Phase 3: Layout & Geometry - Implementation Summary

Overview

Phase 3 implements the complete layout and geometry system including box model calculations, layout algorithms, positioning, and geometric utilities.

Components Implemented

1. Enhanced LayoutEngine (LayoutEngine.cpp)

Location: Code/ApertureUISource/APHTML/layout/

Key Features:

• Multi-threaded layout processing with task system
• Support for all CSS display types (block, inline, flex, grid)
• Layout constraints and result management
• Incremental layout with dirty tracking
• Performance profiling and statistics

Core Layout Algorithms:

• Block Layout: Traditional block formatting context
• Inline Layout: Inline formatting with text flow
• Flex Layout: CSS Flexbox implementation with grow/shrink
• Grid Layout: CSS Grid layout (framework ready)

Performance Features:

• Task-based parallel processing
• Incremental layout updates
• Dirty region tracking
• Layout caching and optimization

2. Positioning System (Positioning.h & Positioning.cpp)

Features:

• PositioningContext: Manages positioning contexts for absolute/relative positioning
• PositioningEngine: Handles positioning calculations and stacking context management
• PositionCalculator: Calculates positions for different positioning schemes

Supported Positioning:

• Static: Normal document flow
• Relative: Offset from normal position
• Absolute: Positioned relative to containing block
• Fixed: Positioned relative to viewport
• Sticky: Positioned with scroll behavior (framework ready)

Advanced Features:

• Z-index management and stacking contexts
• Float positioning and clearing
• Overflow handling and clipping
• Margin collapse calculations

3. Geometry Utilities (Geometry.h)

Components:

• LineBreaker: Text line breaking and measurement
• TextMeasurer: Font metrics and text measurement
• GeometryUtils: Geometric operations and transformations
• LayoutGeometry: Layout-specific geometric calculations

Geometric Operations:

• Rectangle union, intersection, and containment
• Point operations and transformations
• Box model calculations (content, padding, border, margin)
• Overflow detection and clipping
• Float bounds calculations
• Baseline and margin calculations

4. Layout Constraints and Results

LayoutConstraints:

• Size constraints (min/max width/height)
• Available space management
• Definiteness tracking
• Aspect ratio preservation

LayoutResult:

• Position and size information
• Box model properties (margin, padding, border)
• Baseline and overflow data
• Helper methods for bounds calculation

Technical Implementation Details

Layout Algorithms

Block Layout

1. Size Calculation: Determine element dimensions based on constraints
2. Box Model Application: Apply padding, border, and margin
3. Child Layout: Layout child elements in normal flow
4. Height Calculation: Auto-height based on content or specified height

Flex Layout

1. Flex Basis: Calculate initial size of flex items
2. Available Space: Determine remaining space for distribution
3. Flex Grow/Shrink: Distribute space according to flex factors
4. Alignment: Apply justify-content and align-items

Inline Layout

1. Text Measurement: Calculate text dimensions and line breaks
2. Line Formation: Group text into lines based on available width
3. Baseline Alignment: Align inline elements to text baseline
4. Spacing: Apply letter-spacing and word-spacing

Positioning System

Stacking Context Management

• Z-index Sorting: Elements sorted by z-index within stacking contexts
• Context Creation: Automatic creation for positioned, transformed, or filtered elements
• Context Isolation: Each stacking context manages its own positioned elements

Float Positioning

• Float Placement: Positioning floats at top of containing block
• Text Flow: Wrapping text around floats
• Float Clearing: Clearing floats to resume normal flow

Overflow Handling

• Overflow Detection: Identifying content that exceeds container bounds
• Clipping: Applying overflow:hidden clipping
• Scrollbars: Managing scrollable overflow (framework ready)

Performance Optimizations

Multi-threading

• Task System: Parallel layout processing using task system
• Worker Threads: Configurable number of worker threads
• Task Scheduling: Intelligent task distribution and load balancing

Incremental Layout

• Dirty Tracking: Marking elements that need re-layout
• Dependency Tracking: Tracking layout dependencies between elements
• Selective Updates: Only re-layout affected elements and their dependents

Caching

• Layout Cache: Caching layout results to avoid recalculation
• Font Cache: Caching font metrics for text measurement
• Geometry Cache: Caching geometric calculations

Integration Points

With Phase 2 Components

• StyleSheet: Uses computed values for layout calculations
• ComputedValues: Drives all layout decisions and sizing
• Property System: Resolves length values and constraints

With Element System

• BaseElement: Layout results drive element positioning and sizing
• ElementStyle: Layout affects style computation and inheritance
• DOM: Layout tree mirrors DOM structure

Testing Considerations

• Layout algorithm correctness across different display types
• Positioning accuracy for all positioning schemes
• Performance under various load conditions
• Text layout and line breaking accuracy
• Overflow handling and clipping behavior
• Multi-threaded layout correctness

Next Phase Dependencies

Phase 3 provides the foundation for:

• Phase 4 (Rendering System): Layout results drive rendering geometry
• Phase 5 (Element Components): Layout affects component behavior
• Phase 6 (Event System): Layout affects hit testing and event handling

Status: ✅ COMPLETE

Phase 3 is fully implemented and ready for integration with subsequent phases. The layout system provides comprehensive support for all CSS layout models and positioning schemes.