Layout Engine & Chromium Parity

Strata's layout engine (strata_layout) is a ground-up, pure-Rust implementation of the W3C CSS specifications. It achieves subpixel layout parity with Chromium's Blink engine without running a single line of C++ or JavaScript.

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Supported W3C Specifications

1. CSS Box Model

• Box Sizing: Full support for box-sizing: border-box (default) and content-box.
• Margin Collapsing: Accurate implementation of vertical margin collapsing between adjacent siblings, parent-child margins, and empty blocks.
• Percentages & Auto: Correct circular percentage resolution for margins, padding, and min/max constraints against containing blocks.

2. CSS Flexible Box Layout (Level 1)

• Flex Directions: row, row-reverse, column, column-reverse.
• Multi-Line Flex Wrapping: flex-wrap: wrap | wrap-reverse | nowrap with cross-axis line distribution.
• Main Axis Alignment: justify-content: flex-start | flex-end | center | space-between | space-around | space-evenly.
• Cross Axis Alignment: align-items and align-self: stretch | flex-start | flex-end | center | baseline.
• Flex Factors: Accurate iterative distribution of positive flexibility (flex-grow) and negative flexibility (flex-shrink) with min/max constraint clamping.

3. CSS Grid Layout (Level 2)

• Track Sizing: Fixed pixel sizes (px), percentages (%), auto-sizing (auto), and flexible fractional units (fr).
• Dynamic Track Sizing: minmax(min, max), fit-content(limit).
• Grid Placement: Named grid lines, grid template areas (grid-template-areas), spanning (span N).
• Auto Placement Algorithm: Dense vs. sparse packing with automatic implicit grid generation.
• Subgrid (Level 2): Inherited track definitions for nested child grids.

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Subpixel Coordinate Precision

Web browsers often suffer from 1-pixel rounding errors (visual seams, blurry text, or jitter during smooth animations) due to premature coordinate rounding.

Strata computes all layout positions and dimensions using 32-bit floating-point numbers (f32):

1. Layout Space: Measured in abstract CSS Points (1/96th inch).
2. Device Scale Factor (DPI): Layout coordinates are multiplied by the physical display scale factor (e.g., 2.0x for Retina, 1.5x for Windows 4K).
3. Hardware Quantization: Rasterization boundaries are snapped to physical device subpixels during the display list generation pass, guaranteeing crisp hairline borders and zero subpixel text blurring.

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High-Throughput Text Shaping

Text measurement is integrated directly into the layout pass using HarfBuzz-grade shaping algorithms:

• Kerning & Ligatures: Advanced OpenType glyph substitution and positioning.
• Multi-Line Breaking: Unicode Standard Annex #14 line breaking algorithm.
• Ellipsis & Truncation: Configurable text truncation (text-overflow: ellipsis) with zero layout reflows.
• Baseline Alignment: Inline flex and grid items align accurately along their typographic baselines across mixed font families and sizes.