Go bindless with Metal 3

// Write argument buffers in Metal 3

struct Mesh
{
   uint64_t normals; // 64-bit uint for constant packed_float3*
};

NSUInteger meshArgumentSize = sizeof(struct Mesh);

id<MTLBuffer> meshArgumentBuffer = [device newBufferWithLength:meshArgumentSize
                                                       options:storageMode];

struct Mesh* meshes = (struct Mesh *)(meshArgumentBuffer.contents); 
 
meshes->normals = normalBuffer.gpuAddress + normalBufferOffset;

// Shader struct:

struct Mesh
{
   constant packed_float3* normals;
};

// Host-side struct:

struct Mesh
{
    uint64_t normals;
};

// Shared struct:

#if __METAL_VERSION__
#define CONSTANT_PTR(x) constant x*
#else
#define CONSTANT_PTR(x) uint64_t
#endif

struct Mesh
{
    CONSTANT_PTR(packed_float3) normals;
};

// Write unbounded arrays of resources in Metal 3

struct Mesh
{
   uint64_t normals; // 64-bit uint for constant packed_float3*
};

NSUInteger meshArgumentSize = sizeof(struct Mesh) * meshes.count;

id<MTLBuffer> meshArgumentBuffer = [device newBufferWithLength:meshArgumentSize
                                                        options:storageMode];

struct Mesh* meshes = (struct Mesh *)(meshArgumentBuffer.contents); 

for ( NSUInteger i = 0; i < meshes.count; ++i )
{
   meshes[i].normals = normalBuffers[i].gpuAddress + normalBufferOffsets[i];
}

// Metal shading language:

struct Mesh
{
   constant packed_float3* normals;
};


fragment half4 fragmentShader(ColorInOut v          [[stage_in]],
                              constant Mesh* meshes [[buffer(0)]] )
{
    /* determine mesh to read, e.g. geometry_id */

    packed_float3 n0 = meshes[ geometry_id ].normals[0];
    packed_float3 n1 = meshes[ geometry_id ].normals[1];
    packed_float3 n2 = meshes[ geometry_id ].normals[2];

    /* interpolate normals and calculate shading */
}

// Metal shading language:
struct Mesh
{
   constant packed_float3* normals;
};

struct Scene
{
   constant Mesh*     meshes;     // mesh array
   constant Material* materials;  // material array
};

fragment half4 fragmentShader(ColorInOut v          [[stage_in]],
                              constant Scene& scene [[buffer(0)]] )
{
    /* determine mesh to read, e.g. geometry_id */
    packed_float3 n0 = scene.meshes[ geometry_id ].normals[0];
    packed_float3 n1 = scene.meshes[ geometry_id ].normals[1];
    packed_float3 n2 = scene.meshes[ geometry_id ].normals[2];
    /* interpolate normals and calculate shading */
}

heapAccelerationStructureSizeAndAlignWithDescriptor:

// Argument buffer loading
for (NSUInteger i = 0; i < mesh.submeshes.count; ++i) {

    Submesh*      submesh     = mesh.submeshes[i];
    id<MTLBuffer> indexBuffer = submesh.indexBuffer;
    NSArray*      textures    = submesh.textures;

    // Copy index buffer into argument buffer
   submeshAB[i].indices = indexBuffer.gpuAddress;

    // Copy material textures into argument buffer
   for (NSUInteger m = 0; m < textures.count; ++m) {
        submeshAB[i].textures[m] = textures[m].gpuResourceID;
    }

    // Remember indirect resources
    [sceneResources addObject:indexBuffer];
    [sceneResources addObjectsFromArray:textures];
}