From 1248f15e4ff1be78562945654dcf03b040e950d8 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Fri, 28 Jul 2017 14:23:20 +1000
Subject: [PATCH] region: relax assertion to allow zero width/height

some degenerate cases create regions of zero area, but non-zero
dimensions. eg, vertical linear bezier curves.
---
 region.cpp | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/region.cpp b/region.cpp
index 1919db23..2a7cafe0 100644
--- a/region.cpp
+++ b/region.cpp
@@ -50,6 +50,11 @@ util::region<S,T>::region (point_t _a,
                            point_t _b):
     region (_a, extent_t { _b - _a })
 {
+    // This check must allow for zero area (but non-zero dimension) regions.
+    // Some code paths need to support this degenerate case. It's ugly but
+    // simplifies generalisation. eg, vertical linear bezier curves.
+    CHECK (all (_a <= _b));
+
     debug::sanity (*this);
 }