feat: serve platform logos as 80 px webp

Shown at 40 px, the 96 px PNG logos were 136 KiB of the home page. WebP at twice the display size is 27 KiB for the twelve raster marks. SVG stays as each project publishes it.

scripts/fetch_site_images.py

@@ -8,8 +8,9 @@ into ``docs_assets/logos/`` and ``docs_assets/system-icons/``, which are
 committed, and records where each came from in a ``sources.json`` beside
 them. The site build only reads those copies (``sitediagrams.localize_images``).
 
-Raster images are normalised to a square PNG (96 px for logos, 48 px for
-system icons) so every tile has the same weight, and SVG is kept as published.
+Raster logos are normalised to an 80 px square WebP, twice the 40 px they
+are shown at, and system icons to a 48 px PNG, so every tile has the same
+weight. SVG is kept as published.
 Normalising needs Pillow. This is a maintenance tool run by hand when a
 logo changes, not a build step: the build stays on the standard library
 and PyYAML.
@@ -36,7 +37,7 @@ sys.path.insert(0, str(ROOT / "scripts"))
 
 LOGO_DIR = ROOT / "docs_assets" / "logos"
 ICON_DIR = ROOT / "docs_assets" / "system-icons"
-LOGO_SIZE = 96
+LOGO_SIZE = 80
 ICON_SIZE = 48
 AVATAR_HOST = "avatars.githubusercontent.com"
 USER_AGENT = "retrobios-site-images"
@@ -47,7 +48,7 @@ def fetch(url: str) -> bytes:
         return response.read()
 
 
-def square_png(data: bytes, size: int) -> bytes:
+def square_image(data: bytes, size: int, kind: str = "PNG") -> bytes:
     try:
         from PIL import Image
     except ImportError as exc:
@@ -57,7 +58,11 @@ def square_png(data: bytes, size: int) -> bytes:
     tile = Image.new("RGBA", (size, size), (0, 0, 0, 0))
     tile.paste(image, ((size - image.width) // 2, (size - image.height) // 2), image)
     out = io.BytesIO()
-    tile.save(out, "PNG", optimize=True)
+    if kind == "WEBP":
+        # Quality 90: half the bytes of lossless, edges still clean at 40 px.
+        tile.save(out, "WEBP", quality=90, method=6)
+    else:
+        tile.save(out, "PNG", optimize=True)
     return out.getvalue()
 
 
@@ -98,7 +103,7 @@ def fetch_logos() -> None:
         if is_svg(data):
             file_name, payload = f"{name}.svg", safe_svg(data, url)
         else:
-            file_name, payload = f"{name}.png", square_png(data, LOGO_SIZE)
+            file_name, payload = f"{name}.webp", square_image(data, LOGO_SIZE, "WEBP")
         for stale in LOGO_DIR.glob(f"{name}.*"):
             if stale.name != file_name:
                 stale.unlink()
@@ -141,7 +146,7 @@ def fetch_icons() -> None:
                 continue
             raise
         file_name = f"{name}.png"
-        (ICON_DIR / file_name).write_bytes(square_png(data, ICON_SIZE))
+        (ICON_DIR / file_name).write_bytes(square_image(data, ICON_SIZE))
         entries.append({"file": file_name, "source": url})
         print(f"  {file_name}")
     write_manifest(