integrating-metal-shaderconverter-shaders

name

integrating-metal-shaderconverter-shaders

description

ALWAYS use when integrating Metal shader converter (commonly referred to as MSC) shaders at runtime — binding model, top-level argument buffer (TLAB), root signature resource locations, descriptor/sampler heaps, static samplers, bindless resources, vertex fetch, separate stage-in, geometry/tessellation emulation, compute dispatch, unbounded arrays, and append/consume buffers. Do NOT trigger for compiling DXIL/HLSL to metallib — use compiling-with-metal-shaderconverter for that.

Metal shader converter — Integration Guide

Overview

Runtime integration: Metal requirements, binding model, pipeline setup, and common failure modes. Assumes metallib files are compiled.

References

Read the reference file for your use case before writing integration code:

Use case	Reference file
TLAB layout, root signatures, static samplers, descriptor encoding, compute dispatch, unbounded arrays, append/consume	references/binding-model.md
Metal vertex fetch, separate stage-in function	references/vertex-pipelines.md
Geometry and tessellation pipeline emulation	references/geometry-tessellation.md

Source materials — consult to verify API details or look up full implementations:

• metal_irconverter/metal_irconverter.h — Metal shader converter API: root signature, reflection, descriptor format
• metal_irconverter_runtime/metal_irconverter_runtime.h — companion header (header-only: read implementations directly when a helper is not used or to understand the manual path)
• /opt/metal-shaderconverter/docs/UserManual.md — canonical reference; read only if the user's question isn't answered by the reference files above

Metal constraints

Sampler state

All samplers must be created with supportArgumentBuffers = YES. Without it, gpuResourceID returns an invalid handle and the GPU reads a zeroed descriptor.

Texture type mapping

Metal shader converter maps HLSL texture types to Metal as follows. Supply Metal textures of the correct type — mismatches produce sampling errors or black output with no validation warning.

HLSL	Metal
1D *	2D
1D Array	2D Array
2D *	2D
2D Array	2D Array
Cube *	Cube
Cube Array	Cube Array
1D Multisampled *	2D Multisampled
1D Multisampled Array	2D Multisampled Array
2D Multisampled *	2D Multisampled
2D Multisampled Array	2D Multisampled Array
3D	No change

* Metal shader converter 2.x mapped these to the Array variant instead. See version differences below.

Metal shader converter 3.0 changed the Metal texture type for several HLSL types (marked * above) from the Array variant to the non-array variant. If you are using shaders compiled with Metal shader converter 2.x, enable the compatibility flag to preserve the old behavior:

• CLI: --forceTextureArray
• Library: IRCompilerSetCompatibilityFlags(compiler, IRCompatibilityFlagForceTextureArray)

Metal shader converter 3.0 also removed the requirement to use companion draw helpers (IRRuntimeDrawIndexedPrimitives etc.) for standard vertex/fragment draws. Geometry and tessellation emulation variants still require the companion.

Depth and stencil texture reads

D3D12 allows reading depth as Texture2D<float> via an SRV. Metal depth and stencil formats are in a separate format compatibility group from color formats — a Metal shader converter shader expecting texture2d<float> cannot sample a depth texture directly.

Common symptom: post-processing passes (SSAO, DoF, screen-space reflections) that sample the depth buffer produce all-zeros or garbage with no validation error.

Resolution: create an explicit MTLPixelFormatR32Float copy of the depth buffer, or use MTLTextureUsagePixelFormatView to reinterpret the depth data where the format permits.

Reflection

Always verify host-side binding code against Metal shader converter reflection — do not hardcode offsets or threadgroup sizes.

• Offline (at asset build time): --output-reflection-file <path> writes a JSON file per shader stage. Parse and store alongside the metallib.
• Runtime (via libmetalirconverter): IRObjectGetReflection(obj, stage, reflection) followed by stage-specific copy functions (IRShaderReflectionCopyComputeInfo, IRShaderReflectionCopyGeometryInfo, etc.).

Metal shader converter reflection covers top-level TLAB entries only. To determine individual resource offsets within descriptor tables, you need to use DXC/DXIL reflection.

Retrieving functions from synthesized metallibs

When Metal shader converter synthesizes a helper metallib — stage-in (IRMetalLibSynthesizeStageInFunction) or the libraries consumed by geometry/tessellation emulation — the result contains a single Metal function whose name is determined by Metal shader converter, not by your HLSL entry point. Hardcoding the name is fragile across Metal shader converter versions.

