From 5cb36e38cffb88b80b61165c521b35e9009a9dd6 Mon Sep 17 00:00:00 2001
From: samuncle <samuncle@users.noreply.github.com>
Date: Fri, 12 Feb 2021 04:16:38 +0100
Subject: [PATCH] Feature/enable lod autocompute (#3970)

* Enable LoD autocompute

* bring back the autocompute lod function

* Add the area as main function to compute the lod level

* Bring back the area based auto lod computation

Co-authored-by: samuncle <samuncle06@gmail.com>
---
 src/graphics/lod_node.cpp              | 37 ++++++++++++++++++++++++++
 src/graphics/lod_node.hpp              |  8 ++++++
 src/tracks/model_definition_loader.cpp |  3 +--
 3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/src/graphics/lod_node.cpp b/src/graphics/lod_node.cpp
index 90041e4e4..f776a4e03 100644
--- a/src/graphics/lod_node.cpp
+++ b/src/graphics/lod_node.cpp
@@ -50,6 +50,7 @@ LODNode::LODNode(std::string group_name, scene::ISceneNode* parent,
 
     m_forced_lod = -1;
     m_last_tick = 0;
+    m_area = 0;
 }
 
 LODNode::~LODNode()
@@ -249,8 +250,44 @@ void LODNode::OnRegisterSceneNode()
     scene::ISceneNode::OnRegisterSceneNode();
 }
 
+
+void LODNode::autoComputeLevel(float scale)
+{
+    m_area *= scale;
+
+    // Amount of details based on user's input
+    float agressivity = 1.0;
+    if(UserConfigParams::m_geometry_level == 0) agressivity = 1.25;
+    if(UserConfigParams::m_geometry_level == 1) agressivity = 1.0;
+    if(UserConfigParams::m_geometry_level == 2) agressivity = 0.75;
+
+    // First we try to estimate how far away we need to draw
+    float max_draw = 0.0;
+    max_draw = sqrtf((0.5 * m_area + 10) * 200) - 10;
+    // If the draw distance is too big we artificially reduce it
+    if(max_draw > 250)
+    {
+        max_draw = 250 + (max_draw * 0.06);
+    }
+
+    max_draw *= agressivity;
+
+    int step = (int) (max_draw * max_draw) / m_detail.size();
+
+    // Then we recompute the level of detail culling distance
+    int biais = m_detail.size();
+    for(int i = 0; i < m_detail.size(); i++)
+    {
+        m_detail[i] = ((step / biais) * (i + 1));
+        biais--;
+    }
+}
+
 void LODNode::add(int level, scene::ISceneNode* node, bool reparent)
 {
+    Box = node->getBoundingBox();
+    m_area = Box.getArea();
+
     // samuncle suggested to put a slight randomisation in LOD
     // I'm not convinced (Auria) but he's the artist pro, so I listen ;P
     // The last level should not be randomized because after that the object disappears,
diff --git a/src/graphics/lod_node.hpp b/src/graphics/lod_node.hpp
index a60a6ff50..3c15f9fc7 100644
--- a/src/graphics/lod_node.hpp
+++ b/src/graphics/lod_node.hpp
@@ -62,6 +62,9 @@ private:
      *  m_forced_lod is >=0, only this level is be used. */
     int m_forced_lod;
 
+    // Area of the bounding box (for autoLOD computation)
+    float m_area;
+
     enum PreviousVisibility
     {
         FIRST_PASS,
@@ -104,6 +107,11 @@ public:
       */
     void add(int level, scene::ISceneNode* node, bool reparent);
 
+    /**
+      * This method can be used to automatically compute LoD level
+      */
+    void autoComputeLevel(float scale);
+
     void forceLevelOfDetail(int n);
 
     /** Get the highest level of detail node */
diff --git a/src/tracks/model_definition_loader.cpp b/src/tracks/model_definition_loader.cpp
index f0c007293..09898a843 100644
--- a/src/tracks/model_definition_loader.cpp
+++ b/src/tracks/model_definition_loader.cpp
@@ -151,8 +151,7 @@ LODNode* ModelDefinitionLoader::instanciateAsLOD(const XMLNode* node, scene::ISc
         }
         vector3df scale = vector3df(1.f, 1.f, 1.f);
         node->get("scale", &scale);
-        // TODO samuncle: can be enabled after RC
-        //lod_node->autoComputeLevel(scale.getLength());
+        lod_node->autoComputeLevel(scale.getLength());
 
 #ifdef DEBUG
         std::string debug_name = groupname+" (LOD track-object)";