[proto] Speed-up h/v bboxes flip ops (#6877)

* [proto][tests] Added ref functions for h/v flips

* Better dtype handling in reference_affine_bounding_box_helper

* [proto] Speed-up h/v bboxes flip ops

* Use more inplace ops

* Removed _old methods

* Fixed jit issue using a bit slower version

torchvision/prototype/transforms/functional/_geometry.py

@@ -36,17 +36,16 @@ def horizontal_flip_bounding_box(
 ) -> torch.Tensor:
     shape = bounding_box.shape
 
-    # TODO: Investigate if it makes sense from a performance perspective to have an implementation for every
-    #  BoundingBoxFormat instead of converting back and forth
-    bounding_box = convert_format_bounding_box(
-        bounding_box.clone(), old_format=format, new_format=features.BoundingBoxFormat.XYXY, inplace=True
-    ).reshape(-1, 4)
+    bounding_box = bounding_box.clone().reshape(-1, 4)
 
-    bounding_box[:, [0, 2]] = spatial_size[1] - bounding_box[:, [2, 0]]
+    if format == features.BoundingBoxFormat.XYXY:
+        bounding_box[:, [2, 0]] = bounding_box[:, [0, 2]].sub_(spatial_size[1]).neg_()
+    elif format == features.BoundingBoxFormat.XYWH:
+        bounding_box[:, 0].add_(bounding_box[:, 2]).sub_(spatial_size[1]).neg_()
+    else:  # format == features.BoundingBoxFormat.CXCYWH:
+        bounding_box[:, 0].sub_(spatial_size[1]).neg_()
 
-    return convert_format_bounding_box(
-        bounding_box, old_format=features.BoundingBoxFormat.XYXY, new_format=format, inplace=True
-    ).reshape(shape)
+    return bounding_box.reshape(shape)
 
 
 def horizontal_flip_video(video: torch.Tensor) -> torch.Tensor:
@@ -75,17 +74,16 @@ def vertical_flip_bounding_box(
 ) -> torch.Tensor:
     shape = bounding_box.shape
 
-    # TODO: Investigate if it makes sense from a performance perspective to have an implementation for every
-    #  BoundingBoxFormat instead of converting back and forth
-    bounding_box = convert_format_bounding_box(
-        bounding_box.clone(), old_format=format, new_format=features.BoundingBoxFormat.XYXY, inplace=True
-    ).reshape(-1, 4)
+    bounding_box = bounding_box.clone().reshape(-1, 4)
 
-    bounding_box[:, [1, 3]] = spatial_size[0] - bounding_box[:, [3, 1]]
+    if format == features.BoundingBoxFormat.XYXY:
+        bounding_box[:, [1, 3]] = bounding_box[:, [3, 1]].sub_(spatial_size[0]).neg_()
+    elif format == features.BoundingBoxFormat.XYWH:
+        bounding_box[:, 1].add_(bounding_box[:, 3]).sub_(spatial_size[0]).neg_()
+    else:  # format == features.BoundingBoxFormat.CXCYWH:
+        bounding_box[:, 1].sub_(spatial_size[0]).neg_()
 
-    return convert_format_bounding_box(
-        bounding_box, old_format=features.BoundingBoxFormat.XYXY, new_format=format, inplace=True
-    ).reshape(shape)
+    return bounding_box.reshape(shape)
 
 
 def vertical_flip_video(video: torch.Tensor) -> torch.Tensor: