摄像机

需要三个向量：

1. 摄像机位置：

   • glm::vec3 cameraPos = glm::vec3(0.0f, 0.0f, 3.0f);
   • 一个从世界原点指向摄像机的向量

2. 摄像机方向：

   • 1 2	glm::vec3 cameraTarget = glm::vec3(0.0f, 0.0f, 0.0f); glm::vec3 cameraDirection = glm::normalize(cameraPos - cameraTarget);

   • 指向摄像机的z轴正方向（与摄像机面对的方向刚好相反）

3. 右轴：

   • 需要一个右向量代表摄像机的x轴，利用叉乘

   • 1 2	glm::vec3 up = glm::vec3(0.0f, 1.0f, 0.0f); glm::vec3 cameraRight = glm::normalize(glm::cross(up, cameraDirection));

   • up即为向空间正上方的一个向量（大部分情况下这么做够用了）

Look At矩阵

• 一个变换矩阵，可以将位置变换到摄像机空间

• 创建一个看着给定目标的矩阵

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  glm::mat4 view; view = glm::lookAt(glm::vec3(0.0f, 0.0f, 3.0f),//相机位置 glm::vec3(0.0f, 0.0f, 0.0f), //目标 glm::vec3(0.0f, 1.0f, 0.0f));//上向量

  • 输入需要一个位置、目标、上向量

自由移动

• 定义一些全局变量来代表摄像机的状态

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  glm::vec3 cameraPos = glm::vec3(0.0f, 0.0f, 3.0f); glm::vec3 cameraFront = glm::vec3(0.0f, 0.0f, -1.0f); glm::vec3 cameraUp = glm::vec3(0.0f, 1.0f, 0.0f);

  于是，LookAt函数现在变成了：

  view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp);

• 方向是摄像机位置向量加上摄像机注视着的方向（Look At函数以世界而不是摄像机为参考系）

处理按键输入

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void processInput(GLFWwindow *window)
{
    ...
    float cameraSpeed = 0.05f; // adjust accordingly
    if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
        cameraPos += cameraSpeed * cameraFront;
    if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
        cameraPos -= cameraSpeed * cameraFront;
    if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
        cameraPos -= glm::normalize(glm::cross(cameraFront, cameraUp)) * cameraSpeed;
    if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
        cameraPos += glm::normalize(glm::cross(cameraFront, cameraUp)) * cameraSpeed;
}

移动速度

• deltaTime变量：当前帧与上一帧的时间差
• lastFrame变量：上一帧的时间
• 将cameraSpeed乘以deltaTime值可以平衡摄像机速度

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float deltaTime = 0.0f; // 当前帧与上一帧的时间差
float lastFrame = 0.0f; // 上一帧的时间

float currentFrame = glfwGetTime();
deltaTime = currentFrame - lastFrame;
lastFrame = currentFrame;

void processInput(GLFWwindow *window)
{
  float cameraSpeed = 2.5f * deltaTime;
  ...
}

欧拉角

• 俯仰角Pitch、偏航角Yaw、滚转角Roll

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  direction.x = cos(glm::radians(pitch)) * cos(glm::radians(yaw)); // 译注：direction代表摄像机的前轴(Front)，这个前轴是和本文第一幅图片的第二个摄像机的方向向量是相反的 direction.y = sin(glm::radians(pitch)); direction.z = cos(glm::radians(pitch)) * sin(glm::radians(yaw));

鼠标输入

• 设置GLFW使其隐藏光标并捕捉

  • glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

• 创建回调函数

  • 先注册回调函数glfwSetCursorPosCallback(window, mouse_callback);

  • 全局变量储存鼠标上一帧的位置 float lastX = 400, lastY = 300;

  • 储存俯仰角float yaw = 0,pitch = 0

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    void mouse_callback(GLFWwindow* window, double xpos, double ypos) { float xoffset = xpos - lastX; float yoffset = lastY - ypos; // 注意这里是相反的，因为y坐标是从底部往顶部依次增大的 lastX = xpos; lastY = ypos; float sensitivity = 0.05f; xoffset *= sensitivity; yoffset *= sensitivity; yaw += xoffset; pitch += yoffset; //确保玩家看不到自己的屁股 if(pitch > 89.0f) pitch = 89.0f; if(pitch < -89.0f) pitch = -89.0f; //计算得到方向向量 glm::vec3 front; front.x = cos(glm::radians(pitch)) * cos(glm::radians(yaw)); front.y = sin(glm::radians(pitch)); front.z = cos(glm::radians(pitch)) * sin(glm::radians(yaw)); cameraFront = glm::normalize(front); }

• 防止鼠标跳跃

  • 全局变量bool firstMouse = true;

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    if(firstMouse) // 这个bool变量初始时是设定为true的 { lastX = xpos; lastY = ypos; firstMouse = false; }

缩放

• 使用鼠标滚轮回调函数

  • 先注册回调函数glfwSetScrollCallback(window, scroll_callback);

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    void scroll_callback(GLFWwindow* window, double xoffset, double yoffset) { if(fov >= 1.0f && fov <= 45.0f) fov -= yoffset; if(fov <= 1.0f) fov = 1.0f; if(fov >= 45.0f) fov = 45.0f; }

  • 渲染循环中projection = glm::perspective(glm::radians(fov), 800.0f / 600.0f, 0.1f, 100.0f);