使用webgl 2.0，延迟阴影，帧缓冲区对带有三角形网格的场景进行光线追踪

时间：2018-12-13 15:41:11

标签： javascript opengl-es glsl webgl webgl2

在其他堆栈溢出用户将我的原始帖子标记为“过宽”之后。我将以更少的行数重新表述我的问题。我在sharttoy中实现了光线行进器，并且我了解了有关光线与物体相交的所有数学知识。我想下一步进行网格的光线跟踪。我发现，需要使用延迟渲染和帧缓冲区（两次通过渲染，一个用于几何图形，另一个用于照明计算，光线跟踪）来完成此操作，并且相交将通过射线-三角形相交发生。

当然，我将在接下来的几周内发布一些代码，因为我将开始实现这一点。并且我将需要一些具体的帮助，但在此之前，我将不胜感激，以便现在可以浪费时间搜索网络。这就是为什么我在这里发布..

原始帖子被标记为“太宽”

这是我有史以来第一篇关于堆栈溢出的文章。我的目标是编写一个带有网格物体的光线跟踪器。

到目前为止，我唯一要做的就是制作一个具有球体和平面的光线追踪器。这是通过正向渲染完成的，同时在片段着色器中创建所有几何体（很容易生成球体和平面）。

经过所有的研究，我终于找到了解决方案。这可以通过使用延迟着色技术来实现，在该技术中，您可以创建几何并将其作为纹理传递到G缓冲区，然后通过第二遍开始照明和光线跟踪的计算。

我之所以寻求指导，是因为我既不熟悉着色器也不喜欢图形库，因此花了很多天/月（3-4）才能得出这个结论。 我的问题如下：

1）这种方法正确吗？ 2）其次，有人可以引导我到三角形的交点吗？ 术语“三角形相交”不是指射线-三角形相交的数学和过程。我知道这一点。我不知道的是在第一个交叉点之后，如何检查下一个碰撞，如何测试下一个三角形。我需要以哪种方式在G缓冲区中传递顶点以遍历它们并检查相交（一些示例glsl代码很容易理解）？

这里是我为了看得出结论而阅读的链接

  1. https://www.opengl.org/discussion_boards/showthread.php/200487-Ray-intersection-with-GLSL
  2. https://www.imgtec.com/blog/five-steps-to-adding-ray-tracing-to-an-opengl-es-based-deferred-lighting-system/
  3. https://learnopengl.com/Advanced-Lighting/Deferred-Shading
  4. GPU PRO 6书，第351-368页

如果我错过了堆栈溢出社区中的任何链接，请在此处发布。

与答案相关的任何答案，我将不胜感激。 预先谢谢你。

1 个答案:

答案 0 :(得分：1)

我也很自以为是，很难开始。但这很容易。
您需要将网格数据打包为RGB（A）纹理 然后将其打包到片段着色器中
关于此技术的一些非常好的pfds，下面是一个示例： http://www.cs.harvard.edu/~sjg/papers/gim.pdf

纹理布局示例：
使用RGB（Alpha通道可用于材质索引）

             colums       colums      colums
        |      0      |     1     |      2
        |  R   G   B  | R   G   B |  R   G   B
        |-------------|-----------|-----------
    rows|  1   0   0  |           |

CPU端：
gl.texImage2D（gl.TEXTURE_2D，0，gl.RGB32F，dataLenght / channels，1，0，gl.RGB，gl.FLOAT，meshVerts）；
texImage2D reference
GPU端：
texelFetch（uMeshData，ivec2（vertIndex，0），0）;
texelFetch reference

某些资源/链接：
用C ++编写，但实际上与#version 300 es glsl着色器的对话距离并不远：
scratchapixel
OpenGL开发Cookbook具有一些读取obj以将图像分割成片段的说明
the source on github
我个人认为这是网络上最好的pathtracer：
凭我的一点知识，我可以看到这个家伙读完了Physically Based Rendering这本书
这是了解concept of computer graphics的很好的教程
更新/编辑： Peter Shirleys Raytracing in a Weekend是免费下载的

我自己的小尝试

(() => {
'use strict';
// vertex
const vs = `#version 300 es\nin vec2 p;out vec2 vuv;void main(){gl_Position = vec4(vuv = p, 0, 1);}`;

