Load image at path with GLKit services

Property definitions

gamnit :: display_ios $ TextureAsset :: glkit_load
	# Load image at `path` with GLKit services
	private fun glkit_load(path: NSString, premultiply: Bool): GLKTextureInfo
	in "ObjC" `{

		// The premultiplication flag has been inverted between iOS 9 and 10
		NSNumber *premultiply_opt;
		NSComparisonResult order = [[UIDevice currentDevice].systemVersion compare: @"10.0.0" options: NSNumericSearch];
		if (order == NSOrderedSame || order == NSOrderedDescending) {
			// >= 10
			premultiply_opt = premultiply? @NO: @YES;
		} else {
			// < 10
			premultiply_opt = premultiply? @YES: @NO;
		}

		NSDictionary *options = @{GLKTextureLoaderApplyPremultiplication: premultiply_opt};
		NSError *error;
		GLKTextureInfo *spriteTexture = [GLKTextureLoader textureWithContentsOfFile: path options: options error: &error];
		if (error != nil) NSLog(@"Failed to load texture: %@", [error localizedDescription]); // TODO return details to Nit

		return spriteTexture;
	`}
lib/gamnit/display_ios.nit:81,2--102,3