override pyglet text blending

arcade/text.py

@@ -18,6 +18,67 @@
 __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 = None
+    _prev_blend_func = None
+
+    def set_state(self) -> None:
+        import pyglet.gl as gl
+        from ctypes import c_int, c_ubyte
+
+        self.program.use()
+        self.program["scissor"] = False
+
+        gl.glActiveTexture(gl.GL_TEXTURE0)
+        gl.glBindTexture(self.texture.target, self.texture.id)
+
+        blend = c_ubyte()
+        gl.glGetBooleanv(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()
+        gl.glGetIntegerv(gl.GL_BLEND_SRC_RGB, src_rgb)
+        gl.glGetIntegerv(gl.GL_BLEND_DST_RGB, dst_rgb)
+        gl.glGetIntegerv(gl.GL_BLEND_SRC_ALPHA, src_alpha)
+        gl.glGetIntegerv(gl.GL_BLEND_DST_ALPHA, dst_alpha)
+
+        self._prev_blend_func = (src_rgb.value, dst_rgb.value, src_alpha.value, dst_alpha.value)
+
+        gl.glEnable(gl.GL_BLEND)
+        gl.glBlendFuncSeparate(
+            gl.GL_SRC_ALPHA,
+            gl.GL_ONE_MINUS_SRC_ALPHA,
+            gl.GL_ONE,
+            gl.GL_ONE,
+        )
+
+    def unset_state(self) -> None:
+        import pyglet.gl as gl
+
+        if not self._prev_blend:
+            gl.glDisable(gl.GL_BLEND)
+
+        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 +314,8 @@ 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,