ (bitwise not)
• - (negation)
• + (unary plus)
• ++, -- (increment/decrement)

Unary Postfix:

• ++, -- (increment/decrement)

Assignment:

• Simple: =
• Compound: +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=

Ternary:

condition ? then_expr : else_expr

Type Constructors

vec3(1.0, 0.0, 0.0)
vec4(vec3(1.0), 1.0)
mat4(1.0)  // identity matrix

Function Calls

sin(angle)
texture(sampler, uv)
normalize(vec)

Field Access

material.albedo
position.xyz
color.rgb

Array Subscript

array[index]
matrix[row][col]

Statements

Variable Declaration

float x = 0.0;
vec3 position;
int count = 10;

If Statement

if (condition) {
    // ...
} else if (other_condition) {
    // ...
} else {
    // ...
}

For Loop

for (int i = 0; i < 10; i++) {
    // ...
}

While Loop

while (condition) {
    // ...
}

Do-While Loop

WARNING

Do-while loops are currently emitted as regular while loops, losing the guarantee that the body executes at least once. This is a known limitation.

do {
    // ...
} while (condition);

Return Statement

return;
return value;

Control Flow

break;      // exit loop
continue;   // next iteration
discard;    // fragment shader only

Expression Statement

x = x + 1;
function_call();
x++;

Array Syntax

Fixed-Size Arrays

uniform PointLight lights[4];
float values[16];

Runtime-Sized Arrays

Inside buffer/uniform blocks, unbounded arrays are declared with empty brackets:

@std430 @binding(0) buffer InstanceBuffer {
    mat4 models[];
} instance;

This is emitted as [] in GLSL, indicating a runtime-sized array (SSBO feature).

Qualifiers

Parameter Qualifiers

Used on function parameters:

AXSL keyword	GLSL output	Meaning
in	in	Input parameter (default)
out	out	Output parameter
inout	inout	Input/output parameter
const	const	Constant parameter

Example:

void transform(in vec3 pos, out vec4 result) {
    result = vec4(pos, 1.0);
}