Is there a way to use compressed textures with SceneKit background CubeMaps?

Question

SceneKit uses a specific SCNMaterial for the 3D background of a scene.

We have to use scnScene.background.diffuse.contents = one of:

• A vertical strip (single image with height = 6x width)
• An horizontal strip (single image with 6x height = width)
• A spherical projection ( single image with 2xheight = width)
• An array of 6 square images

My background images are currently in JPG or PNG format, but they are slow to decompress, and I would like to use compressed textures (PVRTC or ASTC formats).

I cannot use compressed textures using the vertical, horizontal strips and spherical projections as they are not square images, and PVRTC/ASTC require square textures under iOS. I tried to PVRTC compress the array of 6 square images, but background.diffuse.contents requires an array of 6 UIImages, and although there is no error in the log, I don't see any 3D background when I assign an array of 6 SKTexture to background.diffuse.contents.

My question is the following:

• Is there a way to use PVRTC or ASTC textures as a 3D SceneKit background (CubeMap, Spherical projection...) ?

Answer 1

I found the solution. For anyone interested:

You can assign a Model IO texture to scnScene.background.contents You can load a cube map Model IO texture using the function textureCubeWithImagesNamed:(Array of paths to 6 PVRTC compressed textures)

NSURL* posx = [artworkUrl URLByAppendingPathComponent:@"posx.pvr"]; 
NSURL* negx = [artworkUrl URLByAppendingPathComponent:@"negx.pvr"];
NSURL* posy = [artworkUrl URLByAppendingPathComponent:@"posy.pvr"];
NSURL* negy = [artworkUrl URLByAppendingPathComponent:@"negy.pvr"];
NSURL* posz = [artworkUrl URLByAppendingPathComponent:@"posz.pvr"];
NSURL* negz = [artworkUrl URLByAppendingPathComponent:@"negz.pvr"];

MDLTexture* cubeTexture = [MDLTexture textureCubeWithImagesNamed:@[posx.path,negx.path,posy.path,negy.path,posz.path,negz.path] ]; 
scnScene.background.contents = cubeTexture;