Ray Game

Building a Ray Game From Scratch

A Ray Game is fundamentally a ray casting engine, which is a rendering technique used to create the illusion of a 3D world from a 2D map. The core idea is straightforward: from the player's position, cast a series of rays outward, calculate where each ray intersects a wall in the map grid, and then draw a vertical line on screen whose height is inversely proportional to the distance to that intersection. What happens after that initial description is where the actual work begins, and most people underestimate how many edge cases show up quickly. You need a 2D array representing your map, where 1 means wall and 0 means empty space. Then you pick a programming language and a graphics library. For a first attempt, I'd suggest Processing or even plain Python with Pygame because the overhead is low and you can iterate fast. JavaScript with Canvas works too if you want to run in a browser. The actual ray casting math is roughly the same regardless of language. I built my first Ray Game in C++ using SDL about five years ago, and I spent more time debugging the rendering loop than writing any other part. The problem was that I wasn't clamping the ray distances properly, so walls beyond a certain range would render with incorrect heights and create visual artifacts that looked like floating geometry. The fix was a simple distance cap combined with a normalized mapping function. This is one of those things that seems obvious once someone tells you but almost never appears in beginner tutorials.

The Ray Casting Loop

Here's how the core loop works in practice. You divide your screen width into vertical columns, one per pixel or one per group of pixels if you're optimizing for performance. For each column, you calculate the angle of the ray based on the player's position and viewing direction. Then you step along that ray, checking each grid cell until you hit a wall. The distance to that wall determines how tall the vertical line should be drawn. Closer walls are taller, farther walls are shorter. That's the entire principle. The tricky part is doing this efficiently enough to run at a decent frame rate. A naive implementation will walk cell by cell, which means for distant walls you're checking a lot of empty cells. The standard optimization is to use a grid traversal algorithm, sometimes called DDA or a variant of Bresenham's line algorithm adapted for grids. This skips over empty cells and jumps directly from one grid boundary to the next along the ray direction. I switched to this approach and went from something unplayably slow to around 60 fps on modest hardware. The difference was dramatic and not something I would have guessed from just reading about ray casting. Another detail that matters a lot is vertical field of view correction. Without it, walls appear bowed or stretched, especially near the edges of the screen. The fix is to multiply the ray distance by the cosine of the angle offset from the center of the screen. This is a one-line adjustment but it makes the whole thing look significantly more natural. I learned this the hard way after spending a day wondering why my map looked warped until I found the explanation in an old id Software technical document.

Rendering Textures and Sprites

Once you have the basic wireframe walls working, the next step is usually adding textures. The approach is to map texture coordinates onto the vertical line you drew based on the exact point where the ray hit the wall. You sample the texture at regular intervals along that line. This is where things get finicky because texture alignment can go wrong in subtle ways, producing visible seams or distorted stretches, particularly on diagonal walls where the intersection point is close to a grid corner. I ran into a specific issue where textured walls near corners would show a thin vertical line artifact, about one pixel wide, between adjacent wall segments. This turned out to be a floating point precision problem in the texture coordinate calculation. The workaround was to add a small epsilon offset when computing the texture sampling position, which pushed the coordinates just far enough away from the boundary to eliminate the artifact without introducing any noticeable error. It's the kind of detail that takes serious debugging to uncover and even longer to find a clean solution for. Sprites are another layer of complexity. They're essentially 2D images placed at positions in the world and rendered by casting additional rays to determine visibility. If a sprite is behind a wall, you don't draw it. If it's partially occluded, you only draw the visible portion. This requires a depth sort so that sprites farther away are rendered behind closer ones. I learned the hard way that skipping the depth sort produces a messy visual where sprites overlap each other in completely wrong order. A simple sort by distance before rendering fixes this, though it adds a small per-frame cost.

Map Design and Testing

After the engine works, you need maps to test it on. I started with a simple rectangular room and gradually added corridors, rooms, and obstacles. A good way to validate your engine is to place the player in a known configuration and visually verify that walls appear at the correct distances and angles. If something looks off, trace the rays on paper or on a debug overlay to see where the math diverges from expectation. One approach that helped me was to render a debug overlay showing all the rays as faint lines, along with the grid cells being checked. This made it much easier to spot when a ray was missing a wall or stopping at the wrong location. I kept this feature toggled on for a while during development and then disabled it once I was confident the logic was solid. It saved me several hours of trying to debug by reasoning about invisible data.

Known Limitations of the Ray Casting Approach

Ray casting has real constraints that you should be aware of before committing to it for a full project. It only handles axis-aligned walls in a flat 2D plane. You cannot represent sloped surfaces, staircases, or varying ceiling heights without significant hacks that tend to break visual consistency. The engine also struggles with circular or curved geometry because the grid representation is inherently rectangular. If your game design calls for any of these elements, you'll hit a wall, literally. Another limitation is that ray casters do not natively support soft shadows, ambient occlusion, or dynamic lighting in the way that a full 3D renderer does. You can fake distance-based shading by darkening walls the farther they are, which is standard practice, but anything more sophisticated requires additional passes or techniques that complicate the pipeline considerably. For a simple first-person shooter style game, the standard tricks are usually sufficient, but if you need advanced visual effects, a traditional 3D engine is likely a better choice from the start.

Practical Next Steps

If you want to build a Ray Game, start with a minimal working version and resist the urge to add features too quickly. Get the basic ray casting loop stable, then add textures, then sprites, then movement and collision. Each layer introduces new potential failure modes, and keeping the base simple makes debugging easier. There are several open source implementations online that you can study, and I'd recommend comparing your code against at least one of them once you have a working prototype. A useful resource is the Wolfenstein 3D source code, which has been released publicly and demonstrates many of the techniques in a production-quality context. Reading through it shows how the developers handled optimizations and edge cases that aren't covered in most tutorials. It's a substantial piece of code but very readable if you have some C experience. Understanding the historical context also gives you a better sense of what problems were considered worth solving and what trade-offs were made, which is useful information when you're designing your own implementation. For a downloadable starting point, several community projects provide a minimal Ray Game engine in various languages. Searching for "ray casting engine open source" along with your preferred language will turn up a handful of repositories. Pick one that matches your skill level, clone it, run it, and then modify it piece by piece to see how changes affect the output. This hands-on experimentation is where you'll actually internalize the techniques rather than just understanding them theoretically.

Performance Tuning Tips

As your map grows, performance can become a concern. The main cost is the number of ray wall checks per frame. Reducing the resolution of the output, for example rendering at half horizontal resolution and scaling up, can cut the work in roughly half with minimal visual impact on most displays. Another approach is to use a coarse grid for initial distance estimation and then refine only near potential wall intersections. This is more complex to implement but can yield significant speedups on large maps. Culling is also important. If a section of the map is guaranteed to be out of view based on the player's position and direction, you can skip casting rays through that area entirely. This requires some spatial reasoning on your part, but even a simple culling pass that ignores cells behind the player or outside the field of view can reduce the per-frame workload noticeably. I implemented a basic culling step in my later builds and saw a measurable improvement in frame rates on larger maps, though the gains were less dramatic on smaller levels where the engine was already fast enough. Finally, don't neglect the player movement code. Smooth movement with collision detection against the wall grid is essential for a good feel. A common mistake is to move the player and then check for collision after the fact, which can result in the player passing through thin walls or getting stuck. Instead, test each axis of movement separately, checking for collisions and correcting position before proceeding. This approach is standard in grid-based movement systems and prevents the most annoying collision bugs.