From: Ben Harris <bjh21@bjh21.me.uk>
Date: Thu, 26 Dec 2013 13:58:29 +0000 (+0000)
Subject: Redesign vec_bearing to distinguish all directions.
X-Git-Tag: bedstead-001.000~8
X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~bjharris/git?a=commitdiff_plain;h=702db19779cb6a6e35eeefbf324d39833998ec29;p=bedstead.git

Redesign vec_bearing to distinguish all directions.

It now returns the shortest representable vector parallel to its
argument, so it can be used to distinguish between all possible
directions of vector.  This means that the rest of the code can be
more flexible it what it produces.  This makes no change to the
resulting font.
---

diff --git a/bedstead.c b/bedstead.c
index 0a4e569..f80a644 100644
--- a/bedstead.c
+++ b/bedstead.c
@@ -106,6 +106,7 @@
 #include <ctype.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 #define XSIZE 6
@@ -1355,18 +1356,31 @@ vec_sub(vec v1, vec v2)
 }
 
 static int
-vec_bearing(vec v)
+gcd(int a, int b)
 {
+	int t;
+	while (b != 0) {
+		t = b;
+		b = a % b;
+		a = t;
+	}
+	return a;
+}
 
-	if (v.x == 0 && v.y > 0) return 0;
-	if (v.x == v.y && v.x > 0) return 1;
-	if (v.x > 0 && v.y == 0) return 2;
-	if (v.x == -v.y && v.x > 0) return 3;
-	if (v.x == 0 && v.y < 0) return 4;
-	if (v.x == v.y && v.x < 0) return 5;
-	if (v.x < 0 && v.y == 0) return 6;
-	if (v.x == -v.y && v.x < 0) return 7;
-	return -1;
+/* Return the shortest representable vector parallel to the argument. */
+static vec
+vec_bearing(vec v)
+{
+	vec ret;
+	int d = gcd(abs(v.x), abs(v.y));
+	if (d != 0) {
+		ret.x = v.x / d;
+		ret.y = v.y / d;
+	} else {
+		ret.x = 0;
+		ret.y = 0;
+	}
+	return ret;
 }
 
 /* If p is identical to its successor, remove p. */
@@ -1383,8 +1397,8 @@ static int
 vec_inline3(vec a, vec b, vec c)
 {
 	return
-	    vec_bearing(vec_sub(b, a)) == vec_bearing(vec_sub(c, b)) &&
-	    vec_bearing(vec_sub(b, a)) != -1;
+	    vec_eqp(vec_bearing(vec_sub(b, a)), vec_bearing(vec_sub(c, b))) &&
+	    !vec_eqp(vec_bearing(vec_sub(b, a)), zero);
 }
 
 /* Are a, b, c, and d distinct collinear points in that order? */
@@ -1421,8 +1435,8 @@ fix_edges(point *a0, point *b0)
 	assert(a1->prev == a0); assert(b1->prev == b0);
 	assert(a0 != a1); assert(a0 != b0);
 	assert(a1 != b1); assert(b0 != b1);
-	if (vec_bearing(vec_sub(a0->v, a1->v)) ==
-	    vec_bearing(vec_sub(b1->v, b0->v)) &&
+	if (vec_eqp(vec_bearing(vec_sub(a0->v, a1->v)),
+		    vec_bearing(vec_sub(b1->v, b0->v))) &&
 	    (vec_inline4(a0->v, b1->v, a1->v, b0->v) ||
 	     vec_inline4(a0->v, b1->v, b0->v, a1->v) ||
 	     vec_inline4(b1->v, a0->v, b0->v, a1->v) ||