From 406a254523680ce18dfaf0928ec4282fc85ffc4a Mon Sep 17 00:00:00 2001
From: Frank <91616163+softhack007@users.noreply.github.com>
Date: Mon, 3 Jul 2023 15:43:47 +0200
Subject: [PATCH] inactive segments robustness improvement

* Avoid uint16 underflow in width() and height(): stop > start is possible, and means "inactive segment".

Without these checks, it was possible that width() and height() produce VERY large values due to underflow.
---
 wled00/FX.h         | 6 +++---
 wled00/FX_2Dfcn.cpp | 1 +
 wled00/FX_fcn.cpp   | 2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/wled00/FX.h b/wled00/FX.h
index 19b1fc4a..f0c26cd2 100644
--- a/wled00/FX.h
+++ b/wled00/FX.h
@@ -507,9 +507,9 @@ typedef struct Segment {
     inline bool     hasRGB(void)         const { return _isRGB; }
     inline bool     hasWhite(void)       const { return _hasW; }
     inline bool     isCCT(void)          const { return _isCCT; }
-    inline uint16_t width(void)          const { return stop - start; }       // segment width in physical pixels (length if 1D)
-    inline uint16_t height(void)         const { return stopY - startY; }     // segment height (if 2D) in physical pixels
-    inline uint16_t length(void)         const { return width() * height(); } // segment length (count) in physical pixels
+    inline uint16_t width(void)          const { return (stop > start)   ? (stop - start)   : 0; } // segment width in physical pixels (length if 1D)
+    inline uint16_t height(void)         const { return (stopY > startY) ? (stopY - startY) : 0; } // segment height (if 2D) in physical pixels // softhack007: make sure its always > 0
+    inline uint16_t length(void)         const { return width() * height(); }                      // segment length (count) in physical pixels
     inline uint16_t groupLength(void)    const { return grouping + spacing; }
     inline uint8_t  getLightCapabilities(void) const { return _capabilities; }
 
diff --git a/wled00/FX_2Dfcn.cpp b/wled00/FX_2Dfcn.cpp
index f4dac68d..c9653e10 100644
--- a/wled00/FX_2Dfcn.cpp
+++ b/wled00/FX_2Dfcn.cpp
@@ -191,6 +191,7 @@ uint32_t WS2812FX::getPixelColorXY(uint16_t x, uint16_t y) {
 uint16_t /*IRAM_ATTR*/ Segment::XY(uint16_t x, uint16_t y) {
   uint16_t width  = virtualWidth();   // segment width in logical pixels
   uint16_t height = virtualHeight();  // segment height in logical pixels
+  if ((width == 0) || (height == 0)) return 0; // softhack007 avoid div/0
   return (x%width) + (y%height) * width;
 }
 
diff --git a/wled00/FX_fcn.cpp b/wled00/FX_fcn.cpp
index 23f860de..2550853c 100644
--- a/wled00/FX_fcn.cpp
+++ b/wled00/FX_fcn.cpp
@@ -729,7 +729,7 @@ uint32_t Segment::getPixelColor(int i)
   i += start;
   /* offset/phase */
   i += offset;
-  if (i >= stop) i -= length();
+  if ((i >= stop) && (stop>0)) i -= length(); // avoids negative pixel index (stop = 0 is a possible value)
   return strip.getPixelColor(i);
 }