C / C++ / MFC

19-Jun-11 14:07

Hi,

I got a ball hitting a paddle and I want it's X velocity to increase/decrease depending on where it hits the paddle. The code below works with whole numbers but not for numbers like "0.67" or "2.45". I'm looking for a way to animate objects moving at smaller increments for better precision. Thanks.

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;

// change angle 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);

// Move the ball
Ball_List[b]->gameBall->Location = Point(Ball_List[b]->gameBall->Location.X + Ball_List[b]->xVel, Ball_List[b]->gameBall->Location.Y + Ball_List[b]->yVel);
[/code]

enhzflep19-Jun-11 15:03

19-Jun-11 15:03

Can you tell us what doesn't work when you use non-integers. And non-integers for what?

Cyclone_S19-Jun-11 16:03

19-Jun-11 16:03

I tried using doubles but for a value like 0.6 the ball doesn't move at all. The box control takes doubles but will round them down to the nearest integer. Is there a way to do this over the course of X number of frames?

I'm using non-integers for the box control's position. Right now there's only about 6 different directions the ball takes when hitting the paddle. I need finer control over the speed of the ball.

This problem happens with any sort of animation I try to do. What if I wanted smooth acceleration of a game object? This wouldn't be possible with the problem I'm encountering.

enhzflep19-Jun-11 16:23

19-Jun-11 16:23

Ah, okay gotcha.

Well, in that case you can use floats or doubles for the position and the velocity. It's just a matter of rounding the position to an int before using it to display the ball.

Or of course, you could keep an integer position of last impact, along with an integer number of frames since it occured and a double velocity, or position increment per frame. Each time you display, just show the ball at [impact.x + frames*velocity.x, impact.y + frames*velocity.y]

But the easier is to just keep the position and velocity as doubles, converting to an int when using for display purposes. (You might also have to add code that will check if the ball is within a threshold distance, since non-integers will mean your ball wont hit the walls or paddle 'exactly' - well not at the exact moment of a frame, anyway.

Cyclone_S19-Jun-11 16:49

19-Jun-11 16:49

I'm not sure I understand. Do you understand what I'm trying to do? after the ball hits the paddle it should move left/right depending on how far from the center it is. Just need finer precision on the angle(xvel) of the ball. Thanks.

I tried something like this. I took a number like 1.65 and did

1.65 - Math::Floor(1.65)

to get just the decimal part of the number 0.65.Then every frame I added 0.65 to 0.65 and checked if it was >= 1. If it was I added 1.0 to the left/right property of the box. I then repeated that.

The problem with it was I wasn't encounting for the speed of the ball. If the speed of the ball is 6 it moves 6 frames every timer tick. The code I was trying only moved 1 pixel at a time.

I'm just not sure on the math to incorporate the speed into it.

enhzflep19-Jun-11 18:24

19-Jun-11 18:24

Sorry about that. Um, I think I understand your intention.

It sounds to me much like a game of pong or similar. Lord knows what I've done with my old code. I can't be bothered even think about the physics right now, but I've thrown together some code that will throw a red dot into a parabolic arc.

In such a path, we'll have to both be able to have small increments of movement, and be able to vary them. You just have to assign the ball's velocity and position in an appropriate way for your application.

Enjoy. Smile | :)

#include <windows.h>

/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

/*  Make the class name into a global variable  */
char szClassName[ ] = "CodeBlocksWindowsApp";

int WINAPI WinMain (HINSTANCE hThisInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR lpszArgument,
                     int nCmdShow)
{
    HWND hwnd;               /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
    wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor = LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;                 /* No menu */
    wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */
    wincl.cbWndExtra = 0;                      /* structure or the window instance */
    /* Use Windows's default colour as the background of the window */
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

    /* Register the window class, and if it fails quit the program */
    if (!RegisterClassEx (&wincl))
        return 0;

    /* The class is registered, let's create the program*/
    hwnd = CreateWindowEx (
           0,                   /* Extended possibilites for variation */
           szClassName,         /* Classname */
           "Click to release a ball",       /* Title Text */
           WS_OVERLAPPEDWINDOW, /* default window */
           CW_USEDEFAULT,       /* Windows decides the position */
           CW_USEDEFAULT,       /* where the window ends up on the screen */
           544,                 /* The programs width */
           375,                 /* and height in pixels */
           HWND_DESKTOP,        /* The window is a child-window to desktop */
           NULL,                /* No menu */
           hThisInstance,       /* Program Instance handler */
           NULL                 /* No Window Creation data */
           );

    /* Make the window visible on the screen */
    ShowWindow (hwnd, nCmdShow);

    /* Run the message loop. It will run until GetMessage() returns 0 */
    while (GetMessage (&messages, NULL, 0, 0))
    {
        /* Translate virtual-key messages into character messages */
        TranslateMessage(&messages);
        /* Send message to WindowProcedure */
        DispatchMessage(&messages);
    }

    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return messages.wParam;
}

////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////
float ballPosX, ballPosY, ballVelocityX, ballVelocityY;
const int myTimerId = 1;
const int intervalMs = 50;

