From 06f0a4962640e577bec5897c852ad2dcd8d82e03 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miloslav=20=C4=8C=C3=AD=C5=BE?= <tastyfish@seznam.cz>
Date: Sun, 2 Sep 2018 21:43:44 +0200
Subject: [PATCH] Allow negative coordinates

---
 raycastlib.h | 15 +++++++++++++--
 test.c       |  9 +++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/raycastlib.h b/raycastlib.h
index 26fc3c0..f524fb1 100644
--- a/raycastlib.h
+++ b/raycastlib.h
@@ -404,6 +404,12 @@ void castRayMultiHit(Ray ray, ArrayFunction arrayFunc, HitResult *hitResults,
   currentSquare.x = ray.start.x / UNITS_PER_SQUARE;
   currentSquare.y = ray.start.y / UNITS_PER_SQUARE;
 
+  if (ray.start.x < 0) // round down, not toward zero
+    currentSquare.x--;
+
+  if (ray.start.y < 0)
+    currentSquare.y--;
+
   *hitResultsLen = 0;
 
   int16_t squareType = arrayFunc(currentSquare.x,currentSquare.y);
@@ -446,8 +452,13 @@ void castRayMultiHit(Ray ray, ArrayFunction arrayFunc, HitResult *hitResults,
         break;
     }
 
-    ray.start.x = currentPos.x % UNITS_PER_SQUARE;
-    ray.start.y = currentPos.y % UNITS_PER_SQUARE;
+    ray.start.x = currentPos.x < 0 ?
+      (UNITS_PER_SQUARE + currentPos.x % UNITS_PER_SQUARE - 1) :
+      (currentPos.x % UNITS_PER_SQUARE);
+
+    ray.start.y = currentPos.y < 0 ?
+      (UNITS_PER_SQUARE + currentPos.y % UNITS_PER_SQUARE - 1) :
+      (currentPos.y % UNITS_PER_SQUARE);
 
     castRaySquare(ray,&no,&co);
 
diff --git a/test.c b/test.c
index ad3ae49..1154f9a 100644
--- a/test.c
+++ b/test.c
@@ -124,6 +124,15 @@ int main()
     16))
     return 1;
 
+  if (!testSingleRay(
+    -4 * UNITS_PER_SQUARE - UNITS_PER_SQUARE / 2,
+    7 * UNITS_PER_SQUARE + UNITS_PER_SQUARE / 3,
+    100,-100,
+    0, 2,
+    1, 2900,
+    16))
+    return 1;
+
   for (Unit i = -UNITS_PER_SQUARE; i <= UNITS_PER_SQUARE; i += 64)
   {
     Unit v = sinInt(i);