physac.lua

local ffi = require("ffi")
ffi.cdef([[
/**********************************************************************************************
*
*   Physac v1.1 - 2D Physics library for videogames
*
*   DESCRIPTION:
*
*   Physac is a small 2D physics library written in pure C. The engine uses a fixed time-step thread loop
*   to simluate physics. A physics step contains the following phases: get collision information,
*   apply dynamics, collision solving and position correction. It uses a very simple struct for physic
*   bodies with a position vector to be used in any 3D rendering API.
*
*   CONFIGURATION:
*
*   #define PHYSAC_IMPLEMENTATION
*       Generates the implementation of the library into the included file.
*       If not defined, the library is in header only mode and can be included in other headers
*       or source files without problems. But only ONE file should hold the implementation.
*
*   #define PHYSAC_STATIC (defined by default)
*       The generated implementation will stay private inside implementation file and all
*       internal symbols and functions will only be visible inside that file.
*
*   #define PHYSAC_NO_THREADS
*       The generated implementation won't include pthread library and user must create a secondary thread to call PhysicsThread().
*       It is so important that the thread where PhysicsThread() is called must not have v-sync or any other CPU limitation.
*
*   #define PHYSAC_STANDALONE
*       Avoid raylib.h header inclusion in this file. Data types defined on raylib are defined
*       internally in the library and input management and drawing functions must be provided by
*       the user (check library implementation for further details).
*
*   #define PHYSAC_DEBUG
*       Traces log messages when creating and destroying physics bodies and detects errors in physics
*       calculations and reference exceptions; it is useful for debug purposes
*
*   #define PHYSAC_MALLOC()
*   #define PHYSAC_FREE()
*       You can define your own malloc/free implementation replacing stdlib.h malloc()/free() functions.
*       Otherwise it will include stdlib.h and use the C standard library malloc()/free() function.
*
*
*   NOTE 1: Physac requires multi-threading, when InitPhysics() a second thread is created to manage physics calculations.
*   NOTE 2: Physac requires static C library linkage to avoid dependency on MinGW DLL (-static -lpthread)
*
*   Use the following code to compile:
*   gcc -o $(NAME_PART).exe $(FILE_NAME) -s -static -lraylib -lpthread -lopengl32 -lgdi32 -lwinmm -std=c99
*
*   VERY THANKS TO:
*       - raysan5: helped with library design
*       - ficoos: added support for Linux
*       - R8D8: added support for Linux
*       - jubalh: fixed implementation of time calculations
*       - a3f: fixed implementation of time calculations
*       - define-private-public: added support for OSX
*       - pamarcos: fixed implementation of physics steps
*       - noshbar: fixed some memory leaks
*
*
*   LICENSE: zlib/libpng
*
*   Copyright (c) 2016-2020 Victor Fisac (github: @victorfisac)
*
*   This software is provided "as-is", without any express or implied warranty. In no event
*   will the authors be held liable for any damages arising from the use of this software.
*
*   Permission is granted to anyone to use this software for any purpose, including commercial
*   applications, and to alter it and redistribute it freely, subject to the following restrictions:
*
*     1. The origin of this software must not be misrepresented; you must not claim that you
*     wrote the original software. If you use this software in a product, an acknowledgment
*     in the product documentation would be appreciated but is not required.
*
*     2. Altered source versions must be plainly marked as such, and must not be misrepresented
*     as being the original software.
*
*     3. This notice may not be removed or altered from any source distribution.
*
**********************************************************************************************/
//----------------------------------------------------------------------------------
// Types and Structures Definition
//----------------------------------------------------------------------------------
typedef enum PhysicsShapeType { PHYSICS_CIRCLE, PHYSICS_POLYGON } PhysicsShapeType;

// Previously defined to be used in PhysicsShape struct as circular dependencies
typedef struct PhysicsBodyData *PhysicsBody;

