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Gecko:Overview: Difference between revisions
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The basic unit of frame construction is a run of contiguous children of a single parent element. When asked to construct frames for such a run of children, the frame constructor first determines, based on the siblings and parent of the nodes involved, where in the frame tree the new frames should be inserted. Then the frame constructor walks through the list of content nodes involved and for each one creates a temporary data structure called a '''frame construction item'''. The frame construction item encapsulates various information needed to create the frames for the content node: its style data, some metadata about how one would create a frame for this node based on its namespace, tag name, and styles, and some data about what sort of frame will be created. This list of frame construction items is then analyzed to see whether constructing frames based on it and inserting them at the chosen insertion point will produce a valid frame tree. If it will not, the frame constructor either fixes up the list of frame construction items so that the resulting frame tree would be valid or throws away the list of frame construction items and requests the destruction and re-creation of the frame for the parent element so that it has a chance to create a list of frame construction items that it <em>can</em> fix up. | The basic unit of frame construction is a run of contiguous children of a single parent element. When asked to construct frames for such a run of children, the frame constructor first determines, based on the siblings and parent of the nodes involved, where in the frame tree the new frames should be inserted. Then the frame constructor walks through the list of content nodes involved and for each one creates a temporary data structure called a '''frame construction item'''. The frame construction item encapsulates various information needed to create the frames for the content node: its style data, some metadata about how one would create a frame for this node based on its namespace, tag name, and styles, and some data about what sort of frame will be created. This list of frame construction items is then analyzed to see whether constructing frames based on it and inserting them at the chosen insertion point will produce a valid frame tree. If it will not, the frame constructor either fixes up the list of frame construction items so that the resulting frame tree would be valid or throws away the list of frame construction items and requests the destruction and re-creation of the frame for the parent element so that it has a chance to create a list of frame construction items that it <em>can</em> fix up. | ||
Once the frame constructor has a list of frame construction items | Once the frame constructor has a list of frame construction items and an insertion point that would lead to a valid frame tree, it goes ahead and creates frames based on those items. Creation of a non-leaf frame recursively attempts to create frames for the children of that frame's element, so in effect frames are created in a depth-first traversal of the content tree. | ||
The vast majority of the code in the frame constructor, therefore, falls into one of these categories: | The vast majority of the code in the frame constructor, therefore, falls into one of these categories: | ||
* Code to | * Code to determine the correct insertion point in the frame tree for new frames. | ||
* Code to create, for a given content node, frame construction items. This involves some searches through static data tables for metadata about the frame to be created. | * Code to create, for a given content node, frame construction items. This involves some searches through static data tables for metadata about the frame to be created. | ||
* Code to analyze the list of frame construction items. | * Code to analyze the list of frame construction items. | ||