collide
Lightweight collision tests for games that do not want full Box2D.
This is plain geometry on rectangles, circles, polygons and line segments,
with no SDL or renderer dependency, so it tests headlessly and costs nothing
to call. Rectangles are given the same way rectangle draws them, as a
top-left corner (x, y) with a width and height, and circles as a center and a
radius, so you pass collision the same numbers you pass drawing.
There are three kinds of test here. The pointIn* family asks whether a point
sits inside a shape, which is what you use for a mouse hover or a hit check.
The *Overlap family asks whether two shapes touch, returning a bool. The
resolve* pair goes one step further and returns the smallest move that
pushes one shape out of another, so a body can slide along a wall instead of
stopping dead or passing through.
When you need real dynamics, stacking, joints and forces, reach for the physics module instead. This is the cheap option for the common cases.
It is an opt-in module, imported on its own with import nim2d/collide. The
core engine does not pull it in.
pointInRect ¶
func pointInRect(p: Vec2; x, y, w, h: float): bool
Whether point p is inside the rectangle with top-left (x, y) and the given
width and height. The edges count as inside.
Parameters
-
p(Vec2) -
x(float) -
y(float) -
w(float) -
h(float)
Returns
bool
pointInCircle ¶
func pointInCircle(p: Vec2; cx, cy, r: float): bool
Whether point p is inside the circle centered at (cx, cy) with radius r.
Parameters
-
p(Vec2) -
cx(float) -
cy(float) -
r(float)
Returns
bool
pointInTriangle ¶
func pointInTriangle(p, a, b, c: Vec2): bool
Whether point p is inside the triangle a, b, c. The winding does not
matter, and points on an edge count as inside.
Parameters
-
p(Vec2) -
a(Vec2) -
b(Vec2) -
c(Vec2)
Returns
bool
pointInPolygon ¶
func pointInPolygon(p: Vec2; poly: openArray[Vec2]): bool
Whether point p is inside the polygon outlined by poly, by counting how
many times a ray crosses the edges. Works for convex and concave outlines without holes. Fewer than three points is never inside.
Parameters
-
p(Vec2) -
poly(openArray[Vec2])
Returns
bool
rectsOverlap ¶
func rectsOverlap(ax, ay, aw, ah, bx, by, bw, bh: float): bool
Whether two rectangles overlap. Each is a top-left corner with a width and
height, the same as rectangle takes. Touching edges count as overlapping.
Parameters
-
ax(float) -
ay(float) -
aw(float) -
ah(float) -
bx(float) -
by(float) -
bw(float) -
bh(float)
Returns
bool
circlesOverlap ¶
func circlesOverlap(ax, ay, ar, bx, by, br: float): bool
Whether two circles overlap, each a center and a radius.
Parameters
-
ax(float) -
ay(float) -
ar(float) -
bx(float) -
by(float) -
br(float)
Returns
bool
circleRectOverlap ¶
func circleRectOverlap(cx, cy, r, rx, ry, rw, rh: float): bool
Whether a circle (center, radius) overlaps a rectangle (top-left, size).
The test finds the rectangle point nearest the circle center and checks whether it falls within the radius.
Parameters
-
cx(float) -
cy(float) -
r(float) -
rx(float) -
ry(float) -
rw(float) -
rh(float)
Returns
bool
segmentsIntersect ¶
func segmentsIntersect(a1, a2, b1, b2: Vec2): bool
Whether the line segment a1->a2 crosses the segment b1->b2, touching ends
included. Useful for a line-of-sight check or a laser against walls.
Parameters
-
a1(Vec2) -
a2(Vec2) -
b1(Vec2) -
b2(Vec2)
Returns
bool
resolveRect ¶
func resolveRect(ax, ay, aw, ah, bx, by, bw, bh: float): Vec2
The smallest move to apply to rectangle A so it no longer overlaps
rectangle B, pushing along whichever axis it is least buried in. Returns (0, 0) when they are already clear, so you can add it to A's position unconditionally.
Parameters
-
ax(float) -
ay(float) -
aw(float) -
ah(float) -
bx(float) -
by(float) -
bw(float) -
bh(float)
Returns
Vec2
resolveCircleRect ¶
func resolveCircleRect(cx, cy, r, rx, ry, rw, rh: float): Vec2
The smallest move to apply to the circle so it no longer overlaps the
rectangle. It pushes straight away from the nearest edge, which is what lets a round body slide along a wall. Returns (0, 0) when they are clear.
Parameters
-
cx(float) -
cy(float) -
r(float) -
rx(float) -
ry(float) -
rw(float) -
rh(float)
Returns
Vec2