// Mat2 type (used for polygon shape rotation matrix)
typedef struct Mat2 {
    float m00;
    float m01;
    float m10;
    float m11;
} Mat2;

typedef struct PolygonData {
    unsigned int vertexCount;                   // Current used vertex and normals count
    Vector2 positions[24];     									// Polygon vertex positions vectors
    Vector2 normals[24];       									// Polygon vertex normals vectors
} PolygonData;

typedef struct PhysicsShape {
    PhysicsShapeType type;                      // Physics shape type (circle or polygon)
    PhysicsBody body;                           // Shape physics body reference
    float radius;                               // Circle shape radius (used for circle shapes)
    Mat2 transform;                             // Vertices transform matrix 2x2
    PolygonData vertexData;                     // Polygon shape vertices position and normals data (just used for polygon shapes)
} PhysicsShape;

typedef struct PhysicsBodyData {
    unsigned int id;                            // Reference unique identifier
    bool enabled;                               // Enabled dynamics state (collisions are calculated anyway)
    Vector2 position;                           // Physics body shape pivot
    Vector2 velocity;                           // Current linear velocity applied to position
    Vector2 force;                              // Current linear force (reset to 0 every step)
    float angularVelocity;                      // Current angular velocity applied to orient
    float torque;                               // Current angular force (reset to 0 every step)
    float orient;                               // Rotation in radians
    float inertia;                              // Moment of inertia
    float inverseInertia;                       // Inverse value of inertia
    float mass;                                 // Physics body mass
    float inverseMass;                          // Inverse value of mass
    float staticFriction;                       // Friction when the body has not movement (0 to 1)
    float dynamicFriction;                      // Friction when the body has movement (0 to 1)
    float restitution;                          // Restitution coefficient of the body (0 to 1)
    bool useGravity;                            // Apply gravity force to dynamics
    bool isGrounded;                            // Physics grounded on other body state
    bool freezeOrient;                          // Physics rotation constraint
    PhysicsShape shape;                         // Physics body shape information (type, radius, vertices, normals)
} PhysicsBodyData;

typedef struct PhysicsManifoldData {
    unsigned int id;                            // Reference unique identifier
    PhysicsBody bodyA;                          // Manifold first physics body reference
    PhysicsBody bodyB;                          // Manifold second physics body reference
    float penetration;                          // Depth of penetration from collision
    Vector2 normal;                             // Normal direction vector from 'a' to 'b'
    Vector2 contacts[2];                        // Points of contact during collision
    unsigned int contactsCount;                 // Current collision number of contacts
    float restitution;                          // Mixed restitution during collision
    float dynamicFriction;                      // Mixed dynamic friction during collision
    float staticFriction;                       // Mixed static friction during collision
} PhysicsManifoldData, *PhysicsManifold;

//----------------------------------------------------------------------------------
// Module Functions Declaration
//----------------------------------------------------------------------------------
// Initializes physics values, pointers and creates physics loop thread
void InitPhysics(void);

// Returns true if physics thread is currently enabled
bool IsPhysicsEnabled(void);

// Sets physics global gravity force
void SetPhysicsGravity(float x, float y);

// Creates a new circle physics body with generic parameters
PhysicsBody CreatePhysicsBodyCircle(Vector2 pos, float radius, float density);

// Creates a new rectangle physics body with generic parameters
PhysicsBody CreatePhysicsBodyRectangle(Vector2 pos, float width, float height, float density);

// Creates a new polygon physics body with generic parameters
PhysicsBody CreatePhysicsBodyPolygon(Vector2 pos, float radius, int sides, float density);

// Adds a force to a physics body
void PhysicsAddForce(PhysicsBody body, Vector2 force);

// Adds a angular force to a physics body
void PhysicsAddTorque(PhysicsBody body, float amount);

// Shatters a polygon shape physics body to little physics bodies with explosion force
void PhysicsShatter(PhysicsBody body, Vector2 position, float force);

// Returns the current amount of created physics bodies
int GetPhysicsBodiesCount(void);

// Returns a physics body of the bodies pool at a specific index
PhysicsBody GetPhysicsBody(int index);

// Returns the physics body shape type (PHYSICS_CIRCLE or PHYSICS_POLYGON)
int GetPhysicsShapeType(int index);

// Returns the amount of vertices of a physics body shape
int GetPhysicsShapeVerticesCount(int index);

// Returns transformed position of a body shape (body position + vertex transformed position)
Vector2 GetPhysicsShapeVertex(PhysicsBody body, int vertex);

// Sets physics body shape transform based on radians parameter
void SetPhysicsBodyRotation(PhysicsBody body, float radians);

// Unitializes and destroy a physics body
void DestroyPhysicsBody(PhysicsBody body);

// Unitializes physics pointers and closes physics loop thread
void ClosePhysics(void);
]])

physac = ffi.load("physac")
local mt = { __index = physac }
local ph = setmetatable({}, mt)

ph.PHYSAC_PI                       = 3.14159265358979323846
ph.PHYSAC_DEG2RAD                  = ph.PHYSAC_PI / 180.0

return ph