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← From Beginner to Expert in Fundamentals of Frontend

The Rendering Engine: Layout, Paint, Compositing

20 min read
BlinkWebKitReflowRepaintCompositingGPU Accelerationwill-change

Inside the Rendering Engine

After the Render Tree is built: Layout → Paint → Composite turns it into pixels.

Layout (Reflow)

Calculates exact size and position. Changing one element can affect children, siblings, and parents. Triggered by: width, height, margin, padding, font-size, window resize.

Paint

Fills visual details: backgrounds, borders, text, shadows. Operations are per-layer.

Compositing

GPU assembles painted layers. Elements with transform, opacity, will-change get their own compositor layer.

The 60fps Budget

60fps = 16.67ms per frame for: JavaScript → Style → Layout → Paint → Composite

Rendering Engines

EngineBrowser
BlinkChrome, Edge, Opera
WebKitSafari (all iOS browsers)
GeckoFirefox

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