How to write a 32bit screen saver How to write a 32bit screen saverI have had two kind offers of translations of this document into French and Spanish. Hopefully I will be able to put these translations up soon.
Screen savers start when the mouse and keyboard have been left idle for some time. They have five main purposes:
Be especially careful about any activities which might change the focus. If your saver pops up a top-level window on startup, this will mess up the focus: the control panel will regain focus, and your saver will be started again, and it will pop up another top-level window, and so on. This makes it very difficult for you to debug your preview mode. For debugging of the preview window you can use a utility called ScrPrev which runs its own preview window and is a little less temperamental.
// First we define some global variables and types.
// TScrMode is a global variable storing the mode the saver should be running in.
// TSaverSettings is a class with settings of various sorts.
// ss is a global variable with these settings.
enum TScrMode {smNone,smConfig,smPassword,smPreview,smSaver};
TScrMode ScrMode=smNone;
HINSTANCE hInstance=NULL;
class TSaverSettings; TSaverSettings *ss=NULL;
int WINAPI WinMain(HINSTANCE h,HINSTANCE,LPSTR,int)
{ hInstance=h;
char *c=GetCommandLine();
if (*c=='\"') {c++; while (*c!=0 && *c!='\"') c++;}
else {while( *c!=0 && *c!=' ') c++;}
if (*c!=0) c++;
while (*c==' ') c++;
HWND hwnd=NULL;
if (*c==0) {ScrMode=smConfig; hwnd=NULL;)
else
{ if (*c=='-' || *c=='/') c++;
if (*c=='p' || *c=='P' || *c=='l' || *c=='L')
{ c++; while (*c==' ' || *c==':') c++;
if ((strcmp(c,"scrprev")==0) || (strcmp(c,"ScrPrev")==0) ||
(strcmp(c,"SCRPREV")==0)) hwnd=CheckForScrprev();
else hwnd=(HWND)atoi(c);
ScrMode=smPreview;
}
else if (*c=='s' || *c=='S')
{ ScrMode=smSaver;
}
else if (*c=='c' || *c=='C')
{ c++; while (*c==' ' || *c==':') c++;
if (*c==0) hwnd=GetForegroundWindow(); else hwnd=(HWND)atoi(c); ScrMode=smConfig;
}
else if (*c=='a' || *c=='A')
{ c++; while (*c==' ' || *c==':') c++;
hwnd=(HWND)atoi(c); ScrMode=smPassword;}
}
}
// We create a global TSaverSettings here, for convenience.
// It will get used by the config dialog and by the saver as it runs
ss=new TSaverSettings(); ss->ReadGeneralRegistry(); ss->ReadConfigRegistry();
if (ScrMode==smPassword) ChangePassword(hwnd);
if (ScrMode==smConfig) DialogBox(hInstance,MAKEINTRESOURCE(DLG_CONFIG),
hwnd,ConfigDialogProc);
if (ScrMode==smSaver || ScrMode==smPreview) DoSaver(hwnd);
delete ss;
return 0;
}
// ScrPrev is a freely available utility to make it easier to debug
// savers. Start the saver with argument /p scrprev and it will run its preview
// inside a ScrPrev window.
