Draw the Hirst painting: pen, dot positions, dots, click wait and speed

MIL-002 tasks 1 to 6.

- Add create_pen, which hides the turtle, lifts the pen and switches the screen
  to 0 to 255 colours.
- Add dot_positions: 100 dot centres in 10 rows of 10, 50 apart, centred on the
  origin so the painting fits the default window.
- Add draw_dots, which draws a size-20 dot at every position in a colour chosen
  from the palette, and raises ValueError for an empty palette.
- Add main: draw with the palette of the reference image, then wait for a click
  with exitonclick. Animation is off while drawing and the screen updates once,
  which takes the drawing from 21.1 to 0.35 seconds (SC6 allows 30).
- Add 22 tests: pen setup, positions and spacing, dots on a recording fake pen
  and on a real turtle, no trail, and the order of main's steps. All tests share
  one hidden Tk window, because starting Tk per test fails now and then on
  Windows.

Closes #7
Closes #8
Closes #9
Closes #10
Closes #11
Closes #12

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4
Task: MIL-002#5
Task: MIL-002#6

src/hirst_painting.py

@@ -1,13 +1,19 @@
 """Hirst-style spot painting drawn with turtle."""
 
-from collections.abc import Iterable
+import random
+import turtle
+from collections.abc import Callable, Iterable, Sequence
 from pathlib import Path
+from typing import Protocol
 
 import colorgram
 
 type Colour = tuple[int, int, int]
 """A colour as red, green and blue values from 0 to 255."""
 
+type Position = tuple[int, int]
+"""A point on the turtle screen as x and y, in screen units."""
+
 REFERENCE_IMAGE_PATH = (
     Path(__file__).resolve().parent.parent / "assets" / "20260524_132700.jpg"
 )
@@ -16,6 +22,14 @@ REFERENCE_IMAGE_PATH = (
 # has fewer, so the palette is never padded.
 EXTRACTED_COLOUR_COUNT = 30
 
+GRID_ROWS = 10
+GRID_COLUMNS = 10
+
+DOT_SIZE = 20
+
+# Distance between the centres of neighbouring dots, along rows and columns.
+DOT_SPACING = 50
+
 # A colour counts as a white shade when red, green and blue are all at or above
 # this value: such dots are invisible on the white background (SC3 of BC-001).
 WHITE_THRESHOLD = 240
@@ -41,3 +55,75 @@ def extract_palette(
     extracted = colorgram.extract(str(image_path), colour_count)
     colours = [(found.rgb.r, found.rgb.g, found.rgb.b) for found in extracted]
     return remove_white_shades(colours)
+
+
+class DotPen(Protocol):
+    """The two turtle operations that drawing dots needs."""
+
+    def goto(self, position: Position, /) -> None:
+        """Move to the position."""
+        ...
+
+    def dot(self, size: int, colour: Colour, /) -> None:
+        """Draw a dot of the size and colour at the current position."""
+        ...
+
+
+def create_pen(screen: turtle.TurtleScreen) -> turtle.RawTurtle:
+    """Return a hidden turtle with its pen up on a screen that takes RGB colours.
+
+    The pen is up and the turtle is hidden so that the painting shows no trail
+    and no cursor; the screen takes colours as 0 to 255 values, as `Colour` does.
+    """
+    screen.colormode(255)
+    pen = turtle.RawTurtle(screen)
+    pen.hideturtle()
+    pen.penup()
+    return pen
+
+
+def dot_positions() -> list[Position]:
+    """Return the centre of every dot, rows from the bottom up, left to right.
+
+    The grid is centred on the origin, the middle of the turtle window, so the
+    whole painting fits in a window of the default size.
+    """
+    left = -DOT_SPACING * (GRID_COLUMNS - 1) // 2
+    bottom = -DOT_SPACING * (GRID_ROWS - 1) // 2
+    return [
+        (left + column * DOT_SPACING, bottom + row * DOT_SPACING)
+        for row in range(GRID_ROWS)
+        for column in range(GRID_COLUMNS)
+    ]
+
+
+def draw_dots(
+    pen: DotPen,
+    palette: Sequence[Colour],
+    choose_colour: Callable[[Sequence[Colour]], Colour] = random.choice,
+) -> None:
+    """Draw a dot at every dot position, each in a colour chosen from the palette.
+
+    Raises ValueError when the palette has no colours.
+    """
+    if not palette:
+        raise ValueError("The palette has no colours to draw with.")
+    for position in dot_positions():
+        pen.goto(position)
+        pen.dot(DOT_SIZE, choose_colour(palette))
+
+
+def main() -> None:
+    """Draw the painting with the reference image's palette, then wait for a click."""
+    screen = turtle.Screen()
+    # Animating the 100 moves takes about 20 seconds on screen, against the 30
+    # allowed (SC6 of BC-001), so draw unseen and show the whole painting at once.
+    screen.tracer(0)
+    pen = create_pen(screen)
+    draw_dots(pen, extract_palette(REFERENCE_IMAGE_PATH))
+    screen.update()
+    screen.exitonclick()
+
+
+if __name__ == "__main__":
+    main()

