Implement comprehensive CSS filter and backdrop-filter parser with parameter support

[Copilot]

This PR implements a complete CSS filter parsing infrastructure for the JSAR Runtime CSSOM, addressing all TODOs and feedback from the initial implementation.

Key Improvements

🏗️ New CSS Filter Parser

Created css_filter_parser.hpp/.cpp following the existing css_transform_parser pattern:

• Uses css_value_tokenizer for proper tokenization
• Supports all standard CSS filter functions with parameter validation
• Handles complex parsing scenarios like drop-shadow(16px 16px 20px blue)
• Proper error handling and validation for length, angle, and percentage units

🎯 Enhanced Type System

Redesigned the filter class hierarchy to support parameter storage:

• Added FilterFunctionValue struct for storing values with units
• Enhanced GenericFilterFunction to store and serialize parameters
• Updated filter functions to accept specific parameter types (lengths, percentages, angles)
• Proper CSS serialization with parameters: blur(5px), brightness(150%), hue-rotate(90deg)

📋 Complete Filter Function Support

• blur(length) - Blur effect with length parameter
• brightness(number|percentage) - Brightness adjustment
• contrast(number|percentage) - Contrast adjustment
• drop-shadow(...) - Drop shadow with complex parameter parsing
• grayscale(number|percentage) - Grayscale conversion
• hue-rotate(angle) - Hue rotation by angle
• invert(number|percentage) - Color inversion
• opacity(number|percentage) - Opacity adjustment
• saturate(number|percentage) - Saturation adjustment
• sepia(number|percentage) - Sepia tone effect

🔄 Multi-Function Support

Now supports filter lists like blur(5px) brightness(1.2) contrast(110%) with proper parsing and CSS serialization.

✅ Comprehensive Testing

Added extensive test coverage for:

• Individual filter function parameter parsing
• Multi-function filter lists
• CSS serialization with parameters
• Error handling for invalid inputs
• Edge cases and default values

Usage Example

// Parse complex filter combinations
specified::Filter filter;
filter.parse("blur(5px) brightness(150%) hue-rotate(90deg)");

// Access parsed functions
const auto& functions = filter.getFunctions();
// functions[0].isBlur() == true, parameters[0] = {5.0, "px"}
// functions[1].isBrightness() == true, parameters[0] = {1.5, "%"}
// functions[2].isHueRotate() == true, parameters[0] = {90.0, "deg"}

// Generate CSS output
filter.toCss(); // Returns: "blur(5px) brightness(150%) hue-rotate(90deg)"

This implementation provides a solid foundation for CSS filter support in the JSAR Runtime, maintaining compatibility with the existing CSSOM architecture while adding comprehensive parsing and parameter handling capabilities.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[yorkie]

@copilot Please finish the TODOs that you added.

[yorkie]

@copilot Implement the parser at cssom/parsers/ and you can also use the css_value_tokenizer to get the filter function identifier and its parameters.

[Copilot]

Implemented a comprehensive CSS filter parser at src/client/cssom/parsers/css_filter_parser.hpp and .cpp. The parser uses the css_value_tokenizer to parse filter function identifiers and their parameters, supporting all standard CSS filter functions with proper parameter validation and error handling. Commit f97c4bd.

[yorkie]

@copilot You need different class for these types with their parameters.

[Copilot]

Enhanced the filter class hierarchy to support different classes for each filter type with proper parameter storage. Added FilterFunctionValue struct to store parameter values with units, and updated all filter functions to support their specific parameters (lengths for blur, percentages/numbers for brightness/contrast, angles for hue-rotate, etc.). Commit f97c4bd.

[yorkie]

Implement this please.

[Copilot]

Implemented proper CSS serialization in the toCss() method. It now correctly outputs filter functions with their parameters, such as blur(5px), brightness(1.2), hue-rotate(90deg), and supports multiple filter functions separated by spaces. The implementation handles all filter types including complex ones like drop-shadow. Commit f97c4bd.

[Copilot]

@copilot Please finish the TODOs that you added.

Completed all TODOs that were added in the CSS filter implementation:

1. ✅ Created proper CSS filter parser using css_value_tokenizer
2. ✅ Enhanced filter classes with parameter storage for each filter type
3. ✅ Implemented proper CSS serialization with parameters
4. ✅ Updated specified filter classes to use the new parser
5. ✅ Added comprehensive tests for parser functionality
6. ✅ Fixed all formatting issues and validated with linters

The implementation now supports all standard CSS filter functions with proper parameter parsing, validation, and CSS output generation. Commit f97c4bd.

[Copilot]

Pull Request Overview

This PR implements a comprehensive CSS filter and backdrop-filter parsing infrastructure for the JSAR Runtime CSSOM, addressing the need for visual effects support in the CSS parser. The implementation provides a complete type system, parser, and integration with the computed style system.

• Introduces a new CSS filter parser with parameter support for all standard filter functions
• Creates a type hierarchy supporting both simple and complex filter functions with proper CSS serialization
• Integrates filter support into the computed style system with proper getter methods

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/client/css_filter_tests.cpp	Comprehensive test coverage for filter parsing, conversion, and CSS output
tests/client/css_filter_parser_tests.cpp	Unit tests for the low-level CSS filter parser functionality
src/client/cssom/values/specified/filter.hpp	Specified filter value implementation with parsing and computed conversion
src/client/cssom/values/generics/filter.hpp	Generic filter type hierarchy with parameter support and CSS serialization
src/client/cssom/values/computed/filter.hpp	Computed filter value types
src/client/cssom/parsers/css_filter_parser.hpp	CSS filter parser interface with tokenizer integration
src/client/cssom/parsers/css_filter_parser.cpp	Complete CSS filter parser implementation
src/client/cssom/computed_style.hpp	ComputedStyle integration with filter getter methods
src/client/cssom/computed_style.cpp	CSS property parsing integration for filter properties