圆球相机倒置在90度的方位角

Question

我正在尝试实现一个圆球风格的相机。我使用glm::look来保持相机指向目标，然后使用方位角/倾斜角在球体表面周围移动它来旋转视图。

我遇到了一个问题，当方位角接近90度时，视图会翻转过来。

相关代码如下:

1. 获取投影和视图矩阵。在主循环中运行

   void Visual::updateModelViewProjection()
   {
       model = glm::mat4();
       projection = glm::mat4();
       view = glm::mat4();
       projection = glm::perspective
           (
           (float)glm::radians(camera.Zoom),
           (float)width / height, // aspect ratio
           0.1f, // near clipping plane
           10000.0f // far clipping plane
           );
       view = glm::lookAt(camera.Position, camera.Target, camera.Up);
   }
   

2. 鼠标移动事件，用于相机旋转

   void Visual::cursor_position_callback(GLFWwindow* window, double xpos, double ypos)
   {
       if (leftMousePressed)
       {
          ...
       }
       if (rightMousePressed)
       {
           GLfloat xoffset = (xpos - cursorPrevX) / 4.0;
           GLfloat yoffset = (cursorPrevY - ypos) / 4.0;
           camera.inclination += yoffset;
           camera.azimuth -= xoffset;
           if (camera.inclination > 89.0f)
               camera.inclination = 89.0f;
           if (camera.inclination < 1.0f)
               camera.inclination = 1.0f;
           if (camera.azimuth > 359.0f)
               camera.azimuth = 359.0f;
           if (camera.azimuth < 1.0f)
               camera.azimuth = 1.0f;
           float radius = glm::distance(camera.Position, camera.Target);
           camera.Position[0] = camera.Target[0] + radius * cos(glm::radians(camera.azimuth)) * sin(glm::radians(camera.inclination));
           camera.Position[1] = camera.Target[1] + radius * sin(glm::radians(camera.azimuth)) * sin(glm::radians(camera.inclination));
           camera.Position[2] = camera.Target[2] + radius * cos(glm::radians(camera.inclination));
           camera.updateCameraVectors();
       }
       cursorPrevX = xpos;
       cursorPrevY = ypos;
   }
   

3. 计算相机方向矢量

   void updateCameraVectors()
   {
       Front = glm::normalize(Target-Position);
       Right = glm::rotate(glm::normalize(glm::cross(Front, {0.0, 1.0, 0.0})), glm::radians(90.0f), Front);
       Up = glm::normalize(glm::cross(Front, Right));
   }
   

我很确定这与我计算相机右矢量的方式有关，但我不知道如何补偿。

有人遇到过这种情况吗?有什么建议吗?

Answer 1

使用lookAt旋转相机是一个常见的错误。你不应该。向后/右/向上方向是视图矩阵的列。如果你已经有了它们，那么你甚至不需要lookAt，它会尝试重做一些计算。另一方面，lookAt一开始并不能帮助你找到那些向量。

首先将视图矩阵构建为平移和旋转的组合，然后从其列中提取这些向量:

void Visual::cursor_position_callback(GLFWwindow* window, double xpos, double ypos)
{
    ...
    if (rightMousePressed)
    {
        GLfloat xoffset = (xpos - cursorPrevX) / 4.0;
        GLfloat yoffset = (cursorPrevY - ypos) / 4.0;
        camera.inclination = std::clamp(camera.inclination + yoffset, -90.f, 90.f);
        camera.azimuth = fmodf(camera.azimuth + xoffset, 360.f);
        view = glm::mat4();
        view = glm::translate(view, glm::vec3(0.f, 0.f, camera.radius)); // add camera.radius to control the distance-from-target
        view = glm::rotate(view, glm::radians(camera.inclination + 90.f), glm::vec3(1.f,0.f,0.f));
        view = glm::rotate(view, glm::radians(camera.azimuth), glm::vec3(0.f,0.f,1.f));
        view = glm::translate(view, camera.Target);
        camera.Right = glm::column(view, 0);
        camera.Up = glm::column(view, 1);
        camera.Front = -glm::column(view, 2); // minus because OpenGL camera looks towards negative Z.
        camera.Position = glm::column(view, 3);
        view = glm::inverse(view);
    }
    ...
}

然后从updateModelViewProjection和updateCameraVectors中删除计算视图和方向向量的代码。

免责声明:此代码未经测试。您可能需要修复某个地方的负号，操作顺序，或者约定可能不匹配(Z是上或Y是上，等等…)。