Bola animada - Linguagem C

/* 
   Arquivo: main.c
*/

#include <windows.h>
#include "resource.h"

static char g_szClassName[] = "MyWindowClass";
static HINSTANCE g_hInst = NULL;

const UINT idTimer1 = 1;
UINT nTimerDelay = 10;

HBITMAP hbmBall, hbmMask;
BITMAP bm;

int ballX, ballY;
int deltaX, deltaY;

int deltaValue = 4;

void EraseBall(HDC hdc) {
    RECT rc;
    rc.left = ballX;
    rc.top = ballY;
    rc.right = ballX + bm.bmWidth;
    rc.bottom = ballY + bm.bmHeight;
    FillRect(hdc, &rc, (HBRUSH)(COLOR_BTNFACE+1));
}

void DrawBall(HDC hdc) {
    HDC hdcMemory;
    hdcMemory = CreateCompatibleDC(hdc);

    SelectObject(hdcMemory, hbmMask);
    BitBlt(
        hdc, ballX, ballY, bm.bmWidth,
        bm.bmHeight, hdcMemory, 0, 0, SRCAND
    );

    SelectObject(hdcMemory, hbmBall);
    BitBlt(
        hdc, ballX, ballY, bm.bmWidth,
        bm.bmHeight, hdcMemory, 0, 0, SRCPAINT
    );

    DeleteDC(hdcMemory);
}

void UpdateBall(HWND hwnd) {
    RECT rc;
    GetClientRect(hwnd, &rc);

    ballX += deltaX;
    ballY += deltaY;

    if(ballX < 0){
        ballX = 0;
        deltaX = deltaValue;
    }
    else if(ballX + bm.bmWidth > rc.right){
        ballX = rc.right - bm.bmWidth;
        deltaX = -deltaValue;
    }
    if(ballY < 0) {
        ballY = 0;
        deltaY = deltaValue;
    }
    else if(ballY + bm.bmHeight > rc.bottom){
        ballY = rc.bottom - bm.bmHeight;
        deltaY = -deltaValue;
    }
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wP, LPARAM lP) {
    switch(msg) {
        case WM_CREATE:
            hbmBall = LoadBitmap(g_hInst, "BALLBMP");
            hbmMask = LoadBitmap(g_hInst, "MASKBMP");
            if(!hbmBall || !hbmMask) {
                MessageBox(hwnd, "Load of resources failed.", "Error",
                MB_OK | MB_ICONEXCLAMATION);
                return -1;
            }
            GetObject(hbmBall, sizeof(bm), &bm);
            SetTimer(hwnd, idTimer1, nTimerDelay, NULL);
            ballX = 0;
            ballY = 0;
            deltaX = deltaValue;
            deltaY = deltaValue;
            break;
        case WM_TIMER:
            if(hbmBall && hbmMask) {
                HDC hdcWindow;
                hdcWindow = GetDC(hwnd);
                EraseBall(hdcWindow);
                UpdateBall(hwnd);
                DrawBall(hdcWindow);
                ReleaseDC(hwnd, hdcWindow);
            }
            break;
        case WM_PAINT:
            if(hbmBall && hbmMask) {
                PAINTSTRUCT ps;
                HDC hdcWindow;
                hdcWindow = BeginPaint(hwnd, &ps);
                DrawBall(hdcWindow);
                EndPaint(hwnd, &ps);
            }
            break;
        case WM_CLOSE:
            DestroyWindow(hwnd);
            break;
        case WM_DESTROY:
            KillTimer(hwnd, idTimer1);
            DeleteObject(hbmBall);
            DeleteObject(hbmMask);
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hwnd, msg, wP, lP);
    }
    return 0;
}


int WINAPI WinMain(HINSTANCE hI, HINSTANCE hPI, LPSTR szCL, int iCS) {
    WNDCLASSEX WndClass;
    HWND hwnd;
    MSG Msg;

    g_hInst = hI;

    WndClass.cbSize        = sizeof(WNDCLASSEX);
    WndClass.style         = 0;
    WndClass.lpfnWndProc   = WndProc;
    WndClass.cbClsExtra    = 0;
    WndClass.cbWndExtra    = 0;
    WndClass.hInstance     = hI;
    WndClass.hIcon         = LoadIcon(hI, IDI_ICON);
    WndClass.hCursor       = LoadCursor(NULL, IDC_ARROW);
    WndClass.hbrBackground = (HBRUSH)(COLOR_BTNFACE+1);
    WndClass.lpszMenuName  = NULL;
    WndClass.lpszClassName = g_szClassName;
    WndClass.hIconSm       = LoadIcon(hI, IDI_ICON);

    if(!RegisterClassEx(&WndClass)) {
        MessageBox(
            0, "Window Registration Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK | MB_SYSTEMMODAL
        );
        return 0;
    }

    hwnd = CreateWindowEx(
        WS_EX_CLIENTEDGE,
        g_szClassName,
        "A Bitmap Program",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 320, 240,
        NULL, NULL, g_hInst, NULL
    );

    if(hwnd == NULL) {
        MessageBox(
            0, "Window Creation Failed!", "Error!",
            MB_ICONEXCLAMATION | MB_OK | MB_SYSTEMMODAL
        );
        return 0;
    }

    ShowWindow(hwnd, iCS);
    UpdateWindow(hwnd);

    while(GetMessage(&Msg, NULL, 0, 0)) {
        TranslateMessage(&Msg);
        DispatchMessage(&Msg);
    }
    return Msg.wParam;
}

/* 
   Arquivo: resource.rc
*/

#include "resource.h"
#include "afxres.h"

BALLBMP BITMAP "ball.bmp"
MASKBMP BITMAP "ballmask.bmp"

IDI_ICON ICON "project1.ico"

/* 
   Arquivo: resource.h
*/


#define IDI_ICON 1