الصفحة الرئيسية
Animations

Chicken Crossing the Road

Muhammad Saad


Crossy Road with Three.js: An In-Depth Look at a 3D Web Game

This project is a fantastic demonstration of building a 3D web game from the ground up using HTML, CSS, and JavaScript, with the powerful Three.js library as its core. The project's structure, which separates concerns between the game's visuals, logic, and user interface, serves as an excellent case study for creating interactive, real-time 3D experiences in a browser. By analyzing the index.html, style.css, and script.js files, we can dissect how a modern web game comes to life, from rendering 3D models to managing game state and user input.

The main purpose of this project is to create a playable version of the popular mobile game "Crossy Road" in a web browser. The objective is to guide a character across an infinitely generated, multi-lane road, avoiding oncoming vehicles. It's a testament to the capabilities of modern web browsers and JavaScript to handle complex, real-time 3D rendering and game logic.

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Core Technology Breakdown: Three.js, HTML, and CSS

This project’s technological stack is a masterclass in modern web development, with a clear division of roles for each technology.

  • HTML: The Game's Foundation The index.html file serves as the skeleton of the entire application. It's remarkably minimal, containing only a few key elements: a <canvas> element with the class game, which is the rendering surface for the 3D scene; a div for the on-screen controls with four buttons for movement; a div to display the player's score; and another div for the game-over screen. The use of <script type="module" src="./script.js"></script> is crucial, as it allows the project to use JavaScript modules, enabling the import of the Three.js library.

  • CSS: The Stylist and UX Designer The style.css file provides the visual flair and user interface. It leverages Flexbox (display: flex) and CSS Grid (display: grid) to create a responsive and intuitive layout for the game controls. The controls div is positioned at the bottom of the screen, centered, and its buttons are given a retro, pixel-art feel with box-shadow to simulate depth. The score display is placed in the top-left corner, styled with a pixelated font-family: "Press Start 2P".

    The CSS also handles the game-over screen with #result-container which is initially hidden using visibility: hidden and then made visible via JavaScript when the game ends. A hidden YouTube logo with a hover effect is also included, demonstrating a thoughtful touch for potential monetization or promotion within the game's design. This project's CSS is a great example of how to make a 3D application's 2D interface both functional and visually appealing.

  • JavaScript and Three.js: The 3D Engine The script.js file is the heart of the project, a complex and well-structured file that uses the Three.js library. The script imports the entire Three.js library as a module. The code is organized into functions that create various 3D objects, manage game logic, and handle user input.

    Key components include:

    • Scene, Camera, and Renderer: The script initializes the THREE.Scene, an OrthographicCamera, and a WebGLRenderer. The OrthographicCamera is a smart choice because it prevents perspective distortion, giving the game a stylized, isometric look similar to the original "Crossy Road".

    • Procedural Generation: The game's map is procedurally generated using functions like initializeMap() and addRows(). The metadata array stores information about each row, such as whether it's a forest or a car or truck lane. The generateRows() and generateRow() functions are responsible for randomly creating new sections of the map, ensuring the game is infinitely playable.

    • 3D Models and Textures: Functions like Player(), Car(), Truck(), and Tree() use THREE.Mesh and BoxGeometry to create the game's objects. They also use MeshLambertMaterial and MeshPhongMaterial to define the object's color and how it interacts with light. Crucially, custom textures for the vehicles are generated on the fly using a <canvas> element, a highly efficient and programmatic way to create the pixelated window and door details.

    • Game Loop and Logic: The renderer.setAnimationLoop(animate) function sets up the main game loop, which runs every frame. Within the animate() function, the script calls animateVehicles(), animatePlayer(), and hitTest() to update the game state, move objects, and check for collisions.

    • Collision Detection: The hitTest() function is a critical piece of game logic. It uses Three.js's THREE.Box3 to create bounding boxes around the player and each vehicle on the current row. If playerBoundingBox.intersectsBox(vehicleBoundingBox) returns true, it triggers the game-over state.

Visual Design and User Experience (UX) Analysis

The visual design and UX of this project are directly influenced by the classic "Crossy Road" aesthetic, which is a key part of its appeal.

  • Visual Aesthetic: The project's look is defined by its low-poly, blocky style. The use of flatShading: true on the materials enhances this aesthetic, giving the models a distinct, faceted appearance. The color palette is vibrant and simple, with bright greens for grass (0xbaf455) and varying shades of gray for the roads (0x454a59). The custom-drawn textures for the vehicles, created with a Texture() function, add to the pixelated, retro feel.

  • User Experience (UX) Principles:

    • Clear Feedback: The player's score is prominently displayed in the top-left corner, providing immediate feedback on their progress. The retry button and "Game Over" message on the result screen are clear and concise, guiding the user on what to do next.

    • Intuitive Controls: The game offers two methods of input: on-screen buttons and keyboard arrow keys. The on-screen controls are designed with a large, grid-based layout that is easy to use on mobile devices, while keyboard controls cater to desktop users. The queueMove() function handles the input, adding moves to a queue which are then executed one at a time, preventing erratic movement.

    • Responsiveness: The project is fully responsive. The Camera() function adjusts its OrthographicCamera based on the window's aspect ratio, ensuring the game looks correct on any screen size. The CSS also uses a media query (@media (min-height: 425px)) to conditionally show the YouTube promotion logo, a small but effective way to optimize for different display sizes.

Behind-the-Scenes Mechanics: How It All Comes Together

The inner workings of this game are a testament to modular and well-structured JavaScript.

The initializeGame() function acts as the game's reset and initial setup. It calls initializePlayer() and initializeMap() to create the starting scene and game state. The animate() function is where the game truly runs. On each frame, it updates the position of every vehicle and checks for collisions.

The player's movement is handled by a queue system. When a user presses a button or key, queueMove() adds a direction to the movesQueue array. The animatePlayer() function then processes one move at a time, interpolating the player's position and rotation smoothly over a short period (0.2 seconds) using THREE.MathUtils.lerp. This creates a satisfying, step-by-step movement instead of an instant teleport.

Vehicle movement is managed separately in animateVehicles(). This function iterates through the metadata array and updates the position of each car and truck based on its pre-defined speed and direction. The ref property on each vehicle object is a clever way to link the game logic (metadata) to the actual 3D model (THREE.Group) in the scene. When a vehicle goes off one end of the map, the code wraps it around to the other side, ensuring an infinite, continuous stream of obstacles.

Conclusion: Why It Matters

This "Crossy Road with Three.js" project is a powerful and valuable piece of digital work. It demonstrates that complex 3D applications are not limited to native environments but can be built directly in the browser using open-source libraries.

The project is an excellent educational tool for anyone interested in game development or 3D graphics on the web. It showcases:

  • The power of Three.js for handling low-level 3D rendering tasks.

  • Procedural generation as a technique for creating endless, replayable content.

  • Effective game loop management and state handling.

  • The importance of a well-designed UI (with CSS) to complement a complex 3D scene.

It's a testament to the continued evolution of the web as a platform, proving that the browser can be a stage for engaging, high-performance interactive experiences.

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