HLSL vs GLSL vs WGSL vs Metal: shader languages compared

Shader languages look different on the surface and think the same underneath. They all describe a function that runs on the GPU for every pixel (or vertex), and they all have vectors, matrices and a handful of math functions in common. Once you know one, the others are a matter of vocabulary. Here is how they compare, and which one to start with.

Which language runs where

Language	Where you meet it
HLSL	Unity (Built-in and URP), Unreal Engine, DirectX, most console and PC game engines
GLSL	OpenGL, WebGL, Shadertoy, three.js, GameMaker, LÖVE, Vulkan (via SPIR-V)
Godot shading language	Godot Engine (it is GLSL-like with its own built-ins)
Metal Shading Language	iOS, iPadOS, macOS and Apple's other platforms
WGSL	WebGPU in the browser, and engines such as Bevy

The same idea in four syntaxes

Blend two colors by a factor t, in each language:

// HLSL (Unity, Unreal)
float3 c = lerp(a, b, t);

// GLSL (WebGL, Shadertoy, three.js)
vec3 c = mix(a, b, t);

// Metal
float3 c = mix(a, b, t);

// WGSL (WebGPU, Bevy)
let c = mix(a, b, t);

Vocabulary that changes

Idea	HLSL	GLSL	Metal	WGSL
Vector of 3	float3	vec3	float3	vec3f
Blend	lerp	mix	mix	mix
Fractional part	frac	fract	fract	fract
Clamp to 0..1	saturate	clamp(x, 0.0, 1.0)	saturate	saturate
Remainder	fmod	mod (always positive)	fmod	%
Matrix times vector	mul(M, v)	M * v	M * v	M * v
A function	float f(float x)	float f(float x)	float f(float x)	fn f(x: f32) -> f32

Two differences cause the most surprises. First, remainder of a negative number: HLSL's fmod(-1.0, 2.0) is -1, while GLSL's mod(-1.0, 2.0) is 1, so a pattern can flip when you move code between languages. Second, WGSL is much stricter: it has no ? : operator (you write select), you cannot assign to two components at once, and integers and floats never mix silently.

Which one should you learn first?

• You use Unity or Unreal: HLSL.
• You want to make shader art or work on the web: GLSL (and Shadertoy), then WGSL when you move to WebGPU.
• You use Godot: the Godot shading language; skills from GLSL carry over almost one to one.
• You build for Apple devices: Metal.

The honest answer is that the language matters far less than the concepts: positions, distance fields, noise, lighting, ray marching. That is why ShaderBattle teaches each lesson once and shows it in all eleven targets. Switch languages with the picker in the top bar, and the lessons, hints, starter code and export all follow. For a first lesson on the shared ideas, try Vectors & swizzling and Rotation & matrices.