Add support for font features and variants

[mattt]

This PR adds support for OpenType Font features and font variants using Pango markup attributes.

For example, with the changes in this PR, I can now render proportional and tabular numerals:

Proportional figures (pnum=1; default)

Tabular / monospaced figures (tnum=1)

[mattt]

Here's an script you can use to generate example outputs:

#!/usr/bin/env python3
"""
Focused test for numeral OpenType features in ManimPango.
"""

import manimpango
import os


def test_numeral_features():
    """Test various numeral-related OpenType features."""
    print("=== Testing Numeral Features ===")
    
    # Text with numbers that should show differences
    numeral_text = "0123456789"
    mixed_text = "Price: $1,234.56 (March 2023)"
    
    numeral_features = {
        "default": None,
        "oldstyle": "onum=1",  # Old-style/text figures
        "lining": "lnum=1",    # Lining figures
        "tabular": "tnum=1",   # Tabular (monospaced) figures
        "proportional": "pnum=1",  # Proportional figures
        "tabular_oldstyle": "tnum=1, onum=1",
        "tabular_lining": "tnum=1, lnum=1"
    }
    
    # Test fonts that are more likely to support numeral features
    fonts_to_test = [
        "Times New Roman",
        "Georgia",
        "SF Pro Text",
        "Avenir",
    ]
    
    for font in fonts_to_test:
        print(f"\nTesting font: {font}")
        
        for feature_name, features in numeral_features.items():
            try:
                filename = f"numerals_{font.replace(' ', '_').lower()}_{feature_name}.svg"
                
                result = manimpango.MarkupUtils.text2svg(
                    text=mixed_text,
                    font=font,
                    slant="NORMAL",
                    weight="NORMAL",
                    size=48,  # Large size to see differences clearly
                    _=None,
                    disable_liga=False,
                    file_name=filename,
                    START_X=10,
                    START_Y=60,
                    width=800,
                    height=100,
                    font_features=features
                )
                print(f"  ✓ Created: {filename} ({feature_name})")
                
            except Exception as e:
                print(f"  ✗ Error with {feature_name}: {e}")
                
        # Also test pure numbers
        try:
            filename = f"pure_numbers_{font.replace(' ', '_').lower()}.svg"
            result = manimpango.MarkupUtils.text2svg(
                text=numeral_text,
                font=font,
                slant="NORMAL",
                weight="NORMAL",
                size=64,
                _=None,
                disable_liga=False,
                file_name=filename,
                START_X=10,
                START_Y=80,
                width=600,
                height=120,
                font_features="onum=1"  # Test old-style figures
            )
            print(f"  ✓ Created: {filename} (pure numbers with onum)")
        except Exception as e:
            print(f"  ✗ Error with pure numbers: {e}")


def compare_numeral_files():
    """Compare file sizes and content for numeral features."""
    print("\n=== Comparing Numeral Files ===")
    
    # Get all numerals files
    numeral_files = [f for f in os.listdir(".") if f.startswith("numerals_") and f.endswith(".svg")]
    
    if not numeral_files:
        print("No numeral files found to compare")
        return
    
    # Group by font
    fonts = {}
    for f in numeral_files:
        parts = f.split("_")
        if len(parts) >= 3:
            font_key = "_".join(parts[1:-1])  # everything except 'numerals' and feature name
            if font_key not in fonts:
                fonts[font_key] = {}
            feature = parts[-1].replace(".svg", "")
            fonts[font_key][feature] = f
    
    for font, files in fonts.items():
        print(f"\nFont: {font}")
        
        # Compare file sizes
        file_sizes = {}
        for feature, filename in files.items():
            try:
                size = os.path.getsize(filename)
                file_sizes[feature] = size
                print(f"  {feature}: {size} bytes")
            except:
                print(f"  {feature}: file not found")
        
