SceneKit – How to apply MTL texture to OBJ file?

Question

As a follow up to:

ios - How to apply mtl texture file to OBJ

I would like to add .MTL texture along with my .OBJ file, when importing my model to SceneKit

using code like this:

let scene = SCNScene(named: "rose.obj")

BUT the texture file I have is stored in DOCUMENTS directory (iOS).

How to call this function in Objective-C?

Answer 1

To work with the textured OBJ scene in Xcode you need a bundle of three files: .obj, .mtl and .jpg. To load an .obj scene with its corresponding textures, all three bundle-files must be located in the same Documents directory. Here's how your code might look when using Objective-C app:

#import "ViewController.h"

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    SCNView *sceneView = (SCNView *)self.view;
    
    NSArray<NSURL *> *urls = [NSFileManager.defaultManager 
                              URLsForDirectory:NSDocumentDirectory 
                              inDomains:NSUserDomainMask];

    NSURL *sceneInDocumentsDirectory = [urls[0] 
                                      URLByAppendingPathComponent:@"file.obj"];

    SCNScene *scene = [SCNScene sceneWithURL:sceneInDocumentsDirectory 
                                options:Nil 
                                error:Nil];

    sceneView.scene = scene;
    sceneView.allowsCameraControl = YES;
    sceneView.autoenablesDefaultLighting = YES;
    sceneView.backgroundColor = [UIColor blackColor];

    NSLog(@"%@", sceneInDocumentsDirectory);
}

@end

As you know, a .mtl file is an ASCII-based definitions of materials for .obj file.

Here's how it looks like:

newmtl phong1SG
illum 4
Kd 0.00 0.00 0.00
Ka 0.00 0.00 0.00
Tf 1.00 1.00 1.00
map_Kd texture.jpeg
Ni 1.00
Ks 0.50 0.50 0.50
Ns 18.00