How to setup physical based rendering in SceneKit from code?

Question

I want to present some scene with PBR. I created metalness and roughness textures and want to apply it to the mesh. When I try to do it in Xcode - everything is fine. I can add this model to the scene and then add this textures to the model.

But I want to do it programmatically. Here is my code:

NSData *vertices = [[NSData alloc] initWithBytes:modelPly->vertices length:modelPly->vertexCount * 3 * sizeof(float)];
SCNGeometrySource *vertexSource = [SCNGeometrySource geometrySourceWithData:vertices
                                                                   semantic:SCNGeometrySourceSemanticVertex
                                                                vectorCount:modelPly->vertexCount
                                                            floatComponents:YES
                                                        componentsPerVector:3
                                                          bytesPerComponent:sizeof(float)
                                                                 dataOffset:0
                                                                 dataStride:sizeof(float) * 3];

// Normal source
NSData *normals = [[NSData alloc] initWithBytes:modelPly->normals length:modelPly->vertexCount * 3 * sizeof(float)];
SCNGeometrySource *normalSource = [SCNGeometrySource geometrySourceWithData:normals
                                                                   semantic:SCNGeometrySourceSemanticNormal
                                                                vectorCount:modelPly->vertexCount
                                                            floatComponents:YES
                                                        componentsPerVector:3
                                                          bytesPerComponent:sizeof(float)
                                                                 dataOffset:0
                                                                 dataStride:sizeof(float) * 3];


// Texture coordinates source
NSData *facesTextures = [[NSData alloc] initWithBytes:modelPly->texCoord length:modelPly->vertexCount * 2 * sizeof(float)];
SCNGeometrySource *texcoordSource = [SCNGeometrySource geometrySourceWithData:facesTextures
                                                                     semantic:SCNGeometrySourceSemanticTexcoord
                                                                  vectorCount:modelPly->vertexCount
                                                              floatComponents:YES
                                                          componentsPerVector:2
                                                            bytesPerComponent:sizeof(float)
                                                                   dataOffset:0
                                                                   dataStride:sizeof(float) * 2];


NSData *indicesData = [NSData dataWithBytes:modelPly->indices length:modelPly->indexCount * sizeof(uint) * 3];
SCNGeometryElement *elements = [SCNGeometryElement geometryElementWithData:indicesData
                                                            primitiveType:SCNGeometryPrimitiveTypeTriangles
                                                           primitiveCount:modelPly->indexCount
                                                            bytesPerIndex:sizeof(uint)];

SCNGeometry *geometry = [SCNGeometry geometryWithSources:@[vertexSource, normalSource, texcoordSource] elements:@[elements]];
MDLMesh *mesh = [MDLMesh meshWithSCNGeometry:geometry];

Then I'm trying to create material:

MDLPhysicallyPlausibleScatteringFunction *scatFunction = [MDLPhysicallyPlausibleScatteringFunction new];
MDLMaterial *mdlMaterial = [[MDLMaterial alloc] initWithName:@"material" scatteringFunction:scatFunction];
[mdlMaterial removeAllProperties];
MDLMaterialProperty *bcProperty = [[MDLMaterialProperty alloc] initWithName:@"BaseColor" semantic:MDLMaterialSemanticBaseColor URL:plyItem.textureFileURL];
MDLMaterialProperty *metalnessProperty = [[MDLMaterialProperty alloc] initWithName:@"metallic" semantic:MDLMaterialSemanticMetallic URL:[[NSBundle mainBundle] URLForResource:@"metalness" withExtension:@"jpg"]];
MDLMaterialProperty *roughnessProperty = [[MDLMaterialProperty alloc] initWithName:@"roughness" semantic:MDLMaterialSemanticRoughness URL:[[NSBundle mainBundle] URLForResource:@"roughness" withExtension:@"jpg"]];

[mdlMaterial setProperty:bcProperty];
[mdlMaterial setProperty:metalnessProperty];
[mdlMaterial setProperty:roughnessProperty];

and apply it to my geometry:

SCNNode *node = [SCNNode nodeWithMDLObject:mesh];
SCNMaterial *material = [SCNMaterial materialWithMDLMaterial:mdlMaterial];
material.lightingModelName = SCNLightingModelPhysicallyBased;
node.geometry.firstMaterial = material;

If I check in debugger mdlMaterial contains all information about roughness and metalness, but material doesn't. What's wrong?

Answer 1

Assign it thru any material slot located in SCNGeometry:

// Swift 5.6
let sphereNode = SCNNode(geometry: SCNSphere(radius: 1))
let material = sphereNode.geometry?.firstMaterial
material?.roughness.contents = 0.12
material?.metalness.contents = 0.95
material?.lightingModel = .physicallyBased

// Objective-C
sphereNode.geometry.firstMaterial.roughness.contents = @0.12;
sphereNode.geometry.firstMaterial.metalness.contents = @0.95;
sphereNode.geometry.firstMaterial.lightingModelName = SCNLightingModelPhysicallyBased;

Here's a macOS code sample written in Objective-C for testing:

#import "GameViewController.h"

@implementation GameViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    
    SCNView *sceneView = (SCNView *)self.view;
    SCNScene *scene = [SCNScene scene];
    sceneView.scene = scene;
    sceneView.allowsCameraControl = YES;
    sceneView.autoenablesDefaultLighting = YES;
    sceneView.backgroundColor = [NSColor blackColor];
    
    SCNMaterial *material = [SCNMaterial material];
    material.lightingModelName = SCNLightingModelPhysicallyBased;
    material.diffuse.contents = [NSImage imageNamed:@"YourPicture"];
    material.metalness.contents = [NSColor whiteColor];
    material.roughness.contents = [NSColor blackColor];
    
    SCNNode *sphere = [SCNNode node];
    sphere.geometry = [SCNSphere sphereWithRadius:0.25];
    sphere.geometry.firstMaterial = material;
    [scene.rootNode addChildNode:sphere];
}
@end