Why does my scene camera only show black screen when I use SCNTechnique?

Question

So I'm using SceneKit with iOS 12 (Swift 4.2), and I want to add a twirl/bump distortion to the camera. I found something similar here (Fish Eye Wide-angle with a Scene Kit Camera: Possible?) that supposedly creates a barrel distortion. But when I tried adding it to my project the scene just turns black and I get an error in the console

2019-03-07 13:35:14.982232+0000 TestingSCN[551:66202] [framework] CUIThemeStore: No theme registered with id=0

2019-03-07 13:35:15.064859+0000 TestingSCN[551:66202] [framework] CUIThemeStore: No theme registered with id=0

2019-03-07 13:35:15.097517+0000 TestingSCN[551:66270] [framework] CUIThemeStore: No theme registered with id=0

2019-03-07 13:35:15.118445+0000 TestingSCN[551:66270] [SceneKit] Error: can not render without programs, using default

Now the method is basically using a JSON dictionary file to define a technique and GLSL vertex and fragment shader files. Then in my main swift file, I add that technique to the camera. This is the code I used: barrel.json (located in art.scnassets)

{
    "passes" : {
        "barrel" : {
            "outputs" : {
                "color" : "COLOR"
            },
            "inputs" : {
                "colorSampler" : "COLOR",
                "noiseSampler" : "noiseSymbol",
                "a_position" : "a_position-symbol"
            },
            "program" : "art.scnassets/barrel",
            "draw" : "DRAW_QUAD"
        }
    },
    "sequence" : [
        "barrel"
    ],
    "symbols" : {
        "a_position-symbol" : {
        "semantic" : "vertex"
        },
        "noiseSymbol" : {
            "image" : "noise.png",
            "type" : "sampler2D"
        },
        "barrelPower" : {
            "type" : "float"
        }
    }
}

barrel.fsh

uniform sampler2D colorSampler;
const float PI = 3.1415926535;
uniform float barrelPower;
varying vec2 uv;
vec2 Distort(vec2 p)
{
    float theta  = atan(p.y, p.x);
    float radius = length(p);
    radius = pow(radius, barrelPower);
    p.x = radius * cos(theta);
    p.y = radius * sin(theta);
    return 0.5 * (p + 1.0);
}
void main() {
    vec2 rg = 2.0 * uv.xy - 1.0;
    vec2 uv2;
    float d = length(xy);
    if (d < 1.0){
        uv2 = Distort(xy);
    } else {
        uv2 = uv.xy;
    }
    gl_FragColor = texture2D(colorSampler, uv2);
}

barrel.vsh

attribute vec4 a_position;
varying vec2 uv;

void main() {
    gl_Position = a_position;
    uv = a_position.xy;
}

GameViewController.swift (in viewDidLoad)

let url: URL = Bundle.main.url(forResource: "art.scnassets/barrel", withExtension: "json")!

do {
    let jsonData = try Data(contentsOf: url)
    let jsonObject = try JSONSerialization.jsonObject(with: jsonData, options:JSONSerialization.ReadingOptions(rawValue: 0))
    guard let dictionary = jsonObject as? Dictionary<String, Any> else {
        print("Not a Dictionary")
        return
    }
    var technique: SCNTechnique? = nil
    technique = SCNTechnique(dictionary: dictionary)
    technique?.setValue(NSNumber(value: 0.5), forKey: "barrelPower")
    cameraNode.camera?.technique = technique
}
catch let error as NSError {
    print("Found an error - \(error)")
}

I'm not really an expert in shaders, and I know that it's probably better to write an SCNProgram or something but I have not clue where to even begin with that. Any help is appreciated :)

score 0 · Answer 1 · answered Mar 07 '19 at 21:44

You may try

    let scnView = self.view as! SCNView
    scnView.technique = technique

as you are using a ("draw" : "DRAW_QUAD") which is rendering a texture of render objects.

Also there is a compiler error :

 float d = length(xy);  // `xy` is not defined

Why does my scene camera only show black screen when I use SCNTechnique?

1 Answers1