kintematic

kintematic namespace kint is a c++ library that solves collisions for one kinematic rectangle in a world of static or constant velocity shapes

All logic is done with integers. move_and_slide is implemented by finding a int/int rational raycast point, then quantizing that point on to an integer grid to the best non-colliding point.

Features AABB optimization, non-AABB polygon shapes, one way platforms, and walking up small steps.

Types

• i2d - two dimensional integer vector. Positive y is "down" for documentation, but kintematic's logic is orienation agnostic

• Rational - int/int rational type

• Rational2D - two dimensional rational vector

• Shape_Point, Shape_Line, Shape_Rectangle, Shape_Polygon - collision shapes with velocity. Velocity is in i2d units per timestep. Shape_Line can be a one-way platform.

• Shape_Variant - std::variant of all 4 shapes

• enum Right_Triangle_Corner - used to turn a rectangle into a right triangle by defining which of the 4 points should become the right angle corner

• uint64_t - id value to keep track of shapes

• Impact - return type of raycasts for one shape

• Impact_ID - return type of raycasts for multiple shapes. Has an ID to store which shape it hit.

• Minkowski_Set - collection of shapes that have been minkowski-summed with a rectangle. Useful to prepare before doing a lot of raycasts.

Functions

• Shape::as_polygon(), Shape_Point_from_i2d, Shape_Polygon_right_triangle, Shape_Polygon_from_points, shape_position_point, and convex_hull are useful for creating and converting shapes

• Shape_Polygon_area is usually just used to check the orientation of a Shape_Polygon. Should always be positive.

• collides_unmoving - returns if two shapes are overlapping (not considering velocity).

  A point exactly on the edge of a rectangle is not considered to be overlapping.

  Two lines with the same end are not considered to be overlapping.

  A point exactly on a point is considered to be overlapping.

• minkowski_rectangle - returns minkowski sum of a rectangle and a shape. The two original shapes collide when the minkowski sum collides with the top-left corner of the rectangle.

• minkowski_motion - returns the shape-cast shape as a shape follows its velocity

• minkowski_set_create - returns a Minkowski_Set after running minkowski_rectangle on a lot of shapes, keeping track of shape id's.

• minkowski_set_append - sometimes it is better to create a Minkowski_Set one shape at a time

• raycast_unmoving - returns an std::optional<Impact> for the point when a line defined by a start and end point intersects with a shape

  If the end point is exactly on the edge of a shape, raycast is not considered to hit.

• clip_velocity - simulates moving a Shape_Rectangle forward. Returns what the Shape's velocity should be in order to not collide with anything in a Minkowski_Set

• move_and_slide - Most significant function of kintematic

  Called once per timestep.

  Moves a Shape_Rectangle forward, sliding along anything it hits in a Minkowski_Set.

  The rectangle will get pushed by any shapes in the Minkowski_Set with velocity.

  Returns Impact_IDs for any shapes the rectangle hit.

  Has an optional parameter for moving up small steps, defined by a vector in the upwards direction with a length of the tallest step size,