source: network-game/graphics_library/common/controls.cpp@ c666518

// Include GLFW
#include <GLFW/glfw3.h>
extern GLFWwindow* window; // The "extern" keyword here is to access the variable "window" declared in tutorialXXX.cpp. This is a hack to keep the tutorials simple. Please avoid this.

// Include GLM
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
using namespace glm;

#include "controls.hpp"

glm::mat4 ViewMatrix;
glm::mat4 ProjectionMatrix;

glm::mat4 getViewMatrix(){
        return ViewMatrix;
}
glm::mat4 getProjectionMatrix(){
        return ProjectionMatrix;
}


// Initial position : on +Z
glm::vec3 position = glm::vec3( 0, 0, 5 ); 
// Initial horizontal angle : toward -Z
float horizontalAngle = 3.14f;
// Initial vertical angle : none
float verticalAngle = 0.0f;
// Initial Field of View
float initialFoV = 45.0f;

float speed = 3.0f; // 3 units / second
float mouseSpeed = 0.005f;



void computeMatricesFromInputs(){

        // glfwGetTime is called only once, the first time this function is called
        static double lastTime = glfwGetTime();

        // Compute time difference between current and last frame
        double currentTime = glfwGetTime();
        float deltaTime = float(currentTime - lastTime);

        // Get mouse position
        double xpos, ypos;
        glfwGetCursorPos(window, &xpos, &ypos);

        // Reset mouse position for next frame
        glfwSetCursorPos(window, 1024/2, 768/2);

        // Compute new orientation
        horizontalAngle += mouseSpeed * float(1024/2 - xpos );
        verticalAngle   += mouseSpeed * float( 768/2 - ypos );

        // Direction : Spherical coordinates to Cartesian coordinates conversion
        glm::vec3 direction(
                cos(verticalAngle) * sin(horizontalAngle), 
                sin(verticalAngle),
                cos(verticalAngle) * cos(horizontalAngle)
        );
        
        // Right vector
        glm::vec3 right = glm::vec3(
                sin(horizontalAngle - 3.14f/2.0f), 
                0,
                cos(horizontalAngle - 3.14f/2.0f)
        );
        
        // Up vector
        glm::vec3 up = glm::cross( right, direction );

        // Move forward
        if (glfwGetKey( window, GLFW_KEY_UP ) == GLFW_PRESS){
                position += direction * deltaTime * speed;
        }
        // Move backward
        if (glfwGetKey( window, GLFW_KEY_DOWN ) == GLFW_PRESS){
                position -= direction * deltaTime * speed;
        }
        // Strafe right
        if (glfwGetKey( window, GLFW_KEY_RIGHT ) == GLFW_PRESS){
                position += right * deltaTime * speed;
        }
        // Strafe left
        if (glfwGetKey( window, GLFW_KEY_LEFT ) == GLFW_PRESS){
                position -= right * deltaTime * speed;
        }

        float FoV = initialFoV;// - 5 * glfwGetMouseWheel(); // Now GLFW 3 requires setting up a callback for this. It's a bit too complicated for this beginner's tutorial, so it's disabled instead.

        // Projection matrix : 45° Field of View, 4:3 ratio, display range : 0.1 unit <-> 100 units
        ProjectionMatrix = glm::perspective(FoV, 4.0f / 3.0f, 0.1f, 100.0f);
        // Camera matrix
        ViewMatrix       = glm::lookAt(
                                                                position,           // Camera is here
                                                                position+direction, // and looks here : at the same position, plus "direction"
                                                                up                  // Head is up (set to 0,-1,0 to look upside-down)
                                                   );

        // For the next frame, the "last time" will be "now"
        lastTime = currentTime;
}