rotating a texture works, but only about the origin

Photo.cs

@@ -105,7 +105,7 @@ public class Photo {
   public GpsInfo? Gps = null;
   public Rectangle CropRectangle = Rectangle.Empty;
   public Vector2i ViewOffset = Vector2i.Zero;
-  public float Rotation = 0;
+  public float RotationDegrees = 0;
 
   private static long touchCounter = 0;
   private Texture texture;

Program.cs

@@ -261,16 +261,16 @@ public class StraightenTool : ITool {
 
   public StraightenTool(Photo photo) {
     this.photo = photo;
-    initialRotation = photo.Rotation;
+    initialRotation = photo.RotationDegrees;
   }
 
   public ToolStatus HandleInput(KeyboardState input, MouseState mouse, Transform transform, Game game, Photo photo, UiGeometry geometry) {
     if (input.IsKeyPressed(Keys.Left)) {
-      photo.Rotation += 1;
+      photo.RotationDegrees += 5;
     }
 
     if (input.IsKeyPressed(Keys.Right)) {
-      photo.Rotation -= 1;
+      photo.RotationDegrees -= 5;
     }
 
     if (input.IsKeyPressed(Keys.Enter)) {
@@ -278,7 +278,7 @@ public class StraightenTool : ITool {
     }
 
     if (input.IsKeyPressed(Keys.Escape)) {
-      photo.Rotation = initialRotation;
+      photo.RotationDegrees = initialRotation;
       return ToolStatus.Canceled;
     }
 
@@ -286,7 +286,7 @@ public class StraightenTool : ITool {
   }
 
   public string Status() {
-    return String.Format("[straighten] {0}", photo.Rotation);
+    return String.Format("[straighten] {0}", photo.RotationDegrees);
   }
 }
 
@@ -977,7 +977,7 @@ public class Game : GameWindow {
                                   renderSize.X, renderSize.Y);
     activeOffset = new(photoBox.Min.X, photoBox.Min.Y);
     transform = new Transform(activeScale, activeOffset, activePhoto.Size);
-    DrawTexture(active, photoBox);
+    DrawTexture(active, photoBox, Color4.White, activePhoto.RotationDegrees);
     for (int i = 0; i < 5; i++) {
       Texture star = (activePhoto.Rating > i) ? STAR_FILLED : STAR_EMPTY;
       DrawTexture(star, geometry.StarBoxes[i].Min.X, geometry.StarBoxes[i].Min.Y);
@@ -1088,8 +1088,12 @@ public class Game : GameWindow {
   }
 
   public void DrawTexture(Texture texture, Box2i box, Color4 color) {
+    DrawTexture(texture, box, color, 0);
+  }
+
+  public void DrawTexture(Texture texture, Box2i box, Color4 color, float rotationDegrees) {
     GL.Uniform4(shader.GetUniformLocation("color"), color);
-    SetVertices(box.Min.X, box.Min.Y, box.Size.X, box.Size.Y);
+    SetVertices(box.Min.X, box.Min.Y, box.Size.X, box.Size.Y, rotationDegrees);
     GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices,
                   BufferUsageHint.DynamicDraw);
     GL.BindTexture(TextureTarget.Texture2D, texture.Handle);
@@ -1136,31 +1140,38 @@ public class Game : GameWindow {
     GL.Viewport(0, 0, e.Width, e.Height);
   }
 
-  private void SetVertices(float left, float top, float width, float height) {
+  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;
+
     // top left
-    vertices[0] = left;
-    vertices[1] = top;
+    vertices[0] = topLeft.X;
+    vertices[1] = topLeft.Y;
     vertices[2] = 0f;
     vertices[3] = 0f;
     vertices[4] = 0f;
 
     // top right
-    vertices[5] = left + width;
-    vertices[6] = top;
+    vertices[5] = topRight.X;
+    vertices[6] = topRight.Y;
     vertices[7] = 0f;
     vertices[8] = 1f;
     vertices[9] = 0f;
 
     // bottom right
-    vertices[10] = left + width;
-    vertices[11] = top + height;
+    vertices[10] = bottomRight.X;
+    vertices[11] = bottomRight.Y;
     vertices[12] = 0f;
     vertices[13] = 1f;
     vertices[14] = 1f;
 
     // bottom left
-    vertices[15] = left;
-    vertices[16] = top + height;
+    vertices[15] = bottomLeft.X;
+    vertices[16] = bottomLeft.Y;
     vertices[17] = 0f;
     vertices[18] = 0f;
     vertices[19] = 1f;