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Design Documentation.md

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Design Documentation

Structure

MainWindow

Displays game main menu and redirects user to other windows.

SettingsDialog

Lets the user set game preferences and redirects user to gameboard.

Gameboard

Holds game map, scoreboard and control panel, controls the saving, loading and state of game.

Map

In charge of map items renderings, including foods, walls and snakes.

Scoreboard

Displays the score, lives and undefeatable time of a single player.

Snake

Denotes a single player, handles user commands, food effects and notifies other components of the game.

AISnake

Inherits Snake, implements a simple algorithm that enables AI player to move towards the nearest food while avoiding hitting walls and the body of itself.

Walls

Generates, stores and renders the obstacles on the map, check whether a snake hit the walls.

Foods

Generates, stores and renders the foods on the map, check whether a snake ate a food.

Constants

Defines game configurations, enumerables and types.

Features

5 Modes

  • Single Player
  • Double Players
  • Triple Players
  • Only AI
  • AI and Player

2 Types of Walls

  • No Walls: Snake is teleported to the other side when crossing the borders
  • Surrounding Walls: Walls on 4 sides, player will die when hitting the walls

9 Kinds of Foods

Fruits

  • Grape: 5 points
  • Pear: 10 points
  • Apple: 15 points
  • Peach: 20 points

Speed Change

  • Rocket: speed up
  • Snail: slow down

Survival Aid

  • Shield: extends undefeatable time by 5 secods (extra)
  • Heart: award 1 extra life

Special Effect

  • Green Apple: reset snake length and speed (extra)

How to Play

Move

  • Player 0: Up, Left, Down, Right
  • Player 1: W, A, S, D
  • Player 2: I, J, K, L

Control

You may use game control panel on the right side or keyboard shortcuts specified below.

  • Pause: 'P' key
  • Resume: 'R' key
  • Quit: Escape key

Map Editing

Choose the map item to edit and the type of food from control panel, left-click to add item, right-click to remove.

Implementations

This implemenation utilizes Qt's 'Signals and Slots' feature to decouple the components, making it organized, extensible, and easy to maintain.

Rendering

A QTimer in Map periodically invokes Map::paintEvent, which calls independent rendering functions of Snake, Walls and Foods.

Scoreboard uses a timer of an 1-second interval to update undefeatable time.

For performance concerns, only necessary items are painted, blanks are left as they are, there's nothing like global arrays to hold the entire map.

Snake Movement

A QVector<QPoint> named body stores the positions of snake body, the snake head is the last item of it.

When snake moves, an item is popped from the front of body, the new position of snake head is calculated and pushed to the back of body vector.

Snake Control

Implements an User Input Queue to store user inputs, each time the timer inside a Snake object timeouts, an user command is popped out and processed.

This technique eliminates the chance that the snake may turn around under quick operations.

After a snake moves, it emits a snakeMoved signal with snake ID and the new position of snake head for the judgement of walls and foods.

Judgement of Walls

snakeMoved signal is connected to the checkHit slot of Walls, which checks if the snake hits the wall. If so, a hitWall signal is emitted along with the snake ID, the signal is sent to ths die slot of Snake.

The connection of signals and slots between Snake and Walls is established by Map.

Judgement of Foods

Similar to the judgement of walls, Foods will emit a foodEaten signal to the eatFood of Snake, along with the type of food, Snake then applies the food effect to itself.

The connection of signals and slots between Snake and Foods is established by Map.

Acceleration & Deceleration

As previously stated, each Snake has its own timer, this timer measures its speed in rendering interval. When it accelerates, this interval is decreased, when it decelerates, this interval is increased.

Resurgence after Death

When a snake with more than 1 life dies, it'll be assigned a 3-second undefeatable time to escape from danger, its length and speed will be reset.

Map Editing

When the Edit Map button is clicked, Gameboard notifies Map to enter editing mode and start to monitor mouse press event, it then calls the add or remove method of Walls or Foods.

AI Snake

The algorithm of AI Snake is quite simple, it continuously searches for the nearest food by comparing manhattan distance.

Then it checks all 3 possible directions for the next move and choose the one that moves towards the target food, while avoiding hitting walls or itself.

Undefeatable Time

Uses QDeadlineTimer as countdown

Save & Load Game

Utilizes QDataStream to write and read binary file, since QPoint, QVector and other types support serialization natively, we just need to implement operator overloads for our own types.