Re: Maths for bouncing a ball around a window.. - C# Discussion Boards

Hello,

Can someone help me with this.
I see the following error and I dont understand the reason behind this issue.
I browsed through different sites but I didnt get an appropriate answer for this

ERROR :

System.UriFormatException: Invalid URI: The format of the URI could not be determined.
at System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind)
at SonarEngine.T.Page_Load(Object sender, EventArgs e)Engine Path = "*********"

You get this exception for any of the reasons listed in the appropriate exceptions item here[^]. If you showed us what your Uri looked like, we could help.

I was brought up to respect my elders. I don't respect many people nowadays.

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

Message Closed

That's a whole mess of code to wade through. If you put breakpoints in place and step through your code (or look at the stack trace when the exception is thrown) you should get a better idea of which bit is breaking.

I was brought up to respect my elders. I don't respect many people nowadays.

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

I have issues in hitting the debug points as well.
The main code is a webservice call where the webservice is a vb.net code and it is being invoked by a java application.
When I set the debug point on T_PAGELOAD and invoke the webservice, it doesnt even hit the breakpoint and I get the response of the webservice call.

Okay - put some logging in your code, and use try/catch blocks to see if you can narrow down the area that's causing the problem.

I was brought up to respect my elders. I don't respect many people nowadays.

CodeStash - Online Snippet Management | My blog | MoXAML PowerToys | Mole 2010 - debugging made easier

Hi all

I'm playing around with threading at the moment (self-directed learning) and what I would like to do is bounce balls around in a windows each with a thread of their own. I know this might not be the BEST way to do this, I want to do it purely for the learning.

My idea is that I'll have a ball object that will be updated by a timer Event. At regular intervals, on a separate thread, I'll get the positions off all my balls and Draw them to the window. I will probably attempt to get some collision detection between balls going eventually but for now, they'll just bounce if they hit the sides/top of the window.

Anyway, what I really would like to do is have the balls move around with fairly good physics. ie. gravity. But, my maths although good is inappropriate (I did maths & statistics at A level for my current career in biology). So, what equations can I use to give me x and y coordinates when I plug in an increasing value for time(t)? I realise I'll need to check if for x+radius>=rightWallX and x-radius<=leftWallX etc. it's just the movement in the presence of gravity I need.

Can anyone help me out with the maths? I did try google but I think I'm failing to provide the 'right' search terms to find what I want.

I would use two integer properties for the ball object, called DeltaX and DeltaY. These would represent the number of pixels for the ball to move along the X and Y axis. A good starting point would probably be 3 as a value for both of these variables. When DeltaX is positive, the ball is moving to the right; and when negative, the ball is moving to the left. When DeltaY is positive, the ball is moving down; and when negative, the ball is moving up. When you encounter the edge of the form, simply multiply the appropriate variable by -1 to change its direction.

Something like this:

C#

private bool BallHitBoundary(Ball ball)
{
    /* Check if the game ball hit a form boundary. If so, change the direction of the ball accordingly and
     * return true. Otherwise return false. */
    if (ball.Top <= ClientRectangle.Top || ball.Bottom >= ClientRectangle.Bottom)
    {
        // Game ball hit the top or bottom. Change the Y direction the other way.
        ball.ReverseDeltaY();
        return true;
    }

    if (ball.Left <= ClientRectangle.Left || ball.Right >= ClientRectangle.Right)
    {
        // Game ball hit the left or right side. Change the X direction the other way.
        ball.ReverseDeltaX();
        return true;
    }
    else
    {
        return false;
    }
}

and the ReverseDeltaY() and ReverseDeltaX() are methods for the ball object that simply multiply DeltaY/DeltaX by -1:

XML

/// <summary>
/// Reverses DeltaX by multiplying by -1.
/// </summary>
internal void ReverseDeltaX()
{
    DeltaX *= -1;
}

/// <summary>
/// Reverses DeltaY by multiplying by -1.
/// </summary>
internal void ReverseDeltaY()
{
    DeltaY *= -1;
}

The above is actual code from a project I built to make a Breakout game just for the fun of it. The ball object inherits from a Panel object with a solid circle drawn inside of it. It works good for me.

-NP

Never underestimate the creativity of the end-user.

So you didn't attempt to model gravity in the motion of your ball?
Effectively your ball was in outer space? Smile | :)

I suppose that's one way to look at it. Or in this case, gravity is pulling along the Z-axis keeping the balls on the playing field, like a pool table. Big Grin | :-D

If you want gravity to pull down on the Y-axis (towards the bottom of the form), I'm sure that could be incorporated by changing the value of the DeltaY property, but the math is beyond me too. Sorry.

-NP

Never underestimate the creativity of the end-user.

I think I might have found my own answers here actually. I'll have a play around and see what I come up with. But you were on the right track with what you said. Modify the DeltaY by adding a constant gravity component each iteration.

I guess I could also add a 'friction' component acting in the -Y and -X directions each iteration to have the ball slow due to air resistance too. Hmmm! This could be a fun experiment...

