From 0efe4dc74ddf6341de2f9790755c4fa5b6342d5b Mon Sep 17 00:00:00 2001
From: Zack Buhman <zack@buhman.org>
Date: Fri, 18 Jul 2025 00:46:50 -0500
Subject: [PATCH] physics: add particle_force_generator

---
 src/physics/particle_force_generator.cpp | 31 ++++++++++++++++++++++++
 src/physics/particle_force_generator.hpp | 27 +++++++++++++++++++++
 2 files changed, 58 insertions(+)

diff --git a/src/physics/particle_force_generator.cpp b/src/physics/particle_force_generator.cpp
index 96b5ee4..97be818 100644
--- a/src/physics/particle_force_generator.cpp
+++ b/src/physics/particle_force_generator.cpp
@@ -29,4 +29,35 @@ namespace physics {
 
     particle->add_force(normalize(force) * drag_coeff);
   }
+
+  void particle_spring::update_force(particle * particle, float duration)
+  {
+    vec3 force = particle->position - other->position;
+
+    float intensity = abs<float>(magnitude(force) - rest_length) * spring_constant;
+
+    particle->add_force(normalize(force) * -intensity);
+  }
+
+  void particle_anchored_spring::update_force(particle * particle, float duration)
+  {
+    vec3 force = particle->position - *anchor;
+
+    float intensity = abs<float>(magnitude(force) - rest_length) * spring_constant;
+
+    particle->add_force(normalize(force) * -intensity);
+  }
+
+  void particle_bungee::update_force(particle * particle, float duration)
+  {
+    vec3 force = particle->position - other->position;
+
+    float _magnitude = magnitude(force);
+    if (_magnitude <= rest_length)
+      return;
+
+    float intensity = spring_constant * (rest_length - _magnitude);
+
+    particle->add_force(normalize(force) * -intensity);
+  }
 }
diff --git a/src/physics/particle_force_generator.hpp b/src/physics/particle_force_generator.hpp
index 6f2124d..ee2fe42 100644
--- a/src/physics/particle_force_generator.hpp
+++ b/src/physics/particle_force_generator.hpp
@@ -44,4 +44,31 @@ namespace physics {
 
     void update_force(particle * particle, float duration) override;
   };
+
+  struct particle_spring : particle_force_generator
+  {
+    physics::particle * other;
+    float spring_constant;
+    float rest_length;
+
+    void update_force(particle * particle, float duration) override;
+  };
+
+  struct particle_anchored_spring : particle_force_generator
+  {
+    vec3 * anchor;
+    float spring_constant;
+    float rest_length;
+kk
+    void update_force(particle * particle, float duration) override;
+  };
+
+  struct particle_bungee : particle_force_generator
+  {
+    physics::particle * other;
+    float spring_constant;
+    float rest_length;
+
+    void update_force(particle * particle, float duration) override;
+  };
 }