windows 透明窗体的编程

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

const char szDlgTitle[] = "可变透明度窗体";

// 对话框消息处理函数
BOOL CALLBACK DlgProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam);

int APIENTRY WinMain(HINSTANCE hInstance,
      HINSTANCE hPrevInstance,
      LPSTR     lpCmdLine,
      int       nCmdShow)
{
 DialogBox(hInstance, MAKEINTRESOURCE(IDD_DIALOG1), NULL, DlgProc);
 return 0;
}

BOOL CALLBACK DlgProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{
 const int INIT_TRANSPARENT = 200; //窗体初始透明度
 static HBRUSH    s_hBitmapBrush; //位图画刷

 switch (message)
 {
 case WM_INITDIALOG:
  // 设置对话框标题
  SetWindowText(hDlg, szDlgTitle);

  // 加载背影图片
  HBITMAP hBitmap;
  hBitmap = (HBITMAP)LoadImage(NULL, "005.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE | LR_CREATEDIBSECTION);
  if (hBitmap == NULL)
  {
   MessageBox(hDlg, "LoadImage failed", "Error", MB_ICONERROR);
   exit(0);
  }  

  // 创建位图画刷
  s_hBitmapBrush = CreatePatternBrush(hBitmap);

  // 设置分层属性
  SetWindowLong(hDlg, GWL_EXSTYLE, GetWindowLong(hDlg, GWL_EXSTYLE) | WS_EX_LAYERED);
  // 设置透明度 0 - completely transparent   255 - opaque
  SetLayeredWindowAttributes(hDlg, 0, INIT_TRANSPARENT, LWA_ALPHA);

  // 设置滑动条变化范围
  SendMessage(GetDlgItem(hDlg, IDC_SLIDER_TRANSPARENT), TBM_SETRANGE, (WPARAM)FALSE, MAKELONG(0, 255));
  // 设置滑块初始位置
  SendMessage(GetDlgItem(hDlg, IDC_SLIDER_TRANSPARENT), TBM_SETPOS, (WPARAM)TRUE, INIT_TRANSPARENT);
  return 0;

 case WM_COMMAND:
  switch (LOWORD(wParam))
  {
  case IDCANCEL:
   DeleteObject(s_hBitmapBrush);
   EndDialog(hDlg, LOWORD(wParam));
   return TRUE;
  }
  break;

 case WM_HSCROLL: // slider control 滑块位置有变化时的响应函数
  {
   // 获取当前滑块位置
   int nTransparent = SendMessage(GetDlgItem(hDlg, IDC_SLIDER_TRANSPARENT), TBM_GETPOS, 0, 0);
   // 设置新透明度
   SetLayeredWindowAttributes(hDlg, 0, nTransparent, LWA_ALPHA);
  }
  break;

 case WM_CTLCOLORDLG:  //对话框背影
  return (BOOL)s_hBitmapBrush;
 }
 return FALSE;
}