satc

By Roger Jungemann

What is it?

satc is a SAT (Separating Axis Theorem) collision detection library, written in plain C99, as a single header file, with zero dependencies.

It is a port of sat-js.

This library is readily usable for any 2D game purposes, although it only handles overlap/collision, and is not a physics library. Friction, restitution, drag, velocity, acceleration, etc. will need to be handled yourself if needed. Still, it should be handy for a vast number of use cases.

It compiles with -Wall with no warnings, has 100% documentation coverage, and nearly 100% test coverage.

It internally uses alloca for temporary variables, so they are allocated on the stack, which is quicker than allocating on the heap, and values are deallocated when they fall out of scope. Of course, any points, shapes, or collision response objects you create will have to be deallocated. The docs explain when you are responsible for deallocating a particular object.

Points are represented as arrays of doubles. I am considering allowing this to be easily changed, but for now, it should handle nearly any use case.

Please feel free to file issues or pull requests.

Usage

Simply place the satc.h file somewhere in your header search path, and #include "satc.h" in your file.

To run the tests, from inside the satc directory, run make test.

To generate the docs, from inside the satc directory, run make docs. The docs will be available at html/index.html.

Example

The satc-test.c file has some good examples.

The following example illustrates polygon-to-circle collision:

// Generate a circle.
double *c_pos = sc_point_alloca_xy(50.0, 50.0);
double c_radius = 20.0;
satc_circle_t *circle = satc_circle_create(c_pos, c_radius);

// Generate a polygon.
satc_point_alloca_xy(p_pos, 0.0, 0.0);
satc_point_array_alloca(points, 4);
satc_point_alloca_xy(a, 0.0, 0.0);
satc_point_alloca_xy(b, 40.0, 0.0);
satc_point_alloca_xy(c, 40.0, 40.0);
satc_point_alloca_xy(d, 0.0, 40.0);
points[0] = a;
points[1] = b;
points[2] = c;
points[3] = d;
satc_polygon_t *polygon = satc_polygon_create(p_pos, 4, points);

// Generate a collision response object.
satc_response_t *response = satc_response_create();

// Check for collision.
bool collided = satc_test_polygon_circle(polygon, circle, response);

// Some explanation:
//
// * `collided` is `true` if the circle and polygon overlap.
// * `response->a` is the polygon.
// * `response->b` is the circle.
// * `response->overlap` is numerical amount of overlap.
// * `response->overlap_n` is the unit vector of the overlap.
// * `response->overlap_v` is the vector of the overlap.

// Deallocate the polygon.
satc_polygon_destroy(polygon);

// Deallocate the circle.
satc_circle_destroy(circle);

API Docs

These will be added to README.md, but in the meantime, run doxygen to generate the API docs, and visit html/index.html to view the API docs.