From 74a2e0ab153d43684f30bc2bdd73addc49f869b2 Mon Sep 17 00:00:00 2001
From: Eric Fischer <enf@pobox.com>
Date: Tue, 12 Jun 2018 11:32:40 -0700
Subject: [PATCH] More informative return value from clipping

---
 clip.hpp     | 18 ++++++++++++------
 geometry.cpp | 12 ++++++------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/clip.hpp b/clip.hpp
index 1a40fb1..1bc345e 100644
--- a/clip.hpp
+++ b/clip.hpp
@@ -23,11 +23,17 @@ static int computeOutCode(double x, double y, double xmin, double ymin, double x
 	return code;
 }
 
+#define CLIP_OK 0
+#define CLIP_ELIMINATED 1
+#define CLIP_CHANGED_FIRST 2
+#define CLIP_CHANGED_SECOND 4
+#define CLIP_CHANGED (CLIP_CHANGED_FIRST | CLIP_CHANGED_SECOND)
+
 static int clip(double *x0, double *y0, double *x1, double *y1, double xmin, double ymin, double xmax, double ymax) {
 	int outcode0 = computeOutCode(*x0, *y0, xmin, ymin, xmax, ymax);
 	int outcode1 = computeOutCode(*x1, *y1, xmin, ymin, xmax, ymax);
+	int changed = CLIP_OK;
 	int accept = 0;
-	int changed = 0;
 
 	while (1) {
 		if (!(outcode0 | outcode1)) {  // Bitwise OR is 0. Trivially accept and get out of loop
@@ -65,19 +71,19 @@ static int clip(double *x0, double *y0, double *x1, double *y1, double xmin, dou
 				*x0 = x;
 				*y0 = y;
 				outcode0 = computeOutCode(*x0, *y0, xmin, ymin, xmax, ymax);
-				changed = 1;
+				changed |= CLIP_CHANGED_FIRST;
 			} else {
 				*x1 = x;
 				*y1 = y;
 				outcode1 = computeOutCode(*x1, *y1, xmin, ymin, xmax, ymax);
-				changed = 1;
+				changed |= CLIP_CHANGED_SECOND;
 			}
 		}
 	}
 
-	if (accept == 0) {
-		return 0;
+	if (accept) {
+		return changed;
 	} else {
-		return changed + 1;
+		return CLIP_ELIMINATED;
 	}
 }
diff --git a/geometry.cpp b/geometry.cpp
index c83e889..404de37 100644
--- a/geometry.cpp
+++ b/geometry.cpp
@@ -663,14 +663,14 @@ drawvec clip_lines(drawvec &geom, int z, long long buffer) {
 
 			int c = clip(&x1, &y1, &x2, &y2, min, min, area, area);
 
-			if (c > 1) {  // clipped
+			if (c == CLIP_ELIMINATED) {
+				out.push_back(draw(VT_MOVETO, geom[i].x, geom[i].y));
+			} else if (c == CLIP_OK) {
+				out.push_back(geom[i]);
+			} else {
 				out.push_back(draw(VT_MOVETO, x1, y1));
 				out.push_back(draw(VT_LINETO, x2, y2));
 				out.push_back(draw(VT_MOVETO, geom[i].x, geom[i].y));
-			} else if (c == 1) {  // unchanged
-				out.push_back(geom[i]);
-			} else {  // clipped away entirely
-				out.push_back(draw(VT_MOVETO, geom[i].x, geom[i].y));
 			}
 		} else {
 			out.push_back(geom[i]);
@@ -776,7 +776,7 @@ drawvec impose_tile_boundaries(drawvec &geom, long long extent) {
 
 			int c = clip(&x1, &y1, &x2, &y2, 0, 0, extent, extent);
 
-			if (c > 1) {  // clipped
+			if (c & CLIP_CHANGED) {
 				if (x1 != geom[i - 1].x || y1 != geom[i - 1].y) {
 					out.push_back(draw(VT_LINETO, x1, y1));
 					out[out.size() - 1].necessary = 1;