docs: add teaching examples and video project

show/video/tex_environment.py

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+"""Use system TeX Live, or an explicitly configured local unpacked installation."""
+from pathlib import Path
+import os
+import shutil
+import subprocess
+
+HERE = Path(__file__).resolve().parent
+
+
+def prepare_tex(env):
+    env = dict(env)
+    if shutil.which('latex', path=env['PATH']) and shutil.which('dvisvgm', path=env['PATH']):
+        return env
+    root = Path(env.get('SLIME_TEX_ROOT', HERE / '.native/texlive')).resolve()
+    if not (root/'usr/bin/pdftex').is_file():
+        raise RuntimeError('需要 LaTeX / dvisvgm。Ubuntu: sudo apt install texlive-latex-extra dvisvgm')
+    dist = root/'usr/share/texlive/texmf-dist'
+    formats = root/'formats'
+    formats.mkdir(exist_ok=True)
+    env.update({
+        'PATH': str(root/'usr/bin')+os.pathsep+env['PATH'],
+        'LD_LIBRARY_PATH': str(root/'usr/lib/x86_64-linux-gnu')+os.pathsep+env.get('LD_LIBRARY_PATH', ''),
+        'TEXMFCNF': str(dist/'web2c'),
+        'TEXMFROOT': str(root/'usr/share/texlive'),
+        'TEXMFDIST': str(dist),
+        'TEXMF': '{'+str(dist)+','+str(root/'usr/share/texmf')+'}',
+        'TEXMFVAR': str(root/'var'),
+        'TEXMFCONFIG': str(root/'config'),
+        'TEXMFHOME': str(root/'texmf-home'),
+        'TEXFORMATS': str(formats)+'//:',
+    })
+    gs_roots = sorted((root/'usr/share/ghostscript').glob('*'))
+    if gs_roots:
+        gs = gs_roots[-1]
+        env['GS_LIB'] = os.pathsep.join(str(p) for p in (
+            gs/'Resource/Init', gs/'lib', gs/'Resource/Font',
+            root/'usr/share/fonts/type1/urw-base35'))
+    if not (formats/'latex.fmt').is_file():
+        subprocess.run(['mktexlsr', str(dist), str(root/'usr/share/texmf')], env=env, check=True)
+        subprocess.run(['pdftex', '-ini', '-etex', '-interaction=nonstopmode', '-halt-on-error',
+                        '-jobname=latex', '-progname=latex', 'latex.ini'],
+                       cwd=formats, env=env, check=True)
+    return env