Arcball 相机在 90 度方位角倒转

Question

我正在尝试实现 arcball 风格的相机。我使用 glm::lookAt 将相机保持指向目标，然后使用 azimuth/inclination 角度围绕球体表面移动它以旋转视图。

我运行遇到一个问题，当方位角接近 90 度时，视图会颠倒过来。

相关代码如下：

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);
}

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;
}

计算相机方向向量

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。

有没有人运行以前参与过这个？有什么建议么？

Answer 1

使用lookAt旋转相机是common mistake。你不应该。 backward/right/up 方向是视图矩阵的列。如果您已经拥有它们，那么您甚至不需要 lookAt，它会尝试重做您的一些计算。另一方面，lookAt 并不能帮助您首先找到这些向量。

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。您可能需要在某处修复减号、操作顺序，或者约定可能不匹配（Z 向上或 Y 向上，等等）。

Arcball 相机在 90 度方位角倒转

Arcball camera inverting at 90 deg azimuth

c++

opengl

opengl-3

glm-math

arcball