Lecture
Pre-rendering is a process in which video material is not rendered in real time by the hardware that outputs or plays back the video. Instead, the video is a recording of material that was rendered earlier on different hardware (usually more powerful than the hardware used for playback). Pre-rendered assets (usually movies) can also be outsourced by a developer to a third-party production company. Such assets typically have a level of complexity too great for the target platform to render in real time.
The term «pre-rendered» refers to anything that is not rendered in real time. This includes content that could be run in real time with considerable effort on the part of the developer (for example, a video that spans many game environments without pausing to load, or footage from an early-development video game that was rendered in slow motion and then played back at normal speed). This term is generally not used to refer to video captures of graphics rendered in real time, even though such video is technically pre-rendered by nature. The term is also not used to refer to hand-drawn or photographed assets (these assets were never rendered on a computer in the first place).
The advantage of pre-rendering lies in the ability to use graphical models that are more complex and computationally demanding than those that can be drawn in real time, owing to the possibility of using multiple computers over extended periods of time to render the final results. For example, a comparison can be drawn between the rail shooters Maximum Force (which used pre-rendered 3D levels but 2D sprites for enemies) and Virtua Cop (which used 3D polygons); Maximum Force looked more realistic because of the limitations of Virtua Cop's 3D engine, but Virtua Cop has actual depth (the ability to depict enemies near and far, as well as body-specific and multiple hits) compared with the limitations of Maximum Force's 2D sprite enemies.
The disadvantage of pre-rendering, in the case of video game graphics, is generally a lower level of interactivity, if any, with the player. Another downside of pre-rendered assets is that changes cannot be made during gameplay. A game with pre-rendered backgrounds is forced to use fixed camera angles, and a game with pre-rendered video generally cannot reflect any changes that the game's characters may have undergone during gameplay (for example, injuries or custom clothing) without storing an alternate version of the video. This is generally impractical because of the large amount of storage space required for high-quality pre-rendered assets. However, in some advanced implementations, such as Final Fantasy VIII, real-time assets were composited with pre-rendered video, which allowed for dynamic backgrounds and changing camera angles. Another issue is that a game with pre-rendered lighting cannot easily change the lighting state in a convincing way.
As technology developed further in the mid-2000s, video game graphics were able to achieve a level of photorealism that had previously been limited to pre-rendering, as evidenced by the development of Machinima.
Pre-rendered graphics are used mainly as cutscenes in modern video games, where they are also known as full-motion video. The use of pre-rendered 3D computer graphics for video sequences dates back to two arcade laserdisc video games introduced in late 1983: Interstellar, presented by Funai at the AM show in September, and Star Rider, presented by Williams Electronics at the AMOA show in October.
The enhanced remake of Ys I: Ancient Ys Vanished for the Sharp X68000, released in 1991, used three-dimensional pre-rendered graphics for boss sprites, although this ultimately created what is considered a «strange contrast» with the game's mostly two-dimensional graphics. One of the first games to make extensive use of pre-rendered graphics together with full-motion video was The 7th Guest. Released in 1993 as one of the first PC games available exclusively on CD-ROM, the game was extremely popular, although critical reviews were mixed. The game used pre-rendered video sequences at a resolution of 640x320 at 15 frames per second, which had previously been considered impossible on personal computers. Shortly thereafter, the release of Myst in 1993 made the use of pre-rendered graphics and CD-ROM even more popular; much of Myst's rendered work became the basis for the remake realMyst: Interactive 3D Edition, with its freely navigable real-time 3D graphics. The most graphically advanced use of fully pre-rendered graphics in games is often cited as Myst IV: Revelation, released in 2004.
One of the first significant console games with pre-rendered graphics was Donkey Kong Country, released on the SNES in 1994.
The use of pre-rendered backgrounds and movies also became popular thanks to the Resident Evil and Final Fantasy franchises on the original PlayStation, both of which make extensive use of pre-rendered backgrounds and movies to provide a visual presentation far superior to what a console could offer with real-time 3D. These games incorporate real-time elements (characters, items, and so on) in addition to pre-rendered backgrounds to provide interactivity. Often a game that uses pre-rendered backgrounds can devote additional computing power to the remaining interactive elements, resulting in a level of detail exceeding the norm for the host platform. In some cases, the visual quality of the interactive elements still lags far behind that of the pre-rendered backgrounds.
In the late 1990s and early 2000s, when most 3D game engines had pre-calculated/fixed lightmaps and texture mapping, developers often turned to pre-rendered graphics, which offered a much higher level of realism. However, this fell out of favor from the mid-2000s onward, as advances in graphics for consumer PCs and game consoles made it possible to use the game's own engine to render these cinematic sequences. For example, the id Tech 4 engine used in Doom 3 allowed for bump mapping and dynamic per-pixel lighting, which previously could only be found in pre-rendered video.
Games such as Warcraft III: Reign of Chaos used both types of cutscenes: pre-rendered ones for the beginning and end of the campaign, and the in-game engine for level briefings and character dialogue during missions.
Some games also use a 16-bit pre-rendered skybox, for example Half-Life (GoldSrc version only), Re-Volt, Quake II, and others.
Computer-animated films such as «Toy Story», «Shrek», and «Final Fantasy: The Spirits Within» are fully pre-rendered.
Another increasingly common pre-rendering method is the generation of texture sets for 3D games, which are often used together with complex real-time algorithms to simulate extremely high levels of detail. When creating Doom 3, id Software used pre-rendered models as a basis for generating normal, specular, and diffuse lightmaps, which simulate the detail of the original model in real time.
Pre-rendered lighting is a technique that is losing popularity. Ray-tracing algorithms, which are processor-intensive, can be used during game production to generate light textures that are simply overlaid on top of ordinary, hand-drawn textures.
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