// fragment
const fs = `#version 300 es\n
precision highp float;
precision highp int;
precision highp sampler2D; 
in vec2 vuv;
uniform float time;
uniform vec2 Res, mouse;
uniform sampler2D uMeshData;
uniform int vertsCount;
layout(location = 0) out lowp vec4 fragColor;

struct Ray {
  vec3 orig, dir;
}R_;

mat4 rotate() {
float x = mouse.x, y=mouse.y+sin(time*2.),z=0.;
  float a = sin(x), b = cos(x), c = sin(y), d = cos(y), e = sin(z), f = cos(z), ac = a * c, bc = b * c;
  return mat4(d * f, d * e, -c, 0.0, ac * f - b * e, ac * e + b * f, a * d, 0.0, bc * f + a * e, bc * e - a * f, b * d, 0.0, 0.0, 0.0, 0.0, 1.0);
}

// https://github.com/Jojendersie/gpugi/blob/5d18526c864bbf09baca02bfab6bcec97b7e1210/gpugi/shader/intersectiontests.glsl#L63
bool isTriangle(Ray ray, in vec3 p0, in vec3 p1, in vec3 p2, out vec3 N) {
  vec3 e0 = p1 - p0, e1 = p0 - p2;
  N = cross(e1, e0);
  vec3 e2 = (1.0 / dot(N, ray.dir)) * (p0 - ray.orig);
  vec3 i = cross(ray.dir, e2);
  vec3 b = vec3(0.0, dot(i, e1), dot(i, e0));
  b.x = 1.0 - (b.z + b.y);
  return (dot(N, e2) > 1e-8) && all(greaterThanEqual(b, vec3(0.0)));
}

void Camera(out Ray ray, vec3 lookAt, vec3 up, float angle, float aspect) {
  vec3 g = normalize(lookAt - ray.orig);
  vec3 u = normalize(cross(g, up));
  vec3 v = normalize(cross(u, g));
  u = u * tan(radians(angle * .5));
  v = v * tan(radians(angle * .5)) / aspect;
  ray.dir = normalize(g + ray.dir.x * u + ray.dir.y * v);
}

void main() {
  vec3 SceneCol = vec3(0.5);
  
  vec3 hit = vec3(0.);
  vec4 a = vec4(0.0), b = vec4(0.0), c = vec4(0.0);
  
  R_ = Ray(vec3(0.0, 0.0, 3.0), vec3(vuv, -1.));
  
  Camera(R_, vec3(0., 0., 1.), vec3(0., 1., 0.), 90.0, (Res.x / Res.y));
  
  float mindist = -1000.0;

	// here comes this importend part unpack the texture
  for (int i = 0; i < vertsCount; i += 3) 
  {

    a = rotate() * texelFetch(uMeshData, ivec2(i, 0), 0);
    b = rotate() * texelFetchOffset(uMeshData, ivec2(i, 0), 0, ivec2(1, 0));
    c = rotate() * texelFetchOffset(uMeshData, ivec2(i, 0), 0, ivec2(2, 0));
    
    if (isTriangle(R_, a.xyz, b.xyz, c.xyz, hit))
    {
      float z = hit.z;
      if (z > mindist) {
        mindist = z;
        SceneCol.rgb = vec3(hit.x, hit.y, 1. - (hit.x - hit.y));
      };
    }
  }
  
  vec3 sky = vec3(0.5, 0.25, 0.1) * (-R_.dir.y - 0.1);
  fragColor.rgb = SceneCol + sky;
  fragColor.a = 1.0;
}`;

    const canvas = document.getElementById('c');
    const gl = canvas.getContext('webgl2', {
        alpha: !1,
        depth: !1,
        stencil: !1,
        antialias: !1,
        premultipliedAlpha: !1,
        presereDrawingBuffer: !1,
        failIfMajorPerformanceCaveat: !1
    });

    const { width, height } = canvas.getBoundingClientRect();
    gl.canvas.width = width;
    gl.canvas.height = height;

    // init
    const P = gl.createProgram();

    const Fp = gl.createShader(gl.FRAGMENT_SHADER);
    gl.shaderSource(Fp, fs);
    gl.compileShader(Fp);
    if (!gl.getShaderParameter(Fp, gl.COMPILE_STATUS)) throw '! F r a g: ' + gl.getShaderInfoLog(Fp);
    gl.attachShader(P, Fp);

    const Vp = gl.createShader(gl.VERTEX_SHADER);
    gl.shaderSource(Vp, vs);
    gl.compileShader(Vp);
    if (!gl.getShaderParameter(Vp, gl.COMPILE_STATUS)) throw '! V e r t: ' + gl.getShaderInfoLog(Vp);
    gl.attachShader(P, Vp);

    // link use program
    gl.linkProgram(P);
    gl.useProgram(P);

    // uniform location
    const time_loc = gl.getUniformLocation(P, 'time');
    const res_loc = gl.getUniformLocation(P, 'Res');
    const uLvertices = gl.getUniformLocation(P, 'vertsCount');
    const uLSr = gl.getUniformLocation(P, 'uMeshData');
    const mouse_loc = gl.getUniformLocation(P, 'mouse');

    // free resources
    gl.detachShader(P, Fp);
    gl.detachShader(P, Vp);
    gl.deleteProgram(P);

    // fullscreen quad
    gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer());
    gl.bufferData(gl.ARRAY_BUFFER, new Int8Array([-3, 1, 1, -3, 1, 1]), gl.STATIC_DRAW);
    gl.enableVertexAttribArray(0);
    gl.vertexAttribPointer(0, 2, gl.BYTE, !1, 0, 0);
    gl.bindVertexArray(null);

    // bind texture
    const texture = gl.createTexture();
    gl.bindTexture(gl.TEXTURE_2D, texture);


    // blender 2.79 Icosphere
    // export -> *.raw (needs to be enable first under settings)
    const verts = [
        0.000000, 0.000000, -1.000000, 0.425323, -0.309011, -0.850654, -0.162456, -0.499995, -0.850654,
        0.723607, -0.525725, -0.447220, 0.425323, -0.309011, -0.850654, 0.850648, 0.000000, -0.525736,
        0.000000, 0.000000, -1.000000, -0.162456, -0.499995, -0.850654, -0.525730, 0.000000, -0.850652,
        0.000000, 0.000000, -1.000000, -0.525730, 0.000000, -0.850652, -0.162456, 0.499995, -0.850654,
        0.000000, 0.000000, -1.000000, -0.162456, 0.499995, -0.850654, 0.425323, 0.309011, -0.850654,
        0.723607, -0.525725, -0.447220, 0.850648, 0.000000, -0.525736, 0.951058, -0.309013, 0.000000,
        -0.276388, -0.850649, -0.447220, 0.262869, -0.809012, -0.525738, 0.000000, -1.000000, 0.000000,
        -0.894426, 0.000000, -0.447216, -0.688189, -0.499997, -0.525736, -0.951058, -0.309013, 0.000000,
        -0.276388, 0.850649, -0.447220, -0.688189, 0.499997, -0.525736, -0.587786, 0.809017, 0.000000,
        0.723607, 0.525725, -0.447220, 0.262869, 0.809012, -0.525738, 0.587786, 0.809017, 0.000000,
        0.723607, -0.525725, -0.447220, 0.951058, -0.309013, 0.000000, 0.587786, -0.809017, 0.000000,
        -0.276388, -0.850649, -0.447220, 0.000000, -1.000000, 0.000000, -0.587786, -0.809017, 0.000000,
        -0.894426, 0.000000, -0.447216, -0.951058, -0.309013, 0.000000, -0.951058, 0.309013, 0.000000,
        -0.276388, 0.850649, -0.447220, -0.587786, 0.809017, 0.000000, 0.000000, 1.000000, 0.000000,
        0.723607, 0.525725, -0.447220, 0.587786, 0.809017, 0.000000, 0.951058, 0.309013, 0.000000,
        0.276388, -0.850649, 0.447220, 0.688189, -0.499997, 0.525736, 0.162456, -0.499995, 0.850654,
        -0.723607, -0.525725, 0.447220, -0.262869, -0.809012, 0.525738, -0.425323, -0.309011, 0.850654,
        -0.723607, 0.525725, 0.447220, -0.850648, 0.000000, 0.525736, -0.425323, 0.309011, 0.850654,
        0.276388, 0.850649, 0.447220, -0.262869, 0.809012, 0.525738, 0.162456, 0.499995, 0.850654,
        0.894426, 0.000000, 0.447216, 0.688189, 0.499997, 0.525736, 0.525730, 0.000000, 0.850652,
        0.525730, 0.000000, 0.850652, 0.162456, 0.499995, 0.850654, 0.000000, 0.000000, 1.000000,
        0.525730, 0.000000, 0.850652, 0.688189, 0.499997, 0.525736, 0.162456, 0.499995, 0.850654,
        0.688189, 0.499997, 0.525736, 0.276388, 0.850649, 0.447220, 0.162456, 0.499995, 0.850654,
        0.162456, 0.499995, 0.850654, -0.425323, 0.309011, 0.850654, 0.000000, 0.000000, 1.000000,
        0.162456, 0.499995, 0.850654, -0.262869, 0.809012, 0.525738, -0.425323, 0.309011, 0.850654,
