Fix first person camera rotation

src/main.cc

@@ -22,6 +22,7 @@
 // STDLIB
 #include <cstdint>
 #include <cstdio>
+#include <cmath>
 #include <string>
 #include <vector>
 
@@ -39,9 +40,15 @@ enum exit_codes : int {
 };
 
 struct Camera {
+  // Point in world coordinates where the camera is located
   glm::vec3 position;
+
+  // view_direction is an actual direction vector. When used with glm::lookAt, we add it to the position
+  // to calculate the target the camera is looking at
   glm::vec3 view_direction;
-  glm::vec3 up_vector;
+
+  // The up vector in world coordinates
+  glm::vec3 up;
 };
 
 struct App {
@@ -166,14 +173,14 @@ int init(App &app) {
   );
 
   app.speed                 = 0.02f;
-  app.translation           = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, 0.0f, -1.5f));
+  app.translation           = glm::translate(glm::mat4(1.0f), glm::vec3(0.0f, 0.0f, 1.5f));
   app.rotation              = glm::mat4(1.0f);
   app.scale                 = glm::mat4(1.0f);
-  app.camera.position       = glm::vec3(0.0f);
+  app.camera.position       = glm::vec3(0.0f, 0.0f,  3.0f);
   app.camera.view_direction = glm::vec3(0.0f, 0.0f, -1.0f);
-  app.camera.up_vector      = glm::vec3(0.0f, 1.0f, 0.0f);
+  app.camera.up             = glm::vec3(0.0f, 1.0f,  0.0f);
   app.model_mat             = app.translation * app.rotation * app.scale;
-  app.view_mat              = glm::lookAt(app.camera.position, app.camera.view_direction, app.camera.up_vector);
+  app.view_mat              = glm::lookAt(app.camera.position, app.camera.position + app.camera.view_direction, app.camera.up);
   app.projection_mat        = glm::perspective(glm::radians(60.0f),
                                                (float)WINDOW_WIDTH / (float)WINDOW_HEIGHT,
                                                0.1f,
@@ -439,12 +446,9 @@ void handle_object_movement(App &app) {
 
 void handle_camera_movement(App &app) {
   if (app.event.type == SDL_MOUSEMOTION) {
-    app.current_mouse        += glm::vec2(app.event.motion.xrel, app.event.motion.yrel);
+    glm::vec2 offset          = glm::vec2(app.event.motion.xrel, 0) * 0.1f;
-    glm::vec2 mouse_delta     = app.prev_mouse - app.current_mouse;
+    app.prev_mouse           += offset;
-    app.camera.view_direction = glm::rotate(app.camera.view_direction,
+    app.camera.view_direction = glm::rotate(app.camera.view_direction, glm::radians(offset.x), app.camera.up);
-                                            glm::radians(mouse_delta.x),
-                                            app.camera.up_vector);
-    app.prev_mouse            = app.current_mouse;
   } else {
     switch (app.event.key.keysym.sym) {
       case SDLK_w:
@@ -454,15 +458,15 @@ void handle_camera_movement(App &app) {
           app.camera.position -= app.camera.view_direction * app.speed;
           break;
       case SDLK_d:
-          app.camera.position.x += app.speed;
+          app.camera.position += glm::normalize(glm::cross(app.camera.view_direction, app.camera.up)) * app.speed; 
           break;
       case SDLK_a:
-          app.camera.position.x -= app.speed;
+          app.camera.position -= glm::normalize(glm::cross(app.camera.view_direction, app.camera.up)) * app.speed;
           break;
       default:
           return;
     }
   }
 
-  app.view_mat = glm::lookAt(app.camera.position, app.camera.view_direction, app.camera.up_vector);
+  app.view_mat = glm::lookAt(app.camera.position, app.camera.position + app.camera.view_direction, app.camera.up);
 }