How to Use Raycasting to Make a 3D Game in Scratch

Creating a convincing 3D game in Scratch might seem like a daunting task, especially since Scratch is primarily a 2D programming environment designed for beginners. However, by leveraging the technique of raycasting, you can simulate 3D graphics effectively within Scratch’s limitations. Raycasting is a rendering technique that projects rays from the player’s point of view to determine what objects are visible and how they should be displayed, creating the illusion of depth and space. This method was famously used in early 3D games like Wolfenstein 3D and DOOM, making it a perfect choice for hobbyists and educators looking to explore 3D concepts without complex engines.

Understanding Raycasting and Its Role in 3D Rendering

Raycasting involves casting imaginary rays from a player’s viewpoint into the game world. Each ray corresponds to a vertical slice of the player’s screen. By calculating where each ray intersects with walls or objects, the engine determines the distance to those objects. Closer objects are drawn larger and more prominently, while distant objects appear smaller, thus creating a depth illusion. This approach is computationally efficient and well-suited for the limitations of Scratch, which doesn’t support 3D models but excels at 2D sprite manipulation.

Setting Up Your Scratch Environment

Before diving into coding, prepare your Scratch project:

Create a new project at Scratch.
Design or import sprites for walls, the player, and the environment. Use simple graphics to keep calculations straightforward.
Set up a backdrop to serve as the game map, or create a grid-based map using sprites or variables.

Creating the Map: Grid and Data Structures

For raycasting, a map is essential. Typically, a 2D array represents the game world, where each cell indicates whether it contains a wall or empty space. You can define the map using Scratch lists or variables. For example:

Row / Column	0	1	2	3	4
0	1	0	0	1	1
1	0	0	1	0	0
2	1	0	0	1	0
3	0	1	0	0	1
4	1	0	1	0	0

In Scratch, you can store this map as a list of lists or multiple separate lists for each row, which can then be looped through during rendering.

Player Position and Direction

Define variables for the player’s position and viewing direction:

x and y: the player’s coordinates in the map.
direction: the angle (in degrees or radians) representing where the player is looking.
FOV: field of view, typically around 60 degrees, determining how wide the player’s perspective is.

Example:

set [playerX v] to 2.5
set [playerY v] to 2.5
set [playerDirection v] to 0
set [FOV v] to 60

Raycasting Algorithm in Scratch

Core Steps

Loop through each vertical slice of the screen (e.g., 120 slices for a 120-column display).
Calculate the angle of the ray relative to the player’s current direction.
Cast the ray into the map to find the point of intersection with walls.
Calculate the distance from the player to the wall.
Use this distance to determine the height of the wall slice to draw.
Render the wall slice on the screen with appropriate size and shading to simulate depth.

Calculating Ray Direction and Intersections

For each column (say, i), calculate the ray’s angle:

rayAngle = playerDirection - (FOV / 2) + (i / totalColumns) * FOV

Convert angles to radians if necessary, as Scratch’s math functions operate in radians. For example:

set [rayAngleRad v] to (rayAngle * (pi / 180))

Cast the ray by incrementally checking points along the ray’s path until it hits a wall. This can be done using a loop that steps along the ray at small intervals:

repeat until <touching [wall sprite v] or  maxDistance>>
  change [xCheck v] by (cos(rayAngleRad) * stepSize)
  change [yCheck v] by (sin(rayAngleRad) * stepSize)
  // Check if (xCheck, yCheck) hits a wall

Optimizations and Accuracy

To improve performance, implement DDA (Digital Differential Analyzer) algorithms or precompute steps. Use small step sizes (e.g., 0.05 units) for accuracy but balance with performance constraints.

Rendering the 3D Scene

Once distances are calculated, render vertical slices on the screen. The height of each slice is inversely proportional to the distance:

wallHeight = (screenHeight / distance) * projectionCoefficient

Adjust shading based on distance to simulate lighting effects, making distant walls darker. Use the Scratch editor to draw rectangles representing each wall slice, stacking them side by side to form the scene.

Additional Features for Realism

Implement textures by mapping sprite pixels onto wall slices.
Add ceiling and floor rendering for a complete environment.
Include player movement controls (WASD or arrow keys) with collision detection.
Integrate sprite objects, such as enemies or items, with depth sorting.

Sample Resources and Tutorials

For practical implementations and code snippets, check out these resources:

Statistics and Performance Considerations

While Scratch isn’t optimized for real-time 3D rendering, clever coding and optimization can yield playable experiences. Typically, a well-structured raycaster in Scratch can run at approximately 15-30 frames per second on standard hardware. To maintain smooth gameplay:

Limit the number of rays per frame (e.g., 120-200).
Optimize collision checks and map data structures.
Use efficient loops and avoid unnecessary calculations.

Conclusion

Implementing raycasting in Scratch opens doors for creative projects that simulate 3D environments using simple 2D sprites and logic. It serves as a powerful educational tool to understand fundamental graphics concepts like projection, depth, and rendering. By combining careful map design, mathematical calculations, and creative drawing, developers can craft engaging 3D-like experiences directly within Scratch, inspiring learners and hobbyists alike to explore game development and computer graphics.