HWND CheckForScrprev()
{ HWND hwnd=FindWindow("Scrprev",NULL); // looks for the Scrprev class
if (hwnd==NULL) // try to load it
{ STARTUPINFO si; PROCESS_INFORMATION pi;
ZeroMemory(&si,sizeof(si)); ZeroMemory(&pi,sizeof(pi));
si.cb=sizeof(si);
si.lpReserved=NULL; si.lpTitle=NULL;
si.dwFlags=0; si.cbReserved2=0; si.lpReserved2=0; si.lpDesktop=0;
BOOL cres=CreateProcess(NULL,"Scrprev",0,0,FALSE,
CREATE_NEW_PROCESS_GROUP|CREATE_DEFAULT_ERROR_MODE,0,0,&si,&pi);
if (!cres) {Debug("Error creating scrprev process"); return NULL;}
DWORD wres=WaitForInputIdle(pi.hProcess,2000);
if (wres==WAIT_TIMEOUT)
{ Debug("Scrprev never becomes idle"); return NULL;
}
if (wres==0xFFFFFFFF)
{ Debug("ScrPrev, misc error after ScrPrev execution");return NULL;
}
hwnd=FindWindow("Scrprev",NULL);
}
if (hwnd==NULL) {Debug("Unable to find Scrprev window"); return NULL;}
::SetForegroundWindow(hwnd);
hwnd=GetWindow(hwnd,GW_CHILD);
if (hwnd==NULL) {Debug("Couldn't find Scrprev child"); return NULL;}
return hwnd;
}
class TSaverSettings
{ public:
// Following are the general saver registry settings which we will read in
DWORD PasswordDelay; // in seconds
DWORD MouseThreshold; // in pixels
BOOL MuteSound;
// Following are the configuration options particular to this saver
BOOL FlashScreen;
// Following are variables which the saver uses while it runs
HWND hwnd; // Handle of the currently running saver window
POINT InitCursorPos; // Where the mouse started off
DWORD InitTime; // Time at which we started, in ms
UINT idTimer; // a timer id, because this particular saver uses a timer
BOOL IsDialogActive; // If dialog is active, we ignore certain messages
BOOL ReallyClose; // for NT, so we know if a WM_CLOSE came from us or it.
TSaverSettings();
void ReadGeneralRegistry(); // General settings that apply to all savers
void ReadConfigRegistry(); // Settings particular to this saver
void WriteConfigRegistry();
void CloseSaverWindow(); // A convenient way of closing the saver, if appropriate
void StartDialog(); // We need special protection against dialogs when the
void EndDialog(); // saver is running
};
TSaverSettings::TSaverSettings() {hwnd=NULL; ReallyClose=FALSE; idTimer=0;}
See also ReadConfigRegistry code, ReadGeneralRegistryCode.
DLG_CONFIG DIALOG DISCARDABLE 0, 0, 186, 95
STYLE DS_MODALFRAME | WS_POPUP | WS_CAPTION | WS_SYSMENU
CAPTION "Config dialog"
FONT 8, "MS Sans Serif"
BEGIN
DEFPUSHBUTTON "OK",IDOK,129,7,50,14
PUSHBUTTON "Cancel",IDCANCEL,129,24,50,14
CONTROL "Flash screen",IDC_FLASH,"Button",BS_AUTOCHECKBOX |
WS_TABSTOP,23,13,56,10
END
BOOL CALLBACK ConfigDialogProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam)
{ switch (msg)
{ case WM_INITDIALOG:
{ CheckDlgButton(hwnd,IDC_FLASH,ss->FlashScreen); return TRUE;
}
`:
{ int id=LOWORD(wParam);
if (id==IDOK)
{ ss->FlashScreen=(IsDlgButtonChecked(hwnd,IDC_FLASH)==BST_CHECKED);
ss->WriteConfigRegistry();
}
if (id==IDOK || id==IDCANCEL) EndDialog(hwnd,id);
} break;
}
return FALSE;
}
See also TSaverSettings code, Configuration registry code.
#include <regstr.h>
#define REGSTR_PATH_CONFIG ("Software\\Lu\\Minimal Saver")
// This saver has a single user configuration option: FlashScreen
void TSaverSettings::ReadConfigRegistry()
{ FlashScreen=TRUE;
LONG res; HKEY skey; DWORD valtype, valsize, val;
res=RegOpenKeyEx(HKEY_CURRENT_USER,REGSTR_PATH_CONFIG,0,KEY_ALL_ACCESS,&skey);
if (res!=ERROR_SUCCESS) return;
valsize=sizeof(val);
res=RegQueryValueEx(skey,"Flash Screen",0,&valtype,(LPBYTE)&val,&valsize);
if (res==ERROR_SUCCESS) FlashScreen=val;
RegCloseKey(skey);
}
void TSaverSettings::WriteConfigRegistry()
{ LONG res; HKEY skey; DWORD val, disp;
res=RegCreateKeyEx(HKEY_CURRENT_USER,REGSTR_PATH_CONFIG,0,NULL,
REG_OPTION_NON_VOLATILE,KEY_ALL_ACCESS,NULL,&skey,&disp);
if (res!=ERROR_SUCCESS) return;
val=FlashScreen;
RegSetValueEx(skey,"Flash Screen",0,REG_DWORD,(CONST BYTE*)&val,sizeof(val));
RegCloseKey(skey);
}
Whenever a user brings up the configuration dialog for a particular saver and clicks OK, then the changes to the configuration for that particular saver are written to the registry immediately. But the current choice of screen saver appears in the control panel itself and changes to it do not actually take effect, or get written to the registry, until the user clicks OK or Apply on the Desktop control panel itself! Likewise the password option.
