QT代写: COMP4799 Assignment 1 Create a simple graphical display using QT

The Configuration file stores:

The table which consists of: the size

x

y, colour,

friction
An array of balls each element of which consists of

colour mass radius position

x

y velocity x
y

Words in bold are the actual keys that should be used. Colours can be specified by name eg “red’ or “blue” if they are simple, or by rgb hex value eg “\#112233”. Your program must accept either. All other values are floats.

An example config file is provided.

{
“table” : {

  "colour":"green",
  "size":{
  "x":600,
  "y":300

},

  "friction":0.1
 },

 "balls" : [
  {"colour":"white","position":{"x":50,"y":50},"velocity":{"x":10,"y":1},"mas

 s":1,"radius":10},
  {"colour":"red","position":{"x":150,"y":60},"velocity":{"x":-10,"y":0},"mas

 s":1,"radius":10},
  {"colour":"blue","position":{"x":150,"y":40},"velocity":{"x":-10,"y":0},"mas

 s":1,"radius":10},
  {"colour":"#123456","position":{"x":250,"y":70},"velocity":{"x":-10,"y":

 0},"mass":5,"radius":20}
 ]
 }

Physics

Friction

You are free to implement friction any way you want e.g. constant deceleration or deceleration proportional to velocity, as long the balls eventually come to rest.

Collisions with walls

When a ball collides with a wall it should simply reverse the velocity perpendicular to the wall, e.g., if a ball is travelling to the bottom right with a velocity of (1,1) and bounces off the right wall it will be (­1,1), the x velocity is reversed. If it then proceeds to bounce off the bottom wall it becomes (­1,­1) as the y velocity is reversed. Note that in QT, as in many gui environments, the origin is at the the top left and y increases down the screen.

Ball­Ball collisions

Since the collision mechanics between balls of arbitrary mass are non trivial the code for calculating the resulting velocity changes is provided.

You do not need to understand how the mathematical section works (it is somewhat simplified anyway) but you will have to understand the initial properties and then apply the resulting changes in velocities to the respective balls.

  //QVector2D is a QT class representing a vector in 2D space,
  //it has useful functions like dotproduct(), length() and normalize().
  //You don't need to use it if you would rather do this yourself

  //Properties of two colliding balls,
  //ball A
  QVector2D posA;
  QVector2D velA;

float massA;

//and ball B

  QVector2D posB;
  QVector2D velB;
  float massB;

  //calculate their mass ratio

  float mR = massB / massA;

  //calculate the axis of collision

  QVector2D collisionVector = posB - posA;
  collisionVector.normalize();

 //the proportion of each balls velocity along the axis of collision

double vA = QVector2D::dotProduct(collisionVector, velA);

  double vB = QVector2D::dotProduct(collisionVector, velB);

  //the balls are moving away from each other so do nothing

  if (vA <= 0 && vB >= 0) {
   return;

}

  //The velocity of each ball after a collision can be found by solving the quadratic equation

  //given by equating momentum and energy before and after the collision and finding the veloc
 ities

//that satisfy this
//-(mR+1)x^2 2*(mR*vB+vA)x -((mR-1)*vB^2+2*vA*vB)=0
//first we find the discriminant
double a = -(mR + 1);
double b = 2 * (mR * vB + vA);
double c = -((mR – 1) * vB * vB + 2 * vA * vB);
double discriminant = sqrt(b * b – 4 * a * c);
double root = (-b + discriminant)/(2 * a);
//only one of the roots is the solution, the other pertains to the current velocities if (root – vB < 0.01) {

    root = (-b - discriminant)/(2 * a);
  }

  //The resulting changes in velocity for ball A and B

  QVector2D deltaVA = mR * (vB - root) * collisionVector;
  QVector2D deltaVB = (root - vB) * collisionVector;

Marking
There are two segments to this assignment: The code which is worth 7 and the essay which is worth 3.

The marking (out of 7 marks) for the code section is as follows:

Compiling and running on the lab machines. (10%)

Behaviour is read from the config file (e.g. positions, colour of balls, colour and size of table, etc). (15%)

The balls bounce off the sides and each other and slow down due to friction. (15%)

Appropriate use of design patterns (Use of factory method in creation of game elements and implementation of the builder, and possible bonus marks for other design patterns used). (30%)

Sensible / appropriate OO design (Extensible code design, clear separation of responsibility, etc). (10%) Clear code: meaningful variable and method names. (10%)

Documentation: Doxygen comments for methods/classes as well as in­code comments where appropriate. (10%)

The marking (out of 3 marks) for the essay section is as follows
Explain the application of the design patterns for your concrete code base. (33%)
Explain advantage and disadvantages of the design patterns used with respect to your code. (33%) Graphical visualisation in UML of your design patterns. (33%)

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