From 5a076c32d3b9f58f7db2b5cfbfeb5b5d61455dd6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Motiejus=20Jak=C5=A1tys?= <motiejus@jakstys.lt>
Date: Wed, 19 May 2021 22:57:46 +0300
Subject: [PATCH] return whether self_crossings mutated the bends

---
 tests.sql | 14 +++++++++-----
 wm.sql    |  9 ++++++++-
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/tests.sql b/tests.sql
index 0903db2..f33ab0b 100644
--- a/tests.sql
+++ b/tests.sql
@@ -46,8 +46,8 @@ insert into demo_inflections2 select name, generate_subscripts(ways, 1), unnest(
 
 -- SELF-LINE CROSSING
 drop table if exists selfcrossing, demo_selfcrossing3;
-create table selfcrossing (name text, ways geometry[]);
-insert into selfcrossing select name, self_crossing(ways) from inflections;
+create table selfcrossing (name text, ways geometry[], mutated boolean);
+insert into selfcrossing select name, (self_crossing(ways)).* from inflections;
 create table demo_selfcrossing3 (name text, i bigint, way geometry);
 insert into demo_selfcrossing3 select name, generate_subscripts(ways, 1), unnest(ways) from selfcrossing;
 
@@ -88,9 +88,11 @@ end $$ language plpgsql;
 
 do $$
 declare
+  mutated boolean;
   vcrossings geometry[];
 begin
-  select self_crossing((select ways from inflections where name='fig6')) into vcrossings;
+  select (self_crossing((select ways from inflections where name='fig6'))).* into vcrossings, mutated;
+  perform assert_equals(true, mutated);
   perform assert_equals(
     'LINESTRING(84 47,91 59,114 64,120 45,125 39,141 39,147 32)',
     (select st_astext(
@@ -98,7 +100,8 @@ begin
     ) from (select unnest(vcrossings) way) a)
   );
 
-  select self_crossing((select ways from inflections where name='fig6-rev')) into vcrossings;
+  select (self_crossing((select ways from inflections where name='fig6-rev'))).* into vcrossings, mutated;
+  perform assert_equals(true, mutated);
   perform assert_equals(
     'LINESTRING(84 47,91 59,114 64,120 45,125 39,141 39,147 32)',
     (select st_astext(
@@ -106,7 +109,8 @@ begin
     ) from (select unnest(vcrossings) way) a)
   );
 
-  select self_crossing((select ways from inflections where name='fig6-combi')) into vcrossings;
+  select (self_crossing((select ways from inflections where name='fig6-combi'))).* into vcrossings, mutated;
+  perform assert_equals(true, mutated);
   perform assert_equals(
     'LINESTRING(84 137,91 149,114 154,120 135,125 129,141 129,147 122,164 137,171 149,194 154,200 135,205 129,221 129,227 122)',
     (select st_astext(
diff --git a/wm.sql b/wm.sql
index 4aa2776..0d25b94 100644
--- a/wm.sql
+++ b/wm.sql
@@ -165,7 +165,10 @@ $$ language plpgsql;
 -- self_crossing eliminates self-crossing from the bends, following the
 -- article's section "Self-line Crossing When Cutting a Bend".
 drop function if exists self_crossing;
-create function self_crossing(INOUT bends geometry[]) as $$
+create function self_crossing(
+  INOUT bends geometry[],
+  OUT mutated boolean
+) as $$
 declare
   i int4;
   j int4;
@@ -182,6 +185,7 @@ declare
   multi geometry;
 begin
   pi = radians(180);
+  mutated = false;
 
   -- go through the bends and find one where sum of inflection angle is >180
   for i in 1..array_length(bends, 1) loop
@@ -227,6 +231,9 @@ begin
       continue when st_numgeometries(multi) = 2 and
         (st_contains(bends[j], a) or st_contains(bends[j], b));
 
+      -- stars are aligned, we are changing the bend
+      mutated = true;
+
       -- Sincere apologies to someone who will need to debug the block below.
       -- To understand it, I suggest you take a pencil and paper, draw a
       -- self-crossing bend (fig6 from the article works well), and figure out