So someone might select a saver and spend ages configuring it but then fail to close the control panel: and when they use hot corners to see the effect immediately Windows will not launch the saver they had so painstakingly configured, but instead will launch the previous saver! And then they go to the control panel and turn on password checking and click Preview and it doesn't ask for your password, but when you click Apply and then Preview it does! And then you turn off password checking and you click Preview but it still (under '95) asks you for a password, only you don't know what to do because you think that passwords are turned off and anyway you've forgotten it!
This might seem odd at first, but you might as well get used to it.
#include <regstr.h>
#define REGSTR_PATH_PLUSSCR (REGSTR_PATH_SETUP "\\Screen Savers")
void TSaverSettings::ReadGeneralRegistry()
{ PasswordDelay=15; MouseThreshold=50; IsDialogActive=FALSE;
// default values in case they're not in registry
LONG res; HKEY skey; DWORD valtype, valsize, val;
res=RegOpenKeyEx(HKEY_CURRENT_USER,REGSTR_PATH_PLUSSCR,0,KEY_ALL_ACCESS,&skey);
if (res!=ERROR_SUCCESS) return;
valsize=sizeof(val);
res=RegQueryValueEx(skey,"Password Delay",0,&valtype,(LPBYTE)&val,&valsize);
if (res==ERROR_SUCCESS) PasswordDelay=val;
valsize=sizeof(val);
res=RegQueryValueEx(skey,"Mouse Threshold",0,&valtype,(LPBYTE)&val,&valsize);
if (res==ERROR_SUCCESS) MouseThreshold=val;
valsize=sizeof(val);
res=RegQueryValueEx(skey,"Mute Sound",0,&valtype,(LPBYTE)&val,&valsize);
if (res==ERROR_SUCCESS) MuteSound=val;
RegCloseKey(skey);
}
If all you want to do is read the values, then the above information is adequate. If additionally you want to write your configuration dialog to be able to change these values, or if you want to write a utility which can change them, then you need to worry about three extra configuration values. It is a real drag writing your own general configuration dialog. The author strongly advises you to use his ScrPlus library, which does it all automatically.
If you do offer a configuration dialog with the ability to change these settings, it is conventional to use a dialog box with two or more tabs. The first tab would have general settings, and subsequent tabs would have the settings for this particular saver. When the dialog is shown it would typically be started on its second page. An example resource file for the dialog is given below. (You'll have to implement it all, including the MonitorClass, yourself.) If you wish to provide context-help for the controls in the General tab, in response to WM_HELP and WM_CONTEXTHELP, then you can either use the help topics provided in the Plus!.hlp file (which comes with Windows Plus! only) or you can use the help file SCRPLUS.HLP which is available in the file minimal.zip along with source code for a minimal saver, and which is freely distributable. Or you can of course write your own help file.