Query MTLLibrary.functionNames (count is expected to be 1) and take the first entry:

id<MTLFunction> fn = [lib newFunctionWithName:lib.functionNames.firstObject];

(functionNames()[0] in metal-cpp.)

Companion header

The companion header is optional for standard binding work. It provides:

• Binding point constants (kIR*BindPoint) — always useful; reference files list which constants each use case depends on
• Descriptor setter helpers (IRDescriptorTableSet*) — save encoding work; header-only implementations document the encoding logic for the manual path
• Geometry/tessellation emulation — required; no practical substitute
• Append/consume buffer helpers — convenience; header-only implementations also document the manual path

Metal 3 vs Metal 4: The companion is encoder-agnostic except for the geometry/tessellation emulation draw helpers, which have separate Metal 3 and Metal 4 variants.

Include setup:

#include <Metal/Metal.hpp>          // or Metal/Metal.h
#define IR_RUNTIME_METALCPP         // define before every inclusion (selects metal-cpp types)
#define IR_RUNTIME_METAL4           // optional — exposes IRRuntime4* emulation draw helpers; same "before every inclusion" rule
#define IR_PRIVATE_IMPLEMENTATION   // define in exactly one .cpp/.mm file
#include <metal_irconverter_runtime/metal_irconverter_runtime.h>

IR_RUNTIME_METALCPP must be defined before every inclusion — it selects the Metal types used throughout. Mismatching types between translation units causes silent ABI breakage.

HLSL Metal-language features

Function constants

For shaders that declare function constants in HLSL via MTL_FUNCTION_CONSTANT(), bind values at function retrieval time:

MTLFunctionConstantValues *fcv = [[MTLFunctionConstantValues alloc] init];
simd_float4 color = simd_make_float4(1.0, 1.0, 0.0, 1.0);
[fcv setConstantValue:&color type:MTLDataTypeUInt4 atIndex:0];

Always use MTLDataTypeUInt4 regardless of the declared HLSL type — the runtime treats each function constant as an opaque 16-byte value. Passing the natural Metal type (e.g. MTLDataTypeFloat4) silently binds the wrong data with no validation error.

The companion header provides a convenience helper that handles the packing:

IRRuntimeFunctionConstantValue colorFC = { .f0 = color.x, .f1 = color.y, .f2 = color.z, .f3 = color.w };
IRRuntimeSetFunctionConstantValue(fcv, 0, &colorFC);

Use the resulting MTLFunctionConstantValues when retrieving the function from the metallib (newFunctionWithName:constantValues:error:), then pass that function into your pipeline descriptor.

For HLSL declaration syntax and compile-time setup, see compiling-with-metal-shaderconverter and its references/hlsl-metal-extensions.md.

Framebuffer fetch

No host-side binding code — the feature is enabled at compile time and the shader reads the current attachment value via MTL_LOAD_FRAMEBUFFER. Ensure the render pass attachment uses MTLLoadActionLoad for any target the shader reads; with MTLLoadActionDontCare or MTLLoadActionClear the value the shader sees is undefined or the cleared color.

Anti-patterns

1. Hardcoding binding point values. Use named constants (kIRDescriptorHeapBindPoint, kIRArgumentBufferBindPoint, etc.). Values may change between Metal shader converter versions.
2. Not making resources resident for indirect access. Any resource accessed through a descriptor table or bindless heap must be made resident via useResource or useHeap before the draw or dispatch. The GPU silently reads from unmapped memory without this.

Debugging

Metal shader converter convention violations rarely produce errors at the API level. Wrong TLAB layout, mismatched param counts, bad descriptor entries, and non-resident resources all produce silent GPU-side corruption.

Enable Metal shader validation for additional coverage: MTL_SHADER_VALIDATION=1. Do not rely on it catching everything — it does not cover all binding model violations.

Symptom → where to look:

• Black output or wrong colors → descriptor table GPU addresses (absolute vs relative), sampler lifetime, descriptor type mismatch (buffer vs texture setter)
• Wrong constant values → verify root constants are written inline, not as a pointer; verify host param count matches HLSL root signature
• All zeros from a buffer resource → confirm IRDescriptorTableSetBuffer was used, not IRDescriptorTableSetTexture
• Geometry/tessellation corruption → vertex buffers bound on object stage, all buffers resident, pipeline config values from reflection