diff --git a/TODO.md b/TODO.md
index e45095d..7b39a59 100644
--- a/TODO.md
+++ b/TODO.md
@@ -1,2 +1,6 @@
-[ ] Quaternions
-[ ] Draw rotated pixels in src order
+[-] Quaternions
+[X] Draw rotated pixels in src order
+[X] Use atan2 at beginning and end of line.
+    Interpolation in-between values
+[X] Test pixel perfect 90
+[ ] Optimization for square images?
diff --git a/rotation.cpp b/rotation.cpp
index 0aaa3a6..ed8bf08 100644
--- a/rotation.cpp
+++ b/rotation.cpp
@@ -517,13 +517,13 @@ Image rotate(Image const& src, double angle)
   DPoint bresenham((tr.x - tl.x) / (float) line_nb_steps, (tr.y - tl.y) / (float) line_nb_steps);
   cout << "bresenham: " << bresenham << endl;
 
-  for (int y_i = 0; y_i < (int) origin_nb_steps; ++y_i)
+  for (int y_i = 0; y_i <= (int) origin_nb_steps; ++y_i)
   {
     // first column origin
     DPoint const src_origin(src_tl.x + y_i * origin_x_inc, src_tl.y + y_i * origin_y_inc);
     APoint const rot_origin(tl.x + y_i * rotated_x_inc, tl.y + y_i * rotated_y_inc);
 
-    for (int x_i = 0; x_i < (int) line_nb_steps; ++x_i)
+    for (int x_i = 0; x_i <= (int) line_nb_steps; ++x_i)
     {
       DPoint const src_rotated_point(src_origin.x + x_i * line_x_inc, src_origin.y + x_i * line_y_inc);
       APoint const rot_point(rot_origin.x + x_i * bresenham.x, rot_origin.y + x_i * bresenham.y);
@@ -677,6 +677,30 @@ void check_lines()
   draw_outline(rect1, 90, "rect1");
 }
 
+bool check_90()
+{
+  Image const src("img/lena.ppm");
+  Image const rotated = rotate(src, 90);
+
+  for (unsigned int y = 0; y < rotated.height; ++y)
+  {
+    for (unsigned int x = 0; x < rotated.width; ++x)
+    {
+      unsigned rot_index = y * rotated.width + x;
+      unsigned src_index = x * src.width + (rotated.width - 1 - y);
+
+      if (rotated.r_chan[rot_index] != src.r_chan[src_index])
+        return false;
+      if (rotated.g_chan[rot_index] != src.g_chan[src_index])
+        return false;
+      if (rotated.b_chan[rot_index] != src.b_chan[src_index])
+        return false;
+    }
+  }
+
+  return true;
+}
+
 
 
 //
@@ -697,11 +721,17 @@ int main()
       return 1;
 
     //check_lines();
+
+    if (!check_90())
+    {
+      cerr << __LINE__ << " | 90 degrees check failed" << endl;
+      return 1;
+    }
   }
 
-  Image img("img/luigi.ppm");
+  //Image img("img/luigi.ppm");
   //Image img("img/wallpaper.ppm");
-  // Image img("img/mini_luigi.ppm");
+  Image img("img/mini_lena.ppm");
 
   //for (double rotation : {0, 1, 5, 15, 30, 45, 60, 75, 90, 110, 140, 160, 180, 200, 210, 235, 260, 270, 300, 315, 355, 359})
   for (double rotation : {0, 45, 90})