// Identifiers for the various controls
#define ID_DISMISSGROUP 3630
#define ID_THRESHOLDDESC 3631
#define ID_THRESHOLD 3632
#define ID_WAITDESC 3633
#define ID_WAITTEXT 3634
#define ID_WAITBUDDY 3635
#define ID_WAITBOX 3636
#define ID_WAITMOREDESC 3637
#define ID_SAGEOK 3638
#define ID_SAGEBAD 3639
#define ID_MONITOR 3640
#define ID_MUTE 3641
#define ID_MONITORSCREEN 3642
#define ID_ACTIVECONFIG 3643
#define ID_ABOUT 3650
// Help topics in Plus!.hlp and SCRPLUS.HLP
#define PLUSHELP_CORNERS 3100
#define PLUSHELP_THRESHOLD 3101
#define PLUSHELP_PASSWORDDELAY 3102
#define PLUSHELP_COPYRIGHT 3103
#define PLUSHELP_PREVIEW 3104
#define PLUSHELP_MUTE 3105
// Relation between controls in dialog, and help topic
static DWORD GeneralHelpIds[] = {
ID_DISMISSGROUP, PLUSHELP_THRESHOLD,
ID_THRESHOLDDESC, PLUSHELP_THRESHOLD,
ID_THRESHOLD, PLUSHELP_THRESHOLD,
ID_WAITDESC, PLUSHELP_PASSWORDDELAY,
ID_WAITTEXT, PLUSHELP_PASSWORDDELAY,
ID_WAITBUDDY, PLUSHELP_PASSWORDDELAY,
ID_WAITBOX, PLUSHELP_PASSWORDDELAY,
ID_WAITMOREDESC, PLUSHELP_PASSWORDDELAY,
ID_SAGEOK, PLUSHELP_CORNERS,
ID_SAGEBAD, PLUSHELP_CORNERS,
ID_MONITOR, PLUSHELP_CORNERS,
ID_MUTE, PLUSHELP_MUTE, 0,0};
DLG_GENERAL DIALOG 0,0,237,220
STYLE DS_MODALFRAME|WS_POPUP|WS_VISIBLE|WS_CAPTION|WS_SYSMENU
CAPTION "General"
FONT 8,"MS Sans Serif"
{
CONTROL "You can display the screen saver immediately or prevent it from\n"
"appearing at all,by moving the mouse pointer to a corner on \n"
"the screen. Click the corners you want to use.",
ID_SAGEOK,"STATIC",SS_LEFT|WS_CHILD|WS_VISIBLE|WS_GROUP,13,8,282,43
CONTROL "The system agent must be active in order for you to display \n"
"the screen saver immediately by moving the mouse \n"
"pointer to a corner on the screen.",
ID_SAGEBAD,"STATIC",SS_LEFT|WS_CHILD|WS_VISIBLE|WS_GROUP,13,13,282,43
CONTROL "Options for dismissing the screen saver",
ID_DISMISSGROUP,"BUTTON",BS_GROUPBOX|WS_CHILD|WS_VISIBLE,7,154,223,47
CONTROL "&Mouse sensitivity",
ID_THRESHOLDDESC,"STATIC",SS_LEFT|WS_CHILD|WS_VISIBLE|WS_GROUP,13,169,58,12
CONTROL "",ID_THRESHOLD,"COMBOBOX",
CBS_DROPDOWNLIST|WS_CHILD|WS_VISIBLE|WS_VSCROLL|WS_TABSTOP,74,167,148,72
CONTROL "&Wait",
ID_WAITDESC,"STATIC",SS_RIGHT|WS_CHILD|WS_VISIBLE|WS_GROUP,13,184,16,12
CONTROL "",ID_WAITTEXT,"EDIT",
ES_LEFT|WS_CHILD|WS_VISIBLE|WS_BORDER|WS_TABSTOP,32,184,25,12
CONTROL "Generic1",ID_WAITBUDDY,
"msctls_updown32",54|WS_CHILD|WS_VISIBLE,57,184,11,36
CONTROL "",ID_WAITBOX,"COMBOBOX",
CBS_DROPDOWNLIST|WS_CHILD|WS_VISIBLE|WS_VSCROLL|WS_TABSTOP,74,184,50,36
CONTROL "before requiring a password",ID_WAITMOREDESC,"STATIC",
SS_LEFT|WS_CHILD|WS_VISIBLE|WS_GROUP,130,185,95,11
CONTROL "Always require password",ID_WAITSUMMARY,"STATIC",
SS_LEFT|WS_CHILD|WS_VISIBLE,13,184,282,11
CONTROL "Control corners",ID_MONITOR,MonitorClassName,
MS_CORNERS|WS_CHILD|WS_VISIBLE,108,82,20,20
CONTROL "Mute Sound",ID_MUTE,"button",
BS_AUTOCHECKBOX|WS_CHILD|WS_VISIBLE|WS_TABSTOP,11,202,65,15
}
LANGUAGE LANG_NEUTRAL,SUBLANG_NEUTRAL
void ChangePassword(HWND hwnd)
{ // This only ever gets called under '95, when started with the /a option.
