Scale SVG images bigger

amateurfunk_anki.py

@@ -165,6 +165,23 @@ TECHNISCHE_SHORT_TITLE = "Technische Kenntnisse"
 # inside the package as a deck tree.
 TOPIC_SPLIT_CLASSES = frozenset({"E", "A"})
 
+# The catalog's figures come in two kinds: vector SVGs (the bulk; mostly
+# small — well under ~200 px) and a handful of raster PNGs (all 1024×685). We
+# enlarge only the SVGs: they scale crisply, they're the ones that read tiny
+# on a wide desktop card, and the PNGs are already at roughly the size we're
+# aiming for. The enlargement is `MEDIA_SCALE`× the native size, with
+# `MEDIA_MAX_WIDTH` × `MEDIA_MAX_HEIGHT` acting as an *enlargement ceiling* —
+# it bounds how far a below-cap figure may grow (a figure already at/above a
+# cap is left at native size; we never shrink). The ceiling is the PNGs'
+# ballpark (1024×768) so the largest SVG schematics (up to 635×481 px in the
+# 3rd edition: the NG20x block diagrams, EB309/EB310) grow to a comparable
+# size rather than staying cramped, while folding in native *height* still
+# stops tall-but-narrow figures from growing off the bottom of the card.
+# See `MediaRegistry.image_html`.
+MEDIA_SCALE = 2
+MEDIA_MAX_WIDTH = 1024
+MEDIA_MAX_HEIGHT = 768
+
 # Fallback build epoch if neither the manifest nor `--epoch` supplies
 # one. Picked as 0 so missing-metadata builds are still deterministic
 # and obviously wrong (timestamps would all show 1970).
@@ -837,6 +854,8 @@ class MediaRegistry:
         self.used_paths = set()
         # references that didn't resolve (recorded for diagnostics)
         self.missing = []
+        # Path → intrinsic (w, h) in px (memoised; None when unreadable)
+        self._size_cache = {}
         self._index_media_dir()
 
     def _index_media_dir(self):
@@ -878,12 +897,43 @@ class MediaRegistry:
         return None
 
     def image_html(self, reference):
-        """Return an `<img>` tag for `reference`, or `""` if unresolved."""
+        """Return an `<img>` tag for `reference`, or `""` if unresolved.
+
+        Most catalog SVGs carry small intrinsic dimensions, so on a wide
+        desktop card they render barely legible (a small fixed-px image
+        occupies only a sliver of the column; `max-width: 100%` only
+        ever shrinks, never enlarges). We raise the *preferred* width
+        via an explicit `width` attribute so the figure grows on every
+        viewport until the card's `max-width: 100%` cap engages.
+
+        Only SVGs are scaled — the catalog's PNGs are already large
+        (1024×685), so `_intrinsic_svg_size` returns `None` for them and
+        they fall through to native size. The enlargement factor is
+        `scale_for_size` — `MEDIA_SCALE`×, clamped at the
+        `MEDIA_MAX_WIDTH` × `MEDIA_MAX_HEIGHT` enlargement ceiling.
+        `height: auto` in the CSS keeps the aspect ratio. When the size
+        can't be read (non-SVG, or an unparseable SVG) we fall back to
+        native.
+        """
         path = self.resolve(reference)
         if path is None:
             return ""
         filename = html.escape(path.name, quote=True)
-        return f'<img src="{filename}" class="af-media">'
+        size = self._intrinsic_svg_size(path)
+        if size is None:
+            return f'<img src="{filename}" class="af-media">'
+        width, height = size
+        scale = scale_for_size(width, height)
+        if scale <= 1.0:
+            return f'<img src="{filename}" class="af-media">'
+        scaled = round(width * scale)
+        return f'<img src="{filename}" class="af-media" width="{scaled}">'
+
+    def _intrinsic_svg_size(self, path):
+        """Return the SVG's `(width, height)` in px (memoised; SVG only)."""
+        if path not in self._size_cache:
+            self._size_cache[path] = intrinsic_svg_size(path)
+        return self._size_cache[path]
 
 
 # ============================================================================
@@ -1110,6 +1160,74 @@ def media_bytes_for_package(path):
     return svg_with_white_background(text).encode("utf-8")
 
 
+def scale_for_size(width, height):
+    """Return the display scale for a figure of native `width`×`height`.
+
+    `MEDIA_SCALE`× for legibility, but never so much that the enlarged
+    figure would grow past the `MEDIA_MAX_WIDTH` / `MEDIA_MAX_HEIGHT`
+    ceiling, and never below 1.0 (we only ever enlarge, never shrink —
+    shrinking is the CSS `max-width`'s job). A figure already at/above
+    either cap yields exactly 1.0, i.e. "render at native size" — so a
+    native figure larger than the ceiling is left as-is, not shrunk.
+    """
+    if width <= 0 or height <= 0:
+        return 1.0
+    scale = min(
+        MEDIA_SCALE,
+        MEDIA_MAX_WIDTH / width,
+        MEDIA_MAX_HEIGHT / height,
+    )
+    return max(scale, 1.0)
+
+
+def _svg_dimension(svg_tag, name):
+    """Parse a `width`/`height` length (px or unitless) off an `<svg>` tag.
+
+    The numeric pattern is a well-formed decimal (`12`, `12.7`, `.5`) so
+    malformed values like `1.2.3` or a lone `.` simply don't match and
+    yield `None` rather than reaching `float()`. We still guard the
+    conversion with `try/except` so no parse can ever abort the build.
+    """
+    attr = re.search(
+        rf'\b{name}\s*=\s*"(\d+(?:\.\d+)?|\.\d+)\s*(?:px)?"',
+        svg_tag,
+        flags=re.IGNORECASE,
+    )
+    if not attr:
+        return None
+    try:
+        return float(attr.group(1))
+    except ValueError:
+        return None
+
+
+def intrinsic_svg_size(path):
+    """Return an SVG's intrinsic `(width, height)` in CSS px, or `None`.
+
+    Read from the `width`/`height` attributes on the root `<svg>` tag
+    (the catalog's SVGs use unitless user units, which map 1:1 to px).
+    Only `.svg` files are handled — we deliberately don't size raster
+    figures, because the catalog's PNGs are already large and only the
+    SVGs need enlarging. Anything we can't parse confidently — a non-SVG
+    file, a percentage dimension, a missing attribute — returns `None`
+    so the caller falls back to the image's native size.
+    """
+    if path.suffix.lower() != ".svg":
+        return None
+    try:
+        text = path.read_bytes().decode("utf-8-sig", errors="replace")
+    except OSError:
+        return None
+    match = re.search(r"<svg\b[^>]*>", text, flags=re.IGNORECASE)
+    if not match:
+        return None
+    width = _svg_dimension(match.group(0), "width")
+    height = _svg_dimension(match.group(0), "height")
+    if width is None or height is None:
+        return None
+    return (width, height)
+
+
 def svg_with_white_background(svg_text):
     """Inject a white background `<rect>` after the opening `<svg>`.