A portal is an opening in the walls of a building, gate or fortification, and especially a grand entrance to an important structure. Doors, metal gates or portcullis in the opening can be used to control entry or exit. The surface surrounding the opening may be made of simple building materials or decorated with ornamentation. Elements of a portal can include the voussoir, tympanum, an ornamented mullion or trumeau between doors, and columns with carvings of saints in the westwork of a church.
A game level might contain many graphical polygons; only a few of which may be visible on screen at a given time. Visibility determination allows the renderer to decide which of those fall into that category and thus reduce rendering time.
For example, in a computer game, the game area might be divided to several sectors. These sectors would be then connected to each other by small openings such as doors or windows. These openings are referred as portals. When the sector behind a portal needs to be drawn, the only parts that are visible are the parts that can be seen through the portal. Therefore, the sector can be clipped against the portal boundaries to remove overdraw.
The use of portals simplifies the game engine's task of determining visible areas and objects from any given point of view of the level, and simplifies rendering by allowing it to use each portal as a viewing frustum for the area it leads to.
Portal established a settlement between the French and British Missionaries in Uganda, and on May 29, 1893 he signed a treaty with Kabaka Mwanga of Buganda. On April 1, 1893, he hauled down the flag of the British East Africa Company and hoisted the Union Jack. He returned to Britain and recommended the declaration of Uganda as a protectorate.
Portal sits near the Canadian border and is a major port of entry for road and rail traffic. It is one of three 24-hour ports in North Dakota (the others being Dunseith and Pembina). The town is known for its "international" golf course. The ninth hole is partially in the United States and partially in Canada.
From the depths of the gloom wherein you dwell, you do not see much more distinctly than we the radiant and distant portals of Eden. Only, the priests are mistaken. These holy portals are before and not behind us.