HINSTANCE hmpr=::LoadLibrary("MPR.DLL");
if (hmpr==NULL) {Debug("MPR.DLL not found: cannot change password.");return;}
typedef VOID (WINAPI *PWDCHANGEPASSWORD)
(LPCSTR lpcRegkeyname,HWND hwnd,UINT uiReserved1,UINT uiReserved2);
PWDCHANGEPASSWORD PwdChangePassword=
(PWDCHANGEPASSWORD)::GetProcAddress(hmpr,"PwdChangePasswordA");
if (PwdChangePassword==NULL)
{ FreeLibrary(hmpr);
Debug("PwdChangeProc not found: cannot change password");return;
}
PwdChangePassword("SCRSAVE",hwnd,0,0); FreeLibrary(hmpr);
}
This function makes use of the PwdChangePassword function in MPR.DLL. If you wanted to use your own password configuration system under '95 or Plus!, you could simply write your own ChangePassword routine and your own password verification routine. The situation is more difficult under NT.
The behaviour of a full-screen window /s is more complex:
In the code below we use the same window procedure for both the full-screen and preview modes of the saver. The global variable ScrMode, set in WinMain, determines whether it should respond to things like mouse clicks.
// The function CloseSaverWindow uses ReallyClose, as part of a workaround to deal
// with the WM_CLOSE messages that get sent automatically under NT.
void TSaverSettings::CloseSaverWindow()
{ ReallyClose=TRUE; PostMessage(hwnd,WM_CLOSE,0,0);
}
// When a dialog is up, the IsDialogActive flag prevents things like
// mouse-movement and key presses from terminating the saver. When a dialog
// closes, the mouse origin is re-read for threshold-detection purposes.
void TSaverSettings::StartDialog()
{ IsDialogActive=TRUE; SendMessage(hwnd,WM_SETCURSOR,0,0);
}
void TSaverSettings::EndDialog()
{ IsDialogActive=FALSE; SendMessage(hwnd,WM_SETCURSOR,0,0);
GetCursorPos(&InitCursorPos);
}
// We refer to a global value DEBUG which has have been #defined to
// either TRUE or FALSE. If TRUE then we run the saver in only a quarter of
// the screen without the WS_EX_TOPMOST flag: this makes it easier to switch
// back and forth between the debugger and the saver.
void DoSaver(HWND hparwnd)
{ WNDCLASS wc;
wc.style=CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc=SaverWindowProc;
wc.cbClsExtra=0;
wc.cbWndExtra=0;
wc.hInstance=hInstance;
wc.hIcon=NULL;
wc.hCursor=NULL;
wc.hbrBackground=(HBRUSH)GetStockObject(BLACK_BRUSH);
wc.lpszMenuName=NULL;
wc.lpszClassName="ScrClass";
RegisterClass(&wc);
if (ScrMode==smPreview)
{ RECT rc; GetWindowRect(hparwnd,&rc);
int cx=rc.right-rc.left, cy=rc.bottom-rc.top;
hScrWindow=CreateWindowEx(0,"ScrClass","SaverPreview",WS_CHILD|WS_VISIBLE,
0,0,cx,cy,hparwnd,NULL,hInstance,NULL);
}
else
{ int cx=GetSystemMetrics(SM_CXSCREEN), cy=GetSystemMetrics(SM_CYSCREEN);
DWORD exstyle, style;
if (DEBUG) { cx=cx/3; cy=cy/3; exstyle=0; style=WS_OVERLAPPEDWINDOW|WS_VISIBLE;}
else {exstyle=WS_EX_TOPMOST; style=WS_POPUP|WS_VISIBLE;}
hScrWindow=CreateWindowEx(exstyle,"ScrClass","SaverWindow",style,
0,0,cx,cy,NULL,NULL,hInstance,NULL);
}
if (hScrWindow==NULL) return;
UINT oldval;
if (ScrMode==smSaver) SystemParametersInfo(SPI_SCREENSAVERRUNNING,1,&oldval,0);
