allow user to drag around the crop box

Program.cs

@@ -81,14 +81,14 @@ public class ViewTool : ITool {
 // FIXME: remove unneeded dependencies on "Game" or at least refactor them a bit.
 public class CropTool : ITool {
 
-  Photo activePhoto;
+  Photo photo;
   Vector2i mouseDragStart;
   Vector2i mouseDragEnd;
   bool dragging;
   string status = "";
 
   public CropTool(Photo photo) {
-    activePhoto = photo;
+    this.photo = photo;
     mouseDragStart = new(photo.CropRectangle.Left, photo.CropRectangle.Top);
     mouseDragEnd = new(photo.CropRectangle.Right, photo.CropRectangle.Bottom);
   }
@@ -98,7 +98,7 @@ public class CropTool : ITool {
     Vector2i imagePosition = game.ScreenToImage(mousePosition);
 
     if (mouse.IsButtonPressed(MouseButton.Button1)) {
-      dragging = activePhoto.CropRectangle.Contains(imagePosition.X, imagePosition.Y);
+      dragging = photo.CropRectangle.Contains(imagePosition.X, imagePosition.Y);
     }
 
     if (!dragging) {
@@ -111,23 +111,41 @@ public class CropTool : ITool {
 
       var (left, right, top, bottom) = GetCrop();
       if (left != right && top != bottom) {
-        activePhoto.CropRectangle = Rectangle.FromLTRB(left, top, right, bottom);
+        photo.CropRectangle = Rectangle.FromLTRB(left, top, right, bottom);
       } else {
-        activePhoto.CropRectangle = Rectangle.Empty;
+        photo.CropRectangle = Rectangle.Empty;
       }
     } else {
-      // FIXME
+      if (mouse.IsButtonDown(MouseButton.Button1)) {
+        Vector2 delta = mouse.Delta;
+        Vector2i imageDelta = game.ScreenToImageDelta((int) delta.X, (int) delta.Y);
+        photo.CropRectangle.Offset(imageDelta.X, imageDelta.Y);
+        if (photo.CropRectangle.Left < 0) {
+          photo.CropRectangle.Offset(-photo.CropRectangle.Left, 0);
+        }
+        if (photo.CropRectangle.Right > photo.Size.X) {
+          int overshoot = photo.CropRectangle.Right - photo.Size.X;
+          photo.CropRectangle.Offset(-overshoot, 0);
+        }
+        if (photo.CropRectangle.Top < 0) {
+          photo.CropRectangle.Offset(0, -photo.CropRectangle.Top);
+        }
+        if (photo.CropRectangle.Bottom > photo.Size.Y) {
+          int overshoot = photo.CropRectangle.Bottom - photo.Size.Y;
+          photo.CropRectangle.Offset(0, -overshoot);
+        }
+      }
     }
 
-    Rectangle r = activePhoto.CropRectangle;
-    status = $"({r.Left}, {r.Top}) {r.Width}x{r.Height}";
+    Rectangle r = photo.CropRectangle;
+    status = $"({r.Left}, {r.Top}, {r.Right}, {r.Bottom}) {r.Width}x{r.Height}";
 
     if (input.IsKeyPressed(Keys.Enter)) {
       return ToolStatus.Done;
     }
 
     if (input.IsKeyPressed(Keys.Escape)) {
-      activePhoto.CropRectangle = Rectangle.Empty;
+      photo.CropRectangle = Rectangle.Empty;
       return ToolStatus.Canceled;
     }
 
@@ -828,10 +846,14 @@ public class Game : GameWindow {
     }
   }
 
+  public Vector2i ScreenToImageDelta(int x, int y) {
+    return new((int) (x / activeScale), (int) (y / activeScale));
+  }
+
   public Vector2i ScreenToImage(int x, int y) {
     int rx = (int) ((x - activeOffset.X) / activeScale);
-    rx = Math.Clamp(rx, 0, photos[photoIndex].Size.X);
     int ry = (int) ((y - activeOffset.Y) / activeScale);
+    rx = Math.Clamp(rx, 0, photos[photoIndex].Size.X);
     ry = Math.Clamp(ry, 0, photos[photoIndex].Size.Y);
     return new(rx, ry);
   }