docs/screenshots/generate_screenshots.py

@@ -1,86 +1,76 @@
-"""Render the real output of each lecture step to a PNG file.
-
-Dev-only tool (needs Pillow, installed by `pip install -e ".[dev]"`). It runs
-each command, captures its output and draws it as a terminal image, so no
-screen is captured and the desktop is never touched.
-
-Usage, from the project root:  python docs/screenshots/generate_screenshots.py
-"""
-
-import subprocess
-import sys
-from pathlib import Path
-
-from PIL import Image, ImageDraw, ImageFont
-
-OUTPUT_DIR = Path(__file__).resolve().parent
-ROOT = OUTPUT_DIR.parent.parent
-PYTHON = "python"
-
-# (file name, command shown in the prompt, arguments run after the interpreter)
-SHOTS = [
-    (
-        "step-1-current-time.png",
-        "python -m speed_calc.lecture_steps 1",
-        ["-m", "speed_calc.lecture_steps", "1"],
-    ),
-    (
-        "step-2-decorator-skeleton.png",
-        "python -m speed_calc.lecture_steps 2",
-        ["-m", "speed_calc.lecture_steps", "2"],
-    ),
-    (
-        "step-3-timing-wrapper.png",
-        "python -m speed_calc.lecture_steps 3",
-        ["-m", "speed_calc.lecture_steps", "3"],
-    ),
-    ("step-4-fast-vs-slow.png", "python -m speed_calc", ["-m", "speed_calc"]),
-]
-
-BACKGROUND, FOREGROUND, PROMPT = "#1e1e2e", "#cdd6f4", "#a6e3a1"
-FONT_CANDIDATES = [
-    "C:/Windows/Fonts/consola.ttf",
-    "/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf",
-    "/System/Library/Fonts/Menlo.ttc",
-]
-
-
-def load_font(size: int) -> ImageFont.ImageFont:
-    for candidate in FONT_CANDIDATES:
-        if Path(candidate).exists():
-            return ImageFont.truetype(candidate, size)
-    return ImageFont.load_default()
-
-
-def run(arguments: list[str]) -> str:
-    done = subprocess.run(
-        [sys.executable, *arguments],
-        cwd=ROOT,
-        capture_output=True,
-        text=True,
-        check=True,
-    )
-    return done.stdout.strip()
-
-
-def render(path: Path, command: str, output: str) -> None:
-    font = load_font(20)
-    lines = [f"$ {command}", *output.splitlines()]
-    width = int(max(font.getlength(line) for line in lines)) + 48
-    height = 28 * len(lines) + 48
-    image = Image.new("RGB", (max(width, 640), height), BACKGROUND)
-    draw = ImageDraw.Draw(image)
-    for index, line in enumerate(lines):
-        colour = PROMPT if index == 0 else FOREGROUND
-        draw.text((24, 24 + 28 * index), line, font=font, fill=colour)
-    image.save(path)
-
-
-def main() -> None:
-    for name, command, arguments in SHOTS:
-        render(OUTPUT_DIR / name, command, run(arguments))
-        print("wrote", name)
-
-
-if __name__ == "__main__":
-    main()
+"""Render the real output of each lecture step to a PNG file.
+
+Dev-only tool (needs Pillow, installed by `pip install -e ".[dev]"`). It runs
+each step in-process, captures its output and draws it as a terminal image, so no
+screen is captured and the desktop is never touched.
+
+Usage, from the project root:  python docs/screenshots/generate_screenshots.py
+"""
+
+import contextlib
+import io
+from pathlib import Path
+
+from PIL import Image, ImageDraw, ImageFont
+
+from speed_calc.__main__ import main as speed_calc_main
+from speed_calc.lecture_steps import main as lecture_steps_main
+
+OUTPUT_DIR = Path(__file__).resolve().parent
+ROOT = OUTPUT_DIR.parent.parent
+
+# (file name, command shown in the prompt, lecture step to run; None = the program)
+SHOTS = [
+    ("step-1-current-time.png", "python -m speed_calc.lecture_steps 1", ["1"]),
+    ("step-2-decorator-skeleton.png", "python -m speed_calc.lecture_steps 2", ["2"]),
+    ("step-3-timing-wrapper.png", "python -m speed_calc.lecture_steps 3", ["3"]),
+    ("step-4-fast-vs-slow.png", "python -m speed_calc", None),
+]
+
+BACKGROUND, FOREGROUND, PROMPT = "#1e1e2e", "#cdd6f4", "#a6e3a1"
+FONT_CANDIDATES = [
+    "C:/Windows/Fonts/consola.ttf",
+    "/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf",
+    "/System/Library/Fonts/Menlo.ttc",
+]
+
+
+def load_font(size: int) -> ImageFont.FreeTypeFont | ImageFont.ImageFont:
+    for candidate in FONT_CANDIDATES:
+        if Path(candidate).exists():
+            return ImageFont.truetype(candidate, size)
+    return ImageFont.load_default()
+
+
+def run(step: list[str] | None) -> str:
+    """Run a step in this process and return what it printed."""
+    buffer = io.StringIO()
+    with contextlib.redirect_stdout(buffer):
+        if step is None:
+            speed_calc_main()
+        else:
+            lecture_steps_main(step)
+    return buffer.getvalue().strip()
+
+
+def render(path: Path, command: str, output: str) -> None:
+    font = load_font(20)
+    lines = [f"$ {command}", *output.splitlines()]
+    width = int(max(font.getlength(line) for line in lines)) + 48
+    height = 28 * len(lines) + 48
+    image = Image.new("RGB", (max(width, 640), height), BACKGROUND)
+    draw = ImageDraw.Draw(image)
+    for index, line in enumerate(lines):
+        colour = PROMPT if index == 0 else FOREGROUND
+        draw.text((24, 24 + 28 * index), line, font=font, fill=colour)
+    image.save(path)
+
+
+def main() -> None:
+    for name, command, step in SHOTS:
+        render(OUTPUT_DIR / name, command, run(step))
+        print("wrote", name)
+
+
+if __name__ == "__main__":
+    main()