Question

在我的程序中，我使用Perlin噪音创建地形。地形正在正确生成，现在我正在尝试将计算出的法线存储到名为 normals 的浮点数组中。它正常存储法线直到某个索引，但它只存储0。这是我的代码：

float frequency = 8;
float flagVertices[ N*N*VALS_PER_VERT*VERTICES_PER_QUAD ];
float normals[ N*N*VALS_PER_VERT*VERTICES_PER_QUAD ];
int idxFlag = 0;
int normFlag = 0;
for (int i=0;i < N;i++){
    for (int j=0;j < N;j++){
        // *** Face 1 ***
        // (0,0)
        flagVertices[idxFlag++] = (float)i/N;
        flagVertices[idxFlag++] = 0.2f*PerlinNoise( glm::vec2( (float)i/N*frequency, (float)j/N*frequency ) );
        flagVertices[idxFlag++] = (float)j/N;
        glm::vec3 p0 = glm::vec3(flagVertices[idxFlag-3], flagVertices[idxFlag-2], flagVertices[idxFlag-1]);                

        // (0,1)
        flagVertices[idxFlag++] = (float)i/N;
        flagVertices[idxFlag++] = 0.2f*PerlinNoise( glm::vec2( (float)i/N*frequency, (float)(j+1)/N*frequency ) );
        flagVertices[idxFlag++] = (float)(j+1)/N; 
        glm::vec3 p1 = glm::vec3(flagVertices[idxFlag-3], flagVertices[idxFlag-2], flagVertices[idxFlag-1]); 

        // (1,1)
        flagVertices[idxFlag++] = (float)(i+1)/N;
        flagVertices[idxFlag++] = 0.2f*PerlinNoise( glm::vec2( (float)(i+1)/N*frequency, (float)(j+1)/N*frequency ) );
        flagVertices[idxFlag++] = (float)(j+1)/N; 
        glm::vec3 p2 = glm::vec3(flagVertices[idxFlag-3], flagVertices[idxFlag-2], flagVertices[idxFlag-1]);

        // Adding in normals
        glm::vec3 normal = glm::abs(glm::triangleNormal(p0,p1,p2));
        normals[normFlag++] = normal.x;
        normals[normFlag++] = normal.y;
        normals[normFlag++] = normal.z;

        // *** Face 2 ***
        // (1,1)
        flagVertices[idxFlag++] = (float)(i+1)/N;
        flagVertices[idxFlag++] = 0.2f*PerlinNoise( glm::vec2( (float)(i+1)/N*frequency, (float)(j+1)/N*frequency ) );
        flagVertices[idxFlag++] = (float)(j+1)/N;
        glm::vec3 p3 = glm::vec3(flagVertices[idxFlag-3], flagVertices[idxFlag-2], flagVertices[idxFlag-1]); 

        // (1,0)
        flagVertices[idxFlag++] = (float)(i+1)/N;
        flagVertices[idxFlag++] = 0.2f*PerlinNoise( glm::vec2( (float)(i+1)/N*frequency, (float)j/N*frequency ) );
        flagVertices[idxFlag++] = (float)j/N;
        glm::vec3 p4 = glm::vec3(flagVertices[idxFlag-3], flagVertices[idxFlag-2], flagVertices[idxFlag-1]); 

        // (0,0)
        flagVertices[idxFlag++] = (float)i/N;
        flagVertices[idxFlag++] = 0.2f*PerlinNoise( glm::vec2( (float)i/N*frequency, (float)j/N*frequency ) );
        flagVertices[idxFlag++] = (float)j/N;
        glm::vec3 p5 = glm::vec3(flagVertices[idxFlag-3], flagVertices[idxFlag-2], flagVertices[idxFlag-1]);

        // Adding in normals
        normal = glm::abs(glm::triangleNormal(p3,p4,p5));
        normals[normFlag++] = normal.x;
        normals[normFlag++] = normal.y;
        normals[normFlag++] = normal.z;
    }
}

我确定这是一个C ++问题，我有，因为我已经尝试在创建它之后打印出法线，我看不到0。但是当我从数组中打印出法线（使用正确的索引）时，我得到的是0。

Answer 1

对于normals数组，请将乘法与VALS_PER_VERT一起删除。它会使你的阵列比它需要的大三倍。

您未初始化的元素的值取决于您定义数组的位置：如果它们被定义为全局（或命名空间）变量，它们将被初始化为零;如果它们被定义为函数内的局部变量，则它们的值将是 indeterminate （并且读取它们将导致未定义的行为）。

所以定义应该是

float normals[ N*N*VERTICES_PER_QUAD ];

并记住不要超出界限。这将使所有元素在您显示的循环内初始化。

C ++ - Float数组在某个非常大的索引之后不存储值

1 个答案: