Explore bindless rendering in Metal

if(i.type == intersection_type::triangle)
{
  constant Instance& inst     = get_instance(i);
  constant Mesh&     mesh     = get_mesh(inst, i);
  constant Material& material = get_material(inst, i);
  
  color = shade_pixel(mesh, material, i);
}   

outImage.write(color, tid);

fragment half4 pbrFragment(ColorInOut in [[stage_in]],
                           texture2d< float > albedo    [[texture(0)]],
                           texture2d< float > roughness [[texture(1)]],
                           texture2d< float > metallic  [[texture(2)]],
                           texture2d< float > occlusion [[texture(3)]])
{	
	half4 color = calculateShading(in, albedo, roughness, metallic, occlusion);
	return color;
}

fragment half4 pbrFragmentBindless(ColorInOut in [[stage_in]], 
                                   device const Scene* pScene [[buffer(0)]])
{
	device const Instance& instance = pScene->instances[in.instance_id];
	device const Material& material = pScene->materials[instance.material_id];
	
	half4 color = calculateShading(in, material);
	
	return color;
}

if (intersection.type == intersection_type::triangle) 
{
  // solid blue triangle
  color = float4(0.0f, 0.0f, 1.0f, 1.0f);
}   

outImage.write(color, tid);

struct Instance
{
    constant Mesh*     pMesh            [[id(0)]];
    constant Material* pMaterial        [[id(1)]];
    constant float4x4  modelTransform   [[id(2)]];
};

// Shader code references scene
kernel void RTReflections( constant Scene* pScene [[buffer(0)]] );

MTLArgumentDescriptor* meshArg 
= [MTLArgumentDescriptor argumentDescriptor];

meshArg.index    = 0;
meshArg.dataType = MTLDataTypePointer;
meshArg.access   = MTLArgumentAccessReadOnly;

// Declare all other arguments (material and transform)
   
id<MTLArgumentEncoder> instanceEncoder 
= [device newArgumentEncoderWithArguments:@[meshArg, 
                                            materialArg, 
                                            transformArg]];

// Instance and Mesh

constant Instance& instance = pScene->instances[intersection.instance_id];
constant Mesh&     mesh     = instance.mesh[intersection.geometry_id];

// Primitive indices

ushort3 indices; // assuming 16-bit indices, use uint3 for 32-bit

indices.x = mesh.indices[ intersection.primitive_id * 3 + 0 ];
indices.y = mesh.indices[ intersection.primitive_id * 3 + 1 ];
indices.z = mesh.indices[ intersection.primitive_id * 3 + 2 ];

// Vertex data

packed_float3 n0 = mesh.normals[ indices.x ];
packed_float3 n1 = mesh.normals[ indices.y ];
packed_float3 n2 = mesh.normals[ indices.z ];

// Interpolate attributes

float3 barycentrics = calculateBarycentrics(intersection);
float3 normal       = weightedSum(n0, n1, n2, barycentrics);

if(i.type == intersection_type::triangle)
{
  constant Instance& inst     = get_instance(i);
  constant Mesh&     mesh     = get_mesh(inst, i);
  constant Material& material = get_material(inst, i);
  
  color = shade_pixel(mesh, material, i);
}   

outImage.write(color, tid);

fragment half4 pbrFragment(ColorInOut in [[stage_in]],
                           texture2d< float > albedo    [[texture(0)]],
                           texture2d< float > roughness [[texture(1)]],
                           texture2d< float > metallic  [[texture(2)]],
                           texture2d< float > occlusion [[texture(3)]])
{	
	half4 color = calculateShading(in, albedo, roughness, metallic, occlusion);
	
  return color;
}

fragment half4 pbrFragmentBindless(ColorInOut in [[stage_in]], 
                                   device const Scene* pScene [[buffer(0)]])
{
	device const Instance& instance = pScene->instances[in.instance_id];
	device const Material& material = pScene->materials[instance.material_id];
	
	half4 color = calculateShading(in, material);
	
	return color;
}