Weired results

Hi, I've been looking through stuff on OpenGL for a little while now, and am trying to create my first game, old school PONG. I have gotten everything done with it, collision detection and all, but then I found a flaw that has rendered my project useless.

I made the ball go on a random trajectory by getting a random number between 0 and 359 degrees. No problem there, except the ball doesn't take the given course.

I did some experimenting, and found out that all the degree system I was using was lopsided, literally. I set the ball angle manually to 0 degrees, and it went off to the right. Well, I ended up scrapping the game and starting fresh, but not before I find something to correct the problem. Here is the source for a small program I made from a template that is still having the same problem, it draws a line from the center, to supposidly 270 degrees.

I have no clue what it is, but if I were to put any money on it, it would be in the trig I did to find the ending point of the line.

Any help is appreciated

Code:

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// Include headers
#include <windows.h>
#include <gl/gl.h>
#include <math.h>

#define PI 3.14159265


// Declare functions
LRESULT CALLBACK WndProc (HWND hWnd, UINT message,                // Windows procedure
WPARAM wParam, LPARAM lParam);                                                        // Windows procedure contd..
void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC);        // Initialize OpenGL
void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC);                // DisableOpenGL
void draw_scene();                                                                                // Draw OpenGL Scene

// Declare global variables
char class_name[] = "OpenGL 2D Pong";                                        // Windows class name
char window_name[] = "Pong";                                                        // Window title name
int window_width = 500;                                                                        // Window width
int window_height = 500;                                                                // Window height

WNDCLASS wc;                                                                                        // Windows class handle
HWND hWnd;                                                                                                // Window Handle
HDC hDC;                                                                                                // Device context handle
HGLRC hRC;                                                                                                // Rendering context handle       
MSG msg;                                                                                                // Message handle
bool bQuit = FALSE;                                                                                // Quit the loop
bool keys[256];                                                                                        // Array for the keypress routine

// Windows Main function
int WINAPI WinMain(HINSTANCE hInstance,
                  HINSTANCE hPrevInstance,
                  LPSTR lpCmdLine,
                  int iCmdShow)
{
    // register window class
    wc.style = CS_OWNDC;                                                                                // Window style - own decive context
    wc.lpfnWndProc = WndProc;                                                                        // Which windows procedure to use
    wc.cbClsExtra = 0;                                                                                        // Extra parameters, 0
    wc.cbWndExtra = 0;                                                                                        // Extra parameters, 0
    wc.hInstance = hInstance;                                                                        // Program instance handle
    wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);                                // Program icon
    wc.hCursor = LoadCursor (NULL, IDC_ARROW);                                        // Mouse cursor
    wc.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);                // Background color of our screen
    wc.lpszMenuName = NULL;                                                                                // Menu Name
    wc.lpszClassName = class_name;                                                                // Name of our class
    RegisterClass (&wc);                                                                                // Register the class

    // Create the window
    hWnd = CreateWindow (
      class_name, window_name,
      WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE,
      0, 0, window_width, window_height,
      NULL, NULL, hInstance, NULL);

    // Enable OpenGL
    EnableOpenGL(hWnd, &hDC, &hRC);

    // Main Program Loop
    while (!bQuit)
    {
        // Check for messages in the queue
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            // Handle or dispatch messages
            if (msg.message == WM_QUIT)
            {
                bQuit = TRUE;
            }
            else
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
        }
        else
        {
                        // Draw the OpenGL Scene
                        draw_scene();
        }
    }

    // Shutdown OpenGL
    DisableOpenGL(hWnd, hDC, hRC);

    // Destroy the window
    DestroyWindow(hWnd);

    return msg.wParam;
}

// Windows Procedure
LRESULT CALLBACK WndProc(HWND hWnd, UINT message,
                        WPARAM wParam, LPARAM lParam)
{

    switch (message)
    {
    case WM_CREATE:
        return 0;
        break;
    case WM_CLOSE:
        PostQuitMessage(0);
        return 0;
        break;

    case WM_DESTROY:
        return 0;
        break;
    case WM_KEYDOWN:
                keys[wParam] = true;
        switch (wParam)
        {
                case VK_ESCAPE:
                    PostQuitMessage(0);
                    return 0;
                        break;
        }
        return 0;
        break;
        case WM_KEYUP:
                keys[wParam] = false;
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
}

// Enable OpenGL
void EnableOpenGL(HWND hWnd, HDC *hDC, HGLRC *hRC)
{
    PIXELFORMATDESCRIPTOR pfd;
    int iFormat;

    // Get the device context for the window
    *hDC = GetDC(hWnd);

    // Set PFD
    ZeroMemory (&pfd, sizeof(pfd));
    pfd.nSize = sizeof(pfd);
    pfd.nVersion = 1;
    pfd.dwFlags = PFD_DRAW_TO_WINDOW |
      PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER;
    pfd.iPixelType = PFD_TYPE_RGBA;
    pfd.cColorBits = 24;
    pfd.cDepthBits = 16;
    pfd.iLayerType = PFD_MAIN_PLANE;
    iFormat = ChoosePixelFormat(*hDC, &pfd);
    SetPixelFormat (*hDC, iFormat, &pfd);

    // Create the RC and make it current
    *hRC = wglCreateContext(*hDC);
    wglMakeCurrent(*hDC, *hRC);

}


// Disable OpenGL
void DisableOpenGL(HWND hWnd, HDC hDC, HGLRC hRC)
{
    wglMakeCurrent(NULL, NULL);
    wglDeleteContext(hRC);
    ReleaseDC(hWnd, hDC);
}

// Draw OpenGL Scene
void draw_scene()
{
          glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
        glClear(GL_COLOR_BUFFER_BIT);
   

        glPushMatrix();
                glColor3f(0.2f, 1.0f, 0.2f);
                glBegin(GL_LINES);
            //for (int i = 0; i < 360; i++)
            //{
                glVertex2f(0.0f, 0.0f);
                glVertex2f(cos((270 * (PI / 180)) * 0.9f), sin((270 * (PI / 180)) * 0.9f));
            //}
                glEnd();                                 
        glPopMatrix();

        SwapBuffers(hDC);
}

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From what I'm taking...you're trying to draw the line to be 0.9 units long?

I think you have to move the 0.9f outside of the brackets it is in, i.e.:

Code:

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glVertex2f(cos((270 * (PI / 180)) * 0.9f), sin((270 * (PI / 180)) * 0.9f));

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becomes

Code:

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glVertex2f(cos((270 * (PI / 180))) * 0.9f, sin((270 * (PI / 180))) * 0.9f);

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Right now you're multiplying the rotation angle by 0.9, which would be throwing your degrees off....but that change will take the sin/cos of your angle, and then size it appropriately by your 0.9 value.

Wow, what a way to screw up. :eek: It works perfectly, thank you.