use Box2i instead of Rectangle

Program.cs

@@ -288,6 +288,10 @@ public class Game : GameWindow {
     base.OnUnload();
   }
 
+  private static Box2i makeBox(int left, int top, int width, int height) {
+    return new Box2i(left, top, left + width, top + height);
+  }
+
   protected override void OnRenderFrame(FrameEventArgs e) {
     base.OnRenderFrame(e);
     GL.Clear(ClearBufferMask.ColorBufferBit);
@@ -302,9 +306,9 @@ public class Game : GameWindow {
     int photoWidth = (int) (1.0 * windowHeight / active.Height * active.Width);
     int letterboxWidth = (maxPhotoWidth - photoWidth) / 2;
 
-    DrawTexture(active, new Rectangle(letterboxWidth, 0, photoWidth, windowHeight));
+    DrawTexture(active, makeBox(letterboxWidth, 0, photoWidth, windowHeight));
     for (int i = 0; i < textures.Count; i++) {
-      Rectangle box = new Rectangle(windowWidth - thumbnailWidth, i * thumbnailHeight, thumbnailWidth, thumbnailHeight);
+      Box2i box = makeBox(windowWidth - thumbnailWidth, i * thumbnailHeight, thumbnailWidth, thumbnailHeight);
       DrawTexture(textures[i], box);
       if (i == textureIndex) {
         DrawBox(box, 3, Color4.GreenYellow);
@@ -314,23 +318,23 @@ public class Game : GameWindow {
     SwapBuffers();
   }
 
-  void DrawTexture(Texture texture, Rectangle box) {
+  void DrawTexture(Texture texture, Box2i box) {
     DrawTexture(texture, box, Color4.White);
   }
 
-  void DrawTexture(Texture texture, Rectangle box, Color4 color) {
+  void DrawTexture(Texture texture, Box2i box, Color4 color) {
     GL.Uniform4(shader.GetUniformLocation("color"), color.R, color.G, color.B, color.A);
-    SetVertices(box.Left, box.Top, box.Width, box.Height);
+    SetVertices(box.Min.X, box.Min.Y, box.Size.X, box.Size.Y);
     GL.BufferData(BufferTarget.ArrayBuffer, vertices.Length * sizeof(float), vertices, BufferUsageHint.DynamicDraw);
     GL.BindTexture(TextureTarget.Texture2D, texture.Handle);
     GL.DrawElements(PrimitiveType.Triangles, indices.Length, DrawElementsType.UnsignedInt, 0);
   }
 
-  void DrawBox(Rectangle box, int thickness, Color4 color) {
-    DrawTexture(TEXTURE_WHITE, new Rectangle(box.Left, box.Top, box.Width, thickness), color);
-    DrawTexture(TEXTURE_WHITE, new Rectangle(box.Left, box.Top, thickness, box.Height), color);
-    DrawTexture(TEXTURE_WHITE, new Rectangle(box.Left, box.Top + box.Height - thickness, box.Width, thickness), color);
-    DrawTexture(TEXTURE_WHITE, new Rectangle(box.Left + box.Width - thickness, box.Top, thickness, box.Height), color);
+  void DrawBox(Box2i box, int thickness, Color4 color) {
+    DrawTexture(TEXTURE_WHITE, makeBox(box.Min.X, box.Min.Y, box.Size.X, thickness), color);
+    DrawTexture(TEXTURE_WHITE, makeBox(box.Min.X, box.Min.Y, thickness, box.Size.Y), color);
+    DrawTexture(TEXTURE_WHITE, makeBox(box.Min.X, box.Max.Y - thickness, box.Size.X, thickness), color);
+    DrawTexture(TEXTURE_WHITE, makeBox(box.Max.X - thickness, box.Min.Y, thickness, box.Size.Y), color);
   }
 
   protected override void OnResize(ResizeEventArgs e) {