Getting good at: C++ | #3 - Writing our first program

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3 - Actually Writing The Program

Alright, so now that you know how a program works, let's write one.

Just make sense out of this:

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

LRESULT CALLBACK WindowProc(HWND, UINT, WPARAM, LPARAM);
void EnableOpenGL(HWND hwnd, HDC*, HGLRC*);
void DisableOpenGL(HWND, HDC, HGLRC);

int WINAPI WinMain(HINSTANCE hInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine,
                   int nCmdShow)
{
    WNDCLASSEX wcex;
    HWND hwnd;
    HDC hDC;
    HGLRC hRC;
    MSG msg;
    BOOL bQuit = FALSE;
    float theta = 0.0f;

    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_OWNDC;
    wcex.lpfnWndProc = WindowProc;
    wcex.cbClsExtra = 0;
    wcex.cbWndExtra = 0;
    wcex.hInstance = hInstance;
    wcex.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)GetStockObject(BLACK_BRUSH);
    wcex.lpszMenuName = NULL;
    wcex.lpszClassName = "GLSample";
    wcex.hIconSm = LoadIcon(NULL, IDI_APPLICATION);;

    if (!RegisterClassEx(&wcex))
        return 0;

    hwnd = CreateWindowEx(0,
                          "GLSample",
                          "OpenGL Sample",
                          WS_OVERLAPPEDWINDOW,
                          CW_USEDEFAULT,
                          CW_USEDEFAULT,
                          256,
                          256,
                          NULL,
                          NULL,
                          hInstance,
                          NULL);

    ShowWindow(hwnd, nCmdShow);

    EnableOpenGL(hwnd, &hDC, &hRC);

    while (!bQuit)
    {

        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {

            if (msg.message == WM_QUIT)
            {
                bQuit = TRUE;
            }
            else
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
        }
        else
        {
           

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

            glPushMatrix();
            glRotatef(theta, 0.0f, 0.0f, 1.0f);

            glBegin(GL_TRIANGLES);

                glColor3f(1.0f, 0.0f, 0.0f);   glVertex2f(0.0f,   1.0f);
                glColor3f(0.0f, 1.0f, 0.0f);   glVertex2f(0.87f,  -0.5f);
                glColor3f(0.0f, 0.0f, 1.0f);   glVertex2f(-0.87f, -0.5f);

            glEnd();

            glPopMatrix();

            SwapBuffers(hDC);

            theta += 1.0f;
            Sleep (1);
        }
    }

    DisableOpenGL(hwnd, hDC, hRC);

    DestroyWindow(hwnd);

    return msg.wParam;
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
        case WM_CLOSE:
            PostQuitMessage(0);
        break;

        case WM_DESTROY:
            return 0;

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

        default:
            return DefWindowProc(hwnd, uMsg, wParam, lParam);
    }

    return 0;
}

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);
}

Okay fine, we'll start with something easier.

So before you do anything, start with these 2 lines:

#include <iostream>
using namespace std;

If you don't know what these do, then look at the second blog post, because I'm not explaining it again.

Now, let's make our main variable:

int main()

{

}

Now I haven't told you guys this, but you can add more than one variable to a program. Today, we're going to start out by creating a variable within a variable. The difference between standalone variables (int main(), etc...) and nested variables (int memes) is that with nested variables, you don't need to add parameters and a function to it, whereas with standalone variables, you do. So, to create a nested variable, you need to go into your function, and type:

int a;

a = 69;

or

int a = 69;

This means you have created a variable, and set the value of it to 69 (hehe 69). To display this variable, type:

cout << a << endl;

In case you're wondering, endl; ends the line so text can appear below it.

And of course, finish it off with:

return 0;

After you're finished, your program should look something like this:

For the .01% of you who are wondering how I got the command console to output our variable, you have to go to the toolbar just below the top, and click on this icon.

And that's all there is to it. Next post, I'm going to be covering User-defined variables. Until next time...