From 0eec8e46c99c1bf4cbb758b90ea26a1a4546c62d Mon Sep 17 00:00:00 2001
From: Frank <91616163+softhack007@users.noreply.github.com>
Date: Fri, 17 Jan 2025 21:36:51 +0100
Subject: [PATCH] robustness: prevent negative transitions

fix for a corner case that might lead to unexpected math overflow
---
 wled00/led.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/wled00/led.cpp b/wled00/led.cpp
index 7254184f..73a72af8 100644
--- a/wled00/led.cpp
+++ b/wled00/led.cpp
@@ -194,7 +194,7 @@ void handleTransitions()
   if (transitionActive && transitionDelayTemp > 0)
   {
     float tper = (millis() - transitionStartTime)/(float)transitionDelayTemp;
-    if (tper >= 1.0f)
+    if ((tper >= 1.0f) || (tper < 0.0f)) // WLEDMM also catch "<0" case, that may happen when millis() rolls over
     {
       strip.setTransitionMode(false);
       // restore (global) transition time if not called from UDP notifier or single/temporary transition from JSON (also playlist)
@@ -207,7 +207,7 @@ void handleTransitions()
     }
     if (tper - tperLast < 0.004f) return;
     tperLast = tper;
-    briT = briOld + ((bri - briOld) * tper);
+    briT = briOld + ((int(bri) - int(briOld)) * tper); // WLEDMM avoid undefined behaviour when briOld < bri
 
     applyBri();
   }