CSS View Transition Pseudo-elements Explained

These sources provide a detailed, technical explanation of the View Transition API implementation within the Chromium web browser, focusing on how CSS pseudo-elements enable smooth animations. The first source explains that view transition pseudos (like ::view-transition-old() and ::view-transition-new()) are temporary, browser-synthesized overlays used to capture and animate visual snapshots of elements during state changes. The second, more extensive source describes the low-level C++ classes in the Blink rendering engine and the cc compositor that orchestrate this process, including the DocumentTransition class, which manages the lifecycle, snapshot capture, and pseudo-element creation, and the SurfaceAnimationManager in the Viz component, which handles the final, performant GPU-accelerated animation of the saved frames using specialized layers and directives. Together, the texts map the high-level CSS API to the complex, multi-process architecture of Chromium, explaining how old and new content are matched, isolated on the top layer, and composited for animation.