From 0eae2fa257ddd2b0f5883882d2f4bb33810b383c Mon Sep 17 00:00:00 2001
From: Mike Nolan <tesses@tesses.net>
Date: Fri, 18 Sep 2026 09:26:17 -0500
Subject: [PATCH] Fix image index underflow when navigating past boundaries

---
 viewer.cpp | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/viewer.cpp b/viewer.cpp
index 9b237a4..447dc4e 100644
--- a/viewer.cpp
+++ b/viewer.cpp
@@ -153,6 +153,18 @@ struct App {
 
         LoadImageList(curFile);
     }
+    void Prev()
+    {
+        this->imageIndex--;
+        if(this->imageIndex >= this->filenames.size())
+            this->imageIndex=this->filenames.size()-1;
+    }
+    void Next()
+    {
+        this->imageIndex++;
+        if(this->imageIndex >= this->filenames.size())
+            this->imageIndex=0;
+    }
     bool Update() {
         if(!window || !renderer) return false;
         SDL_Event evt;
@@ -188,22 +200,28 @@ struct App {
                             break;
                          case SDL_SCANCODE_PAGEUP:
                         {
-                            SetNewImage(this->imageIndex-20);
+                            for(size_t i = 0; i < 20; i++)
+                                Prev();
+                            SetNewImage(this->imageIndex);
                         }
                             break;
                         case SDL_SCANCODE_PAGEDOWN:
                         {
-                            SetNewImage(this->imageIndex+20);
+                            for(size_t i = 0; i < 20; i++)
+                                Next();
+                            SetNewImage(this->imageIndex);
                         }
                             break;
                         case SDL_SCANCODE_LEFT:
                         {
-                            SetNewImage(this->imageIndex-1);
+                            Prev();
+                            SetNewImage(this->imageIndex);
                         }
                             break;
                         case SDL_SCANCODE_RIGHT:
                         {
-                            SetNewImage(this->imageIndex+1);
+                            Next();
+                            SetNewImage(this->imageIndex);
                         }
                             break;
                         case SDL_SCANCODE_F:
@@ -218,6 +236,8 @@ struct App {
                             }
                         }
                             break;
+                        default:    
+                            break;
                     }
                 }
                     break;