c++ - OpenGL-在任意轴上平移对象

Question

我有一个球体，也有一个通过其原点的轴。我想上下移动球体的轴。在它的起始位置没有问题，因为轴开始平行于全局y轴。但是，一旦我旋转球体，因此绕着z轴的球体轴也就变得复杂了。

我的第一个想法是对轴进行归一化，并简单地将其用作转换矩阵中的转换 vector 。然后将平移矩阵乘以归一化的轴，然后将球体推到轴上一个单位。

这是我已经得到的代码:

class Object
{
public:
    inline Object()
        : vao(0),
        positionBuffer(0),
        colorBuffer(0),
        indexBuffer(0),
        elements(0),
        vertices(0)
    {}

    inline ~Object() { // GL context must exist on destruction
        glDeleteVertexArrays(1, &vao);
        glDeleteBuffers(1, &indexBuffer);
        glDeleteBuffers(1, &colorBuffer);
        glDeleteBuffers(1, &positionBuffer);
    }

    GLuint vao;        // vertex-array-object ID

    GLuint positionBuffer; // ID of vertex-buffer: position
    GLuint colorBuffer;    // ID of vertex-buffer: color

    GLuint indexBuffer;    // ID of index-buffer

    GLuint elements; // Number of Elements

    vector<glm::vec3> vertices;
    glm::vec3 mp;

    glm::mat4x4 model; // model matrix
};

glm::vec3 axis = glm::normalize(glm::vec3{ 
    sphereax.vertices[0].x - sphereax.vertices[1].x,
    sphereax.vertices[0].y - sphereax.vertices[1].y, 
    sphereax.vertices[0].z - sphereax.vertices[1].z}
);
translateObject(earth, axis);

void translateObject(Object &obj, glm::vec3 &translation)
{
    glm::mat4x4 trans_mat = glm::translate(glm::mat4(1.0f), translation);
    for (int i = 0; i < obj.vertices.size(); i++)
    {
        obj.vertices[i] = glm::vec3(glm::vec4(obj.vertices[i], 1.0f) * trans_mat);
    }
    obj.mp = glm::vec3(glm::vec4(obj.mp, 1.0f) * trans_mat);
}

translateObject();中的转换矩阵似乎是正确的，但是将点之一与转换矩阵相乘却没有效果。

Answer 1

我建议执行以下操作:

围绕球的旋转轴旋转球

通过球体沿x轴的中心距球体的距离来平移

围绕世界中心旋转球体

glm::vec3 rotation_axis      = ...; // sphere axis
float     axis_rot_angle     = ...; // current axis rotation angle in radians
float     distance_to_center = ...; // distance from the center of the world
float     world_rot_angle    = ...; // current world rotation angle in radians

glm::mat4 sphere_rot   = glm::rotation(glm::mat4(1.0f), axis_rot_angle, rotation_axis);
glm::mat4 sphere_trans = glm::translate(glm::mat4(1.0f), glm::vec3(distance_to_center, 0.0f, 0.0f));
glm::mat4 world_rot    = glm::rotation(glm::mat4(1.0f), world_rot_angle, glm::vec3(0.0f, 0.0f, 1.0f));

glm::mat4 model_mat = world_rot * sphere_trans * sphere_rot;