GDI32 - Forest Fire

#include <windows.h>
#include <time.h>

//Author: name22 (www.autoit.de)

#define WIDTH 600
#define HEIGHT 600
#define ID_VOID 0
#define ID_TREE 1
#define ID_FIRE 2
#define COLOR_VOID RGB(0, 0, 0)
#define COLOR_TREE RGB(0, 255, 0)
#define COLOR_FIRE RGB(255, 0, 0)

#define P_INIT 0.55
#define P_GROW 0.008
#define P_FIRE 0.000001

HDC hDC_Bitmap;
BYTE aGrid[WIDTH][HEIGHT], aGridOld[WIDTH][HEIGHT];

VOID OnPaint(HDC);
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

INT WINAPI WinMain(HINSTANCE hInstance, HINSTANCE, PSTR, INT iCmdShow)
{
    HWND                hWnd;
    MSG                 msg;
    WNDCLASS            wndClass;
    BOOL                bQuit = FALSE;

    HDC                 hDC_Window;
    HBITMAP             hBitmap;
    HGDIOBJ             hOldObj;

    wndClass.style          = CS_HREDRAW | CS_VREDRAW;
    wndClass.lpfnWndProc    = WndProc;
    wndClass.cbClsExtra     = 0;
    wndClass.cbWndExtra     = 0;
    wndClass.hInstance      = hInstance;
    wndClass.hIcon          = LoadIcon(NULL, IDI_APPLICATION);
    wndClass.hCursor        = LoadCursor(NULL, IDC_ARROW);
    wndClass.hbrBackground  = (HBRUSH)GetStockObject(WHITE_BRUSH);
    wndClass.lpszMenuName   = NULL;
    wndClass.lpszClassName  = TEXT("GDIWindow");

    RegisterClass(&wndClass);

    hWnd = CreateWindow(
               TEXT("GDIWindow"),   // window class name
               TEXT("GDI32 - Forest Fire"),  // window caption
               WS_OVERLAPPEDWINDOW,      // window style
               CW_USEDEFAULT,            // initial x position
               CW_USEDEFAULT,            // initial y position
               WIDTH,                    // initial x size
               HEIGHT,                   // initial y size
               NULL,                     // parent window handle
               NULL,                     // window menu handle
               hInstance,                // program instance handle
               NULL);                    // creation parameters

    hDC_Window = GetDC(hWnd);
    hDC_Bitmap = CreateCompatibleDC(hDC_Window);
    hBitmap = CreateCompatibleBitmap(hDC_Window, WIDTH, HEIGHT);
    hOldObj = SelectObject(hDC_Bitmap, hBitmap);

    //Fill grids with zeros
    memset(aGrid, ID_VOID, (sizeof aGrid[0][0]) * WIDTH * HEIGHT);
    memset(aGridOld, ID_VOID, (sizeof aGridOld[0][0]) * WIDTH * HEIGHT);

    //Seed random-number generator with time
    srand((unsigned) time(NULL));

    //Plant trees
    for (int y = 0; y < HEIGHT; y++) for (int x = 0; x < WIDTH; x++) if (rand() < RAND_MAX * P_INIT)
    {
        aGrid[x][y] = ID_TREE;
        SetPixelV(hDC_Bitmap, x, y, COLOR_TREE);
    }
    memcpy(aGridOld, aGrid, sizeof aGrid);

    ShowWindow(hWnd, iCmdShow); //Make GUI visible

    BitBlt(hDC_Window, 0, 0, WIDTH, HEIGHT, hDC_Bitmap, 0, 0, SRCCOPY); //Swap buffers

    while(!bQuit)
    {
        if (PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
        {
            if (msg.message == WM_QUIT) bQuit = TRUE;
            else
            {
                TranslateMessage(&msg);
                DispatchMessage(&msg);
            }
        }
        else
        {
            for (int y = 0; y < HEIGHT; y++)
            {
                for (int x = 0; x < WIDTH; x++)
                {
                    switch (aGridOld[x][y])
                    {
                    case ID_VOID: //Cell is void
                        if (rand() < RAND_MAX * P_GROW) //Grow tree with propability of P_GROW
                        {
                            aGrid[x][y] = ID_TREE;
                            SetPixelV(hDC_Bitmap, x, y, COLOR_TREE);
                        }
                        break;
                    case ID_TREE: //Cell is a tree
                        for (int i = -1; i < 2; i++) for (int j = -1; j < 2; j++) //8 bounding neighbours
                        {
                            if (i != 0 && j != 0 && x + i >= 0 && x + i < WIDTH && y + j >= 0 && y + j < HEIGHT) //Check if neighbouring cell is valid
                            {
                                if (aGridOld[x + i][y + j] == ID_FIRE) //Set cell on fire if a neighbouring cell is on fire
                                {
                                    aGrid[x][y] = ID_FIRE;
                                    SetPixelV(hDC_Bitmap, x, y, COLOR_FIRE);
                                    goto CELL_DONE;
                                }
                            }
                            else
                            {
                                if (rand() < RAND_MAX * P_FIRE) //Set cell on fire anyway with propability of 0.01%
                                {
                                    aGrid[x][y] = ID_FIRE;
                                    SetPixelV(hDC_Bitmap, x, y, COLOR_FIRE);
                                    goto CELL_DONE;
                                }
                            }
                        }
                        break;
                    case ID_FIRE: //Cell is on fire -> decay into void
                        aGrid[x][y] = ID_VOID;
                        SetPixelV(hDC_Bitmap, x, y, COLOR_VOID);
                        break;
                    }
                    CELL_DONE:;
                }
            }
            BitBlt(hDC_Window, 0, 0, WIDTH, HEIGHT, hDC_Bitmap, 0, 0, SRCCOPY); //Swap buffers
            memcpy(aGridOld, aGrid, sizeof aGrid); //Copy new grid into old one
        }
    }

    SelectObject(hDC_Bitmap, hOldObj);
    ReleaseDC(hWnd, hDC_Window);
    DeleteDC(hDC_Bitmap);
    DeleteObject(hBitmap);

    return msg.wParam;
}  // WinMain

VOID OnPaint(HDC hDC)
{
    BitBlt(hDC, 0, 0, WIDTH, HEIGHT, hDC_Bitmap, 0, 0, SRCCOPY);
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message,
                         WPARAM wParam, LPARAM lParam)
{
    HDC          hDC;
    PAINTSTRUCT  ps;

    switch(message)
    {
    case WM_PAINT:
        hDC = BeginPaint(hWnd, &ps);
        OnPaint(hDC);
        EndPaint(hWnd, &ps);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
} // WndProc