Resize SVG; via viewbox and corresponding transform element wrap

svg_transform_resizer.py

import xml.etree.ElementTree as ET
import argparse
import sys

def resize_svg(input_file, width=None, height=None):
    """
    Resize an SVG by wrapping its contents in a transform that scales to new dimensions
    while preserving aspect ratio.
    
    Args:
        input_file (str): Path to input SVG file
        width (float, optional): Desired width
        height (float, optional): Desired height
        
    Returns:
        str: Modified SVG content as string
    """
    # Parse the SVG file
    tree = ET.parse(input_file)
    root = tree.getroot()
    
    # Get the viewBox attribute
    viewbox = root.get('viewBox')
    if not viewbox:
        raise ValueError("SVG must have a viewBox attribute")
    
    # Parse viewBox values
    vb_min_x, vb_min_y, vb_width, vb_height = map(float, viewbox.split())
    
    # Calculate actual width and height accounting for negative origins
    orig_width = abs(vb_width)
    orig_height = abs(vb_height)
    
    # If only one dimension is provided, use it for both
    if width is None and height is None:
        raise ValueError("At least one of width or height must be specified")
    elif width is None:
        width = height
    elif height is None:
        height = width
    
    # Calculate scale factors
    scale_x = width / orig_width
    scale_y = height / orig_height
    
    # Create a new root element with the new dimensions
    new_root = ET.Element('svg')
    new_root.set('xmlns', 'http://www.w3.org/2000/svg')
    new_root.set('width', str(width))
    new_root.set('height', str(height))
    
    # Calculate new viewBox values
    new_vb_width = width
    new_vb_height = height
    new_vb_min_x = vb_min_x * scale_x
    new_vb_min_y = vb_min_y * scale_y
    new_root.set('viewBox', f"{new_vb_min_x} {new_vb_min_y} {new_vb_width} {new_vb_height}")
    
    # Create a group to hold the transformed content
    group = ET.SubElement(new_root, 'g')
    group.set('transform', f'scale({scale_x} {scale_y})')
    
    # Move all original content to the transformed group
    for child in list(root):
        group.append(child)
    
    # Convert to string
    return ET.tostring(new_root, encoding='unicode')

def main():
    # Using add_help=False to avoid conflict with -h argument
    parser = argparse.ArgumentParser(description="Resize SVG file.", add_help=False)
    parser.add_argument("input_file", help="Input SVG file")
    parser.add_argument("-w", "--width", type=float, help="New width")
    parser.add_argument("-t", "--height", type=float, help="New height")  # Using -t instead of -h
    parser.add_argument("-o", "--output", default="-", help="Output file (default: stdout)")
    parser.add_argument("--help", action="help", help="Show this help message")
    
    args = parser.parse_args()
    
    try:
        resized_svg = resize_svg(args.input_file, args.width, args.height)
        
        if args.output == "-":
            print(resized_svg)
        else:
            with open(args.output, "w") as f:
                f.write(resized_svg)
            print(f"Successfully resized SVG to {args.width}x{args.height}")
            
    except Exception as e:
        print(f"Error: {e}", file=sys.stderr)
        sys.exit(1)

if __name__ == "__main__":
    main()