Contact

Generated from engine/collision/contacts.h at 862e08b. The text under each declaration is the header's own comment, word for word. About the reference says how these pages are made.

Browse the collision module

#include "engine/collision/contacts.h" · namespace labrador

struct Contact

struct Contact

One overlapping pair, and the smallest translation that separates it.

The frame's contacts are a list the caller can look at before anything responds to them - which is the whole reason this is a value and not a callback fired from inside the sweep. A test can assert on the list, and a scene can hand it to the game after resolution instead of during it.

a · b

CollisionObject* a = nullptr;
CollisionObject* b = nullptr;

normal

mattmath::Vector2F normal = mattmath::Vector2F::ZERO;

Unit, pointing from a towards b.

penetration

float penetration = 0.0f;

Overlap along normal, always greater than zero.

find_contacts

void find_contacts(std::span<CollisionObject* const> objects,
  std::vector<Contact>& contacts,
  BroadPhase* broad_phase = nullptr);

Fills contacts with every overlapping pair among objects, each pair once.

contacts is cleared first and reused, so a caller that keeps one vector across frames allocates nothing after the first busy frame - which is the point of taking it by reference rather than returning it.

Three filters, cheapest first: layer/mask, then the shapes' bounding boxes, then narrow_phase. Objects already flagged for deletion take part in nothing.

With no broad phase, the pair enumeration is all-pairs - O(n^2), which bench/ measures at 106 ms for four thousand objects, six times a 60 Hz frame from one call. Pass one and it enumerates only the pairs whose bounding boxes overlap, in the same order.

The parameter is a pointer with a default rather than a required argument because the exhaustive sweep is the specification: it is what the grid is tested against (tests/collision/broad_phase_tests.cpp), and a caller with a handful of objects has no reason to build a grid.

broad_phase is borrowed, and it holds the buffers that make the steady state allocation-free, so a caller that wants that keeps one across frames - exactly as it does with contacts.

dispatch_contacts

void dispatch_contacts(std::span<const Contact> contacts);

Tells both participants of every contact, once each, with the normal oriented for the object receiving it.

Two things a response does are accounted for here, because they are properties of dispatching a list rather than of any one response:

- A response can retire an object, and a retired object's remaining contacts are dropped. A projectile that hits a wall does not go on to hit the player behind it. The rule applies to both sides of every pair. - A response can move an object, so every pair is measured again immediately before it is dispatched, and a pair an earlier response has already separated is dropped. The depths in the list describe the frame before anything responded to it, which is what a caller inspecting the list wants and not what a caller acting on it does.

Related types

Named in the public declarations above: BroadPhase, CollisionObject, Vector2F.

In the samples and tests

The files that include this header directly. A file can also reach it through another header.

• tests/collision/ broad_phase_tests.cpp, contacts_tests.cpp