Author: Scott Gibson

Ray Casting With Squeak

On the Squeak developers mailing list, Lauren Pullen shared her experience (found here) using Squeak while working on a rendering engine for a first-person maze game, similar to the technique used to render the original Wolfenstein 3D game. Wolfenstein 3D used a rendering technique known as ray casting. Her project captured our attention prompting us to seek additional information from her about it.

What is Ray Casting?

Ray casting is an early rendering technique used in computer graphics and video games, particularly in 2.5D and 3D environments. It is a simplified form of ray tracing, where a ray is cast from the player’s or camera’s perspective into the environment, and the distance to the nearest object along that ray is calculated. This process is repeated for each column on the screen, creating a 3D representation of the 2D world. Ray casting was widely used in the early days of 3D gaming, particularly in games like Wolfenstein 3D (1992).

From Lisp to Squeak

Lauren, with her extensive experience in Common Lisp, initially chose it to create a GUI application. However, she faced significant challenges. The graphics library was unreliable, often failing to start, and the outdated documentation made it difficult to work with. She studied MVC while designing her application but struggled with basic functionality, such as displaying a simple window.

She decided to switch to Smalltalk, specifically Squeak, which had an immediate impact. The graphical elements worked seamlessly from the start, and although she missed some features from Common Lisp, like restarts and method combinations, Squeak provided a development environment that allowed her to focus on development without drastically changing her mental approach to problems.

Comparing Development Tools

For game development, she initially relied on a much earlier version of Game Maker Pro. When she explored Godot, she found its complexity overwhelming compared to Smalltalk. The disorganization in Godot’s tutorials made her question how to create a basic viable product efficiently. In contrast, though seemingly minimal, Squeak’s classes Form and UserInputEvent provided all that was needed.

Advantages of Squeak

In Squeak, she found it easy to work with graphical elements. Drawing interface components and importing graphics were straightforward, thanks to the source code access for built-in drawing functions. This simplicity was crucial for her development process. While working on the game, she realized that making changes and seeing immediate results was invaluable for debugging. Her experience with Forth taught her the value of functions that do one thing well, and Smalltalk’s debugging tools like Inspect-It and Debug-It further streamlined the process.

Challenges and Solutions

However, she encountered challenges. While most errors in Smalltalk were easy to handle—usually, closing the Debugger was all that was needed—some issues could freeze the image, making recovery a bit more manual than desired. She found herself needing to use the Recover Changes window to restore unsaved changes more often than she would have liked.

In terms of rendering, she faced performance limits with BitBlt when texturing the floor and ceiling. To overcome this, she turned to the AbstractGPU library, leveraging the graphics card for drawing. She continued to use the ray caster to determine what the player could see to speed up the game, but introduced edge pop-in, where objects on the screen edges would suddenly appear while turning the camera, because of differences between the ray caster’s projection and the GPU’s projection. Increasing the field of view used by the ray caster resolved this issue.

Testing Using Morphic Dungeon

Morphic Dungeon is what Lauren developed and uses to test the movement and texturing code. She wants to work with textures that are not symmetrical, which requires mapping the top-left corner of the texture to different positions on each face of the 3D objects. This approach also allowed her to test back-face culling—a technique that improves performance by not drawing faces of a 3D object that are not visible to the camera—in the GPU mode. In this mode, the “back faces” are flipped horizontally and appear further away, as if looking at the inside of a transparent painted box instead of the outside. Back-face culling will be essential for rendering the “walls” of tiles that the player can enter or see through, such as grass or support beams along the grid edges.

Lauren implemented three movement modes:

• Free Movement and Free Turning
• Grid-Locked Movement and Free Turning
• Grid-Locked Movement and Grid-Locked Turning

Full Free Movement is similar to Wolfenstein 3D, allowing sub-pixel steps and small increment camera rotations.

Grid-Locked Movement is useful for first-person dungeon crawlers. Grid-Locked Turning forces camera rotation to 90-degree increments, similar to classic non-raycaster games like Wizardry or modern titles like Etrian Odyssey. Free camera rotation, with Grid-Locked Movement, is also supported which is similar to the modern title Operencia.

While using Morphic Dungeon to test the different movement modes, Lauren encountered an amusing floating point error whereby the player would step repeatedly through walls and out of the play area. This provided a humorous insight into the potential bugs she might encounter.

Additionally, Lauren tested the game with a family member, revealing that the 40×40 maze, though not difficult from an overhead view, proved challenging from a first-person perspective without an overhead view or compass. This feedback helped her adjust the difficulty of the first area to better suit new players.

Future Plans

Looking ahead, she plans to explore non-flat levels and dynamically stitching multiple maps together. This might result in overlaps while rendering, so the ray caster will be in charge of telling the graphics card what to draw. Meanwhile, she will focus on improving floor and ceiling loading performance, although this is currently less critical due to the few vertices involved.

Lauren believes that developing a game is a great way to introduce people to programming. While tools are useful, having something that you can play with is fun. Old tile-based games and raycasters are particularly appealing to her because they are simple to work with, even for beginners.

Overall, Lauren believes that Squeak has proven to be an excellent choice for her project, offering the simplicity and functionality needed for a successful game development experience.

Why Not Give It a Try?

If you would like to experiment with ray casting in Squeak, you can find out more about her project from SqueakSource here. To use the 3D accelerated package, you will also need AbstractGPU by Ronie Salgado, available (here). Ronie is the author of a number of terrific 3D development tools, including Woden (here) and Sysmel (here). Be sure to explore these excellent resources as well!

Have a great time with Smalltalk and keep on Squeaking!