From a855da29dbd7a80c4d87a421c1f88a8603c020fa Mon Sep 17 00:00:00 2001 From: Nigel Tao Date: Thu, 5 Jan 2017 17:37:54 +1100 Subject: [PATCH] image: fix the overlap check in Rectangle.Intersect. The doc comment for Rectangle.Intersect clearly states, "If the two rectangles do not overlap then the zero rectangle will be returned." Prior to this fix, calling Intersect on adjacent but non-overlapping rectangles would return an empty but non-zero rectangle. The fix essentially changes if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y { etc } to if r.Min.X >= r.Max.X || r.Min.Y >= r.Max.Y { etc } (note that the > signs have become >= signs), but changing that line to: if r.Empty() { etc } seems clearer (and equivalent). Change-Id: Ia654e4b9dc805978db3e94d7a9718b6366005360 Reviewed-on: https://go-review.googlesource.com/34853 Reviewed-by: David Crawshaw --- src/image/geom.go | 6 +++++- src/image/geom_test.go | 7 ++++--- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/src/image/geom.go b/src/image/geom.go index e1cd4dc1e3..ed7dde2c84 100644 --- a/src/image/geom.go +++ b/src/image/geom.go @@ -161,7 +161,11 @@ func (r Rectangle) Intersect(s Rectangle) Rectangle { if r.Max.Y > s.Max.Y { r.Max.Y = s.Max.Y } - if r.Min.X > r.Max.X || r.Min.Y > r.Max.Y { + // Letting r0 and s0 be the values of r and s at the time that the method + // is called, this next line is equivalent to: + // + // if max(r0.Min.X, s0.Min.X) >= min(r0.Max.X, s0.Max.X) || likewiseForY { etc } + if r.Empty() { return ZR } return r diff --git a/src/image/geom_test.go b/src/image/geom_test.go index 6e9c6a13c2..9fede02721 100644 --- a/src/image/geom_test.go +++ b/src/image/geom_test.go @@ -28,6 +28,7 @@ func TestRectangle(t *testing.T) { rects := []Rectangle{ Rect(0, 0, 10, 10), + Rect(10, 0, 20, 10), Rect(1, 2, 3, 4), Rect(4, 6, 10, 10), Rect(2, 3, 12, 5), @@ -62,9 +63,9 @@ func TestRectangle(t *testing.T) { if err := in(a, s); err != nil { t.Errorf("Intersect: r=%s, s=%s, a=%s, a not in s: %v", r, s, a, err) } - if a.Empty() == r.Overlaps(s) { - t.Errorf("Intersect: r=%s, s=%s, a=%s: empty=%t same as overlaps=%t", - r, s, a, a.Empty(), r.Overlaps(s)) + if isZero, overlaps := a == (Rectangle{}), r.Overlaps(s); isZero == overlaps { + t.Errorf("Intersect: r=%s, s=%s, a=%s: isZero=%t same as overlaps=%t", + r, s, a, isZero, overlaps) } largerThanA := [4]Rectangle{a, a, a, a} largerThanA[0].Min.X-- -- 2.48.1