Gui/blend text (#2459)

* Small cleanup
* Check transparency to determine if background clears the widgets area or use rect draw.
  This can be overwritten by setting UIWidget._strong_background for now.
* override pyglet text blending

arcade/gui/widgets/__init__.py

@@ -1,14 +1,14 @@
 from __future__ import annotations
 
 from abc import ABC
-from typing import NamedTuple, Iterable, Optional, Union, TYPE_CHECKING, TypeVar, Tuple, List, Dict
+from typing import Dict, Iterable, List, NamedTuple, Optional, TYPE_CHECKING, Tuple, TypeVar, Union
 
-from pyglet.event import EventDispatcher, EVENT_HANDLED, EVENT_UNHANDLED
+from pyglet.event import EVENT_HANDLED, EVENT_UNHANDLED, EventDispatcher
 from pyglet.math import Vec2
 from typing_extensions import Self
 
 import arcade
-from arcade import Sprite, Texture, LBWH, Rect
+from arcade import LBWH, Rect, Sprite, Texture
 from arcade.color import TRANSPARENT_BLACK
 from arcade.gui.events import (
     UIEvent,
@@ -19,9 +19,9 @@
     UIOnUpdateEvent,
 )
 from arcade.gui.nine_patch import NinePatchTexture
-from arcade.gui.property import Property, bind, ListProperty
+from arcade.gui.property import ListProperty, Property, bind
 from arcade.gui.surface import Surface
-from arcade.types import Color, AnchorPoint, AsFloat
+from arcade.types import AnchorPoint, AsFloat, Color
 from arcade.utils import copy_dunders_unimplemented
 
 if TYPE_CHECKING:
@@ -73,6 +73,11 @@ class UIWidget(EventDispatcher, ABC):
     _padding_right = Property(0)
     _padding_bottom = Property(0)
     _padding_left = Property(0)
+    _strong_background = Property(False)
+    """If True, the background will clear the surface, even if it is not fully opaque.
+    This is not part of the public API and subject to change.
+    UILabel have a strong background if set.
+    """
 
     def __init__(
         self,
@@ -116,6 +121,7 @@ def __init__(
         bind(self, "_padding_right", self.trigger_render)
         bind(self, "_padding_bottom", self.trigger_render)
         bind(self, "_padding_left", self.trigger_render)
+        bind(self, "_strong_background", self.trigger_render)
 
     def add(self, child: W, **kwargs) -> W:
         """Add a widget as a child.
@@ -253,7 +259,10 @@ def do_render_base(self, surface: Surface):
 
         # draw background
         if self._bg_color:
-            surface.clear(self._bg_color)
+            if self._bg_color.a == 255 or self._strong_background:
+                surface.clear(self._bg_color)
+            else:
+                arcade.draw_rect_filled(LBWH(0, 0, self.width, self.height), color=self._bg_color)
         # draw background texture
         if self._bg_tex:
             surface.draw_texture(x=0, y=0, width=self.width, height=self.height, tex=self._bg_tex)

arcade/gui/widgets/text.py

@@ -119,6 +119,8 @@ def __init__(
             multiline=multiline,
             **kwargs,
         )
+        self._strong_background = True
+
         if adaptive_multiline:
             # +1 is required to prevent line wrap
             width = self._label.content_width + 1

arcade/text.py

@@ -4,6 +4,7 @@
 
 from __future__ import annotations
 
+from ctypes import c_int, c_ubyte
 from pathlib import Path
 from typing import Any, Union
 
@@ -18,6 +19,62 @@
 __all__ = ["load_font", "Text", "create_text_sprite", "draw_text"]
 
 
+class _ArcadeTextLayoutGroup(pyglet.text.layout.TextLayoutGroup):
+    """Create a text layout rendering group.
+
+    Overrides pyglet blending handling to allow for additive blending.
+    Furthermore, it resets the blend function to the previous state.
+    """
+
+    _prev_blend: bool
+    _prev_blend_func: tuple[int, int, int, int]
+
+    def set_state(self) -> None:
+        self.program.use()
+        self.program["scissor"] = False
+
+        pyglet.gl.glActiveTexture(pyglet.gl.GL_TEXTURE0)
+        pyglet.gl.glBindTexture(self.texture.target, self.texture.id)
+
+        blend = c_ubyte()
+        pyglet.gl.glGetBooleanv(pyglet.gl.GL_BLEND, blend)
+        self._prev_blend = bool(blend.value)
+
+        src_rgb = c_int()
+        dst_rgb = c_int()
+        src_alpha = c_int()
+        dst_alpha = c_int()
+        pyglet.gl.glGetIntegerv(pyglet.gl.GL_BLEND_SRC_RGB, src_rgb)
+        pyglet.gl.glGetIntegerv(pyglet.gl.GL_BLEND_DST_RGB, dst_rgb)
+        pyglet.gl.glGetIntegerv(pyglet.gl.GL_BLEND_SRC_ALPHA, src_alpha)
+        pyglet.gl.glGetIntegerv(pyglet.gl.GL_BLEND_DST_ALPHA, dst_alpha)
+
+        self._prev_blend_func = (src_rgb.value, dst_rgb.value, src_alpha.value, dst_alpha.value)
+
+        pyglet.gl.glEnable(pyglet.gl.GL_BLEND)
+        pyglet.gl.glBlendFuncSeparate(
+            pyglet.gl.GL_SRC_ALPHA,
+            pyglet.gl.GL_ONE_MINUS_SRC_ALPHA,
+            pyglet.gl.GL_ONE,
+            pyglet.gl.GL_ONE,
+        )
+
+    def unset_state(self) -> None:
+        if not self._prev_blend:
+            pyglet.gl.glDisable(pyglet.gl.GL_BLEND)
+
+        pyglet.gl.glBlendFuncSeparate(
+            self._prev_blend_func[0],
+            self._prev_blend_func[1],
+            self._prev_blend_func[2],
+            self._prev_blend_func[3],
+        )
+        self.program.stop()
+
+
+pyglet.text.layout.TextLayout.group_class = _ArcadeTextLayoutGroup
+
+
 def load_font(path: str | Path) -> None:
     """
     Load fonts in a file (usually .ttf) adding them to a global font registry.
@@ -253,7 +310,8 @@ def __init__(
             bold=bold,
             italic=italic,
             multiline=multiline,
-            rotation=rotation,  # type: ignore  # pending https://github.com/pyglet/pyglet/issues/843
+            rotation=rotation,
+            # type: ignore  # pending https://github.com/pyglet/pyglet/issues/843
             batch=batch,
             group=group,
             **kwargs,