feat(gui): UILabel avoids full render if background set

arcade/gui/widgets/text.py

@@ -35,6 +35,9 @@ class UILabel(UIWidget):
     By default, a label will fit its initial content. If the text is changed use
     :py:meth:`~arcade.gui.UILabel.fit_content` to adjust the size.
 
+    If the text changes frequently, ensure to set a background color or texture, which will
+    prevent a full rendering of the whole UI and only render the label itself.
+
     :param text: Text displayed on the label.
     :param x: x position (default anchor is bottom-left).
     :param y: y position (default anchor is bottom-left).
@@ -166,7 +169,11 @@ def text(self, value):
             self.label.text = value
             self._update_layout()
             self._update_size_hint_min()
-            self.trigger_full_render()
+
+            if self._bg_color or self._bg_tex:
+                self.trigger_render()
+            else:
+                self.trigger_full_render()
 
     def _update_layout(self):
         # Update Pyglet layout size

tests/unit/gui/test_uilabel.py

@@ -1,6 +1,9 @@
+from unittest.mock import Mock
+
 import pytest
 
 from arcade.gui import UILabel, Rect
+from arcade.types import Color
 
 
 def test_uilabel_inits_with_text_size(window):
@@ -64,3 +67,31 @@ def test_adaptive_width_support_for_multiline_text(window):
     label = UILabel(text="Multiline\ntext\nwhich\n", multiline=True)
     assert label.width < 100
     assert label.height > 20
+
+
+def test_change_text_does_full_render_without_background(window):
+    """
+    This test is a bit tricky. Enabling multiline without a width
+    should fit the size to the text. This is not natively supported by either arcade.Text or pyglet.Label.
+    Because text length variates between different os, we can only test boundaries, which indicate a proper implementation.
+    """
+
+    label = UILabel(text="First Text")
+    label.parent = Mock()
+
+    label.text = "Second Text"
+    label.parent.trigger_render.assert_called_once()
+
+
+def test_change_text_does_normal_render_with_background(window):
+    """
+    This test is a bit tricky. Enabling multiline without a width
+    should fit the size to the text. This is not natively supported by either arcade.Text or pyglet.Label.
+    Because text length variates between different os, we can only test boundaries, which indicate a proper implementation.
+    """
+
+    label = UILabel(text="First Text").with_background(color=Color(255, 255, 255, 255))
+    label.parent = Mock()
+
+    label.text = "Second Text"
+    label.parent.trigger_render.assert_not_called()