C ++ - 浮点数组不在某个非常大的索引之后存储值

Question

在我的程序中，我使用 Perlin 噪声创建地形。地形生成正确，现在我正在尝试将计算出的法线存储到一个名为 normals 的浮点数组中。它正确地将法线存储到某个索引，但随后它只存储 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，我遇到了，因为我已经尝试在创建法线后打印出法线，但我没有看到任何 0。但是当我从数组中打印出法线时（具有正确的索引），我只得到一个 0.

Answer 1

对于 normals 数组，删除与 VALS_PER_VERT 的乘法。它将使您的数组比需要的数组大三倍。

您不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（或名称空间）变量，它们将被初始化为零；如果它们被定义为函数内部的局部变量，它们的值将是不确定（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 ];

记住不要越界。这将使所有元素在您显示的循环内初始化。

C ++ - 浮点数组不在某个非常大的索引之后存储值

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