        -0.262869, 0.809012, 0.525738, -0.723607, 0.525725, 0.447220, -0.425323, 0.309011, 0.850654,
        -0.425323, 0.309011, 0.850654, -0.425323, -0.309011, 0.850654, 0.000000, 0.000000, 1.000000,
        -0.425323, 0.309011, 0.850654, -0.850648, 0.000000, 0.525736, -0.425323, -0.309011, 0.850654,
        -0.850648, 0.000000, 0.525736, -0.723607, -0.525725, 0.447220, -0.425323, -0.309011, 0.850654,
        -0.425323, -0.309011, 0.850654, 0.162456, -0.499995, 0.850654, 0.000000, 0.000000, 1.000000,
        -0.425323, -0.309011, 0.850654, -0.262869, -0.809012, 0.525738, 0.162456, -0.499995, 0.850654,
        -0.262869, -0.809012, 0.525738, 0.276388, -0.850649, 0.447220, 0.162456, -0.499995, 0.850654,
        0.162456, -0.499995, 0.850654, 0.525730, 0.000000, 0.850652, 0.000000, 0.000000, 1.000000,
        0.162456, -0.499995, 0.850654, 0.688189, -0.499997, 0.525736, 0.525730, 0.000000, 0.850652,
        0.688189, -0.499997, 0.525736, 0.894426, 0.000000, 0.447216, 0.525730, 0.000000, 0.850652,
        0.951058, 0.309013, 0.000000, 0.688189, 0.499997, 0.525736, 0.894426, 0.000000, 0.447216,
        0.951058, 0.309013, 0.000000, 0.587786, 0.809017, 0.000000, 0.688189, 0.499997, 0.525736,
        0.587786, 0.809017, 0.000000, 0.276388, 0.850649, 0.447220, 0.688189, 0.499997, 0.525736,
        0.000000, 1.000000, 0.000000, -0.262869, 0.809012, 0.525738, 0.276388, 0.850649, 0.447220,
        0.000000, 1.000000, 0.000000, -0.587786, 0.809017, 0.000000, -0.262869, 0.809012, 0.525738,
        -0.587786, 0.809017, 0.000000, -0.723607, 0.525725, 0.447220, -0.262869, 0.809012, 0.525738,
        -0.951058, 0.309013, 0.000000, -0.850648, 0.000000, 0.525736, -0.723607, 0.525725, 0.447220,
        -0.951058, 0.309013, 0.000000, -0.951058, -0.309013, 0.000000, -0.850648, 0.000000, 0.525736,
        -0.951058, -0.309013, 0.000000, -0.723607, -0.525725, 0.447220, -0.850648, 0.000000, 0.525736,
        -0.587786, -0.809017, 0.000000, -0.262869, -0.809012, 0.525738, -0.723607, -0.525725, 0.447220,
        -0.587786, -0.809017, 0.000000, 0.000000, -1.000000, 0.000000, -0.262869, -0.809012, 0.525738,
        0.000000, -1.000000, 0.000000, 0.276388, -0.850649, 0.447220, -0.262869, -0.809012, 0.525738,
        0.587786, -0.809017, 0.000000, 0.688189, -0.499997, 0.525736, 0.276388, -0.850649, 0.447220,
        0.587786, -0.809017, 0.000000, 0.951058, -0.309013, 0.000000, 0.688189, -0.499997, 0.525736,
        0.951058, -0.309013, 0.000000, 0.894426, 0.000000, 0.447216, 0.688189, -0.499997, 0.525736,
        0.587786, 0.809017, 0.000000, 0.000000, 1.000000, 0.000000, 0.276388, 0.850649, 0.447220,
        0.587786, 0.809017, 0.000000, 0.262869, 0.809012, -0.525738, 0.000000, 1.000000, 0.000000,
        0.262869, 0.809012, -0.525738, -0.276388, 0.850649, -0.447220, 0.000000, 1.000000, 0.000000,
        -0.587786, 0.809017, 0.000000, -0.951058, 0.309013, 0.000000, -0.723607, 0.525725, 0.447220,
        -0.587786, 0.809017, 0.000000, -0.688189, 0.499997, -0.525736, -0.951058, 0.309013, 0.000000,
        -0.688189, 0.499997, -0.525736, -0.894426, 0.000000, -0.447216, -0.951058, 0.309013, 0.000000,
        -0.951058, -0.309013, 0.000000, -0.587786, -0.809017, 0.000000, -0.723607, -0.525725, 0.447220,
        -0.951058, -0.309013, 0.000000, -0.688189, -0.499997, -0.525736, -0.587786, -0.809017, 0.000000,
