Grafik med WINAPI

Man bruger kun BeginPaint og EndPaint ved WM_PAINT.
I alle andre tilfælde bruger man GetDC til at få fat i en DC og ReleaseDC til at release den.

Kode 

#include <windows.h>
#include <windowsx.h>
#include <commctrl.h>
#include <string.h>

HINSTANCE hInst;     // Instance handle
HWND hwndMain;    //Main window handle

LRESULT CALLBACK MainWndProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam);

POINT Point = {100, 200};

void Draw(HDC dc)
{
   MoveToEx(dc, Point.x - 10, Point.y - 10, NULL);
   LineTo(dc, Point.x + 10, Point.y - 10);
   LineTo(dc, Point.x + 10, Point.y + 10);
   LineTo(dc, Point.x - 10, Point.y + 10);
   LineTo(dc, Point.x - 10, Point.y - 10);
}

static BOOL InitApplication(void)
{
   WNDCLASS wc;

   memset(&wc,0,sizeof(WNDCLASS));
   wc.style = CS_HREDRAW|CS_VREDRAW |CS_DBLCLKS ;
   wc.lpfnWndProc = (WNDPROC)MainWndProc;
   wc.hInstance = hInst;
   wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
   wc.lpszClassName = "ng39WndClass";
   wc.hCursor = LoadCursor(NULL,IDC_ARROW);
   if (!RegisterClass(&wc))
      return 0;

   return 1;
}

HWND Createng39WndClassWnd(void)
{
   return CreateWindow("ng39WndClass","ng39",
                       WS_MINIMIZEBOX|WS_VISIBLE|WS_CLIPSIBLINGS|WS_CLIPCHILDREN|WS_MAXIMIZEBOX|WS_CAPTION|WS_BORDER|WS_SYSMENU|WS_THICKFRAME,
                       CW_USEDEFAULT,0,CW_USEDEFAULT,0,
                       NULL,
                       NULL,
                       hInst,
                       NULL);
}

LRESULT CALLBACK MainWndProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam)
{
   switch (msg)
   {
   case WM_SIZE:
      break;
   case WM_DESTROY:
      PostQuitMessage(0);
      break;
   case WM_LBUTTONDOWN:
   {
      HDC dc = GetDC(hwnd);
      Point.x = GET_X_LPARAM(lParam);
      Point.y = GET_Y_LPARAM(lParam);
      Draw(dc);
      ReleaseDC(hwnd, dc);
   }
   break;
   case WM_PAINT:
   {
      PAINTSTRUCT PaintStruct;
      HDC dc = BeginPaint(hwnd, &PaintStruct);
      Draw(dc);
      EndPaint(hwnd, &PaintStruct);
   }
   break;
   default:
      return DefWindowProc(hwnd,msg,wParam,lParam);
   }

   return 0;
}

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, INT nCmdShow)
{
   MSG msg;

   hInst = hInstance;
   if (!InitApplication())
      return 0;

   if ((hwndMain = Createng39WndClassWnd()) == (HWND)0)
      return 0;

   ShowWindow(hwndMain,SW_SHOW);
   while (GetMessage(&msg,NULL,0,0))
   {
      TranslateMessage(&msg);
      DispatchMessage(&msg);
   }
   return msg.wParam;
}