VOID CALLBACK myTimerProc(HWND hwnd,        // handle to window for timer messages
    UINT message,     // WM_TIMER message
    UINT idTimer,     // timer identifier
    DWORD dwTime)     // current system time
{
	ballPosX += ballVelocityX;
	ballPosY += ballVelocityY;
	ballVelocityY -= 0.1;
	InvalidateRect(hwnd, NULL, true);
}

/*  This function is called by the Windows function DispatchMessage()  */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	PAINTSTRUCT ps;
	HDC hdc;

    switch (message)                  /* handle the messages */
    {
        case WM_DESTROY:
            KillTimer(hwnd, myTimerId);
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;

        case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);

            SetPixel(hdc, ballPosX, ballPosY, RGB(250,0,0));
            SetPixel(hdc, ballPosX, ballPosY+1, RGB(250,0,0));
            SetPixel(hdc, ballPosX+1, ballPosY, RGB(250,0,0));
            SetPixel(hdc, ballPosX+1, ballPosY+1, RGB(250,0,0));

            EndPaint(hwnd, &ps);
            break;

        case WM_LBUTTONUP:
            ballPosX=0;
            ballPosY=0;
            ballVelocityX=3.2;
            ballVelocityY=8.1;

            KillTimer(hwnd, myTimerId);
            SetTimer(hwnd, myTimerId, intervalMs, myTimerProc);
            break;

        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}

enhzflep19-Jun-11 21:35

19-Jun-11 21:35

I got bored. Here try if this if you like - it's two balls, a red one and a white one. If you hit the red one with the white one it will move in a direction away from the white one before being slowed to a halt by friction. Of course your collision handling stuff will be different(hopefully pixel-accurate, unlike mine) for the paddle and the ball, but it's the same concepts at work.

Rose | [Rose]

#include <math.h>
#include <windows.h>
#include <windowsx.h>
#include <wingdi.h>

/*  Declare Windows procedure  */
LRESULT CALLBACK WindowProcedure (HWND, UINT, WPARAM, LPARAM);

void handleCollisions();

/*  Make the class name into a global variable  */
char szClassName[ ] = "CodeBlocksWindowsApp";

int WINAPI WinMain (HINSTANCE hThisInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR lpszArgument,
                     int nCmdShow)
{
    HWND hwnd;               /* This is the handle for our window */
    MSG messages;            /* Here messages to the application are saved */
    WNDCLASSEX wincl;        /* Data structure for the windowclass */

    /* The Window structure */
    wincl.hInstance = hThisInstance;
    wincl.lpszClassName = szClassName;
    wincl.lpfnWndProc = WindowProcedure;      /* This function is called by windows */
    wincl.style = CS_DBLCLKS;                 /* Catch double-clicks */
    wincl.cbSize = sizeof (WNDCLASSEX);

    /* Use default icon and mouse-pointer */
    wincl.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hIconSm = LoadIcon (NULL, IDI_APPLICATION);
    wincl.hCursor =LoadCursor (NULL, IDC_ARROW);
    wincl.lpszMenuName = NULL;                 /* No menu */
    wincl.cbClsExtra = 0;                      /* No extra bytes after the window class */
    wincl.cbWndExtra = 0;                      /* structure or the window instance */
    /* Use Windows's default colour as the background of the window */
    wincl.hbrBackground = (HBRUSH) COLOR_BACKGROUND;

    /* Register the window class, and if it fails quit the program */
    if (!RegisterClassEx (&wincl))
        return 0;

    /* The class is registered, let's create the program*/
    hwnd = CreateWindowEx (
           0,                   /* Extended possibilites for variation */
           szClassName,         /* Classname */
           "Click to release a ball",       /* Title Text */
           WS_OVERLAPPEDWINDOW, /* default window */
           CW_USEDEFAULT,       /* Windows decides the position */
           CW_USEDEFAULT,       /* where the window ends up on the screen */
           544,                 /* The programs width */
           375,                 /* and height in pixels */
           HWND_DESKTOP,        /* The window is a child-window to desktop */
           NULL,                /* No menu */
           hThisInstance,       /* Program Instance handler */
           NULL                 /* No Window Creation data */
           );

    /* Make the window visible on the screen */
    ShowWindow (hwnd, nCmdShow);

    /* Run the message loop. It will run until GetMessage() returns 0 */
    while (GetMessage (&messages, NULL, 0, 0))
    {
        /* Translate virtual-key messages into character messages */
        TranslateMessage(&messages);
        /* Send message to WindowProcedure */
        DispatchMessage(&messages);
    }

    /* The program return-value is 0 - The value that PostQuitMessage() gave */
    return messages.wParam;
}

////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////
float ballPosX, ballPosY, ballVelocityX, ballVelocityY;
float curMouseX, lastMouseX, curMouseY, lastMouseY;
int clientWidth, clientHeight;

const int myTimerId = 1;
const int intervalMs = 50;
const int ballRadius = 10; // pixels
const int cursorRadius = 15; // pixels


void handleCollisions()
{
    float dx, dy, dist;

