双缓冲的释放

Question

一般地，使用双缓冲作图（WIN32应用程序）：

/*

注释

 POINT pBeg,pEnd;

HDC hdc,hdcMem;

HBITMAP hBitmap;

HWND hWnd;

static int a=1;

HPEN hPen=CreatePen(PS_SOLID,iW,rgbCurrent);

*/

switch (message)
 {

case WM_LBUTTONDOWN:

a*=-1;

pBeg.x=LOWORD(lParam);
  pBeg.y=HIWORD(lParam);

return 0;

case WM_MOUSEMOVE:

hdc=GetDC(hWnd);
    hdcMem=CreateCompatibleDC(hdc);
    hPen=CreatePen(PS_SOLID,iW,rgbCurrent);
    pEnd.x=LOWORD(lParam);
    pEnd.y=HIWORD(lParam);
    SelectObject(hdcMem,hPen);
    if(a==-1)
    {
     SetCursor(LoadCursor(NULL,IDC_CROSS));
     if(UNDO>0)
      hBitmap=Frame(UndoName[UNDO]);//这里hBitmap为自定义
     SelectObject(hdc,hBitmap);
     GetClientRect(hWnd,&rect);
     Rectangle(hdcMem,0,0,cxClient,cyClient);
     FillRect(hdcMem,&rect,CreateSolidBrush(RGB(255,255,255)));
     hBitmap1=(HBITMAP)SelectObject(hdcMem,hBitmap);
     Arc(hdcMem,pBeg.x,pBeg.y,pEnd.x,pEnd.y,
      pBeg.x,pBeg.y,pBeg.x,pBeg.y);
     BitBlt(hdc,0,0,cxClient,cyClient,hdcMem,0,0,SRCCOPY);
     InvalidateRect(hWnd,NULL,TRUE);
     SelectObject(hdcMem,hBitmap1);
    }
    DeleteDC(hdcMem);
    DeleteObject(hBitmap1);
    DeleteObject(hPen);
    ReleaseDC(hWnd,hdc);

return 0;

}

当按下右健移动鼠标时，发现SelectObject(hdcMem,hBitmap)使内存占用量急剧上升，可否实时释放hdcMem中的hBitmap,求解,不胜感激!!!!!!!!!!!

QQ:1327729940

---

程学武

Answer 1

可以阿 tmp = SelectObject(hdc,hBitmap); 先把选出来的句柄保存然后在删除的时候需要把原来的放回去 SelectObject(hdc, tmp); 这样才能删除hBitmap MSDN上写的很清楚

---

0xDEADBEEF

Answer 2

您可以把一些不变的东西放到其他的地方去做初始化，比如代码中的CreateSolidBrush()创建画刷，LoadCursor()加载光标可以放到WM_CREATE/WM_INITDIALOG中。

另外您Debug下调试可以发现您DeleteObject(hPen);操作会失败，原因是您需要将原来的HPEN对象SelectObject()，这样才能删除，否则DeleteObject()失败。

---

Visual C++ enthusiast, like network programming and driver development. At present is being engaged in the WinCE/Windows Mobile platform embedded development.

Answer 3

谢谢~~~

---

程学武

Answer 4

OK，我先试试

---

程学武

Answer 5

...

...

case WM_MOUSEMOVE:
  b=1;
  if(r==0)
  {
   switch(d)
   {
   case 1:
    if(a==-1)
    {
     hdc=GetDC(hWnd);
     hPen=CreatePen(PS_SOLID,iW,rgbCurrent);
     SetCursor(LoadCursor(NULL,IDC_CROSS));
     pEnd.x=LOWORD(lParam);
     pEnd.y=HIWORD(lParam);
     
     hBitmap=Frame(UndoName[UNDO]);
     hdcMem=CreateCompatibleDC(NULL);
     SelectObject(hdcMem,hPen);
     SelectObject(hdcMem,hBitmap);
     DeleteObject(hBitmap);
     MoveToEx(hdcMem,pBeg.x,pBeg.y,NULL);
     LineTo(hdcMem,pEnd.x,pEnd.y);
     BitBlt(hdc,0,0,cxClient,cyClient,hdcMem,0,0,SRCCOPY);
     SelectObject(hdcMem,hBitmap);
     
     DeleteDC(hdcMem);
     DeleteObject(hPen);
     ReleaseDC(hWnd,hdc);
    }
    return 0;

这样就可以了，好简单啊，老程序占用一下下降到1000K，真不知所谓的"双缓冲“到底是什么！！

---

程学武

Answer 6

完全正确，谢谢！！

---

程学武

Answer 7

完全正确，谢谢！！

---

程学武