[proto][tests] Added ref functions for h/v flips (#6876)

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

* Better dtype handling in reference_affine_bounding_box_helper

test/prototype_transforms_kernel_infos.py

@@ -145,6 +145,29 @@ def sample_inputs_horizontal_flip_video():
         yield ArgsKwargs(video_loader)
 
 
+def reference_horizontal_flip_bounding_box(bounding_box, *, format, spatial_size):
+    affine_matrix = np.array(
+        [
+            [-1, 0, spatial_size[1]],
+            [0, 1, 0],
+        ],
+        dtype="float32",
+    )
+
+    expected_bboxes = reference_affine_bounding_box_helper(bounding_box, format=format, affine_matrix=affine_matrix)
+
+    return expected_bboxes
+
+
+def reference_inputs_flip_bounding_box():
+    for bounding_box_loader in make_bounding_box_loaders(extra_dims=[()]):
+        yield ArgsKwargs(
+            bounding_box_loader,
+            format=bounding_box_loader.format,
+            spatial_size=bounding_box_loader.spatial_size,
+        )
+
+
 KERNEL_INFOS.extend(
     [
         KernelInfo(
@@ -158,6 +181,8 @@ KERNEL_INFOS.extend(
         KernelInfo(
             F.horizontal_flip_bounding_box,
             sample_inputs_fn=sample_inputs_horizontal_flip_bounding_box,
+            reference_fn=reference_horizontal_flip_bounding_box,
+            reference_inputs_fn=reference_inputs_flip_bounding_box,
         ),
         KernelInfo(
             F.horizontal_flip_mask,
@@ -409,15 +434,13 @@ def _compute_affine_matrix(angle, translate, scale, shear, center):
     return true_matrix
 
 
-def reference_affine_bounding_box(bounding_box, *, format, spatial_size, angle, translate, scale, shear, center=None):
-    if center is None:
-        center = [s * 0.5 for s in spatial_size[::-1]]
-
-    def transform(bbox):
-        affine_matrix = _compute_affine_matrix(angle, translate, scale, shear, center)
-        affine_matrix = affine_matrix[:2, :]
-
-        bbox_xyxy = F.convert_format_bounding_box(bbox, old_format=format, new_format=features.BoundingBoxFormat.XYXY)
+def reference_affine_bounding_box_helper(bounding_box, *, format, affine_matrix):
+    def transform(bbox, affine_matrix_, format_):
+        # Go to float before converting to prevent precision loss in case of CXCYWH -> XYXY and W or H is 1
+        in_dtype = bbox.dtype
+        bbox_xyxy = F.convert_format_bounding_box(
+            bbox.float(), old_format=format_, new_format=features.BoundingBoxFormat.XYXY, inplace=True
+        )
         points = np.array(
             [
                 [bbox_xyxy[0].item(), bbox_xyxy[1].item(), 1.0],
@@ -426,7 +449,7 @@ def reference_affine_bounding_box(bounding_box, *, format, spatial_size, angle,
                 [bbox_xyxy[2].item(), bbox_xyxy[3].item(), 1.0],
             ]
         )
-        transformed_points = np.matmul(points, affine_matrix.T)
+        transformed_points = np.matmul(points, affine_matrix_.T)
         out_bbox = torch.tensor(
             [
                 np.min(transformed_points[:, 0]).item(),
@@ -434,14 +457,16 @@ def reference_affine_bounding_box(bounding_box, *, format, spatial_size, angle,
                 np.max(transformed_points[:, 0]).item(),
                 np.max(transformed_points[:, 1]).item(),
             ],
-            dtype=bbox.dtype,
         )
-        return F.convert_format_bounding_box(out_bbox, old_format=features.BoundingBoxFormat.XYXY, new_format=format)
+        out_bbox = F.convert_format_bounding_box(
+            out_bbox, old_format=features.BoundingBoxFormat.XYXY, new_format=format, inplace=True
+        )
+        return out_bbox.to(dtype=in_dtype)
 
     if bounding_box.ndim < 2:
         bounding_box = [bounding_box]
 
-    expected_bboxes = [transform(bbox) for bbox in bounding_box]
+    expected_bboxes = [transform(bbox, affine_matrix, format) for bbox in bounding_box]
     if len(expected_bboxes) > 1:
         expected_bboxes = torch.stack(expected_bboxes)
     else:
@@ -450,6 +475,18 @@ def reference_affine_bounding_box(bounding_box, *, format, spatial_size, angle,
     return expected_bboxes
 
 
+def reference_affine_bounding_box(bounding_box, *, format, spatial_size, angle, translate, scale, shear, center=None):
+    if center is None:
+        center = [s * 0.5 for s in spatial_size[::-1]]
+
+    affine_matrix = _compute_affine_matrix(angle, translate, scale, shear, center)
+    affine_matrix = affine_matrix[:2, :]
+
+    expected_bboxes = reference_affine_bounding_box_helper(bounding_box, format=format, affine_matrix=affine_matrix)
+
+    return expected_bboxes
+
+
 def reference_inputs_affine_bounding_box():
     for bounding_box_loader, affine_kwargs in itertools.product(
         make_bounding_box_loaders(extra_dims=[()]),
@@ -643,6 +680,20 @@ def sample_inputs_vertical_flip_video():
         yield ArgsKwargs(video_loader)
 
 
+def reference_vertical_flip_bounding_box(bounding_box, *, format, spatial_size):
+    affine_matrix = np.array(
+        [
+            [1, 0, 0],
+            [0, -1, spatial_size[0]],
+        ],
+        dtype="float32",
+    )
+
+    expected_bboxes = reference_affine_bounding_box_helper(bounding_box, format=format, affine_matrix=affine_matrix)
+
+    return expected_bboxes
+
+
 KERNEL_INFOS.extend(
     [
         KernelInfo(
@@ -656,6 +707,8 @@ KERNEL_INFOS.extend(
         KernelInfo(
             F.vertical_flip_bounding_box,
             sample_inputs_fn=sample_inputs_vertical_flip_bounding_box,
+            reference_fn=reference_vertical_flip_bounding_box,
+            reference_inputs_fn=reference_inputs_flip_bounding_box,
         ),
         KernelInfo(
             F.vertical_flip_mask,