GENERATING A VISUAL DESCRIPTION TREE BASED ON A LAYOUT INTERRUPTION RECORD

摘要

A layout engine generates a visual layout tree for a visual description tree of a document whose content is to be rendered in one or more display areas. A visual description tree describes the content of a document along with formatting and logical arrangement the content. Visual description nodes of a visual description tree represent the organization of the constituent elements a document hierarchically. A visual layout tree defines the layout of a document within one or more display areas. Visual layout nodes of a visual layout tree represent the layout of the content of a document hierarchically. The layout engine receives as input a visual description tree and generates the corresponding visual layout tree. A rendering engine then inputs the visual layout tree and generates a graphics buffer containing the pixels representing the layout of the document as defined by the visual layout tree.

主权项

1. A method performed by a computing device for generating a visual layout tree for a visual description tree of a document whose content is to be fragmented across multiple display areas, the visual description tree having visual description nodes and the visual layout tree having visual layout nodes, the method comprising:
providing a layout interruption record to identify visual description nodes whose processing has been interrupted; and for each display area that is to contain content of the document, processing the visual description tree by:
for visual description nodes of the layout interruption record,
setting a current state for processing the visual description node based on a state indicated by the layout interruption record for that visual description node;populating the visual layout tree with one or more visual layout nodes representing content of the visual description node to be included in the display area given the current state; andwhen processing of the content of the visual description node is interrupted for the display area, adding to a layout interruption record for the next display area the then-current state of processing of the visual description node and an identifier of the visual description node so that for the next display area the processing of the virtual description tree can continue from where processing was interrupted for the display area.