tests/test_hirst_painting.py

@@ -1,15 +1,27 @@
 """Tests for the colour palette helpers of the Hirst painting program."""
 
+import tkinter
+import turtle
+from collections import Counter
+from collections.abc import Iterator, Sequence
+from dataclasses import dataclass, field
 from pathlib import Path
 
 import pytest
 from PIL import Image
 
+import hirst_painting
 from hirst_painting import (
     REFERENCE_IMAGE_PATH,
     Colour,
+    DotPen,
+    Position,
+    create_pen,
+    dot_positions,
+    draw_dots,
     extract_palette,
     is_white_shade,
+    main,
     remove_white_shades,
 )
 
@@ -118,3 +130,273 @@ def test_reference_image_palette_has_two_colours_and_no_white_shade() -> None:
 
     assert len(palette) >= 2
     assert not any(is_white_shade(colour) for colour in palette)
+
+
+@pytest.fixture(scope="session")
+def tk_root() -> Iterator[tkinter.Tk]:
+    """Create one hidden Tk window for the whole run.
+
+    Starting Tk again and again in one process fails now and then on Windows
+    (Tk cannot read its own library files), so every test shares this one.
+    """
+    root = tkinter.Tk()
+    root.withdraw()
+    yield root
+    root.destroy()
+
+
+@pytest.fixture
+def canvas(tk_root: tkinter.Tk) -> Iterator[tkinter.Canvas]:
+    """Yield a canvas on the hidden window, so no window appears."""
+    canvas = tkinter.Canvas(tk_root)
+    yield canvas
+    canvas.destroy()
+
+
+@pytest.fixture
+def screen(canvas: tkinter.Canvas) -> turtle.TurtleScreen:
+    """Return a turtle screen that draws on the hidden canvas."""
+    return turtle.TurtleScreen(canvas)
+
+
+def test_create_pen_hides_the_turtle(screen: turtle.TurtleScreen) -> None:
+    assert not create_pen(screen).isvisible()
+
+
+def test_create_pen_lifts_the_pen(screen: turtle.TurtleScreen) -> None:
+    assert not create_pen(screen).isdown()
+
+
+def test_create_pen_switches_the_screen_to_255_level_colours(
+    screen: turtle.TurtleScreen,
+) -> None:
+    create_pen(screen)
+
+    assert screen.colormode() == 255
+
+
+def test_create_pen_draws_on_the_given_screen(screen: turtle.TurtleScreen) -> None:
+    assert create_pen(screen).getscreen() is screen
+
+
+def test_dot_positions_returns_100_positions() -> None:
+    assert len(dot_positions()) == 100
+
+
+def test_dot_positions_are_all_different() -> None:
+    positions = dot_positions()
+
+    assert len(set(positions)) == len(positions)
+
+
+def test_dot_positions_have_10_heights_with_10_dots_each() -> None:
+    dots_per_height = Counter(y for _, y in dot_positions())
+
+    assert list(dots_per_height.values()) == [10] * 10
+
+
+def test_dot_positions_are_50_apart_along_each_row() -> None:
+    positions = dot_positions()
+
+    for start in range(0, 100, 10):
+        row = positions[start : start + 10]
+        assert [x for x, _ in row] == list(range(-225, 226, 50))
+        assert len({y for _, y in row}) == 1
+
+
+def test_dot_positions_are_50_apart_between_rows() -> None:
+    heights = sorted({y for _, y in dot_positions()})
+
+    assert heights == list(range(-225, 226, 50))
+
+
