[Feature] visualizer.draw_texts() adds a font_properties argument (#887)

* [Feature] visualizer.draw_texts() add a font_properties argument in order to show Chinese characters.

* [Fix] move font_properties argument to the end.

* Update docstring of font_properties parameter.

* [Fix] moving FontProperties import clause to draw_texts() and add TYPE_CHECKING

* Update mmengine/visualization/visualizer.py

---------

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

mmengine/visualization/visualizer.py

@@ -1,7 +1,10 @@
 # Copyright (c) OpenMMLab. All rights reserved.
 import os.path as osp
 import warnings
-from typing import Dict, List, Optional, Sequence, Tuple, Union
+from typing import TYPE_CHECKING, Dict, List, Optional, Sequence, Tuple, Union
+
+if TYPE_CHECKING:
+    from matplotlib.font_manager import FontProperties
 
 import cv2
 import numpy as np
@@ -391,15 +394,18 @@ class Visualizer(ManagerMixin):
 
     @master_only
     def draw_texts(
-            self,
-            texts: Union[str, List[str]],
-            positions: Union[np.ndarray, torch.Tensor],
-            font_sizes: Optional[Union[int, List[int]]] = None,
-            colors: Union[str, tuple, List[str], List[tuple]] = 'g',
-            vertical_alignments: Union[str, List[str]] = 'top',
-            horizontal_alignments: Union[str, List[str]] = 'left',
-            font_families: Union[str, List[str]] = 'sans-serif',
-            bboxes: Optional[Union[dict, List[dict]]] = None) -> 'Visualizer':
+        self,
+        texts: Union[str, List[str]],
+        positions: Union[np.ndarray, torch.Tensor],
+        font_sizes: Optional[Union[int, List[int]]] = None,
+        colors: Union[str, tuple, List[str], List[tuple]] = 'g',
+        vertical_alignments: Union[str, List[str]] = 'top',
+        horizontal_alignments: Union[str, List[str]] = 'left',
+        font_families: Union[str, List[str]] = 'sans-serif',
+        bboxes: Optional[Union[dict, List[dict]]] = None,
+        font_properties: Optional[Union['FontProperties',
+                                        List['FontProperties']]] = None
+    ) -> 'Visualizer':
         """Draw single or multiple text boxes.
 
         Args:
@@ -448,7 +454,21 @@ class Visualizer(ManagerMixin):
                 the texts will have the same bbox. Reference to
                 https://matplotlib.org/stable/api/_as_gen/matplotlib.patches.FancyBboxPatch.html#matplotlib.patches.FancyBboxPatch
                 for more details. Defaults to None.
+            font_properties (Union[FontProperties, List[FontProperties]],
+                optional): The font properties of texts. FontProperties is
+                a `font_manager.FontProperties()` object.
+                If you want to draw Chinese texts, you need to prepare
+                a font file that can show Chinese characters properly.
+                For example: `simhei.ttf`,`simsun.ttc`,`simkai.ttf` and so on.
+                Then set font_properties=matplotlib.font_manager.FontProperties
+                        (fname='path/to/font_file')
+                ``font_properties`` can have the same length with texts or
+                just single value. If ``font_properties`` is single value,
+                all the texts will have the same font properties.
+                Defaults to None.
+                `New in version 0.6.0.`
         """
+        from matplotlib.font_manager import FontProperties
         check_type('texts', texts, (str, list))
         if isinstance(texts, str):
             texts = [texts]
@@ -489,6 +509,14 @@ class Visualizer(ManagerMixin):
                               num_text)
         font_families = value2list(font_families, str, num_text)
 
+        if font_properties is None:
+            font_properties = [None for _ in range(num_text)]  # type: ignore
+        else:
+            check_type_and_length('font_properties', font_properties,
+                                  (FontProperties, list), num_text)
+            font_properties = value2list(font_properties, FontProperties,
+                                         num_text)
+
         if bboxes is None:
             bboxes = [None for _ in range(num_text)]  # type: ignore
         else:
@@ -505,6 +533,7 @@ class Visualizer(ManagerMixin):
                 verticalalignment=vertical_alignments[i],
                 horizontalalignment=horizontal_alignments[i],
                 family=font_families[i],
+                fontproperties=font_properties[i],
                 color=colors[i])
         return self