C / C++ / MFC

31-May-11 14:48

I got two questions. First I'm making a brick game. I want the ball to bounce off the paddle at different angles depending on where the ball hits the paddle. If the angle variable is specified directly it bounces off in the correct angle but I'm not sure how to calculate the angle depending on where the ball hits the paddle.

double a = 135;
double angle = (Math::PI / 180) * a;
Ball_List[b]->xVel = speed*Math::Cos(angle);
Ball_List[b]->yVel = -speed*Math::Sin(angle);

Second. I want to animate a box going in a circle but I'm Not sure on the math.

Thanks in advance.

Luc Pattyn31-May-11 14:59

31-May-11 14:59

Cyclone_S wrote:
I want the ball to bounce off the paddle at different angles depending on where the ball hits the paddle

That is pretty vague, and probably not according to normal physics.
Maybe what you want is: the outgoing angle equals the supplement of the incoming angle plus some delta, which is zero in the center and grows when the hit point is away from the center; so maybe calculate that distance and use it to add to or multiply the outgoing angle.

Cyclone_S wrote:
going in a circle

the equations for a circle in two dimensional space are:

(x - xc)^2 + (y - yc)^2 = r^2

x = xc + r * cos(a)
y = yc + r * sin(a)

where (x,y) is a point on the circle, (xc,yc) is the center, r the radius, a an angle in radians.
I cannot believe you would not know that. Look at the equations, they say the point(x,y) is at a fixed distance r from a fixed point (xc,yc).

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

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modified on Tuesday, May 31, 2011 9:17 PM

David Crow31-May-11 15:39

David Crow

31-May-11 15:39

Luc Pattyn wrote:
I cannot believe you would not know that.

Just out of curiosity, why would you assume he would know?

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Luc Pattyn31-May-11 15:50

31-May-11 15:50

Assuming he is adolescent or older, he would have learned this and much more at school, both as formula's for describing a circle, and as a geometric illustration for explaining what a sine and cosine actually are. He already was using angles, sine and cosine, in his post, so it puzzles me how he would not come up with the equations if he had ever seen and understood them.

And then there are books, and Google, and Wolfram, etc.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Cyclone_S5-Jun-11 16:15

5-Jun-11 16:15

Thanks for the replies. Both problems are mostly solved. I have the paddle/ball equation figured out but I'm having a problem where any value less then 1 is ignored... any ideas? I need finer precision. Thanks.

Luc Pattyn5-Jun-11 16:26

5-Jun-11 16:26

Cyclone_S wrote:
I need finer precision

then scale it all up in integers; or use floating-point arithmetic throughout.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Cyclone_S11-Jun-11 15:38

11-Jun-11 15:38

I am using doubles in the function. The problem is I can't move the panel(ball) anything less then 1 pixel. Maybe move the ball 1pixel over a couple of frames? I'm not sure how to do that.

Here is the code.

int speed=Ball_List[b]->speed;
// Paddle center.
int paddle_center = Player->Location.X + Player->Width / 2;

// Ball center.
int ball_center = Ball_List[b]->gameBall->Location.X + Ball_List[b]->gameBall->Width / 2;

// Find the location on the paddle that the ball hit
int paddle_location = ball_center - paddle_center;

// Increase X speed according to distance from center of paddle.
double a=(90-paddle_location);
double angle = (Math::PI / 180) * a; // angle in radians.
Ball_List[b]->xVel = speed*Math::Cos(angle);
Ball_List[b]->yVel = -speed*Math::Sin(angle);

Ball_List[b]->gameBall->Top = Player->Location.Y - 16;

Thanks

Luc Pattyn11-Jun-11 15:49

11-Jun-11 15:49

All of that could have been floats or doubles; it is only when painting that it eventually needs to be rounded to pixels, hence integers.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Cyclone_S11-Jun-11 16:28

11-Jun-11 16:28

so there's no solution then?

Garbage Collector vs Reference Couter

Stefan_Lang31-May-11 22:51

Stefan_Lang

31-May-11 22:51

You might want to check out this site[Physics engines for dummies] for an easy introduction into the basics of vector algebra used to emulate quasi-physical simulations. You will find that in stead of angles and sinus/cosinus it explains the calculations needed for reflections with the help of vector algebra. Although the code is not C/C++ it should be easy enough to translate the relevant code for your problems.

Pranit Kothari31-May-11 4:53

31-May-11 4:53

Hello,
In several posts I have read that Garbage Collector and Reference counter are not same? I wanted to know how?

Regards

http://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29[^]

http://en.wikipedia.org/wiki/Reference_counting[^]

http://en.wikipedia.org/wiki/Reference_counting#Use_in_garbage_collection[^]

C^hris L^osinger31-May-11 4:58

C^hris L^osinger

31-May-11 4:58

image processing toolkits | batch image processing

Maximilien31-May-11 5:12

Maximilien

31-May-11 5:12

Reference counting is one (of many) mechanisms to implement garbage collection.

Watched code never compiles.

Nemanja Trifunovic31-May-11 6:08

Nemanja Trifunovic

31-May-11 6:08

Strictly speaking, reference counting is a technique for implementing garbage collection.

In practice, term "Garbage Collector" usually implies non-deterministic cleanup and that rules out reference counting. In other words, with (automatic) reference counting there is no garbage to be collected: an object gets released at the moment the last reference to it goes out of scope.

utf8-cpp

Difference between Unicode and Multibyte

Stefan_Lang1-Jun-11 0:08

Stefan_Lang

1-Jun-11 0:08

GC is a form of global memory management that keeps track of memory resources and returns freed memory at undefined intervals. For performance reasons, GC often does not immediately return freed memory, but instead just marks it as freed later.

RC is a method to locally ensure that an object is freed as soon as it isn't needed anymore. It determines this by keeping count of the references to the object that have been handed out.

In a way you coud consider RC as a very localized GC. Also, as has been pointed out, RC is often used to implement a GC and find out which memory blocks may be released.

GC has better overall performance, but may lead to heavier use of memory. Using only RC keeps the memory footprint at a minimum, but is somewhat slower.

Pranit Kothari31-May-11 4:16

31-May-11 4:16

Hello,
I wanted to know what is difference between Unicode and Multi-byte character.

Regards

Luc Pattyn31-May-11 5:06

31-May-11 5:06

If you want to know something, you come up with a good subject line (you have), and then give that to Google. It will provide you with good answers.

Smile | :)

Luc Pattyn [My Articles] Nil Volentibus Arduum

Pranit Kothari31-May-11 6:45

31-May-11 6:45

I googled on this topic. I got programming example. But I want theoretical topic or at least one line which shows difference between Unicode and Multibye.

David Crow31-May-11 8:14

David Crow

31-May-11 8:14

Multibyte, or wide character, refers to the size of the datatype in memory, not how each value is defined. Unicode, however, is a character set that provides that definition.

Nemanja Trifunovic31-May-11 6:11

Nemanja Trifunovic

31-May-11 6:11

I suggest you read Joel Spolsky's article on Unicode and character sets[^]. A pretty easy read and gives a decent intro to the topic.

utf8-cpp

Pranit Kothari31-May-11 6:44

31-May-11 6:44

This is OK. But it doesn't show difference between Unicode and Multi-byte char.

Nemanja Trifunovic31-May-11 8:29

Nemanja Trifunovic

31-May-11 8:29

Character sets descended from ASCII that are described in the "A Historical Perspective" section are multi-byte.

utf8-cpp

Richard MacCutchan31-May-11 7:40

Richard MacCutchan

31-May-11 7:40

Lots of detail about this can be found in this white paper[^].

The best things in life are not things.