Fix create_text_sprite atlas sharing, anchors, position, and empty text

CHANGELOG.md

@@ -5,6 +5,13 @@ Arcade [PyPi Release History](https://pypi.org/project/arcade/#history) page.
 
 ## Unreleased
 
+### Fixes
+- Fixed several `arcade.create_text_sprite()` bugs:
+  - Sprites with the same text shared one image in the texture atlas, so creating a second one (for example in another color or size) changed the first one and drew the second stretched. Each sprite now gets its own image.
+  - `anchor_x="center"` cut off the left half of the text, and `anchor_x="right"` made an empty sprite.
+  - The sprite was placed too high. It now covers the same area as an `arcade.Text` with the same arguments at the same position.
+  - An empty string raised `ValueError`. It now makes a transparent sprite, as documented.
+
 ### New Features
 - Added `arcade.sweep_sprite(sprite, dx, dy, sprite_list)`, which checks the whole path of a moving sprite and returns a `SweepInfo` for the first sprite it would hit (the `sprite`, how far along the move as a `fraction` and `distance`, and the surface `normal`), or `None`. Fast sprites can't pass through thin walls this way. A sprite that already overlaps one is an immediate hit. Added the `sprite_bullets_sweep` example comparing it with a plain collision check.
 

arcade/text.py

@@ -2,8 +2,10 @@
 Drawing text with pyglet label
 """
 
+import math
 from pathlib import Path
 from typing import Any
+from uuid import uuid4
 
 import pyglet
 from pyglet.enums import Style, Weight
@@ -913,12 +915,23 @@ def create_text_sprite(
         multiline=multiline,
     )
 
+    # Where the text is with its anchor at (0, 0), as a Text object would be
+    left = text_object.left
+    bottom = text_object.bottom
+    # At least 1 pixel, so an empty string still makes a (transparent) texture
     size = (
-        int(text_object.right - text_object.left),
-        int(text_object.top - text_object.bottom),
+        max(1, math.ceil(text_object.right - left)),
+        max(1, math.ceil(text_object.top - bottom)),
     )
-    text_object.y = -text_object.bottom
-    texture = arcade.Texture.create_empty(text, size)
+
+    # Draw it into the texture with its bottom left corner at (0, 0)
+    text_object.x = -left
+    text_object.y = -bottom
+
+    # Each sprite needs its own image in the atlas. A name based on the text
+    # would make sprites with the same text, but different colors or sizes,
+    # share one.
+    texture = arcade.Texture.create_empty(f"create_text_sprite_{uuid4().hex}", size)
 
     if not texture_atlas:
         texture_atlas = arcade.get_window().ctx.default_atlas
@@ -927,10 +940,11 @@ def create_text_sprite(
         fbo.clear(color=background_color or arcade.color.TRANSPARENT_BLACK)
         text_object.draw()
 
+    # Place the sprite where the Text object was drawn
     return arcade.Sprite(
         texture,
-        center_x=text_object.right - (size[0] / 2),
-        center_y=text_object.top,
+        center_x=left + size[0] / 2,
+        center_y=bottom + size[1] / 2,
     )
 
 

tests/unit/text/test_text_sprite.py

@@ -8,3 +8,78 @@ def test_create(window, color):
     assert isinstance(sprite, arcade.Sprite)
     assert sprite.width == pytest.approx(75, rel=10)
     assert sprite.height == pytest.approx(20, rel=5)
+
+
+def _ink(image):
+    """Total alpha of an image, as a measure of how much was drawn"""
+    return sum(value * count for value, count in enumerate(image.getchannel("A").histogram()))
+
+
+def _sprite_bounds(sprite):
+    return sprite.left, sprite.right, sprite.bottom, sprite.top
+
+
+def _text_bounds(text):
+    return text.left, text.right, text.bottom, text.top
+
+
+@pytest.mark.parametrize(
+    "kwargs",
+    [
+        {},
+        {"anchor_x": "center"},
+        {"anchor_x": "right"},
+        {"font_size": 40},
+        {"multiline": True, "width": 120},
+        {"multiline": True, "width": 90, "align": "center", "anchor_x": "center"},
+    ],
+)
+def test_position_matches_text(window, kwargs):
+    """The sprite covers the same area as a Text object at the same position"""
+    text = "Two lines of text gj"
+    sprite = arcade.create_text_sprite(text, **kwargs)
+    text_object = arcade.Text(text, 0, 0, anchor_y="baseline", **kwargs)
+    assert _sprite_bounds(sprite) == pytest.approx(_text_bounds(text_object), abs=1)
+
+
+@pytest.mark.parametrize("anchor_x", ["left", "center", "right"])
+def test_anchor_draws_all_text(window, anchor_x):
+    """Every anchor puts all of the text inside the texture"""
+    atlas = window.ctx.default_atlas
+    # Read each image right away, so this doesn't depend on the sprites
+    # having separate images (tested below)
+    anchored = arcade.create_text_sprite("Hello World", font_size=20, anchor_x=anchor_x)
+    actual = _ink(atlas.read_texture_image_from_atlas(anchored.texture))
+    left = arcade.create_text_sprite("Hello World", font_size=20)
+    expected = _ink(atlas.read_texture_image_from_atlas(left.texture))
+    assert expected > 0
+    assert actual == pytest.approx(expected, rel=0.01)
+
+
+def test_same_text_different_style(window):
+    """Sprites with the same text keep their own images"""
+    atlas = window.ctx.default_atlas
+    small_red = arcade.create_text_sprite("Same", color=arcade.color.RED, font_size=20)
+    red_image = atlas.read_texture_image_from_atlas(small_red.texture)
+
+    big_blue = arcade.create_text_sprite("Same", color=arcade.color.BLUE, font_size=40)
+
+    # Each texture has an atlas region of its own size
+    for sprite in (small_red, big_blue):
+        region = atlas.get_texture_region_info(sprite.texture.atlas_name)
+        assert (region.width, region.height) == sprite.texture.size
+    assert big_blue.texture.size != small_red.texture.size
+
+    # Creating the second sprite didn't change the first one's image
+    assert atlas.read_texture_image_from_atlas(small_red.texture).tobytes() == red_image.tobytes()
+    red, _green, blue, _alpha = red_image.getextrema()
+    assert red[1] > 200 and blue[1] == 0
+
+
+def test_empty_text(window):
+    """An empty string makes a transparent sprite instead of failing"""
+    sprite = arcade.create_text_sprite("")
+    assert sprite.texture.width >= 1
+    assert sprite.texture.height >= 1
+    image = window.ctx.default_atlas.read_texture_image_from_atlas(sprite.texture)
+    assert _ink(image) == 0