使用SCNTechnique与SceneKit和OpenGL ES

Question

我正在尝试调整此页面http://www.geeks3d.com/20140213/glsl-shader-library-fish-eye-and-dome-and-barrel-distortion-post-processing-filters/6/

中描述的着色器

我真正想做的是让SCNCamera使用用户可控制的镜头虚拟焦距渲染我的SCNScene。

以下是我可以通过调整此着色器的最佳方法。结果是整个视口中的单一颜色。我绝对不会使用这个GLSL。

我没有停止使用Open GL而不介意使用Metal shader，我只是没有看到任何关于如何在这里使用它的例子。

片段

uniform sampler2D tex0;
varying vec2 uv;
uniform vec2 size;
uniform float lensSize; // 0.4



void main(void)
{
    vec2 p = gl_FragCoord.xy / uv.xy;
    vec2 m = uv.xy;
    //vec2 m = mouse.xy / a_position.xy;

    vec2 d = p - m;
    float r = sqrt(dot(d, d)); // distance of pixel from mouse

    vec2 uv2;
    vec3 col = vec3(0.0, 0.0, 0.0);
    if (r > lensSize+0.01)
    {
        uv2 = p;
        col = texture2D(tex0, vec2(uv2.x, -uv2.y)).xyz;
    }
    else if (r < lensSize-0.01)
    {
        // Thanks to Paul Bourke for these formulas; see
        // http://paulbourke.net/miscellaneous/lenscorrection/
        // and .../lenscorrection/lens.c
        // Choose one formula to uncomment:
        // SQUAREXY:
        // uv = m + vec2(d.x * abs(d.x), d.y * abs(d.y));
        // SQUARER:
        uv2 = m + d * r; // a.k.a. m + normalize(d) * r * r
        // SINER:
        // uv = m + normalize(d) * sin(r * 3.14159 * 0.5);
        // ASINR:
        // uv = m + normalize(d) * asin(r) / (3.14159 * 0.5);
        col = texture2D(tex0, vec2(uv2.x, -uv2.y)).xyz;
    }
    gl_FragColor = vec4(col, 1.0);
}

顶点

attribute vec4 a_position;
varying vec2 uv;

void main()
{
    gl_Position = a_position;
    uv = (a_position.xy + 1.0) * 0.5;
}

SCNTechnique init词典

{
  "passes": {
    "barrel": {
      "outputs": {
        "color": "COLOR"
      },
      "inputs": {
        "tex0": "COLOR",
        "a_position": "a_position-symbol"
      },
      "program": "art.scnassets/barrel",
      "draw": "DRAW_QUAD"
    }
  },
  "sequence": [
    "barrel"
  ],
  "symbols": {
    "a_position-symbol": {
      "semantic": "vertex"
    },
    "lensSize": {
      "type": "float"
    }
  }
}

夫特

let technique = SCNTechnique(dictionary: propsDict as! Dictionary)
technique?.setValue(1, forKey: "lensSize")
myNode.camera = SCNCamera()
myNode.camera?.technique = technique