    // part 1 - check for collisions with the mouse cursor
    dx = ballPosX - curMouseX;
    dy = ballPosY - curMouseY;

    dist = sqrt( dx*dx + dy*dy);
    if (dist<ballRadius+cursorRadius)
    {
        ballVelocityX = 0.5 * dx;
        ballVelocityY = 0.5 * dy;
    }

    // part 2 - check for collisions with the walls
    if (ballPosX < ballRadius)
        ballVelocityX = abs(ballVelocityX);

    if (ballPosY < ballRadius)
        ballVelocityY = abs(ballVelocityY);

    if (ballPosX > clientWidth-ballRadius)
        ballVelocityX = -1 * abs(ballVelocityX);

    if (ballPosY > clientHeight-ballRadius)
        ballVelocityY = -1 * abs(ballVelocityY);
}

VOID CALLBACK myTimerProc(HWND hwnd,        // handle to window for timer messages
    UINT message,     // WM_TIMER message
    UINT idTimer,     // timer identifier
    DWORD dwTime)     // current system time
{
	ballPosX += ballVelocityX;
	ballPosY += ballVelocityY;
	ballVelocityX *= 0.9;
	ballVelocityY *= 0.9;

    handleCollisions();

	InvalidateRect(hwnd, NULL, true);
}

/*  This function is called by the Windows function DispatchMessage()  */
LRESULT CALLBACK WindowProcedure (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	PAINTSTRUCT ps;
	HDC hdc;
    RECT clientRect;

    HBRUSH newBr, oldBr;


    switch (message)                  /* handle the messages */
    {
        case WM_CREATE:
            ballPosX = 100;
            ballPosY = 100;
            SetTimer(hwnd, myTimerId, intervalMs, myTimerProc);
            GetClientRect(hwnd, &clientRect);
            clientWidth = clientRect.right;
            clientHeight = clientRect.bottom;
            return true;

        case WM_DESTROY:
            KillTimer(hwnd, myTimerId);
            PostQuitMessage (0);       /* send a WM_QUIT to the message queue */
            break;

        case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);

            //draw the red ball
            newBr = CreateSolidBrush(RGB(250,0,0));
            oldBr = (HBRUSH)SelectObject(hdc, newBr);
            Ellipse(hdc, ballPosX-ballRadius,ballPosY-ballRadius,ballPosX+ballRadius,ballPosY+ballRadius);
            SelectObject(hdc, oldBr);
            DeleteObject(newBr);

            // draw the white ball
            Ellipse(hdc, curMouseX-cursorRadius, curMouseY-cursorRadius, curMouseX+cursorRadius, curMouseY+cursorRadius);

            EndPaint(hwnd, &ps);
            break;

        case WM_MOUSEMOVE:
            lastMouseX = curMouseX;
            lastMouseY = curMouseY;
            curMouseX = GET_X_LPARAM(lParam);
            curMouseY = GET_Y_LPARAM(lParam);
            InvalidateRect(hwnd,NULL,true);
            break;

        case WM_LBUTTONUP:
            // shoot the red ball from the top left corner
            ballPosX=11;
            ballPosY=11;
            ballVelocityX=6.2;
            ballVelocityY=18.1;
            break;

        default:                      /* for messages that we don't deal with */
            return DefWindowProc (hwnd, message, wParam, lParam);
    }

    return 0;
}
}

Cyclone_S20-Jun-11 14:33

20-Jun-11 14:33

Thanks for the examples. The first one has smooth transitions in motion. Exactly what I need. However I'm using .net(managed code) not winAPI. It seems .net rounds the floats down to a whole number?

Would you be able to help me with the formula for moving an object using my previous post idea?

Thanks.

enhzflep20-Jun-11 18:45

20-Jun-11 18:45

That's okay. I had fun playing around with it.

Cyclone_S wrote:
However I'm using .net(managed code) not winAPI. It seems .net rounds the floats down to a whole number?

I'd be very surprised.
You're not giving it the impression that this is your intention, by (I don't know, say) multiplying floats with ints - I've no idea what the result is - real or integer..

I don't understand, you have the formula for moving the ball. - BallPos += Velocity - You also have a way of applying gravity or friction - just alter the velocity.

Perhaps you'd be better off in the right forum?
Perhaps
http://www.codeproject.com/Forums/3785/Managed-Cplusplus-CLI.aspx[^]
or
http://www.codeproject.com/Forums/1649/Csharp.aspx[^]

All the best. Smile | :)

WSA Events

csrss19-Jun-11 3:32

csrss

19-Jun-11 3:32

Hi. I got the following situation,

void FunctionA(some params)
{
// do something
SOCKET sock = create new socket();
WSAEVENT hEvent = new event();
wsaeventselect(sock, event, some flags);
FunctionB(sock);
delete event();
}

void FunctionB(sock)
{
// here do something else with a socket
}

The thing is, i dont have access to FunctionA() but it calls

FunctionB()

, where i am the master and can do anything. In function B i am receiving a socket which has an event associated with it but nothing else. I got no handle to an event - nothing, just a socket. Is there any way to get this event handle having only socket descriptor? If there is no such API, windows system should store these events somewhere, right? Is there any way to dig into this place and grab events from there?
Thanks

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0110010101110011

Re: WSA Events

enhzflep19-Jun-11 4:13