Three.js / 计算置换后顶点着色器中索引PlaneBufferGeometry的顶点法线

Question

我一直在努力解决这个问题。我有一个用于 GPGPU 布料物理模拟的索引 PlaneBufferGeometry，在将模拟渲染到纹理后，我无法在最终顶点着色器中正确计算法线。

这是我当前的设置（包括相关部分），我认为它不起作用，因为我需要一种方法来了解当前顶点的顺序以及它在“面”中的邻居。只是不能完全正确。

javascript:

// get faces
const indices = geometry.index.array;
const faces = [];
for(let i = 0; i < indices.length; i += 3)
{
    faces.push([indices[i + 0] * 3, indices[i + 1] * 3, indices[i + 2] * 3]);
}

const vertices = geometry.attributes.position.array;

// begin loop

// initializing data texture vertex positions
dataTexturePixels[index * 4 + 0] = vertices[index * 3 + 0];
dataTexturePixels[index * 4 + 1] = vertices[index * 3 + 1];
dataTexturePixels[index * 4 + 2] = vertices[index * 3 + 2];
dataTexturePixels[index * 4 + 3] = 0;

// storing lookup uv's in an attribute for looking up positions
positionReference[index * 3 + 0] = (index % size) / size;
positionReference[index * 3 + 1] = Math.floor(index / size) / size;

// end loop

这是我的大脑跳闸的地方。我尝试以各种方式使用 faces 数组中的人脸索引值，但由于索引重复，数据被覆盖。想不出如何正确存储每个面的顶点索引信息，以便可以使用 positionReference（或其他方式）在顶点着色器中查找它。

顶点着色器/模拟运行后：

// how I'd calculate the normals if I could get a proper ordered reference
vec2 coord1 = faceVert1UvReference.xy;
vec3 pos1 = texture2D(tPositions, coord1).xyz;

vec2 coord2 = faceVert2UvReference.xy;
vec3 pos2 = texture2D(tPositions, coord2).xyz;

vec2 coord3 = faceVert3UvReference.xy;
vec3 pos3 = texture2D(tPositions, coord3).xyz;

vec3 tangent = pos3 - pos2;
vec3 bitangent = pos1 - pos2;
vec3 normal = normalMatrix * normalize(cross(tangent, bitangent));

片段着色器/光照：

vec3 lightDirection = normalize(lightPosition); // also tried normalize(lightPosition - vWorldPosition);
vec3 normal = normalize(vNormal);
float lightValue = max(0.0, dot(normal, lightDirection)) * lightIntensity;
finalColor.rgb *= lightValue;

不确定我是否遗漏了一些明显的东西/做了一些愚蠢的事情，或者这个问题确实很难。没有发布我尝试过的许多失败的方法，有人有什么想法吗？

非常感谢任何帮助。

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[编辑 1]： 我添加了几个示例，this one 使用平面着色和面法线，this one 显示了我当前混乱的平滑顶点法线进度。很难找到我的错误...

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[编辑 2]： 这就是我将面部数据传递到每个顶点的方式。从数据的角度来看，一切对我来说都是正确的，但在视觉上却完全一团糟。终其一生都找不到错误的地方。

javascript

const indices = geometry.index.array;
const faces = [];

// store faces for each vertex
for(let i = 0; i < indices.length; i += 3)
{
    const vertIndex1 = indices[ i + 0 ];
    const vertIndex2 = indices[ i + 1 ];
    const vertIndex3 = indices[ i + 2 ];

    faces[ vertIndex1 ] = faces[ vertIndex1 ] || [];
    faces[ vertIndex2 ] = faces[ vertIndex2 ] || [];
    faces[ vertIndex3 ] = faces[ vertIndex3 ] || [];

    faces[ vertIndex1 ].push([ vertIndex1, vertIndex2, vertIndex3 ]);
    faces[ vertIndex2 ].push([ vertIndex1, vertIndex2, vertIndex3 ]);
    faces[ vertIndex3 ].push([ vertIndex1, vertIndex2, vertIndex3 ]);
}

const size = 128;
const vertices = geometry.attributes.position;
const faceIndices = new Uint16Array( vertices.array.length );
const indices0 = gpuCompute.createTexture(size * 2, size * 2); // need 256x256 texture for all the data.
const indicesPixels0 = indices0.image.data;

let faceVertPixelIndex = 0,
    faceIndexRangeStart = 0,
    faceIndexRangeEnd = -1,
    index;

for(let i = 0; i < size; i++)
{
    for(let j = 0; j < size; j++)
    {
        index = j + (i * size);

