There are two main methods of rendering used in interactive media and static media: real-time rendering and pre-rendering. Real-time rendering applies to interactive media such as video games, virtual reality (VR), and simulations, where the scene needs to change responsively to the user’s inputs. Real-time rendering is fast and renders images and animations in the range of 20-120 frames per second (FPS), the most common being 30 or 60 FPS. Because it takes considerable processing power to render in real-time with visually smooth motion, the graphics for real-time rendered media usually sacrifice some amount of quality compared to pre-rendered graphics. For real-time rendering, 3D models may have a lower polygon count and less detailed textures, and lighting and other effects may be simpler and more optimized for performance.
With pre-rendering (also called offline rendering), graphic quality can be more detailed and complex, and more accurately depict the physics of light and particle dynamics from fire, smoke, wind, water, and so on. Pre-rendering is used for media that is entirely passive rather than interactive, such as 3D animation, visual effects for film and TV, and design or architectural visualization. With pre-rendering, artists can make their 3D models and graphics as high-quality and photorealistic as they wish and use advanced effects and rendering techniques like ray tracing and global illumination. The trade-off for that level of detail comes in the time and computing power needed to render it. Pre-rendering, particularly for the highest-end animation and VFX, could take several hours to render a single frame, or days or weeks to render entire scenes or movies.
