Testing

The IOCT Masters Showcase Event at The Phoenix on Friday, 25th of July 2008 offered an opportunity to demonstrate the game and get feedback from players.

Feedback was extremely positive, with people staying to play the game for a while. Comments suggested that the game was interesting to play and once you had started playing you didn’t want to stop, and also suggested it would be better to play the game on a faster computer in order for the game to run slightly smoother. This is an issue I was already aware of and was just demonstrating the game on the laptop I have been using to code it on. Ideally, I would have demonstrated the game on a desktop computer, however, I did not have access to one during the event.

Other comments suggested that people liked the design of the bricks in the different levels, as I had created posters to show print screens of the different levels. People were keen to play the game and interested in how the object detection worked, asking about how the movement of the AIBO ball (used as I only had a limited space in which to demonstrate my work) controlled the paddle on the screen.

Sound effects

Bloop:






Used during the countdown, synchronised with the countdown

Explosion:





Used when a brick explodes

Waaaa:







Used when a "life" is lost

Boing:






Used when the ball collides with an object on the game screen, including:

• ball hits brick
• ball hits border
• ball hits paddle

Completion:








Used when a level is completed

Sound

I have carried out some research into the use of sound in game and have decided to add sound to the game, to make playing the game a more interesting experience, as it involves more of the senses.

Times in the game that may benefit from sound:

• Ball and border collision
• Ball and paddle collision
• Ball and brick collision
• Brick explosion

Other times during the game when sound effects or music could be used:

• Losing a “life”
• Completing a level
• Congratulation state
• During the countdown
• Introduction to the game

Collision detection: Paddle

The ball must be projected on to the paddle and the point at which the ball would have contacted the paddle and this point must be calculated. As the paddle has curved edges I tried to angle the edges of the paddle collision detection lines, however, having tried to use the intersection of two lines I could not get the collision detection process to work as desired. I have decided to extend the line across the top of the paddle, so that the collision occurs whenever the ball collides within the length of the paddle.

paddley = top edge of paddle in the y axis

Test:
paddley > position in y – radius

y1=paddley – ball position y + radius
t=y1/vely
x1=t*velx


Test condition, ensure ball hits between paddle edges:
previous ball position x + x1 > paddle position – paddle half width
&&
previous ball position x + x1 < paddle position + paddle half width

ball position x = previous ball position x + x1
ball position y = previous ball position y + y1
vely=-vely
ball position x = ball position x + (1-t)*velx
ball position y = ball position y + (1-t)*vely

Collision detection: Left border

Collision detection needs to be calculated, as the ball contacts and needs to rebound from the borders around the game board, the paddle and the bricks.

This works on the physics equation:
speed=distance/time

To calculate the movement of the ball after collision I need to know how much time it has taken to reach the collision, as a proportion of a time step. The remaining time in the time step after the collision is used by the ball travelling in the opposite direction.
x1=ball position x – minimum x + ball radius //calculate distance ball travelled before collision








t //amount of time step as proportion, between 0 and 1
y1 //distance travelled in y before collision
velx //total distance moved (real and projected) in x in time step
vely //total distance moved (real and projected) in y in time step

t=x1/velx //distance travelled in x in proportion to whole distance to be travelled in time step
y1=t*vely //calculate distance travelled in y before time step, multiply whole distance the ball would travel in time step by proportion already travelled
velx=-velx //reverse direction

Developing ball movement

The movement of the ball is based on the mathematical principles of trigonometry and Pythagoras theorem, so these principles were researched.
h = overall velocity of the ball (the hypotenuse)
x = x component of the ball velocity
y = y component of the ball velocity
0 = theta, angle of the path of the ball, set to a randomly generated number between 35o and 55o

x = sin 0 * h
y = cos 0 * h

Trigonometry:
Trigonometry can be used to calculate angles. In right-angled triangles, where there is a hypotenuse, the term SOHCAHTOA can be used:

• SOH = sine = opposite/hypotenuse
• CAH = cosine = adjacent/hypotenuse
• TOA = tan = opposite/adjacent

Pythagoras theorem:
In a right-angled triangle, the hypotenuse is equal to the sum of the other two sides. Often written as: a2+b2=c2

Random number generation:
For the ball to leave the paddle at the start of each game using a different angle, a random number between two set boundary numbers should be generated and control the ball’s initial movement. The boundary numbers are 35o and 55o as these were considered suitable angles between which to project the ball from the paddle.
To create a random number between these boundaries the srand code is implemented to initialise the random number generator, using processor clicks, as these values are different every time the program runs. The boundary angles are then set and the angle must be between these values, it is then multiplied by 2pi/360, and converted to radians. The ball velocity in x and y are then calculated and the remainder of the random number is divided by 2, giving an answer of 0 or 1, allowing the x component to be reversed, changing to direction the ball takes as it leaves the paddle.

Creating the paddle

The paddle consists of a rectangle and two circles, one at either end of the rectangle. This gives the paddle curved edges, which makes it more visually interesting than just a rectangular design.

The paddle is created using a number of variables. These variables are used to calculate the position of the paddle, the distances it can travel along the x axis inside of the game board and the way in which it interacts with the ball, through collision detection.

The design ideas for the paddle include a highlight and lowlight stripe in the code to add detail and to help create the pseudo 3D effect.

Image Processing

I've started to code the game by working on the image processing needed to capture the video signal from the web-cam, turning this into a binary Hue and Saturation image and also creating a flipped copy of the video image in it's original state.

The binary image is used to calculate the weighted-centroid of the bright pink colour of an AIBO ball. The AIBO ball is being used during development, whilst I wait for the larger pink gym ball to arrive.

The copy of the video image has been flipped and will used as the background for the game board, so that players can see themselves, as well as the gym ball. The players will be able to see that the way in which they move the gym ball has an effect on the paddle used in the game.