        // ----------------------------------------------
        // writing vertex positions to data texture here
        // ----------------------------------------------


        if(faces[index])
        {
            const face = faces[index];
            const fLen = face.length;

            faceIndexRangeStart = faceIndexRangeEnd + 1;
            faceIndexRangeEnd = faceIndexRangeStart + fLen - 1;

            // face index range for looking up up all faces a single vertex is in
            faceIndices[index * 3 + 0] = faceIndexRangeStart;
            faceIndices[index * 3 + 1] = faceIndexRangeEnd;
            faceIndices[index * 3 + 2] = 0; // unused

            for(let v = 0; v < fLen; v++)
            {
                // store face vertex indices in each pixel rgb
                indicesPixels0[faceVertPixelIndex * 4 + 0] = face[v][0]; // current face, vertex 1 index
                indicesPixels0[faceVertPixelIndex * 4 + 1] = face[v][1]; // current face, vertex 2 index
                indicesPixels0[faceVertPixelIndex * 4 + 2] = face[v][2]; // current face, vertex 3 index
                indicesPixels0[faceVertPixelIndex * 4 + 3] = 0; // unused

                faceVertPixelIndex++;
            }
        }
    }
}

geometry.addAttribute('faceIndices', new THREE.BufferAttribute(faceIndices, 3));

uniforms.tIndices.value = indices0;

顶点着色器（相关部分）

uniform vec2 resolution;
uniform sampler2D tPositions;
uniform sampler2D tIndices;

attribute vec3 faceIndices;

varying vec3 vNormal;

vec2 getCoord(in float index, in vec2 size)
{
    return vec2(mod(index, size.x) / size.x, floor(index / size.y) / size.y);
}

void addNormal(inout vec3 nrml, in float index)
{
    vec2 coord = getCoord(index, resolution * 2.0); // 256x256 sized texture for faces
    vec4 face = texture2D(tIndices, coord);

    // get uv for each vertex index in the face and grab positions.
    vec2 v1Coord = getCoord(face.x, resolution);
    vec3 v1 = texture2D(tPositions, v1Coord).xyz;

    vec2 v2Coord = getCoord(face.y, resolution);
    vec3 v2 = texture2D(tPositions, v2Coord).xyz;

    vec2 v3Coord = getCoord(face.z, resolution);
    vec3 v3 = texture2D(tPositions, v3Coord).xyz;

    vec3 tangent = v3 - v2;
    vec3 bitangent = v1 - v2;

    vec3 n = normalize(cross(tangent, bitangent));

    nrml += n;
}

void main()
{
    vec3 nrml = vec3(0.0);
    vec2 faceIndexRange = faceIndices.xy;

    float from = faceIndexRange.x;
    float to = faceIndexRange.y;
    float index = from;

    for(int i = 0; i < 6; i++)
    {
        if(index <= to)
        {
            addNormal(nrml, index);
            index += 1.0;
        }
        else
        {
            break;
        }
    }

    vNormal = normalMatrix * normalize(nrml);
}

Answer 1

感谢@luigi-de-rosa 的帮助，我最终放弃了上述共享面孔方法并使用了邻居查找方法。我之前曾尝试过，但使用不正确的值从查找纹理中获取邻居，这让我认为它不起作用。

这是我现在在顶点着色器中计算法线的方法。

float diff = 0.06; // tweak this value to yield different results.
vec2 coord = positionReference.xy;
vec3 transformed = texture2D(tPositions, coord).xyz;
vec3 neighbour1 = texture2D(tPositions, coord + vec2(diff, 0.0)).xyz;
vec3 neighbour2 = texture2D(tPositions, coord + vec2(0.0, diff)).xyz;
vec3 tangent = neighbour1 - transformed;
vec3 bitangent = neighbour2 - transformed;            
vec3 nrml = cross(tangent, bitangent);
vNormal = normalMatrix * -normalize(nrml); // pass to fragment shader

更简单的方法...叹息。