MSG msg;
while (GetMessage(&msg,NULL,0,0))
{ TranslateMessage(&msg);
DispatchMessage(&msg);
}
if (ScrMode==smSaver) SystemParametersInfo(SPI_SCREENSAVERRUNNING,0,&oldval,0);
return;
}
LRESULT CALLBACK SaverWindowProc(HWND hwnd,UINT msg,WPARAM wParam,LPARAM lParam)
{ switch (msg)
{ case WM_CREATE:
{ Debug("WM_CREATE... reading initial position and time, and starting timer");
ss->hwnd=hwnd;
GetCursorPos(&(ss->InitCursorPos)); ss->InitTime=GetTickCount();
ss->idTimer=SetTimer(hwnd,0,100,NULL);
} break;
case WM_TIMER:
{ if (ss->FlashScreen)
{ HDC hdc=GetDC(hwnd); RECT rc; GetClientRect(hwnd, &rc);
FillRect(hdc,&rc,GetSysColorBrush((GetTickCount()>>8)%25));
ReleaseDC(hwnd,hdc);
}
} break;
case WM_ACTIVATE: case WM_ACTIVATEAPP: case WM_NCACTIVATE:
{ if (ScrMode==smSaver && !ss->IsDialogActive &&
LOWORD(wParam)==WA_INACTIVE && !DEBUG)
{ Debug("WM_ACTIVATE: about to inactive window, so sending close");
ss->CloseSaverWindow();
}
} break;
case WM_SETCURSOR:
{ if (ScrMode==smSaver && !ss->IsDialogActive && !DEBUG)
{ Debug("WM_SETCURSOR: Saver is running at the moment: so no cursor");
SetCursor(NULL);
}
else
{ Debug("WM_SETCURSOR: dialog up, or Preview or Debug mode: normal cursor");
SetCursor(LoadCursor(NULL,IDC_ARROW));
}
} break;
case WM_LBUTTONDOWN: case WM_MBUTTONDOWN: case WM_RBUTTONDOWN: case WM_KEYDOWN:
{ if (ScrMode==smSaver && !ss->IsDialogActive)
{ Debug("WM_BUTTONDOWN: sending close");
ss->CloseSaverWindow();
}
} break;
case WM_MOUSEMOVE:
{ if (ScrMode==smSaver && !ss->IsDialogActive && !DEBUG)
{ POINT pt; GetCursorPos(&pt);
int dx=pt.x-ss->InitCursorPos.x; if (dx<0) dx=-dx;
int dy=pt.y-ss->InitCursorPos.y; if (dy<0) dy=-dy;
if (dx>(int)ss->MouseThreshold || dy>(int)ss->MouseThreshold)
{ Debug("WM_MOUSEMOVE: moved beyond threshold, sending close");
ss->CloseSaverWindow();
}
}
} break;
case WM_SYSCOMMAND:
{ if (ScrMode==smSaver)
{ if (wParam==SC_SCREENSAVE)
{ Debug("WM_SYSCOMMAND: gobbling up SC_SCREENSAVE to stop new saver running.");
return FALSE;
}
if (wParam==SC_CLOSE && !DEBUG)
{ Debug("WM_SYSCOMMAND: gobbling up SC_CLOSE");
return FALSE;
}
}
} break;
case (WM_CLOSE):
{ if (ScrMode==smSaver && ss->ReallyClose && !ss->IsDialogActive)
{ Debug("WM_CLOSE: maybe we need a password");
BOOL CanClose=TRUE;
if (GetTickCount()-ss->InitTime > 1000*ss->PasswordDelay)
{ ss->StartDialog(); CanClose=VerifyPassword(hwnd); ss->EndDialog();
}
if (CanClose) {Debug("WM_CLOSE: doing a DestroyWindow"); DestroyWindow(hwnd);}
else {Debug("WM_CLOSE: but failed password, so doing nothing");}
}
if (ScrMode==smSaver) return FALSE;
// return FALSE here so that DefWindowProc doesn't get called,
// because it would just DestroyWindow itself
} break;
case WM_DESTROY:
{ if (ss->idTimer!=0) KillTimer(hwnd,ss->idTimer); ss->idTimer=0;
Debug("POSTQUITMESSAGE from WM_DESTROY!!");
PostQuitMessage(0);
} break;
}
return DefWindowProc(hwnd,msg,wParam,lParam);
}
BOOL VerifyPassword(HWND hwnd)
{ // Under NT, we return TRUE immediately. This lets the saver quit,
// and the system manages passwords. Under '95, we call VerifyScreenSavePwd.
