法线贴图错误

Question

我正在使用 LWJGL 开发 3D OpenGL 引擎。我设法用 Assimp 完成了模型导入部分，现在正在处理法线映射。 幸运的是，Assimp 可以为我计算切线空间，但它不能正常工作。 这是一张图片，它是如何在 sponza 模型上工作的：

这是从 TBN 矩阵可视化的 T：

代码在顶点着色器中如下所示：

mat3 normalMatrix = transpose(inverse(mat3(transformationMatrix)));
vec3 T = normalize(normalMatrix * tangent);
vec3 N = normalize(normalMatrix * normal);
T = normalize(T - dot(T, N) * N);
vec3 B = normalize(normalMatrix * bitangent);

if (dot(cross(N, T), B) < 0.0){
        T = T * -1.0;
}
TBN = transpose(mat3(T, B, N));

它检查模型是否具有对称 UV，并修复它。 我认为这会导致问题，因为 TBN 中的 B 看起来更糟。

几周后，我尝试自己计算切线和副切线，但我的副切线看起来比 Assimps 差：

private void generateTangentBitangent(){
    for(int i = 0; i < indices.size(); i+=3){
        Vector3f v0 = new Vector3f (vertices.get(indices.get(i)).getPos());
        Vector3f v1 = new Vector3f (vertices.get(indices.get(i+1)).getPos());
        Vector3f v2 = new Vector3f (vertices.get(indices.get(i+2)).getPos());

        Vector2f uv0 = new Vector2f (vertices.get(indices.get(i)).getTextureCoord());
        Vector2f uv1 = new Vector2f (vertices.get(indices.get(i+1)).getTextureCoord());
        Vector2f uv2 = new Vector2f (vertices.get(indices.get(i+2)).getTextureCoord());

        Vector3f e1 = new Vector3f (v1.sub(v0));
        Vector3f e2 = new Vector3f (v2.sub(v0));

        Vector2f deltaUV1 = new Vector2f (uv1.sub(uv0));
        Vector2f deltaUV2 = new Vector2f (uv2.sub(uv0));

        float r = (float) (1.0f / (deltaUV1.x() * deltaUV2.y() - deltaUV1.y() * deltaUV2.x()));

        Vector3f tangent = new Vector3f ((e1.mul(deltaUV2.y()).sub(e2.mul(deltaUV1.y()))).mul(r));
        //System.out.println(tangent);
        Vector3f bitangent = new Vector3f ((e2.mul(deltaUV1.x()).sub(e1.mul(deltaUV2.x()))).mul(r));

        if(vertices.get(indices.get(i)).getTangent() == null)
            vertices.get(indices.get(i)).setTangent(new Vector3f(0,0,0));
        if(vertices.get(indices.get(i)).getBitangent() == null)
            vertices.get(indices.get(i)).setBitangent(new Vector3f(0,0,0));
        if(vertices.get(indices.get(i+1)).getTangent() == null)
            vertices.get(indices.get(i+1)).setTangent(new Vector3f(0,0,0));
        if(vertices.get(indices.get(i+1)).getBitangent() == null)
            vertices.get(indices.get(i+1)).setBitangent(new Vector3f(0,0,0));
        if(vertices.get(indices.get(i+2)).getTangent() == null)
            vertices.get(indices.get(i+2)).setTangent(new Vector3f(0,0,0));
        if(vertices.get(indices.get(i+2)).getBitangent() == null)
            vertices.get(indices.get(i+2)).setBitangent(new Vector3f(0,0,0));

        vertices.get(indices.get(i)).getTangent().add(tangent);
        vertices.get(indices.get(i)).getBitangent().add(bitangent);
        vertices.get(indices.get(i+1)).getTangent().add(tangent);
        vertices.get(indices.get(i+1)).getBitangent().add(bitangent);
        vertices.get(indices.get(i+2)).getTangent().add(tangent);
        vertices.get(indices.get(i+2)).getBitangent().add(bitangent);
    }

    for (int i = 0 ; i < vertices.size() ; i++) {
        vertices.get(i).getTangent().normalize();
        vertices.get(i).getBitangent().normalize();
    } 
}

谁能帮我看看是什么原因造成的？

Answer 1

您在图像上呈现的切线/双切线/法线位于哪个空间？从您的代码示例来看，它们可能位于切线空间中。

但是，获得切线空间向量可以更容易实现。您不必使用normalMatrix 转换tangent、normal 和bitangent，而只需使用对象空间中的轴：

vec3 normalOS    = normalize(normal);
vec3 tangentOS   = normalize(tangent);
vec3 bitangentOS = normalize(bitangent) // or calculate via cross(normalOS, tangentOS);
mat3 TStoOS      = mat3(tangentOS, bitangentOS, normalOS); // transform from tangent space into object space
mat3 OStoTS      = transpose(matrixTStoOS); // The transpose of an orthogonal matrix is it's inverse matrix

如果您需要从切线空间转换到世界空间的矩阵，您可以按如下方式计算：

vec3 normalWS    = normalize(normalMatrix * normal);
vec3 tangentWS   = normalize(normalMatrix * tangent);
vec3 bitangentWS = normalize(cross(normalWS, tangentWS))
mat3 TStoWS      = mat3(tangentWS, bitangentWS, normalWS); // transform from tangent space into world space
mat3 WStoTS      = transpose(matrixTStoWS); // transform from world space into tangent space