From 469368530baa74e7deb41b66f80e3b653c40d804 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Miloslav=20=C4=8C=C3=AD=C5=BE?= <tastyfish@seznam.cz>
Date: Sat, 17 Nov 2018 17:33:09 +0100
Subject: [PATCH] Prevent infinite loops

---
 s3l.h     | 29 ++++++++++++++++-------------
 testSDL.c |  2 +-
 2 files changed, 17 insertions(+), 14 deletions(-)

diff --git a/s3l.h b/s3l.h
index d983ec2..0f4234b 100644
--- a/s3l.h
+++ b/s3l.h
@@ -199,7 +199,10 @@ void S3L_drawTriangle(int16_t x0, int16_t y0, int16_t x1, int16_t y1, int16_t x2
     v##Inc = v##Dx >= 0 ? 1 : -1;\
     v##Err = 2 * helperDxAbs - helperDyAbs;\
     v##ErrAdd = 2 * helperDxAbs;\
-    v##ErrSub = 2 * helperDyAbs;
+    v##ErrSub = 2 * (helperDyAbs != 0 ? helperDyAbs : 1);\
+    v##ErrSub = v##ErrSub != 0 ? v##ErrSub : 1; /* don't allow 0, could lead
+                                                   to an infinite substracting
+                                                   loop */
 
   #define stepSide(s)\
     while (s##Err > 0)\
@@ -216,6 +219,18 @@ void S3L_drawTriangle(int16_t x0, int16_t y0, int16_t x1, int16_t y1, int16_t x2
 
   while (currentY <= endY)
   {
+    if (currentY == splitY)
+    {
+      if (splitOnLeft)
+      {
+        initSide(l,l,r);
+      }
+      else
+      {
+        initSide(r,r,l);
+      }
+    }
+
     p.y = currentY;
 
     // draw the line
@@ -229,18 +244,6 @@ void S3L_drawTriangle(int16_t x0, int16_t y0, int16_t x1, int16_t y1, int16_t x2
     stepSide(r)
     stepSide(l)
 
-    if (currentY == splitY)
-    {
-      if (splitOnLeft)
-      {
-        initSide(l,l,r);
-      }
-      else
-      {
-        initSide(r,r,l);
-      }
-    }
-
     ++currentY;
   }
 
diff --git a/testSDL.c b/testSDL.c
index a6fce61..383a508 100644
--- a/testSDL.c
+++ b/testSDL.c
@@ -42,7 +42,7 @@ const int16_t test_coords[] =
     100,100, 99,101,    101,101,  // 0, small triangle
     190,50,  200,10,    400,80,   // 1, arbitrary
     40,80,   20,50,     100,30,   // 2, arbitrary
-    300,300, 290,400,   310,400,  // 3, regular
+    150,300, 290,400,   450,400,  // 3, regular
     105,300, 120,300,   201,300,  // 4, horizontal line
     400,300, 400,320,   400,400   // 5, vertical line
   };