Raycasting is a computer graphics technique that creates a 3D perspective from a 2D environment. It was widely used in early first-person shooters (FPS) to simulate three-dimensional spaces without requiring the heavy processing power needed for true 3D rendering. This method allowed classic games like Wolfenstein 3D and Doom to run smoothly on hardware from the late 1980s and early 1990s.
This article explores how raycasting works, why it was revolutionary for gaming, its advantages and limitations, and how it paved the way for modern rendering techniques.
How Raycasting Works
Raycasting is based on a simple but effective principle: it simulates a 3D environment by casting imaginary rays from the player’s viewpoint to detect obstacles in a 2D map. Each ray extends outward until it hits a solid object, determining the depth and perspective of the scene.
In FPS games, the game engine casts one ray for each vertical slice of the screen. The distance to the object determines how tall or short that slice will appear. If an object is closer to the player, the rendered wall segment will be taller. If it’s farther away, the wall segment will be shorter, creating an illusion of depth.
Unlike true 3D rendering, raycasting does not simulate a full 3D world. Instead, it only calculates what is visible to the player at any given moment. This significantly reduces the processing load, making it ideal for early gaming hardware.
Raycasting in Classic FPS Games
Raycasting became a breakthrough technology for early FPS games. Before its introduction, most games used top-down perspectives or simple side-scrolling mechanics. The ability to simulate 3D spaces from a first-person view revolutionized immersion in gaming.
The first game to bring raycasting into the mainstream was Wolfenstein 3D, released in 1992. This game used a raycasting engine to create mazelike corridors with smooth movement, allowing players to explore in a way that felt much more immersive than previous games.
Following Wolfenstein 3D, the legendary Doom was released in 1993, taking raycasting to the next level. While Doom still relied on raycasting for rendering, it incorporated Binary Space Partitioning (BSP), an optimization technique that allowed for more complex level designs, height variations, and dynamic lighting effects. This made Doom feel much more advanced compared to Wolfenstein 3D.
Other notable games that used raycasting or similar techniques include:
- Blake Stone: Aliens of Gold (1993) – Used a modified Wolfenstein 3D engine.
- Rise of the Triad (1994) – Expanded raycasting with advanced visual effects.
- Duke Nukem 3D (1996) – While not fully raycasted, it used similar rendering techniques for walls and objects.
These games demonstrated how raycasting allowed developers to create immersive 3D-like worlds, despite the technical limitations of early gaming hardware.
Advantages of Raycasting
Raycasting was widely used because of its efficiency and simplicity. Some of its key advantages include:
1. High Performance on Limited Hardware
Early gaming consoles and personal computers had very limited processing power. True 3D rendering was computationally expensive, requiring more advanced hardware. Raycasting provided a way to create 3D-like environments without overloading the system.
2. Simple Implementation
Compared to more complex rendering techniques, raycasting was relatively easy to program. Developers could use a 2D grid-based map and apply mathematical formulas to determine object positions and distances.
3. Fast Rendering Speed
Since raycasting only calculates what is visible to the player, it avoids unnecessary processing of unseen areas. This made games run much smoother, even on slower CPUs.
4. A Foundation for Future 3D Engines
Although raycasting is not true 3D rendering, it laid the groundwork for more advanced techniques. Many of the principles used in raycasting influenced the development of modern game engines.
Limitations of Raycasting
Despite its advantages, raycasting had several technical limitations, which led to its decline as gaming hardware improved.
1. No Room Over Room Design
One major drawback was the lack of vertical level complexity. In games like Wolfenstein 3D, every level was a single flat plane, meaning that rooms could not be stacked on top of one another.
2. Blocky, Simplistic Graphics
Because raycasting was a simplified way to simulate 3D, early FPS games using this technique often had blocky environments, simple textures, and limited lighting effects.
3. No Real Dynamic Lighting
Raycasting engines had pre-rendered lighting, meaning that shadows and brightness were not dynamically calculated. This made environments feel less realistic compared to later games that used full 3D rendering.
4. Limited Enemy AI and Object Placement
Since raycasting engines were optimized for speed, enemy AI and object placement were often restricted to a grid-like system. This made movement and interaction feel predictable.
Raycasting vs. True 3D Rendering
As gaming technology advanced, true 3D rendering engines replaced raycasting. By the late 1990s, games like Quake (1996) and Unreal (1998) introduced full 3D polygonal environments with true depth, verticality, and realistic lighting. These engines rendered entire 3D scenes in real-time, rather than just what was visible on-screen.
However, raycasting is still used today in certain applications. Some indie game developers use raycasting engines to create retro-style FPS games, and it remains a valuable teaching tool for those learning computer graphics.
The Lasting Impact of Raycasting
Raycasting was a critical stepping stone in the evolution of 3D gaming. Without it, the first-person shooter genre may not have evolved as quickly. Games like Wolfenstein 3D and Doom paved the way for modern FPS titles, inspiring countless developers.
Although modern game engines have surpassed raycasting, its influence remains deeply embedded in gaming history. Many of the optimization techniques used in modern rendering engines can be traced back to the early days of raycasting-based games.
What’s your favorite classic FPS that used raycasting? Let us know in the comments!