Portal rendering is a computer graphics technique used in video games to limit the amount of pixels rendered at any one time. To achieve this, most games are composed of sections, and the user can only see a certain area, such as a room. These sections are commonly small and confined, because this is easier to program, but portal rendering also can be used with outside landscapes if the programmer takes the user’s field of vision into account. The primary reason for using this rendering technique is to improve performance by requiring less memory. While the problems tend to be minimal and mostly affect older games, there may be loading problems if the user moves unexpectedly.
With portal rendering, the programmer will often split the game’s world into many portals, or sections. When someone is in a certain section, the programmer knows the other sections will not be seen and, thus, do not have to be rendered. This is commonly done by making rooms, with each room used as a section.
To make rendering even easier, most sections are confined with clearly visible walls. If confined space is used, then it makes portal rendering easier, because the programmer has to make few guesses about what the user will be able to see. Some games feature outside landscapes with no walls. In this case, the programmer has to take the user’s field of vision into account, so only the landscape that can be viewed immediately will be rendered.
The main reason to use portal rendering is that it limits the amount of memory needed immediately. For example, if the game’s map is not sectioned, then the game has to render all the pixels simultaneously. This requires a lot of memory, meaning the game’s performance will likely suffer from lags and other problems. The user is usually not close enough to see another section, so this delayed rendering commonly does not cause any problems.
While there are usually no problems with portal rendering, it is possible that some pixels will not load correctly if the user does not move as expected. For example, if the programmer assumes the user will not go to the previous section and he or she does, then the game may take a few seconds to load the section. There may be a wall or small area that appears black for a second, but this rarely affects the game’s performance.