.METAL

Introduction

A .metal file holds shaders written in the Metal Shading Language, the language of Apple’s Metal graphics and compute API on macOS, iOS and Apple’s other systems. The language is based on C++, with vector and matrix types and attributes that tie functions and their arguments to the pipeline.

Xcode compiles the .metal files in a project into a Metal library, default.metallib, which is shipped inside the app and loaded at run time. Source can also be compiled while the app runs.

Structure

A Metal file is plain text in C++ syntax. It usually includes <metal_stdlib> and uses the metal namespace. Each shader is a function marked vertex, fragment or kernel (for compute). Attributes in double square brackets say where values come from, such as [[buffer(0)]], [[stage_in]] or [[position]].

#include <metal_stdlib>
using namespace metal;

struct VertexOut {
    float4 position [[position]];
    float4 colour;
};

fragment float4 fragmentMain(VertexOut in [[stage_in]]) {
    return in.colour;
}

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