SWEN20003 - Object Oriented Software Development ShadowFlap - Project 2A - Solved

Bagel
The Basic Academic Game Engine Library (Bagel) is a game engine that you will use to develop your game. You can find the documentation for Bagel here.

Graphics Concepts Revision
Coordinates
Every coordinate on the screen is described by an (x,y) pair. (0,0) represents the top-left of the screen, and coordinates increase towards the bottom-right. Each of these coordinates is called a pixel. The Bagel Point class encapsulates this, and additionally allows floating-point positions to be represented.

Frames
The program’s logic is updated 60 times per second, each time the screen is cleared to a blank state, and all of the graphics are drawn again. Each of these steps is called a frame. Every time a frame is to be rendered, the update() method in ShadowFlap is called. It is in this method that you are expected to update the state of the game.

Velocity
Moving objects have a velocity that can be represented by a vector (vx,vy). A vector is composed of magnitude and a direction. Often, the magnitude is the step size that the object takes. In this case, we scale the vector to have magnitude 1 (called a unit vector) and simply use its direction component, which was described in detail in Workshop 4. Calculating the new position can be done via vector addition of the position and velocity; Bagel contains the Vector2 class to facilitate this. You are not required to use this class; it is merely provided for convenience. You can refer to Workshop 4 solution for an implementation of ’moving’ objects. However, the implementation in Workshop 4 solution does not consider acceleration.

Collision
It is sometimes useful to be able to tell when two images are overlapping. This is called collision detection and can get quite complex. For this game, you can assume images are rectangles. Bagel contains the Rectangle class to help you.

Game Elements
Below is an outline the different game elements you will need to implement. ShadowFlap has 2 different levels in this project. Each level comes with different images for each game element, as well as differing game logic. The following are game elements that are common to both levels (despite using different images).

Background
The background should be rendered on the screen and completely fill up your window throughout the game. The image that acts as the background is supplied to you in the skeleton package. There is no need to scale or rotate the image in anyway. Remember that the default window size should be 1024 * 768 pixels. You can find the background image for each level in their respective subfolders within res.

Bird
In addition to the basic functionalities implemented in Project 1 (spawning, flying, falling, wingflap, collision with pipes), the Bird also has a life bar in this project and the ability to pick up/shoot weapons at pipes in Level 1. The implementation details of Life Bar and Weapons are described in later sections of this document. The functionalities implemented in Project 1 are attached below for your convenience. When the player first presses SPACE to start the game, the bird should start by flying.

Wing-Flapping
To imitate the flapping motion, birdWingUp.png should be rendered once every 10 frames. In all other frames where the bird is active, birdWingDown.png should be rendered. The bird images to be used in Level 0 and Level 1 are to be found in their respective subfolders in res.

Spawning
When the player hits the space-bar for the first time to start the game, the bird should initially spawn at (200, 350). The bird’s x coordinate should remain constant throughout the game. The image to be used in spawning is birdWingDown.png.

Falling
After the game has started, the bird (albeit very briefly) has an initial speed of 0 pixel per frame before gravity comes into play. When not flying (see the following section for flying behaviour), the bird’s falling speed is accelerated by gravity at of 0.4 pixel per frame-squared (not 9.8 like on Earth!). However, the bird cannot fall faster than 10 pixels per frame. Remember that every time a frame is rendered, the update() method in the main ShadowFlap class is called.

Flying
After the game has started, the player can press the space bar for the bird to fly. Whenever the space bar is pressed, the bird should start flying upwards by 6 pixels per frame. Then, gravity should pull it down in the same behaviour as described in the Falling section above.

Pipes
In this game, a set of pipes consists of a top pipe (which stems from top of the window and points downwards) and a bottom pipe (which stems from the bottom of the window and points upwards). You are provided with an image of a top pipe in both levels, which you must rotate to become a bottom pipe when appropriate. The top pipe image you are provided with is long enough to span the entire window height, but remember that you can draw images at negative coordinates.

The logic for spawning pipes in Level 0 and Level 1 is different, and will be described in the Level 0 and Level 1 sections later in this document. However, in both levels, sets of pipes should be spawned continuously every 100 frames from the right border of the window, until one of the following scenarios is encountered.

