C ++ - Diamond-Square算法输出是随机且有噪声的

Question

我已经在C ++中对 Diamond-Square算法进行了粗略的解释，以创建一些半真实的分形地形，但输出看起来像是每个点的随机y值而不是光滑的岩石形状。我已经更改了参数，但感觉外观看代码可能会帮助我理解这个问题。以下是输出的示例：

我明白了：

应该是这样的：

代码：

//Diamond-square algorithm
HeightMap::HeightMap(float maxY) {
//type = GL_POINTS; 
//type = GL_LINES;
numVertices = RAW_WIDTH*RAW_HEIGHT; //256^2 squares => 257^2 vertices
numIndices = (RAW_WIDTH - 1)*(RAW_HEIGHT - 1) * 6; //each square is 2 triangles (6 indices)
vertices = new Vector3[numVertices];
textureCoords = new Vector2[numVertices];
indices = new GLuint[numIndices];
colours = new Vector4[numVertices];

int cornerA, cornerB, cornerC, cornerD; //Identify corners
cornerA = 0;
cornerB = RAW_WIDTH - 1;
cornerC = RAW_WIDTH*RAW_HEIGHT - RAW_WIDTH;
cornerD = RAW_WIDTH*RAW_HEIGHT - 1;

//Create vertices
for (int x = 0; x < RAW_WIDTH; ++x) {
    for (int z = 0; z < RAW_HEIGHT; ++z) {
        int offset = (x * RAW_WIDTH) + z;
        float y = 0; //Start with vertices set flat
        if (offset == cornerA ||
            offset == cornerB ||
            offset == cornerC ||
            offset == cornerD) {
            vertices[offset] = Vector3(x * HEIGHTMAP_X, maxY/2, z * HEIGHTMAP_Z); //Initialise corners to mid height
            std::cout << "Corners: " << offset << std::endl;
        }

        if (vertices[offset] == Vector3(0, 0, 0)) {
            vertices[offset] = Vector3(x * HEIGHTMAP_X, y * HEIGHTMAP_Y, z * HEIGHTMAP_Z);
        }
        //  textureCoords[offset] = Vector2(x * HEIGHTMAP_TEX_X, z * HEIGHTMAP_TEX_Z);
    }
}

Vector3 tl, tr, bl, br;
tl = vertices[cornerA];
tr = vertices[cornerB];
bl = vertices[cornerC];
br = vertices[cornerD];

float roughness = 1.0f;

Square square = Square(tl, tr, bl, br);
diamondSquare(vertices, numVertices, square, roughness);

//Colour
for (int x = 0; x < RAW_WIDTH; ++x) {
    for (int z = 0; z < RAW_HEIGHT; ++z) {
        int offset = (x*RAW_WIDTH) + z;
        float shade;
        if (vertices[offset].y > 0) {
            shade = 1 - 1.0f / (vertices[offset].y / maxY * 2);
        }
        else {
            shade = 0.1f;
        }
        colours[offset] = Vector4(shade, shade, shade, 1.0f);
        //Colour any vertex that hasn't been passed over red
        if (vertices[offset].y == maxY / 2 + 100) {
            colours[offset] = Vector4(1, 0, 0, 1);
        }
    }
}

//Create indices
numIndices = 0;
for (int x = 0; x < RAW_WIDTH - 1; ++x) {
    for (int z = 0; z < RAW_HEIGHT - 1; ++z) {
        int a = (x*(RAW_WIDTH)) + z;
        int b = ((x + 1)*(RAW_WIDTH)) + z;
        int c = ((x + 1)*(RAW_WIDTH)) + (z + 1);
        int d = (x*(RAW_WIDTH)) + (z + 1);

        indices[numIndices++] = c;
        indices[numIndices++] = b;
        indices[numIndices++] = a;
        indices[numIndices++] = a;
        indices[numIndices++] = d;
        indices[numIndices++] = c;

    }
}
BufferData();

}

void HeightMap::squareStep(Vector3 vertices[], int len, Vector3 tl, Vector3 tr, Vector3 bl, Vector3 br, float mid, float roughness) {
for (int i = 0; i < len; i++) {
    Vector3 top = (tl + tr) / 2;
    Vector3 bot = (bl + br) / 2;
    Vector3 left = (tl + bl) / 2;
    Vector3 right = (tr + br) / 2;
    top.y = 0;
    bot.y = 0;
    left.y = 0;
    right.y = 0;
    if (vertices[i] == top ||
        vertices[i] == bot ||
        vertices[i] == left ||
        vertices[i] == right) {
        float y = rand() % (int)(mid/5);
        y *= roughness;
        vertices[i] = Vector3(vertices[i].x, mid + y, vertices[i].z); //Set Diamond centre points to mid height + rand
        std::cout << "Square: " << vertices[i];
    }
}

}

float HeightMap::diamondStep(Vector3 vertices[], int len, Vector3 tl, Vector3 tr, Vector3 bl, Vector3 br, float roughness) {
float avg;
float y;
    for (int i = 0; i < len; i++) {
        Vector3 corners = (tl + tr + bl + br) / 4;
        avg = corners.y;
        y = rand() % (int)(avg/5);
        y *= roughness;
        corners.y = 0;
        if (vertices[i] == corners) {
            vertices[i] = Vector3(vertices[i].x, avg + y, vertices[i].z);         //Set Square centre point to avg height of corners + rand
            std::cout << "Diamond: " << vertices[i];
        }
    }
return avg + y;

}

void HeightMap::diamondSquare(Vector3 vertices[], int numVertices, Square s, float roughness) {
Vector3 tl = s.tl;
Vector3 tr = s.tr;
Vector3 bl = s.bl;
Vector3 br = s.br;
float mid = diamondStep(vertices, numVertices, tl, tr, bl, br, roughness);
squareStep(vertices, numVertices, tl, tr, bl, br, mid, roughness);
roughness *= 0.75f;
if (s.width > 2 * HEIGHTMAP_X) {
    std::vector<Square> squares = s.split();
    for (int i = 0; i < 4; i++) {
        diamondSquare(vertices, numVertices, squares[i], roughness);
    }
}

}

Answer 1

您的中点计算看起来不对劲。该算法应将该正方形或菱形的中点设置为四个角点的平均值加上随机值。但是在你的代码中我看到了：

y = rand() % (int)(avg/5);

这基本上说，将y设置为0和0之间的随机数。角落平均值的五分之一。相反，我希望看到这样的事情：

// get a random float in the range 0 to 1
float r = (float)(rand()) / (float)(RAND_MAX);
// scale r to be in the range -magnitude to magnitude
r = (r * 2 * magnitude) - magnitude;
// add the scaled random value to the average of the corners
y = avg + r;

注意：这种方法可能会使y值小于零。如果这是一个问题，请通过找到最低值＆amp;来规范化数据。从每个y中减去该数量。