+def test_dot_positions_start_bottom_left_and_fill_rows_upward() -> None:
+    positions = dot_positions()
+
+    assert positions[0] == (-225, -225)
+    assert positions[1] == (-175, -225)
+    assert positions[10] == (-225, -175)
+    assert positions[-1] == (225, 225)
+
+
+def test_dot_positions_are_centred_on_the_origin() -> None:
+    positions = dot_positions()
+
+    assert min(x for x, _ in positions) == -max(x for x, _ in positions)
+    assert min(y for _, y in positions) == -max(y for _, y in positions)
+
+
+class RecordingPen:
+    """A pen that records the dots it was asked to draw and where."""
+
+    def __init__(self) -> None:
+        """Start at the origin with no dots drawn."""
+        self.position: Position = (0, 0)
+        self.dots: list[tuple[Position, int, Colour]] = []
+
+    def goto(self, position: Position, /) -> None:
+        """Remember the position the next dot is drawn at."""
+        self.position = position
+
+    def dot(self, size: int, colour: Colour, /) -> None:
+        """Record a dot at the current position."""
+        self.dots.append((self.position, size, colour))
+
+
+PALETTE: list[Colour] = [(200, 30, 40), (30, 90, 160), (20, 120, 60)]
+
+
+def test_draw_dots_draws_a_dot_at_every_position_in_order() -> None:
+    pen = RecordingPen()
+
+    draw_dots(pen, PALETTE)
+
+    assert [position for position, _, _ in pen.dots] == dot_positions()
+
+
+def test_draw_dots_draws_dots_of_size_20() -> None:
+    pen = RecordingPen()
+
+    draw_dots(pen, PALETTE)
+
+    assert {size for _, size, _ in pen.dots} == {20}
+
+
+def test_draw_dots_colours_every_dot_from_the_palette() -> None:
+    pen = RecordingPen()
+
+    draw_dots(pen, PALETTE)
+
+    assert {colour for _, _, colour in pen.dots} <= set(PALETTE)
+
+
+def test_draw_dots_asks_the_chooser_for_the_colour_of_each_dot() -> None:
+    pen = RecordingPen()
+    asked: list[Sequence[Colour]] = []
+
+    def choose_last(colours: Sequence[Colour]) -> Colour:
+        asked.append(colours)
+        return colours[-1]
+
+    draw_dots(pen, PALETTE, choose_colour=choose_last)
+
+    assert len(asked) == 100
+    assert {colour for _, _, colour in pen.dots} == {(20, 120, 60)}
+
+
+def test_draw_dots_raises_when_the_palette_is_empty() -> None:
+    with pytest.raises(ValueError, match="no colours"):
+        draw_dots(RecordingPen(), [])
+
+
+def _item_option(canvas: tkinter.Canvas, item: int, option: str) -> str:
+    """Return one option of a canvas item, such as its width or fill colour."""
+    # typeshed leaves Canvas.itemcget untyped, which strict mypy refuses to call.
+    return str(canvas.itemcget(item, option))  # type: ignore[no-untyped-call]
+
+
+def _drawn_dots(canvas: tkinter.Canvas) -> list[tuple[Position, str]]:
+    """Return the position and fill colour of every dot on the canvas.
+
+    Turtle draws a dot as a round-capped line whose width is the dot size.
+    """
+    dots: list[tuple[Position, str]] = []
+    for item in canvas.find_all():
+        is_dot = (
+            str(canvas.type(item)) == "line"
+            and _item_option(canvas, item, "width") == "20.0"