•    Level 0: Level-Up after score reaches 10 points.

•    Level 1: Win after score reaches 30 points.

•    Both Levels: Game-Over after life bar depletes.

Once spawned, the set of pipes should start moving from their initial position to the left border of the screen when the player presses the space bar to start the game, at a speed of 3 pixels per frame. If there is no collision with the bird, the pair of pipes should leave the window from the left border. The player is able to adjust the speed at which the pipes move towards the left border of the window by mechanisms described in the Timescale Controls section below.

There are multiple types of pipes for Level 1 with different strengths. They are specified in the Level 1 section later in this document.

Timescale Controls
The movement rate of pipes in this project specification assume a timescale of 1. In the complete ShadowFlap game, we might want to speed things up to increase the difficulty of the game.

When the ‘L’ key is pressed, the timescale should increase by 1 (if possible). When the K key is pressed, the timescale should decrease by 1 (if possible). The timescale should not go below 1 or above 5. Each change in timescale makes the movement rate of pipes increase or decrease by 50%.

The effect of a change in the timescale should be reflected immediately within the game.

Life Bar
Life Bar composes of full-hearts and empty-hearts, where a full-heart represents 1 life and an emptyheart represents a used life. Note that a heart should never disappear. Life Bar should update in real time throughout the game.

Life Bar should be rendered from the left. That is, the first heart (leftmost heart) should be rendered with its top-left coordinate at (100, 15). From this heart onwards, every heart should be spaced apart with 50 pixels in between them.

The bird has 3 lives in Level 0 and 6 lives in Level 1. The left-over lives from Level 0 does not carry over to Level 1. The bird loses a life when it collides with a pipe or goes out-of-bound (described below).

Out-of-Bound
If the bird’s centre y-coordinate exceeds the window’s top border or the bottom border, it is considered out-of-bound. Once an out-of-bound is detected, a life is lost and the bird should be re-spawned at its original position of (200, 350).

Game Over Screen
The Game-Over screen should be rendered when the game is lost. The game is lost when the Life Bar is depleted. The Game-Over screen is the same as what you have implemented in Project 1, that is, a message of GAME OVER should be rendered at the centre of the window. Additionally, the score should be rendered at 75 pixels below the GAME OVER message, in the format of FINAL SCORE: k. The only difference between the Game-Over screen of Level 0 and Level 1 is the background.

Score Counter
While the bird is active, a score counter should be rendered in the top left corner of the screen, in the format of SCORE: k, with k being the correct score at any moment of the game. The bottom left of the score counter message should be located at (100, 100).

The logic for score-counting is different in Level 0 and Level 1, this differing behaviour is described below in each level’s respective section.

Level 0
Start Screen
A Start screen for Level 0 should be rendered when the game is first run, and it should be rendered until the player presses SPACE to start the game. An instruction message that reads PRESS SPACE TO START should be rendered at the centre of your window, on top of the Level 0 background and in the font provided.

Scoring Logic
When the bird’s centre x-coordinate crosses the right-hand-side x-coordinate of a pipe set, 1 point is earned.

Pipe Spawning
There are 3 ”types” of pipe sets in Level 0. They will be referred to as ’High-Gap’, ’Mid-Gap’ and ’Low-Gap’ for convenience here, but you do not need to name them accordingly in your implementation. The gap between top and bottom pipe is still 168 pixels for all 3 ”types” of pipe sets. However:

•    High-Gap: The gap should start at position (100) on the y-axis of the Window.

•    Mid-Gap: The gap should start at position (300) on the y-axis of the Window. • Low-Gap: The gap should start at position (500) on the y-axis of the Window.

In Level 0, every pipe set you spawn should be randomly chosen from the 3 types listed above.

Level-Up Screen
When the level-up score threshold of 10 has been reached, a Level-Up screen should be rendered for 20 frames before Level 1 is loaded. The Level-Up screen should have the same background as Level 0, with the message ”LEVEL-UP!” rendered at the centre of the window. Nothing else (bird, pipes, scores, life bar etc.) should be rendered.

