Make the minimum distance for a LoD transition depend on the object's…

… size

Also:
- Since draw distance is used to account for the object's size, have parameters depending on geometry detail correct for it. The minimum switch distance increases slightly with each geometry detail level.
- Clarify what the formula spreading the distances for each LoD level does
- Adjust slightly the auto-LoD multipliers.

src/graphics/lod_node.cpp

@@ -226,35 +226,45 @@ void LODNode::autoComputeLevel(float scale)
 
     float max_draw = p4_ratio * p4_component + (1.0f - p4_ratio) * p2_component;
 
-    float m_min_switch_dist = 90;
-
-    // Step 2 - Distance multiplier based on the user's input
+    // Step 2a - Distance multiplier based on the user's input
     float aggressivity = 1.0;
     if(     UserConfigParams::m_geometry_level == 2) aggressivity = 1.0; // 2 in the params is the lowest setting
-    else if(UserConfigParams::m_geometry_level == 1) aggressivity = 1.4;
-    else if(UserConfigParams::m_geometry_level == 0) aggressivity = 1.95;
-    else if(UserConfigParams::m_geometry_level == 3) aggressivity = 2.7;
-    else if(UserConfigParams::m_geometry_level == 4) aggressivity = 3.75;
-    else if(UserConfigParams::m_geometry_level == 5) aggressivity = 5.25;
+    else if(UserConfigParams::m_geometry_level == 1) aggressivity = 1.42;
+    else if(UserConfigParams::m_geometry_level == 0) aggressivity = 2.0;
+    else if(UserConfigParams::m_geometry_level == 3) aggressivity = 2.84;
+    else if(UserConfigParams::m_geometry_level == 4) aggressivity = 4.0;
+    else if(UserConfigParams::m_geometry_level == 5) aggressivity = 5.7;
 
     max_draw *= aggressivity;
 
+    // Step 2b - Determine the minimum distance for a model switch based on user input
+    float temp_switch_dist = max_draw;
+    if(     UserConfigParams::m_geometry_level == 2) temp_switch_dist *= 0.75f; // 2 in the params is the lowest setting
+    else if(UserConfigParams::m_geometry_level == 1) temp_switch_dist *= 0.55f;
+    else if(UserConfigParams::m_geometry_level == 0) temp_switch_dist *= 0.4f;
+    else if(UserConfigParams::m_geometry_level == 3) temp_switch_dist *= 0.3f;
+    else if(UserConfigParams::m_geometry_level == 4) temp_switch_dist *= 0.23f;
+    else if(UserConfigParams::m_geometry_level == 5) temp_switch_dist *= 0.18f;
+
+    temp_switch_dist = (temp_switch_dist + 100.0f) / 2.0f;
+
+    m_min_switch_distance = (int)temp_switch_dist;
+
     // Step 3 - As it is faster to compute the squared distance than distance, at runtime
     //          we compare the distance saved in the LoD node with the square of the distance
     //          between the camera and the object. Therefore, we apply squaring here.
     max_draw *= max_draw;
-    m_min_switch_dist *= m_min_switch_dist;
+    m_min_switch_distance *= m_min_switch_distance;
 
+    // Step 4 - Then we recompute the level of detail culling distance
+    //          If there are N levels of detail, the highest level
+    //          is displayed when under 1/Nth of the max display distance.
+    //          Other levels are spaced approximately at the geometrical mean points.
     int step = (int) (max_draw) / m_detail.size();
     int biais = m_detail.size();
 
     for(unsigned i = 0; i < m_detail.size(); i++)
     {
-        // Step 4 - Then we recompute the level of detail culling distance
-        //          If there are N levels of detail, the transition distance
-        //          between each level is currently each SQRT(1/N)th of the max
-        //          display distance
-        // TODO - investigate a better division scheme
         m_detail[i] = ((step / biais) * (i + 1));
         biais--;
     }