From 8eadda99311617e780cdab25d90a6800ac11d9b2 Mon Sep 17 00:00:00 2001
From: jacob <jacob@cagori.com>
Date: Tue, 29 Oct 2024 18:35:35 -0500
Subject: [PATCH] store & calculate friction

---
 src/entity.c |  2 ++
 src/entity.h |  7 +++++++
 src/game.c   | 12 ++++++++----
 3 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/entity.c b/src/entity.c
index d6f8ed94..7a252062 100644
--- a/src/entity.c
+++ b/src/entity.c
@@ -16,6 +16,7 @@ READONLY struct entity _g_entity_nil = {
     .local_xform = XFORM_IDENT_NOCAST,
     .cached_global_xform = XFORM_IDENT_NOCAST,
     .cached_global_xform_dirty = false,
+    .friction = 0.5f,
     .mass_unscaled = 1,
     .inertia_unscaled = 1,
     .sprite_local_xform = XFORM_IDENT_NOCAST,
@@ -27,6 +28,7 @@ GLOBAL READONLY struct entity g_entity_default = {
     .local_xform = XFORM_IDENT_NOCAST,
     .cached_global_xform = XFORM_IDENT_NOCAST,
     .cached_global_xform_dirty = true,
+    .friction = 0.5f,
     .mass_unscaled = 1,
     .inertia_unscaled = 1,
     .sprite_local_xform = XFORM_IDENT_NOCAST,
diff --git a/src/entity.h b/src/entity.h
index d489daae..697254f9 100644
--- a/src/entity.h
+++ b/src/entity.h
@@ -91,6 +91,8 @@ struct contact_constraint {
     struct contact_point points[2];
     u32 num_points;
 
+    f32 friction;
+
     struct math_spring_result softness;
     f32 pushout_velocity;
 
@@ -275,8 +277,13 @@ struct entity {
 
     /* ENTITY_PROP_PHYSICAL */
 
+    //f32 density;            /* Density in kg/m^2 */
+
+    f32 friction;
+
     f32 mass_unscaled;      /* Mass of entity in kg before any transformations */
     f32 inertia_unscaled;   /* Inertia of entity in kg*m^2 before any transformations */
+
     f32 linear_ground_friction;
     f32 angular_ground_friction;
 
diff --git a/src/game.c b/src/game.c
index 0a3e7145..4ede1961 100644
--- a/src/game.c
+++ b/src/game.c
@@ -176,11 +176,13 @@ INTERNAL void spawn_test_entities(f32 offset)
         e->angular_ground_friction = 100;
 
 
+        //e->control_force = 500;
         e->control_force = 500;
         e->control_force_max_speed = 4;
-        e->control_torque = 5000;
+        e->control_torque = 500;
 
         entity_enable_prop(e, ENTITY_PROP_PHYSICAL);
+
         e->mass_unscaled = 10;
         e->inertia_unscaled = 10;
 
@@ -189,7 +191,7 @@ INTERNAL void spawn_test_entities(f32 offset)
         player_ent = e;
 
 
-#if 0
+#if 1
         {
             struct entity *joint_ent = entity_alloc(root);
             entity_enable_prop(joint_ent, ENTITY_PROP_PHYSICAL);
@@ -487,6 +489,8 @@ INTERNAL void create_contacts(void)
             if (res.num_points > 0) {
                 struct contact_constraint *constraint = &constraint_ent->contact_constraint_data;
 
+                constraint->friction = math_sqrt(e0->friction * e1->friction);
+
                 /* Delete old contacts that are no longer present */
                 for (u32 i = 0; i < constraint->num_points; ++i) {
                     struct contact_point *old = &constraint->points[i];
@@ -769,10 +773,10 @@ INTERNAL void solve_contacts(f32 dt, b32 apply_bias)
                 f32 vt = v2_dot(vrel, tangent);
                 f32 j = vt * k;
 
-                f32 friction = 0.6f;
+                //f32 friction = 0.6f;
                 //f32 friction = 1.0f;
                 //f32 friction = F32_INFINITY;
-                f32 max_friction = friction * point->normal_impulse;
+                f32 max_friction = constraint->friction * point->normal_impulse;
                 f32 old_impulse = point->tangent_impulse;
                 f32 new_impulse = clamp_f32(old_impulse + j, -max_friction, max_friction);
                 f32 delta = new_impulse - old_impulse;