Level 1
Start Screen
After the Level-Up screen in Level 0 has been rendered for 20 frames, a Start screen for Level 1 should be rendered. An instruction message that reads PRESS SPACE TO START should be rendered at the centre of your window, on top of the Level 1 background and in the font provided. Additionally, a message that reads "PRESS ’S’ TO SHOOT" should be rendered 68 pixels below the instruction message. Note that nothing else should be in the window at this time. This Start screen is rendered until the player presses SPACE to start Level 1.

Weapons
The bird in Level 1 can use rocks and bombs as weapons to destroy pipes and earn points. You can find their respective images in the level-1 subfolder under res.

Weapons should be spawned from the right border of the screen at a random y-coordinate between 100 and 500. The type of weapon (rock or bomb) spawned at anytime should also be random. Weapons should be spawned at an interval that does not overlap with the spawning of pipe sets. That is, you can decide how frequently the weapons are spawned as long as there is no overlapping behaviour: there should never be a weapon on a pipe since they are non-retrievable by the bird. Of course, the weapons should never overlap with each other or be out-of-bound either. However, since flames shoot from the steel pipes randomly, it is okay for a weapon to overlap with a flame.

When the bird touches a weapon, the weapon is picked up and attached to the beak of the bird. That is, wherever the bird goes, the weapon should be rendered at its beak (you can take the right-hand border of the bird’s rectangle for convenience). The bird can only hold one weapon at anytime and cannot store weapons.

If a weapon is picked up by a bird, the player can press ’S’ to shoot. Each type of weapon has a shooting range and the type of pipes it can destroy:

Weapon
Shooting

Range
Target

Types
Rock
25 pixels
plastic pipes
Bomb
50 pixels
all pipes
If the weapon does not collide with a pipe within the shooting range, it should disappear after reaching the shooting range. The point at which the player presses ’S’ is its firing point. After being shot, the weapon travels at the speed of 5 pixels per frame, in a straight line, to reach its shooting range and detect if it hit any pipes.

Once collided with a pipe, the weapon and pipe set (if the weapon collides with a top pipe, the corresponding bottom pipe should also disappear, and vice versa) should both disappear. The score counter increments by 1 in this case.

If a weapon is never picked up by a bird, it should travel from its spawning point to the left border of the window at the speed of 3 pixels per frame (same speed as pipes) and disappear once it leaves the window.

Scoring Logic
When the bird’s centre x-coordinate crosses the right-hand-side x-coordinate of a pipe set, 1 point is earned.

Additionally, whenever a pipe is destroyed by a weapon, 1 point is earned.

Pipes
There are 2 different types of pipes in Level 1: plastic pipes and steel pipes. You can find the respective images of each in the level-1 subfolder under res. The pipes have different strengths against attacks from the weapons, and other differing features as follows:

•    Plastic Pipes: Destroyed after 1 hit from any weapon.

•    Steel Pipes: Destroyed after 1 hit from bomb only. The steel pipe set also shoots flames from both its top and bottom pipes simultaneously every 20 frames while it is on-screen. You can find the image of flame in the level-1 subfolder under res. When the pipes are shooting flames, a collision between the bird and the flames has the same result as a collision between the bird and the pipe body itself.

Pipe Spawning
The gap between top and bottom pipe is still 168 pixels for plastic pipe sets in Level 1. For steel pipe sets, the gap is shortened whenever the flames appear as described in the previous section, but the gap is still 168 pixels when there is no flame. The gap of 168 pixels can start at any y-coordinate between the range of 100 to 500.

For every pipe set spawned in Level 1, a new random number between 100 and 500 should be generated. This will be the start of the 168-pixel gap between top and bottom pipe of this pipe set.

Win Screen
When the win score threshold of 30 has been reached, a Win screen should be rendered. This marks the end of your program and should remain static until the player quits the game by pressing ESCAPE to close the window. The Win screen should have the same background as Level 1, with the message ”CONGRATULATIONS!” rendered at the centre of the window. Nothing else (bird, pipes, scores, life bar etc.) should be rendered.