From 08c5c9e8dabc328e9f61156f69a766b3c03a4c77 Mon Sep 17 00:00:00 2001
From: Tibo De Peuter <tibo.depeuter@ugent.be>
Date: Sat, 5 Oct 2024 17:32:28 +0200
Subject: [PATCH] fix: Vertical flip

Fix the difference in (0,0) assumption of jpg and computer graphics.
---
 main.cpp            | 6 ++++--
 src/viewing_ray.cpp | 6 +++---
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/main.cpp b/main.cpp
index 41dbb17..c20ed74 100644
--- a/main.cpp
+++ b/main.cpp
@@ -72,7 +72,7 @@ int main(int argc, char * argv[])
   printf("\r");
   
   // For each pixel (i,j)
-  for(int i=0; i<height; ++i) 
+  for(int i=0; i<height; ++i)
   {
     for(int j=0; j<width; ++j)
     {
@@ -87,7 +87,9 @@ int main(int argc, char * argv[])
 
       // Compute viewing ray
       Ray ray;
-      viewing_ray(camera,i,j,width,height,ray);
+      /* NOTE I flipped the vertical axis of the pixels, because in computer graphics we assume the bottom left pixel
+       * is (0,0), while traditional jpg assumes (0,0) to be the upper left pixel. */
+      viewing_ray(camera,height - i,j,width,height,ray);
 
       // Find first visible object hit by ray and its surface normal n
       double t;
diff --git a/src/viewing_ray.cpp b/src/viewing_ray.cpp
index 57659db..2a7ae6d 100644
--- a/src/viewing_ray.cpp
+++ b/src/viewing_ray.cpp
@@ -15,9 +15,9 @@ void viewing_ray(
      */
 
     /* Determine the direction of the ray, using the camera and pixel location. */
-    double u = 0 - camera.width / 2 + camera.width * (j + 0.5)/ width;
-    double v = 0 - camera.height /2 + camera.height * (i + 0.5)/ height;
+    double u = 0 - camera.width / 2 + camera.width * (j + 0.5) / width;
+    double v = 0 - camera.height / 2 + camera.height * (i + 0.5) / height;
 
     ray.origin = camera.e;
-    ray.direction = (0 - camera.d)* camera.w + u * camera.u + v * camera.v;
+    ray.direction = (0 - camera.d) * camera.w + u * camera.u + v * camera.v;
 }