+        )
+        if is_dot:
+            x, y = canvas.coords(item)[:2]
+            dots.append(((round(x), -round(y)), _item_option(canvas, item, "fill")))
+    return dots
+
+
+def _other_lines(canvas: tkinter.Canvas) -> int:
+    """Count the line items that are not dots, such as a trail behind the pen."""
+    lines = [item for item in canvas.find_all() if str(canvas.type(item)) == "line"]
+    return len(lines) - len(_drawn_dots(canvas))
+
+
+def test_draw_dots_draws_100_dots_at_the_dot_positions_on_a_real_turtle(
+    screen: turtle.TurtleScreen, canvas: tkinter.Canvas
+) -> None:
+    screen.tracer(0)
+    pen = create_pen(screen)
+
+    draw_dots(pen, PALETTE)
+
+    positions = [position for position, _ in _drawn_dots(canvas)]
+    assert sorted(positions) == sorted(dot_positions())
+
+
+def test_draw_dots_colours_the_dots_of_a_real_turtle_from_the_palette(
+    screen: turtle.TurtleScreen, canvas: tkinter.Canvas
+) -> None:
+    screen.tracer(0)
+    pen = create_pen(screen)
+
+    draw_dots(pen, PALETTE)
+
+    palette_fills = {f"#{red:02x}{green:02x}{blue:02x}" for red, green, blue in PALETTE}
+    assert {fill for _, fill in _drawn_dots(canvas)} <= palette_fills
+
+
+def test_draw_dots_draws_no_trail_between_dots(
+    screen: turtle.TurtleScreen, canvas: tkinter.Canvas
+) -> None:
+    screen.tracer(0)
+    pen = create_pen(screen)
+    other_lines_before = _other_lines(canvas)
+
+    draw_dots(pen, PALETTE)
+
+    assert _other_lines(canvas) == other_lines_before
+
+
+@dataclass
+class MainRun:
+    """What happened during one run of main() on a fake screen."""
+
+    events: list[str] = field(default_factory=list)
+    palettes: list[Sequence[Colour]] = field(default_factory=list)
+    animation_while_drawing: list[int] = field(default_factory=list)
+
+
+@pytest.fixture
+def main_run(monkeypatch: pytest.MonkeyPatch, canvas: tkinter.Canvas) -> MainRun:
+    """Run main() once with drawing and the click wait replaced by recorders."""
+    run = MainRun()
+
+    class RecordingScreen(turtle.TurtleScreen):
+        def update(self) -> None:
+            run.events.append("update")
+
+        def exitonclick(self) -> None:
+            run.events.append("exitonclick")
+
+    screen = RecordingScreen(canvas)
+
+    def record_draw(pen: DotPen, palette: Sequence[Colour]) -> None:
+        run.events.append("draw_dots")
+        run.palettes.append(palette)
+        run.animation_while_drawing.append(screen.tracer())
+
+    monkeypatch.setattr(turtle, "Screen", lambda: screen)
+    monkeypatch.setattr(hirst_painting, "draw_dots", record_draw)
+    main()
+    return run
+
+
+def test_main_draws_with_the_palette_of_the_reference_image(
+    main_run: MainRun,
+) -> None:
+    assert main_run.palettes == [extract_palette(REFERENCE_IMAGE_PATH)]
+
+
+def test_main_turns_the_animation_off_while_drawing(main_run: MainRun) -> None:
+    assert main_run.animation_while_drawing == [0]
+
+
+def test_main_shows_the_painting_then_waits_for_a_click(main_run: MainRun) -> None:
+    assert main_run.events == ["draw_dots", "update", "exitonclick"]