ARKit, metal shader for ARSCNView

user_1579275 0
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Trying to figure out how to solve my issue of applying shaders to my ARSCNView. Previously, when using a standard SCNView, i have successfully been able to apply a distortion shader the following way: 

if let path = Bundle.main.path(forResource: "art.scnassets/distortion", ofType: "plist") {
    if let dict = NSDictionary(contentsOfFile: path)  {
        let technique = SCNTechnique(dictionary: dict as! [String : AnyObject])

        scnView.technique = technique
    }
}

Replacing SCNView with ARSCNView gives me the following error(s):

"Error: Metal renderer does not support nil vertex function name"

"Error: _executeProgram - no pipeline state"

I was thinking it's because that ARSCNView uses a different renderer than SCNView. But logging ARSCNView.renderingAPI tells me nothing about the renderer, and i can't seem to choose one when i construct my ARSCNView instance. I must be missing something obvious, because i can't seem to find a single resource when scouring for references online.

My initial idea was instead use a SCNProgram to apply the shaders. But i can't find any resources of how to apply it to an ARSCNView, or if it's even a correct/possible solution, SCNProgram seems to be reserved for materials.

Anyone able to give me any useful pointers of how to solve vertex+fragment shaders for ARSCNView?

scenekit arkit swift opengl-es ios
2 Answers

SCNTechnique for ARSCNView does not work with GLSL shaders, instead Metal functions need to be provided in the technique's plist file under the keys metalVertexShader and metalFragmentShader.

To the contrary, documentation says any combination of shader should work:

You must specify both fragment and vertex shaders, and you must specify either a GLSL shader program, a pair of Metal functions, or both. If both are specified, SceneKit uses whichever shader is appropriate for the current renderer.

So it might be a mistake, but I guess the documentation is outdated. Since all ARKit running devices also run Metal, GLSL support has not been added to ARSCNViews. As iOS12 deprecates OpenGL this looks like planned.

user_20508920

I had this issue in ARKit iOS11.4 and 12 and it came down to a series of miss-spelt shaders. I hope this might help someone.

user_38103320
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