A step-by-step guide to building a sticky, stretchy scroll view header in SwiftUI, similar to the Spotify album screen. Covers combining scroll offset tracking (via preference keys and coordinate namespaces) with a stretchable header (GeometryReader) to create a ScrollViewWithStickyHeader component. Explains how to calculate a headerVisibleRatio, overlay a second header when the original scrolls past the navigation bar, make the navbar transparent using toolbarBackground, and add bonus pull-down tilt (rotation3DEffect) and parallax (vertical offset) effects. The final component is available in the open-source ScrollKit library.
