Instruction file imported from twardoch/qlith (.cursor/rules/layout-engine-algorithms.mdc). Copyright stays with the author.

description: Specification for core HTML/CSS layout engine algorithms and rendering business logic globs: /src/render_.cpp,/src/layout_.cpp,/src/css_.cpp,/flex_.cpp,*/table.cpp alwaysApply: false

layout-engine-algorithms

The layout engine implements several key business-specific algorithms:

1. Block Formatting Context (external/litehtml/src/render_block.cpp)

• Margin collapsing engine with hierarchical margin calculation
• Float positioning system with collision detection
• Block size computation considering containing blocks
• Anonymous block box generation for mixed inline/block content

2. Flex Layout System (external/litehtml/src/render_flex.cpp)

• Main/cross axis space distribution algorithm
• Flex factor normalization (multiplied by 1000) for precise distribution
• Baseline alignment calculations for flex lines
• Flex shrink/grow calculations with min/max constraints

3. Table Layout Engine (external/litehtml/src/render_table.cpp)

• Grid cell size distribution algorithm:
  • Fixed width columns
  • Percentage width columns
  • Auto width columns
• Border collapse model with specific cell overlap rules
• Row height distribution with vertical alignment

4. Inline Context Processor (external/litehtml/src/render_inline_context.cpp)

• Line box management with vertical rhythm
• Whitespace collapsing per CSS white-space property
• Text indentation and list marker positioning
• Float interference calculation for line boxes

5. Text Layout System

• Text run segmentation with support for:
  • CJK character boundaries
  • Forced line breaks
  • Soft hyphens
  • Word boundaries
• Justification space distribution

6. Box Model Implementation

• Margin auto calculation for centering
• Border radius clipping for backgrounds
• Box shadow rendering with spread and blur
• Relative/absolute positioning offsets

The layout engine focuses on implementing CSS visual formatting models while handling complex interactions between positioning schemes, floats, and formatting contexts.

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