The HDi runtime is responsible for execution and final rendering of the movie playback and navigation application. The markup is parsed into a Document Object Model, which allows ECMAScript code to control and modify the UI layout during execution. By dynamically altering the layout of UI widgets is how animations and interactivity is achieved. The DOM and associated APIs is used to enable other scenarios such as pausing playback and replacing it with the navigation UI, or seeking to a certain area in the movie (used for either manual seek or seeking to bookmarks). For the rendering stack, it presents six planes (which are containers for graphics) that are layered in front of each other. The final image displayed is the composition of the images from the individual planes. The composition of the planes into the final image is handled by the HDi runtime. These rendering layers, from back to front, are:
