New feature: Add limit_render_to_text_bbox to Label to limit text…

… rendering to the text bounding box, improving `Label` alignments. (kivy#8510)

* add limit_render_to_text_bbox

* flake8

kivy/core/text/__init__.py

@@ -185,6 +185,17 @@ class LabelBase(object):
             or `'weak_rtl'` (Pango only)
         `text_language`: str, defaults to None (user locale)
             RFC-3066 format language tag as a string (Pango only)
+        `limit_render_to_text_bbox`: bool, defaults to False. PIL only.
+            If set to ``True``, this parameter indicates that rendering should
+            be limited to the bounding box of the text, excluding any
+            additional white spaces designated for ascent and descent.
+            By limiting the rendering to the bounding box of the text, it
+            ensures a more precise alignment with surrounding elements when
+            utilizing properties such as `valign`, `y`, `pos`, `pos_hint`, etc.
+
+    .. versionadded:: 2.3.0
+        `limit_render_to_text_bbox` was added to allow to limit text rendering
+        to the text bounding box (PIL only).
 
     .. deprecated:: 2.2.0
         `padding_x` and `padding_y` have been deprecated. Please use `padding`
@@ -249,6 +260,7 @@ def __init__(
         outline_width=None, outline_color=None, font_context=None,
         font_features=None, base_direction=None, font_direction='ltr',
         font_script_name='Latin', text_language=None,
+        limit_render_to_text_bbox=False,
         **kwargs):
 
         # Include system fonts_dir in resource paths.
@@ -273,7 +285,8 @@ def __init__(
                    'base_direction': base_direction,
                    'font_direction': font_direction,
                    'font_script_name': font_script_name,
-                   'text_language': text_language}
+                   'text_language': text_language,
+                   'limit_render_to_text_bbox': limit_render_to_text_bbox}
 
         kwargs_get = kwargs.get
         options['color'] = color or (1, 1, 1, 1)

kivy/core/text/text_pil.py

@@ -37,8 +37,11 @@ def get_extents(self, text):
         left, top, right, bottom = font.getbbox(text)
         ascent, descent = font.getmetrics()
 
+        if self.options['limit_render_to_text_bbox']:
+            h = bottom - top
+        else:
+            h = ascent + descent
         w = right - left
-        h = ascent + descent
 
         return w, h
 
@@ -52,6 +55,14 @@ def _render_begin(self):
 
     def _render_text(self, text, x, y):
         color = tuple([int(c * 255) for c in self.options['color']])
+
+        # Adjust x and y position to avoid text cutoff
+        if self.options['limit_render_to_text_bbox']:
+            font = self._select_font()
+            bbox = font.getbbox(text)
+            x -= bbox[0]
+            y -= bbox[1]
+
         self._pil_draw.text((int(x), int(y)),
                             text, font=self._select_font(), fill=color)
 

kivy/uix/label.py

@@ -311,7 +311,8 @@ class Label(Widget):
                         'split_str', 'ellipsis_options', 'unicode_errors',
                         'markup', 'font_hinting', 'font_kerning',
                         'font_blended', 'font_context', 'font_features',
-                        'base_direction', 'text_language')
+                        'base_direction', 'text_language',
+                        'limit_render_to_text_bbox')
 
     def __init__(self, **kwargs):
         self._trigger_texture = Clock.create_trigger(self.texture_update, -1)
@@ -1177,3 +1178,19 @@ def print_it(instance, value):
     :attr:`font_blended` is a :class:`~kivy.properties.BooleanProperty` and
     defaults to True.
     '''
+
+    limit_render_to_text_bbox = BooleanProperty(False)
+    '''If set to ``True``, this parameter indicates that rendering should be
+    limited to the bounding box of the text, excluding any additional white
+    spaces designated for ascent and descent.
+
+    By limiting the rendering to the bounding box of the text, it ensures a
+    more precise alignment with surrounding elements when utilizing properties
+    such as `valign`, `y`, `pos`, `pos_hint`, etc.
+
+    .. note::
+        This feature requires the PIL text provider.
+
+    :attr:`limit_render_to_text_bbox` is a
+    :class:`~kivy.properties.BooleanProperty` and defaults to False.
+    '''