        -0.688189, -0.499997, -0.525736, -0.276388, -0.850649, -0.447220, -0.587786, -0.809017, 0.000000,
        0.000000, -1.000000, 0.000000, 0.587786, -0.809017, 0.000000, 0.276388, -0.850649, 0.447220,
        0.000000, -1.000000, 0.000000, 0.262869, -0.809012, -0.525738, 0.587786, -0.809017, 0.000000,
        0.262869, -0.809012, -0.525738, 0.723607, -0.525725, -0.447220, 0.587786, -0.809017, 0.000000,
        0.951058, -0.309013, 0.000000, 0.951058, 0.309013, 0.000000, 0.894426, 0.000000, 0.447216,
        0.951058, -0.309013, 0.000000, 0.850648, 0.000000, -0.525736, 0.951058, 0.309013, 0.000000,
        0.850648, 0.000000, -0.525736, 0.723607, 0.525725, -0.447220, 0.951058, 0.309013, 0.000000,
        0.425323, 0.309011, -0.850654, 0.262869, 0.809012, -0.525738, 0.723607, 0.525725, -0.447220,
        0.425323, 0.309011, -0.850654, -0.162456, 0.499995, -0.850654, 0.262869, 0.809012, -0.525738,
        -0.162456, 0.499995, -0.850654, -0.276388, 0.850649, -0.447220, 0.262869, 0.809012, -0.525738,
        -0.162456, 0.499995, -0.850654, -0.688189, 0.499997, -0.525736, -0.276388, 0.850649, -0.447220,
        -0.162456, 0.499995, -0.850654, -0.525730, 0.000000, -0.850652, -0.688189, 0.499997, -0.525736,
        -0.525730, 0.000000, -0.850652, -0.894426, 0.000000, -0.447216, -0.688189, 0.499997, -0.525736,
        -0.525730, 0.000000, -0.850652, -0.688189, -0.499997, -0.525736, -0.894426, 0.000000, -0.447216,
        -0.525730, 0.000000, -0.850652, -0.162456, -0.499995, -0.850654, -0.688189, -0.499997, -0.525736,
        -0.162456, -0.499995, -0.850654, -0.276388, -0.850649, -0.447220, -0.688189, -0.499997, -0.525736,
        0.850648, 0.000000, -0.525736, 0.425323, 0.309011, -0.850654, 0.723607, 0.525725, -0.447220,
        0.850648, 0.000000, -0.525736, 0.425323, -0.309011, -0.850654, 0.425323, 0.309011, -0.850654,
        0.425323, -0.309011, -0.850654, 0.000000, 0.000000, -1.000000, 0.425323, 0.309011, -0.850654,
        -0.162456, -0.499995, -0.850654, 0.262869, -0.809012, -0.525738, -0.276388, -0.850649, -0.447220,
        -0.162456, -0.499995, -0.850654, 0.425323, -0.309011, -0.850654, 0.262869, -0.809012, -0.525738,
        0.425323, -0.309011, -0.850654, 0.723607, -0.525725, -0.447220, 0.262869, -0.809012, -0.525738,
    ];
    const meshVerts = new Float32Array(verts);
    const vertsLenght = meshVerts.length / 3;
    gl.uniform1i(uLvertices, vertsLenght);
    gl.pixelStorei(gl.UNPACK_ALIGNMENT, 1);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGB32F, vertsLenght, 1, 0, gl.RGB, gl.FLOAT, meshVerts);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);

    // mouse click
    let mousePosition = [0, 0];
    gl.canvas.addEventListener('mousemove', (e) => {
        if (!e.buttons) return;
        if (e.buttons == 1) mousePosition = [e.clientX * .01, e.clientY * .01];
    }, !1);

    // animation
    const draw = (clock) => {
        clock *= 0.001;
        gl.viewport(0.0, 0.0, gl.drawingBufferWidth, gl.drawingBufferHeight);
        gl.activeTexture(gl.TEXTURE0);
        gl.bindTexture(gl.TEXTURE_2D, texture);
        gl.uniform1i(uLSr, 0);
        gl.uniform1f(time_loc, clock);
        gl.uniform2f(mouse_loc, mousePosition[0], mousePosition[1]);
        gl.uniform2f(res_loc, width, height);
        gl.drawArrays(gl.TRIANGLE_STRIP, 0, 3);
        requestAnimationFrame(draw);
    };
    requestAnimationFrame(draw);
})()
<canvas id="c"></canvas>

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