svg2png-centered.py

# !/usr/bin/env python3
# Convert SVG files to centered PNGs of fixed size.
# Licensed under CC0-1.0
#
# Using resvg_py lib: https://github.com/baseplate-admin/resvg-py
# pip install resvg_py

import resvg_py
from pathlib import Path
import xml.etree.ElementTree as ET


WIDTH = 256
HEIGHT = 256
DIR = Path(__file__).parent
# DIR = Path(__file__).parent / "BLACK" / "SVG"


def _parse_length(value: str | None) -> float | None:
  if not value:
    return None
  for suffix in ("px", "pt", "cm", "mm", "in"):
    if value.endswith(suffix):
      value = value[: -len(suffix)]
      break
  try:
    return float(value)
  except ValueError:
    return None


def prepare_svg(svg_text: str) -> str:
  """Normalize SVG to have viewBox and target size for centered fit."""
  root = ET.fromstring(svg_text)

  view_box = root.attrib.get("viewBox") or root.attrib.get("viewbox")
  width_attr = root.attrib.get("width")
  height_attr = root.attrib.get("height")

  if view_box:
    parts = view_box.replace(",", " ").split()
    if len(parts) != 4:
      raise ValueError("Invalid viewBox format; expected four numbers.")
    try:
      # Validate numeric values even though we only need the attribute to exist.
      _ = list(map(float, parts))
    except ValueError as exc:
      raise ValueError("viewBox values must be numeric.") from exc
  else:
    vb_width = _parse_length(width_attr)
    vb_height = _parse_length(height_attr)
    if vb_width and vb_height:
      root.set("viewBox", f"0 0 {vb_width} {vb_height}")

  # If we still don't have geometry, bail out early.
  if not root.attrib.get("viewBox"):
    raise ValueError("SVG missing viewBox/width/height; cannot center content.")

  root.set("width", str(WIDTH))
  root.set("height", str(HEIGHT))
  if "preserveAspectRatio" not in root.attrib:
    root.set("preserveAspectRatio", "xMidYMid meet")

  return ET.tostring(root, encoding="unicode")



def convert_SVG2PNG_centered(svg_dir: Path) -> None:
  """Convert all SVG files in svg_dir to PNGs with the same basename."""
  if not svg_dir.is_dir():
    raise FileNotFoundError(f"Directory not found: {svg_dir}")

  for svg_path in sorted(svg_dir.glob("*.svg")):
    png_path = svg_path.with_suffix(".png")
    svg_text = svg_path.read_text(encoding="utf-8")
    prepared_svg = prepare_svg(svg_text)
    png_bytes: bytes = resvg_py.svg_to_bytes(
      svg_string=prepared_svg,
      width=WIDTH,
      height=HEIGHT,
      background=None,
    )
    png_path.write_bytes(png_bytes)
    print(f"Converted {svg_path.name} -> {png_path.name}")



if __name__ == "__main__":
  convert_SVG2PNG_centered(DIR)