        # Look for size differences (indicating different rendering)
        if len(file_sizes) > 1:
            sizes = list(file_sizes.values())
            if len(set(sizes)) > 1:
                print(f"  ✓ Size differences detected - features may be working!")
            else:
                print(f"  ? All files same size - features may not be working")


def test_markup_numerals():
    """Test numeral features using markup."""
    print("\n=== Testing Numerals in Markup ===")
    
    markup_tests = [
        ("Default numbers", "Numbers: 0123456789"),
        ("Old-style figures", "<span font_features='onum=1'>Numbers: 0123456789</span>"),
        ("Tabular figures", "<span font_features='tnum=1'>123.45  678.90  234.56</span>"),
        ("Combined features", "<span font_features='onum=1, tnum=1'>Old+Tab: 0123456789</span>"),
    ]
    
    for name, markup in markup_tests:
        try:
            # Validate markup first
            error = manimpango.MarkupUtils.validate(markup)
            if error:
                print(f"✗ Markup error for '{name}': {error}")
                continue
            
            filename = f"markup_numerals_{name.replace(' ', '_').replace('+', '_').lower()}.svg"
            result = manimpango.MarkupUtils.text2svg(
                text=markup,
                font="Times New Roman",
                slant="NORMAL",
                weight="NORMAL",
                size=36,
                _=None,
                disable_liga=False,
                file_name=filename,
                START_X=10,
                START_Y=50,
                width=600,
                height=80
            )
            print(f"✓ Created: {filename} ({name})")
            
        except Exception as e:
            print(f"✗ Error with '{name}': {e}")


def analyze_svg_numerals():
    """Analyze SVG content specifically for numeral differences."""
    print("\n=== Analyzing SVG Numeral Content ===")
    
    # Find files to compare
    default_file = None
    onum_file = None
    
    for f in os.listdir("."):
        if "numerals_times_new_roman_default.svg" in f:
            default_file = f
        elif "numerals_times_new_roman_oldstyle.svg" in f:
            onum_file = f
    
    if default_file and onum_file:
        try:
            with open(default_file, 'r') as f:
                default_content = f.read()
            with open(onum_file, 'r') as f:
                onum_content = f.read()
            
            # Look for differences in glyph usage
            default_glyphs = set()
            onum_glyphs = set()
            
            # Extract glyph references
            import re
            glyph_pattern = r'xlink:href="#glyph-\d+-(\d+)"'
            
            default_matches = re.findall(glyph_pattern, default_content)
            onum_matches = re.findall(glyph_pattern, onum_content)
            
            print(f"Default file glyphs used: {sorted(set(default_matches))}")
            print(f"Old-style file glyphs used: {sorted(set(onum_matches))}")
            
            if set(default_matches) != set(onum_matches):
                print("✓ Different glyphs used - numeral features are working!")
            else:
                print("? Same glyphs used - numeral features may not be working")
                
            # Check file sizes
            default_size = len(default_content)
            onum_size = len(onum_content)
            print(f"File sizes: default={default_size}, oldstyle={onum_size}")
            
        except Exception as e:
            print(f"Error analyzing files: {e}")
    else:
        print("Could not find both default and oldstyle files to compare")


def main():
    """Run all numeral tests."""
    print("ManimPango Numeral Features Test")
    print("=" * 40)
    
    try:
        test_numeral_features()
        test_markup_numerals()
        compare_numeral_files()
        analyze_svg_numerals()
        
        print("\n" + "=" * 40)
        print("Numeral test completed!")
        print("Check the generated SVG files to see numeral differences.")
        print("Look for files with 'oldstyle', 'tabular' variations.")
        
    except Exception as e:
        print(f"\nError running numeral tests: {e}")


if __name__ == "__main__":
    main()

[naveen521kk]

Hi @matt, Thanks for your contribution. I'll take a look at this PR later today.

[naveen521kk]

Hi, sorry for the late review. I thought I already reviewed it, and it looks like I've forgotten 😅

I've some questions, please answer and I'll merge these changes and create a new release.

[naveen521kk]

Q: Is this function used anywhere, or are we exposing it as an API?

[naveen521kk]

Q: Are we using this anywhere? Or is it a new API? If it's a new API, I don't see the use of this one much; the validate method itself should suffice this need.