From 08cb8d6a585dd552b69a488d9db1be123f01467a Mon Sep 17 00:00:00 2001
From: tech kaczynski <tk@techkaczynski.dev>
Date: Tue, 22 Sep 2026 22:38:57 +1000
Subject: initial commit.

---
 physics.h | 156 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 156 insertions(+)
 create mode 100644 physics.h

(limited to 'physics.h')

diff --git a/physics.h b/physics.h
new file mode 100644
index 0000000..0a92118
--- /dev/null
+++ b/physics.h
@@ -0,0 +1,156 @@
+#ifndef PHYSICS_H
+#define PHYSICS_H
+
+#include "common.h"
+
+typedef enum {
+	PHYS_SHAPE_BOX,
+	PHYS_SHAPE_SPHERE,
+	PHYS_SHAPE_CAPSULE,
+	PHYS_SHAPE_CYLINDER,
+	PHYS_SHAPE_CONVEX_HULL,
+	PHYS_SHAPE_STATIC_TRIMESH,
+} PhysicsShapeTag;
+
+typedef enum {
+	PHYS_JOINT_SPHERICAL,
+	PHYS_JOINT_REVOLUTE,
+	PHYS_JOINT_PRISMATIC,
+	PHYS_JOINT_WELD,
+	PHYS_JOINT_WHEEL,
+	PHYS_JOINT_DISTANCE,
+} PhysicsJointTag;
+
+typedef enum {
+	PHYS_JOINT_LIMIT,
+	PHYS_JOINT_SPRING,
+	PHYS_JOINT_MOTOR,
+} PhysicsJointFlags;
+
+typedef enum {
+	PHYS_MODE_STATIC,
+	PHYS_MODE_KINEMATIC,
+	PHYS_MODE_DYNAMIC,
+} PhysicsMode;
+
+typedef enum {
+	PHYS_MASK_DEFAULT,
+	PHYS_MASK_WORLD,
+	PHYS_MASK_PROP,
+	PHYS_MASK_PLAYER,
+	PHYS_MASK_PARTICLE,
+
+	PHYS_MASK_EDITOR_SELECTABLE,
+	PHYS_MASK_EDITOR_RAYCAST,
+} PhysicsMask;
+
+typedef struct {
+	PhysicsShapeTag tag;
+	union {
+		struct {
+			Vec3 sz;
+		} Box;
+
+		struct {
+			f32 radius;
+		} Sphere;
+
+		struct {
+			f32 height, radius;
+		} Capsule, Cylinder;
+
+		struct {
+			Vec3 *points;
+			u32 point_cnt;
+		} ConvexHull;
+
+		struct {
+			Vec3 *points;
+			u32 *indices;
+			u32 point_cnt, idx_cnt;
+		} TriMesh;
+	};
+
+	/* local to body */
+	Vec3 pos;
+	Quaternion rot;
+
+	f32 density, friction, restitution;
+	Flags32 category_bits, mask_bits;
+} PhysicsShape;
+
+typedef struct {
+	PhysicsShape *shapes;
+	u32 shape_cnt;
+
+	/* local to entity */
+	Vec3 pos;
+	Quaternion rot;
+
+	f32 linear_damping, angular_damping;
+	f32 gravity_scale;
+	PhysicsMode mode;
+	bool enable_sleep;
+} PhysicsBody;
+
+/*
+	physics joint fields meaning changes depending on their context.
+
+	anchor_a/axis_a are local to body_a.
+	anchor_b/axis_b are local to body_b.
+	axes should be normalized.
+
+	lower/upper are generic limits
+	- revolute: radians
+	- prismatic: metres
+	- distance: metres
+	- wheel: suspension travel
+
+	springs:
+	- spring_hz: frequency of the spring response; higher = stiffer/faster
+	- spring_damping: damping ratio; controls oscillation
+
+	motors:
+		revolute:
+		motor_speed = angular velocity
+		motor_force = maximum torque
+
+		prismatic:
+		motor_speed = linear velocity
+		motor_force = maximum force
+
+		wheel:
+		motor_speed = wheel angular velocity
+		motor_force = maximum drive/braking torque
+*/
+typedef struct {
+	PhysicsJointTag tag;
+	u32 body_a, body_b;
+	Flags32 flags;
+
+	Vec3 anchor_a, anchor_b;
+	Vec3 axis_a, axis_b;
+
+	f32 lower, upper;
+	f32 spring_hz, spring_damping;
+	f32 motor_speed, motor_force;
+} PhysicsJoint;
+
+typedef struct {
+	b3BodyId id;
+	b3ShapeId *shapes; // count is stored in PhysicsCmp
+} PhysicsBodyRuntime;
+
+typedef struct {
+	b3WorldDef world_def;
+	b3WorldId world_id;
+	bool simulate;
+} PhysicsInfo;
+
+extern PhysicsInfo physics;
+
+void 		physics_init(void);
+void 		physics_exit(void);
+void 		physics_update(void);
+
+#endif
-- 
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