From 5b5272e7a8bd71a6c7f55951659df69a355486c8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Viktor=20Chlumsk=C3=BD?= <viktor.chlumsky@gmail.com>
Date: Sun, 8 Mar 2020 23:34:51 +0100
Subject: [PATCH] Scanline rasterization edge case fix

---
 core/edge-segments.cpp | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/core/edge-segments.cpp b/core/edge-segments.cpp
index c57d783f..0bdaaaac 100644
--- a/core/edge-segments.cpp
+++ b/core/edge-segments.cpp
@@ -228,7 +228,7 @@ int QuadraticSegment::scanlineIntersections(double x[3], int dy[3], double y) co
         if (solutions >= 2 && t[0] > t[1])
             tmp = t[0], t[0] = t[1], t[1] = tmp;
         for (int i = 0; i < solutions && total < 2; ++i) {
-            if (t[i] > 0 && t[i] < 1) {
+            if (t[i] >= 0 && t[i] <= 1) {
                 x[total] = p[0].x+2*t[i]*ab.x+t[i]*t[i]*br.x;
                 if (nextDY*(ab.y+t[i]*br.y) >= 0) {
                     dy[total++] = nextDY;
@@ -253,8 +253,11 @@ int QuadraticSegment::scanlineIntersections(double x[3], int dy[3], double y) co
     if (nextDY != (y >= p[2].y ? 1 : -1)) {
         if (total > 0)
             --total;
-        else
+        else {
+            if (fabs(p[2].y-y) < fabs(p[0].y-y))
+                x[total] = p[2].x;
             dy[total++] = nextDY;
+        }
     }
     return total;
 }
@@ -287,7 +290,7 @@ int CubicSegment::scanlineIntersections(double x[3], int dy[3], double y) const
             }
         }
         for (int i = 0; i < solutions && total < 3; ++i) {
-            if (t[i] > 0 && t[i] < 1) {
+            if (t[i] >= 0 && t[i] <= 1) {
                 x[total] = p[0].x+3*t[i]*ab.x+3*t[i]*t[i]*br.x+t[i]*t[i]*t[i]*as.x;
                 if (nextDY*(ab.y+2*t[i]*br.y+t[i]*t[i]*as.y) >= 0) {
                     dy[total++] = nextDY;
@@ -312,8 +315,11 @@ int CubicSegment::scanlineIntersections(double x[3], int dy[3], double y) const
     if (nextDY != (y >= p[3].y ? 1 : -1)) {
         if (total > 0)
             --total;
-        else
+        else {
+            if (fabs(p[3].y-y) < fabs(p[0].y-y))
+                x[total] = p[3].x;
             dy[total++] = nextDY;
+        }
     }
     return total;
 }