Web · Pro
Build a Browser Rendering Engine
Parse a subset of HTML and CSS into a DOM and style tree, lay it out with the box model, and paint the resulting boxes to a bitmap.
You build the core of a browser rendering engine: an HTML parser that produces a DOM tree, a CSS parser and a selector matcher that builds a styled tree, a layout engine that computes box positions and sizes using the block box model, and a painter that rasterizes those boxes to an image. It is worth building because the browser is the most complex piece of software most engineers use daily yet treat as a black box, and re-implementing even a slice of it demystifies how markup and stylesheets become pixels. It is resume-defining for frontend and full-stack engineers because it replaces hand-wavy knowledge of the cascade and the box model with implementation-level understanding of specificity, inheritance, and layout. You finish able to explain precisely why a `display`, `margin`, or `width` value renders the way it does.
What you build
- HTML parser that builds a DOM node tree
- CSS parser producing stylesheets of selectors and declarations
- Selector matching with specificity to assemble a style tree
- Block-layout engine computing box dimensions and positions
- Box model handling of content, padding, border, and margin
- Painter that rasterizes the layout tree into a bitmap or canvas
- Outputs a rendered PNG of a sample HTML and CSS document
What it teaches
- HTML and CSS parsing into trees
- The CSS cascade, specificity, and inheritance
- The box model and block layout algorithm
- Tree transformations from DOM to render output
- Rasterization and painting
- How a browser turns source into pixels
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Take it further
- Add inline layout and text flow with line boxes.
- Support more CSS such as flexbox or positioned elements.
- Build an interactive viewer that re-renders on input changes.