It seems at a first glance that it can only bounce once in one timestep, but it can in fact bounce multiple times in succession in one timestep. If you take any shortcuts there, balls can "escape", usually through the corners, and it will be uncommon enough that it could go undetected essentially forever (you can use that to decide that it's really OK, or that it's a very nasty bug, but it's good to be aware of it). If the speeds of the balls are reasonably low and the timestep is reasonably short, balls can still bounce twice, in the corners.
Also, the simple implementation of bouncing actually bounces off of a virtual surface some distance outside the box depending on how far the ball traveled outside in a step. A more correct way to implement it is calculating the intersection of the box with the half-line in the direction that the ball is traveling, then bouncing "some time in the past when it was at that position" (flipping a speed and, crucially, updating the balls position by mirroring it around the line it bounced into*), then looping until the ball is inside the box. Like the other problem, this effect gets worse and worse for higher speeds and longer time steps.
So yes, it's actually pretty complicated.

* that is why you calculate the intersection point - to get the line it first bounced into. There would otherwise be an ambiguity when the ball is in the "outside quadrant" of a corner.

modified 8-Jul-13 12:28pm.

As Harold mentioned you have to make a computation strategy for collisions e.g. ball vs ball and ball vs frame. Here are some terms that you can google.

You can go the variable time step way - good for getting the simulation right.
You can go fixed time step - good for having the simulation go fast.

One computation strategy could be as follows until no more collisions occur in a time step:
- within a time step calculate the next collision
- calculate the physics for involved objects

Collision checking is a discipline in itself - a moving ball within a time step can be looked at as a sweeping volume being a capsule. Collision checking results in a collision time within a time step and a set of contact points.

The physics can be as complicated as you want to. You can keep it very simple by sticking with kinematics (position, velocity) added some impulse calculation or go very exotic by adding lots of dynamics (gravity, friction, spin, energy loss, etc.).

About gravity:
If gravity is g (9.82[m/s^2]) downwards and you have a time step of deltaTime [s], all balls need to have their velocity changed by

velocity change due to gravity: deltaVg = deltaTime * g

In any case, have fun Smile | :)

Kind Regards,

Keld Ølykke

We are using a web service(asmx) to communicate with service provider.

Problem: We are getting a web exception while sending and receiving response.

Exception Details :
1) Exception Message : The request was aborted: The operation has timed out.
2) Exception Status : timeout

We are getting this timeout status within 40 seconds whereas we have set webrequests timeout property to 180 seconds.

Can anybody please suggest me the solution of this problem??

Vishal

vishalmudrale wrote:
We are getting this timeout status within 40 seconds whereas we have set webrequests timeout property to 180 seconds.

Can you verify that it's the WebRequest that's actually timing out? Can you post the entire exception?

Bastard Programmer from Hell Suspicious | :suss:

If you can't read my code, try converting it here[^]

Thanks for your reply friend,

Can you please send your solution again????

vishalmudrale wrote:
Can you please send your solution again????

I did not send a solution, I asked a question.

So, no, can't do.

Bastard Programmer from Hell Suspicious | :suss:

If you can't read my code, try converting it here[^]

The request was aborted: The operation has timed out.

You already mentioned that. I did (and will not) post a solution; there's a question that needs to be answered to find out what might be going wrong. If you are having trouble with the language, try and find someone who can help.

Bastard Programmer from Hell Suspicious | :suss:

If you can't read my code, try converting it here[^]

I started to develop a Point of sale system for Restaurant/Hotel which also include a facility of sms confirmation for customers for home delivery etc.
I think first we need a thermal printer for bills slips etc,
Please give some ideas how to start the project and what types of packages or tools used.

I use .Net C# as a developer.

modified 8-Jul-13 12:56pm.

This forum is supposed to be used to get people help you with with programming issues and not to collect (rip off) ideas/requirements from us.
If you are indeed developing something like that, you should come with these ideas yourself. You might even ask your potential customers for ideas if you can't come with anything by yourself.

Regards,

— Manfred

"I had the right to remain silent, but I didn't have the ability!"

Ron White, Comedian

Well, you START by gathering very detailed requirements from your customer. They're the ones paying you and they're the ones who will dictate what they want, in detail. If they don't get what they want, you don't get paid, so make sure THEY know what they want.

Really, this is a question that you should NEVER have to ask in a forum.

A guide to posting questions on CodeProject[^]

Dave Kreskowiak

I agree completely with the other responses - you need to gather requirements from your users to know what to build.

A restaurant and a hotel are really completely different businesses. The restaurant may include both what you think of as "point of sale" as well as kitchen systems - printers and screens, mostly - to facilitate the preparation of the food. The hotel presumably needs to be able to deal with reservations, credit card pre-approval, and incidental charges (movies, meals, crap from the little store most hotels have).

There are probably existing hotel systems that include modules for running in-house restaurants, but I would think that the only real integration point would be managing to bill meals back to the guest's room.

The bottom line is that you need to gather detailed requirements for what they want, and you need to understand WHY they're hiring someone to write a system when there are no doubt quite mature systems available for purchase. What do they think is unique about their operation?

If you're a general consultant as opposed to a coder for hire, the right thing for you to do is probably find an existing package that meets their needs, and try to get a fee from them or the vendor for helping the two of them get it going.

If you're going forward with writing something once you have requirements, you should be looking at Microsoft's Point Of Sale for .Net. It's a .Net implementation of the OPOS standard to make dealing with the specialized POS hardware easier.

Point of Sale is its own unique little niche market, and if you're not generally familiar with it (and you're clearly not) you may want to just steer clear.

You really have to learn basics. "thermal printer" is nothing important for the project.
Learn some programming and design, e.g. with the book "Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and Iterative Development" by Craig Larman. An example used in that book is a POS, too.