actually rotate displayed photo correctly

Program.cs

@@ -1140,13 +1140,20 @@ public class Game : GameWindow {
     GL.Viewport(0, 0, e.Width, e.Height);
   }
 
+  private Vector2 RotateAboutCenter(Vector2 vec, Vector2 center, Matrix2 transform) {
+    Vector2 centerRelative = vec - center;
+    centerRelative *= transform;
+    return centerRelative + center;
+  }
+
   private void SetVertices(float left, float top, float width, float height, float rotationDegrees) {
     Matrix2 transform = Matrix2.CreateRotation(MathHelper.DegreesToRadians(rotationDegrees));
 
-    Vector2 topLeft = new Vector2(left, top) * transform;
-    Vector2 topRight = new Vector2(left + width, top) * transform;
-    Vector2 bottomRight = new Vector2(left + width, top + height) * transform;
-    Vector2 bottomLeft = new Vector2(left, top + height) * transform;
+    Vector2 center = new(left + width / 2, top + height / 2);
+    Vector2 topLeft = RotateAboutCenter(new Vector2(left, top), center, transform);
+    Vector2 topRight = RotateAboutCenter(new Vector2(left + width, top), center, transform);
+    Vector2 bottomRight = RotateAboutCenter(new Vector2(left + width, top + height), center, transform);
+    Vector2 bottomLeft = RotateAboutCenter(new Vector2(left, top + height), center, transform);
 
     // top left
     vertices[0] = topLeft.X;