diff --git a/Engine.cc b/Engine.cc
index 2b44f52..4f710f6 100644
--- a/Engine.cc
+++ b/Engine.cc
@@ -14,7 +14,7 @@
 #include <iostream>
 #include <sstream>
 #include <string>
-#include <math.h>                   /* fabs() */
+#include <math.h>                   /* fabs(), tan() */
 #include <GL/gl.h>
 #include <GL/glu.h>
 #include "SDL.h"
@@ -99,6 +99,7 @@ Engine::Engine(const string & path, Video & video)
     m_engine_cursor_visible = m_video.getCursorVisible();
     m_script_cursor_visible = false;
     m_input_grabbed = m_video.getInputGrabbed();
+    m_screen_dist = (m_video.getWidth() / 2.0) / tan(30.0 * M_PI / 180.0);
 
     size_t pos = path.find_last_of("\\/");
     m_engine_path = (pos != string::npos) ? string(path, 0, pos) : ".";
@@ -622,6 +623,28 @@ void Engine::clearWorld()
     }
 }
 
+refptr< vector<int> > Engine::pickObjects(int x, int y)
+{
+    dMatrix3 r;
+    dVector3 right, forward, up;
+    dVector3 rotated_direction, initial_direction;
+    up[0] = m_up[0];
+    up[1] = m_up[1];
+    up[2] = m_up[2];
+    forward[0] = m_center[0] - m_eye[0];
+    forward[1] = m_center[1] - m_eye[1];
+    forward[2] = m_center[2] - m_eye[2];
+    cross_product(right, forward, up);
+    dRFrom2Axes(r, right[0], right[1], right[2],
+            forward[0], forward[1], forward[2]);
+    initial_direction[0] = x - m_video.getWidth() / 2;
+    initial_direction[1] = m_screen_dist;
+    initial_direction[2] = m_video.getHeight() / 2 - y;
+    dMultiply0(rotated_direction, initial_direction, r, 1, 3, 3);
+
+    /* TODO: finish */
+}
+
 void Engine::debug_hook(lua_Debug * debug)
 {
     Uint32 ticks = SDL_GetTicks();
diff --git a/Engine.h b/Engine.h
index b2843fb..66bcaf8 100644
--- a/Engine.h
+++ b/Engine.h
@@ -195,6 +195,7 @@ class Engine
             updateCursorVisibility();
         }
         bool getScriptCursorVisible() { return m_script_cursor_visible; }
+        refptr< std::vector<int> > pickObjects(int x, int y);
 
         void getScreenSize(int * width, int * height);
         void drawText(const char * text, GLfloat r, GLfloat g, GLfloat b,
@@ -274,6 +275,7 @@ class Engine
         SDL_Event       m_exitEvent;
         Uint32          m_event_time;
         FTFont *        m_font;
+        double          m_screen_dist;
 
         bool            m_event_init_present;
         bool            m_event_reinit_present;