A Game loop using PeekMessage function

main.cpp

// Set project as empty windows project.
// A game loop using PeekMessage function.
// Uses double buffering.

#include <Windows.h>
#include <time.h>
#include <math.h>

#pragma comment(lib, "winmm.lib")

#define __FPS 60

int FRAMES;

void Update();
void Render();

LRESULT CALLBACK WndProc(HWND hWnd, UINT iMessage, WPARAM wParam, LPARAM lParam);
WCHAR lpszName[MAX_PATH] = L"Gravity Simulation";

int sw, sh;
int window;
HDC hScreenDC;
HDC hRenderDC;
HBITMAP hBitmap;

int APIENTRY WinMain(
	HINSTANCE hInstance,
	HINSTANCE hPrevInstance,
	LPSTR     lpszCmdParam,
	int       nCmdShow
)
{
	HWND hWnd;
	MSG Message;
	WNDCLASS WndClass;

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

	RegisterClass(&WndClass);

	hWnd = CreateWindow(lpszName, lpszName, WS_CAPTION | WS_SYSMENU,
		CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, (HMENU)NULL, hInstance, NULL);
	ShowWindow(hWnd, nCmdShow);

	window = sh * 2 / 3;

	hScreenDC = GetDC(hWnd);
	hRenderDC = CreateCompatibleDC(hScreenDC);
	hBitmap = CreateBitmap(window, window, 1, 32, NULL);
	SelectObject(hRenderDC, hBitmap);
	PatBlt(hRenderDC, 0, 0, window, window, WHITENESS);

	FRAMES = 0;

	const int TICKS_PER_SECOND = __FPS;
	const int SKIP_TICKS = 1000 / TICKS_PER_SECOND;

	timeBeginPeriod(1);
	SetPriorityClass(GetCurrentProcess(), REALTIME_PRIORITY_CLASS);
	DWORD next_game_tick = timeGetTime();

	srand((unsigned int)time(NULL));

	while (true)
	{
		if (PeekMessage(&Message, 0, 0, 0, PM_REMOVE))
		{
			if (Message.message == WM_QUIT) break;
			TranslateMessage(&Message);
			DispatchMessage(&Message);
		}
		else
		{
			Sleep(1);

			if (timeGetTime() > next_game_tick)
			{
				FRAMES++;
				Update();
				Render();
				next_game_tick += SKIP_TICKS;
			}
		}
	}
	timeEndPeriod(1);
	return (int)Message.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT iMessage, WPARAM wParam, LPARAM lParam)
{
	switch (iMessage)
	{
	case WM_CREATE:
		sw = GetSystemMetrics(SM_CXSCREEN);
		sh = GetSystemMetrics(SM_CYSCREEN);
		MoveWindow(hWnd, sw / 2 - sh / 3, sh / 6, sh * 2 / 3, sh * 2 / 3, TRUE);
		break;

	case WM_RBUTTONUP:
		MessageBox(hWnd, L"Quit Program", L"Simulation Notice", MB_OK);
	case WM_DESTROY:
		DeleteDC(hScreenDC);
		DeleteDC(hRenderDC);
		DeleteObject(hBitmap);
		PostQuitMessage(0);
		return 0;
	default:
		break;
	}
	return DefWindowProc(hWnd, iMessage, wParam, lParam);
}

int x = 100, y = 100, r = 10;

void Update()
{
	PatBlt(hRenderDC, 0, 0, window, window, WHITENESS);

	SelectObject(hRenderDC, GetStockObject(LTGRAY_BRUSH));

	x = (int)(window / 2 + window / 5 * cos(4 * 3.14 * FRAMES / 1000));
	y = (int)(window / 2 + window / 3 * sin(4 * 3.14 * FRAMES / 1000));

	Ellipse(hRenderDC, x - r, y - r, x + r, y + r);
}

WCHAR framestr[MAX_PATH];

void Render()
{
	BitBlt(hScreenDC, 0, 0, window, window, hRenderDC, 0, 0, SRCCOPY);

	wsprintf(framestr, L"FRAME : %d", FRAMES);
	TextOut(hScreenDC, 4, 0, framestr, wcslen(framestr));
}