13 Rectangle Collision Detection

9.0.0.11

Racket

13 Rectangle Collision Detection🔗ℹ

This section covers rectangle creation and collision detection using both integer-based (SDL_Rect) and floating-point (SDL_FRect) rectangles.

13.1 Creating Rectangles🔗ℹ

procedure
(make-rect x y w h) → SDL_Rect?
  x : real?
  y : real?
  w : real?
  h : real?

Creates an integer rectangle.

Values are truncated to integers.

(define player-hitbox (make-rect 100 200 32 32))

procedure
(make-frect x y w h) → SDL_FRect?
  x : real?
  y : real?
  w : real?
  h : real?

Creates a floating-point rectangle.

(define player-hitbox (make-frect 100.5 200.0 32.0 32.0))

13.2 Rectangle Accessors🔗ℹ

procedure
(rect-x r) → exact-integer?
r : SDL_Rect?

Returns the x coordinate.

procedure
(rect-y r) → exact-integer?
r : SDL_Rect?

Returns the y coordinate.

procedure
(rect-w r) → exact-integer?
r : SDL_Rect?

Returns the width.

procedure
(rect-h r) → exact-integer?
r : SDL_Rect?

Returns the height.

procedure
(frect-x r) → real?
r : SDL_FRect?

Returns the x coordinate.

procedure
(frect-y r) → real?
r : SDL_FRect?

Returns the y coordinate.

procedure
(frect-w r) → real?
r : SDL_FRect?

Returns the width.

procedure
(frect-h r) → real?
r : SDL_FRect?

Returns the height.

procedure
(rect->values r) →
exact-integer?
exact-integer?
exact-integer?
exact-integer?
r : SDL_Rect?

Destructures a rectangle into multiple values.

(define-values (x y w h) (rect->values player-hitbox))

procedure
(frect->values r) →
real? real? real? real?
r : SDL_FRect?

Destructures a floating-point rectangle into multiple values.

13.3 Collision Detection🔗ℹ

procedure
(rects-intersect? a b) → boolean?
a : SDL_Rect?
b : SDL_Rect?

Returns #t if two rectangles overlap.

(when (rects-intersect? player-hitbox enemy-hitbox)
(handle-collision!))

procedure
(rect-intersection a b) → (or/c SDL_Rect? #f)
a : SDL_Rect?
b : SDL_Rect?

Returns the overlapping region of two rectangles, or #f if they don’t intersect.

(define overlap (rect-intersection a b))
(when overlap
(printf "Overlap area: ~a x ~a~n"
(rect-w overlap) (rect-h overlap)))

procedure
(frects-intersect? a b) → boolean?
a : SDL_FRect?
b : SDL_FRect?

Returns #t if two floating-point rectangles overlap.

procedure
(frect-intersection a b) → (or/c SDL_FRect? #f)
a : SDL_FRect?
b : SDL_FRect?

Returns the overlapping region of two floating-point rectangles, or #f if they don’t intersect.

13.4 Rectangle Utilities🔗ℹ

procedure
(rect-union a b) → SDL_Rect?
a : SDL_Rect?
b : SDL_Rect?

Returns the smallest rectangle that contains both input rectangles.

(define bounds (rect-union a b))

procedure
(frect-union a b) → SDL_FRect?
a : SDL_FRect?
b : SDL_FRect?

Returns the smallest floating-point rectangle that contains both input rectangles.

procedure
(rect-enclosing-points points [clip]) → (or/c SDL_Rect? #f)
points : (listof point?)
clip : (or/c SDL_Rect? #f) = #f

Returns the smallest rectangle that encloses all the given points.

Points can be:

SDL_Point structs
Lists of two numbers: (list x y)
Vectors of two numbers: #(x y)

If clip is provided, points are first clipped to that rectangle. Returns #f if no points are enclosed (or the list is empty).

(define bounds (rect-enclosing-points
(list '(10 20) '(50 60) '(30 40))))

procedure
(frect-enclosing-points points [clip]) → (or/c SDL_FRect? #f)
points : (listof point?)
clip : (or/c SDL_FRect? #f) = #f

Returns the smallest floating-point rectangle that encloses all the given points.

13.5 Line Intersection🔗ℹ

procedure
(rect-line-intersection rect x1 y1 x2 y2)
→
(or/c (values exact-integer? exact-integer?
              exact-integer? exact-integer?) #f)
  rect : SDL_Rect?
  x1 : real?
  y1 : real?
  x2 : real?
  y2 : real?

Clips a line segment to a rectangle.

Returns (values x1-clipped y1-clipped x2-clipped y2-clipped) with the clipped line endpoints, or #f if the line doesn’t intersect the rectangle.

(define-values (cx1 cy1 cx2 cy2)
(or (rect-line-intersection viewport 0 0 800 600)
(values 0 0 0 0)))

procedure
(frect-line-intersection rect x1 y1 x2 y2)
→ (or/c (values real? real? real? real?) #f)
  rect : SDL_FRect?
  x1 : real?
  y1 : real?
  x2 : real?
  y2 : real?

Clips a line segment to a floating-point rectangle.

Returns (values x1-clipped y1-clipped x2-clipped y2-clipped) with the clipped line endpoints, or #f if the line doesn’t intersect the rectangle.

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13.1	Creating Rectangles
13.2	Rectangle Accessors
13.3	Collision Detection
13.4	Rectangle Utilities
13.5	Line Intersection