From 7193bcbc41a18ad6786273554811eb7e88a9479c Mon Sep 17 00:00:00 2001
From: NishiOwO <nishi@nishi.boats>
Date: Sun, 1 Feb 2026 00:38:33 +0900
Subject: [PATCH] basic physics

---
 engine/include/GearSrc/TypeDefs.h |  5 ++--
 engine/src/physics.c              | 39 ++++++++++++++++++++++++++++---
 2 files changed, 39 insertions(+), 5 deletions(-)

diff --git a/engine/include/GearSrc/TypeDefs.h b/engine/include/GearSrc/TypeDefs.h
index 488ad10..6a7be03 100644
--- a/engine/include/GearSrc/TypeDefs.h
+++ b/engine/include/GearSrc/TypeDefs.h
@@ -316,8 +316,9 @@ struct _GSNetSocket {
 struct _GSPhysics {
 	GSEngine engine;
 
-	dWorldID world;
-	dSpaceID space;
+	dWorldID      world;
+	dSpaceID      space;
+	dJointGroupID contact_group;
 };
 
 struct _GSClient {
diff --git a/engine/src/physics.c b/engine/src/physics.c
index 45aff69..9e3e51b 100644
--- a/engine/src/physics.c
+++ b/engine/src/physics.c
@@ -15,8 +15,11 @@ GSPhysics GSPhysicsCreate(GSServer server) {
 
 	physics->engine = server->engine;
 
-	physics->world = dWorldCreate();
-	physics->space = dSimpleSpaceCreate(0);
+	physics->world	       = dWorldCreate();
+	physics->space	       = dSimpleSpaceCreate(0);
+	physics->contact_group = dJointGroupCreate(0);
+
+	dWorldSetGravity(physics->world, 0, 0, -9.81);
 
 	GSLog(server->engine, GSLogInfo, "Created physics engine");
 
@@ -24,6 +27,7 @@ GSPhysics GSPhysicsCreate(GSServer server) {
 }
 
 void GSPhysicsDestroy(GSPhysics physics) {
+	dJointGroupDestroy(physics->contact_group);
 	dSpaceDestroy(physics->space);
 	dWorldDestroy(physics->world);
 
@@ -32,5 +36,34 @@ void GSPhysicsDestroy(GSPhysics physics) {
 	free(physics);
 }
 
-void GSPhysicsStep(GSPhysics physics) {
+static void near_callback(void* data, dGeomID o1, dGeomID o2) {
+	const int N = 256;
+	dContact  contact[256];
+	GSPhysics physics = data;
+
+	if(dGeomIsSpace(o1) || dGeomIsSpace(o2)) {
+		dSpaceCollide2(o1, o2, data, near_callback);
+		if(dGeomIsSpace(o1)) dSpaceCollide((dSpaceID)o1, data, near_callback);
+		if(dGeomIsSpace(o2)) dSpaceCollide((dSpaceID)o2, data, near_callback);
+	} else {
+		int how_many = dCollide(o1, o2, N, &contact[0].geom, sizeof(dContact));
+		int i;
+
+		for(i = 0; i < how_many; i++) {
+			dJointID joint;
+
+			contact[i].surface.mode = dContactApprox1;
+			contact[i].surface.mu	= 2;
+
+			joint = dJointCreateContact(physics->world, physics->contact_group, &contact[i]);
+
+			dJointAttach(joint, dGeomGetBody(contact[i].geom.g1), dGeomGetBody(contact[i].geom.g2));
+		}
+	}
+}
+
+void GSPhysicsStep(GSPhysics physics) {
+	dSpaceCollide(physics->space, physics, near_callback);
+	dWorldStep(physics->world, 1.0 / physics->engine->tps);
+	dJointGroupEmpty(physics->contact_group);
 }