在SceneKit中模拟折射

Question

我正在尝试为一个项目创建一个ios 9应用程序,它将使用这些特殊的理论镜头(称为glenses)来显示3D场景.

一个名为TIM的射线追踪程序已经从头开始编写,用于模拟这些格伦等等,但简单地将其移植到ios是不可行的.

我在搜索网站时的理解(即这个答案以及着色器上的许多其他内容)是它应该是可能的,但我很难获得理想的效果.

我决定在开始进行更复杂的glens类型折射之前,首先实现一种更简单的折射形式:

我能够在相机上使用桶形失真(鱼眼镜头)效果SCNTechnique,但是看起来你只能在相机或整个场景上使用技术,而不是单个几何体.

之后我尝试通过使用SCNMaterial's shaderModifiers属性注入opengl代码来获得应用于几何的桶形失真效果:

    var shaders = [SCNShaderModifierEntryPoint: String]()

    try! shaders[SCNShaderModifierEntryPoint.fragment] = String(contentsOfFile: Bundle.main.path(forResource: "FishEye", ofType: "fsh")!, encoding: String.Encoding.utf8)

    try! shaders[SCNShaderModifierEntryPoint.geometry] = String(contentsOfFile: Bundle.main.path(forResource: "FishEye", ofType: "vsh")!, encoding: String.Encoding.utf8)

    let material = SCNMaterial()
    material.shaderModifiers = shaders
    object.geometry?.materials = [material]

我在这里使用了稍加修改的着色器:

fisheye.vsh

varying vec2 uv;

#pragma body

gl_Position = a_position;
uv = a_position.xy;

fisheye.fsh

uniform sampler2D colorSampler;
const float PI = 3.1415926535;
const float barrelPower = 0.5;
uniform vec2 rg;
uniform vec2 uv2;
varying vec2 uv;
uniform float d;
uniform vec2 xy;
uniform vec2 Vertex_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);
}

#pragma body
#pragma transparent

vec2 xy = 2.0 * Vertex_UV.xy - 1.0;
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);

这些着色器编译并加载到场景中的对象上,但什么都不做; 如果没有注入的着色器,它几乎是透明的,对象是不透明的和白色的,并且#pragma transparent指令应该使它透明.

为了说清楚,我在这里想要实现的是在一个场景中有一个3D镜头,你可以通过它看到另一边的任何东西的折射图像.

任何帮助将非常感谢!

Answer 1

如果您想使用自己的顶点和片段着色器而不是 SceneKit 默认着色器程序，则也必须使用 SCNProgram 而不是 SCNShaderModifierEntryPoint。

SCNShaderModifierEntryPoints 只允许修改 Swift 的默认着色器程序。

let material = SCNMaterial()
            let program:SCNProgram = SCNProgram()
            do {
                program.vertexShader = try String(contentsOfFile: Bundle.main.path(forResource: "fisheye", ofType: "vsh")!, encoding: String.Encoding.utf8)
            } catch let error {
                print("shaderReadingError:\(error)")
            }
            do {
                program.fragmentShader = try String(contentsOfFile: Bundle.main.path(forResource: "fisheye", ofType: "fsh")!, encoding: String.Encoding.utf8)
            } catch let error {
                print("shaderReadingError:\(error)")
            }

    // and also your vertex shader has lack. 
    // You have to add some geometry source and transformation matrix to the vertex shader first with setSemantic method. 

            program.setSemantic(SCNGeometrySource.Semantic.vertex.rawValue, forSymbol: "vPosition", options: nil)
            program.setSemantic(SCNGeometrySource.Semantic.texcoord.rawValue, forSymbol: "uv", options: nil)
            program.setSemantic(SCNModelViewProjectionTransform, forSymbol: "uMVPMatrix", options: nil)





    // and also your fragment shader expect some realtime data like
    // colorSampler, rg, uv2, d, xy, Vertex_UV
    // you have to use handleBinding block to update this values before rendering the object.
            material.handleBinding(ofSymbol: "resolution", handler: { (programId:UInt32, location:UInt32, node:SCNNode?, renderer:SCNRenderer) in


            })


            material.program = program
            yourNode.geometry.firstMaterial = material