GLKit: Transparent texture when dealing with big 3D object

Question

I'm writing a 3D Viewer that displays .obj file and offers some basic gestures (pinning, rotating, zooming) by following 2 Raywenderlich tutorials: http://www.raywenderlich.com/48293/how-to-export-blender-models-to-opengl-es-part-1

http://www.raywenderlich.com/50398/opengl-es-transformations-gestures

I'm able to load and display correctly small .obj files but for big .obj files, the textures become suddenly transparent ! I have tested with the same texture files so I think the image size is not the cause . Please take a look at the below screenshot to have an idea:

Big obj: about 20000 vertices

Small obj: about 5000 vertices:

Quite big obj: about 67000 vertices:

A texture bitmap with only 2 colors (blue and yellow) which are used in big and quite big objs

The capsule texture (I don't use the 2 colors texture so that we can see clearly there is no transparency in the small obj)

I have tried different textures on different obj and it's always the same problem: the texture starts to be transparent when the obj file is big. I have also tested on different physical Iphone so it's not specific to the simulator. Enable/disable gl_blend doesn't solve the problem neither.

You can find the full code at http://pastecode.org/index.php/view/32247978 Here is the code I use to create the GLKBaseEffect and load texture image:

// Initialize
self.effect = [[GLKBaseEffect alloc] init];

// Texture
NSDictionary* options = @{ GLKTextureLoaderOriginBottomLeft: @YES };
NSError* error;
NSString* path = [[NSBundle mainBundle] pathForResource:@"capsule0.jpg" ofType:nil];

GLKTextureInfo* texture = [GLKTextureLoader textureWithContentsOfFile:path
                                                              options:options
                                                                error:&error];

if(texture == nil)
    NSLog(@"Error loading file: %@", [error localizedDescription]);

self.effect.texture2d0.name = texture.name;
self.effect.texture2d0.enabled = true;
self.effect.texture2d0.envMode = GLKTextureEnvModeReplace;


// Light
self.effect.light0.enabled = GL_TRUE;
self.effect.light0.position = GLKVector4Make(1.0f, 1.0f, 1.0f, 1.0f);
self.effect.lightingType = GLKLightingTypePerVertex;

And this part is for setting up OpenGL in viewDidLoad() after creating the effect:

// OpenGL ES Settings
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);

Answer 1

I have finally found the solution:

First, you need to set the depth format to 24 or 16 in the storyboard for the GLKView:

Then enable the depth in viewDidLoad() by

    glEnable(GL_DEPTH_TEST);

And finally for each draw call, you need to clear the depth buffer:

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);