I am encountering very poor performance with a long dance animation with 70 frames. Sprite Kit stutters often and the SKSpriteNode has small dimensions.
In the atlas I see many of my frames are rotated 90 degrees. I get the impression Sprite Kit stutters every time it hits one of the rotated frames.
Is there a build setting that will tell Xcode that rotation is not allowed?
You could try TexturePacker. It allows you to disable rotation and besides that has far more features than the built-in TextureAtlas tool.
Xcode's texture atlas tool has no option to disable rotation of images. You can find the tool in
../Xcode.app/Contents/Developer/usr/bin/TextureAtlas