Don't draw spritelists with alpha 0 + tests (#1640)

arcade/sprite_list/sprite_list.py

@@ -958,7 +958,7 @@ def draw(self, *, filter=None, pixelated=None, blend_function=None):
         :param blend_function: Optional parameter to set the OpenGL blend function used for drawing the
                          sprite list, such as 'arcade.Window.ctx.BLEND_ADDITIVE' or 'arcade.Window.ctx.BLEND_DEFAULT'
         """
-        if len(self.sprite_list) == 0 or not self._visible:
+        if len(self.sprite_list) == 0 or not self._visible or self.alpha_normalized == 0.0:
             return
 
         self._init_deferred()

tests/unit/spritelist/test_spritelist_draw.py

@@ -0,0 +1,30 @@
+import pytest
+import arcade
+from arcade.gl import Geometry
+
+
+def test_visible(window, monkeypatch):
+    """Ensure invisible spritelists are not drawn"""
+    sp = arcade.SpriteList()
+    # Monkeypatch Geometry.render to raise an error if called
+    def mock_draw(*args, **kwargs):
+        raise AssertionError("Should not be called")
+    monkeypatch.setattr(Geometry, "render", mock_draw)
+
+    # Empty spritelist should not be rendered
+    sp.draw()
+
+    # It will draw if it has sprites
+    sp.append(arcade.SpriteSolidColor(10, 10, color=arcade.color.RED))
+    # Geometry.render should be called
+    with pytest.raises(AssertionError):
+        sp.draw()
+
+    # Invisible should not be rendered
+    sp.visible = False
+    sp.draw()
+    sp.visible = True
+
+    # Alpha 0 should not be rendered
+    sp.alpha = 0
+    sp.draw()