glOrtho

I am using glOrtho simple 2d app, and I’m just trying to draw a rectangle, but it’s not working, and I think it has to do with my glOrtho, what I put was:

glOrtho(0.0f,800.0f,0.0f,600.0f,1.0f,-1.0f);

any one have ideas?

if you want, here is the rest of my code.

#include <windows.h>
#include <gl/gl.h>

LRESULT CALLBACK WndProc (HWND hWnd, UINT message,
WPARAM wParam, LPARAM lParam);
void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC);
void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC);

int WINAPI WinMain (HINSTANCE hInstance,
                    HINSTANCE hPrevInstance,
                    LPSTR lpCmdLine,
                    int iCmdShow)
{
    WNDCLASS wc;
    HWND hWnd;
    HDC hDC;
    HGLRC hRC;        
    MSG msg;
    BOOL bQuit = FALSE;
    
    wc.style = CS_OWNDC;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor (NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = "WinClass";
    RegisterClass (&wc);

    hWnd = CreateWindow (
      "WinClass", "Rectangle", 
      WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE,
      100, 75, 800, 600,
      NULL, NULL, hInstance, NULL);

    EnableOpenGL (hWnd, &hDC, &hRC);

    while (!bQuit)
    {
        /* check for messages */
        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
        {
            /* OpenGL animation code goes here */
            glOrtho(0.0f,800.0f,0.0f,600.0f,1.0f,-1.0f);

            glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
            glClear (GL_COLOR_BUFFER_BIT);

            glPushMatrix ();
            glBegin (GL_POLYGON);
                glColor3f(0.0,0.0,1.0);
                glVertex2f(10.0f,10.0f);
                glVertex2f(50.0f,10.0f);
                glVertex2f(50.0f,5.0f);
                glVertex2f(10.0f,5.0f);
            glEnd ();
            glPopMatrix ();

            SwapBuffers (hDC);
            Sleep (1);
        }
    }

    DisableOpenGL (hWnd, hDC, hRC);
    DestroyWindow (hWnd);
    return msg.wParam;
}

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

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

    case WM_DESTROY:
        return 0;

    case WM_KEYDOWN:
        switch (wParam)
        {
        case VK_ESCAPE:
            PostQuitMessage(0);
            return 0;
        }
        return 0;

    default:
        return DefWindowProc (hWnd, message, wParam, lParam);
    }
}

void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC)
{
    PIXELFORMATDESCRIPTOR pfd;
    int iFormat;
    *hDC = GetDC (hWnd);

    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);

    *hRC = wglCreateContext( *hDC );
    wglMakeCurrent( *hDC, *hRC );
}

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

I only had a quick look, but try:
glOrtho(0.0f,800.0f,0.0f,600.0f,-1.0f,1.0f);

Otherwise your near-plane is actually farther away than your far-plane.

Hope that helps,
Jan.

Ok, thanks, I just tried that and it didn’t work, like it compiles, but it doesn’t show the rectangle, so I tried using glVertex3f to draw my rectangle, but it didn’t work either.

Make sure you call glMatrixMode(GL_PROJECTION) and glLoadIdentity() before you call glOrtho. The glOrtho call performs a postmultiplication with the current value of the projection matrix.

N.

aha! That’s exactly what I needed, thanks a lot. I appreciate it.