add camera:look_at optional interpolation parameter

doc/en/scripting/builtins/libcameras.md

@@ -61,6 +61,9 @@ cam:get_up() -> vec3
 
 -- makes camera look to a given point
 cam:look_at(point:vec3)
+
+-- makes camera look to a given point with given interpolation factor
+cam:look_at(point: vec3, t: number)
 ```
 
 Use player.set_camera to switch cameras.

doc/ru/scripting/builtins/libcameras.md

@@ -61,6 +61,9 @@ cam:get_up() -> vec3
 
 -- направляет камеру на заданную точку
 cam:look_at(point: vec3)
+
+-- направляет камеру на заданную точку с фактором интерполяции
+cam:look_at(point: vec3, t: number)
 ```
 
 Переключение камеры возможно через функцию player.set_camera.

res/scripts/classes.lua

@@ -16,7 +16,7 @@ local Camera = {__index={
     get_front=function(self) return cameras.get_front(self.cid) end,
     get_right=function(self) return cameras.get_right(self.cid) end,
     get_up=function(self) return cameras.get_up(self.cid) end,
-    look_at=function(self, v) return cameras.look_at(self.cid, v) end,
+    look_at=function(self, v, f) return cameras.look_at(self.cid, v, f) end,
 }}
 
 local wrappers = {}

src/logic/scripting/lua/libcamera.cpp

@@ -92,7 +92,14 @@ static int l_look_at(lua::State* L) {
     size_t index = static_cast<size_t>(lua::tointeger(L, 1));
     auto& camera = *level->cameras.at(index);
     auto center = lua::tovec<3>(L, 2);
-    camera.rotation = glm::inverse(glm::lookAt(glm::vec3(), center-camera.position, glm::vec3(0, 1, 0)));
+    auto matrix = glm::inverse(glm::lookAt(glm::vec3(), center-camera.position, glm::vec3(0, 1, 0)));
+    if (lua::isnumber(L, 3)) {
+        matrix = glm::mat4_cast(glm::slerp(
+            glm::quat(camera.rotation),
+            glm::quat(matrix),
+            static_cast<float>(lua::tonumber(L, 3))));
+    }
+    camera.rotation = matrix;
     camera.updateVectors();
     return 0;
 }