// This checks the appropriate registry key and, if necessary,
// pops up a verify dialog
OSVERSIONINFO osv; osv.dwOSVersionInfoSize=sizeof(osv); GetVersionEx(&osv);
if (osv.dwPlatformId==VER_PLATFORM_WIN32_NT) return TRUE;
HINSTANCE hpwdcpl=::LoadLibrary("PASSWORD.CPL");
if (hpwdcpl==NULL) {Debug("Unable to load PASSWORD.CPL. Aborting");return TRUE;}
typedef BOOL (WINAPI *VERIFYSCREENSAVEPWD)(HWND hwnd);
VERIFYSCREENSAVEPWD VerifyScreenSavePwd;
VerifyScreenSavePwd=
(VERIFYSCREENSAVEPWD)GetProcAddress(hpwdcpl,"VerifyScreenSavePwd");
if (VerifyScreenSavePwd==NULL)
{ Debug("Unable to get VerifyPwProc address. Aborting");
FreeLibrary(hpwdcpl);return TRUE;
}
Debug("About to call VerifyPwProc");
BOOL bres=VerifyScreenSavePwd(hwnd); FreeLibrary(hpwdcpl);
return bres;
}
STRINGTABLE DISCARDABLE
BEGIN
1 "Minimal screen saver"
END
#define DEBUG FALSE
#if DEBUG
void Debug(char *c) {OutputDebugString(c); OutputDebugString("\n");}
#else
void Debug(char *) {}
#endif
Explorer uses the first icon resource in the saver as its icon. Either create your own icon from scratch, or base it upon one of the standard saver icons:
- Hippy age: strange visions of the future
- Industrial age: blocky machinery
- Information age: clean, simple and elegant
Next, compile the saver and rename it with the suffix .scr. Copy it into the windows directory: then it will appear in the Display Properties control panel. See also Installation of a saver.
BOOL IsSaverRunning()
{ BOOL isNT;
OSVERSIONINFO ovi; ovi.dwOSVersionInfoSize=sizeof(ovi);
GetVersionEx(&ovi); isNT=(ovi.dwPlatformId==VER_PLATFORM_WIN32_NT);
if (!isNT)
{ UINT dummy, srunning=0;
BOOL res=SystemParametersInfo(SPI_SCREENSAVERRUNNING,0,&srunning,0);
SystemParametersInfo(SPI_SCREENSAVERRUNNING,srunning,&dummy,0);
if (srunning==0) return FALSE; else return TRUE;
}
// That works fine under '95. But NT simply doesn't return the old value to us.
// Hence we need some magic.
HWND hfw=GetForegroundWindow();
// Sometimes hfw is null. I presume this is because a screensaver is running on another
// desktop. It's sometimes also cause by the user having just exited a game like X-wing.
// I don't know how to check about desktops. So, I'll assume it's because the screensaver
// is running. This means that, immediately after you exit X-wing, you won't be able to
// detect a saver. No great loss.
if (hfw==NULL) return TRUE;
LONG wl=GetWindowLong(hfw,GWL_STYLE);
if ((wl&0xF0000000)!=WS_POPUP|WS_VISIBLE) return FALSE;
RECT rc; GetWindowRect(hfw,&rc);
if (rc.right-rc.left!=GetSystemMetrics(SM_CXSCREEN) ||
rc.bottom-rc.top!=GetSystemMetrics(SM_CYSCREEN)) return FALSE;
return TRUE;
}
// Code to launch saver full-screen
if (IsScreensaverRunning()) return;
// We don't want to try and set it running again.
HWND hfw=GetForegroundWindow();
if (hfw==NULL) DefWindowProc(hwnd,WM_SYSCOMMAND,SC_SCREENSAVE,0);
else PostMessage(hfw,WM_SYSCOMMAND,SC_SCREENSAVE,0);
// Code to launch configuration dialog
char scr[MAX_PATH];
DWORD res=GetPrivateProfileString("boot","SCRNSAVE.EXE","",scr,MAX_PATH,"system.ini");
STARTUPINFO si; PROCESS_INFORMATION pi;
ZeroMemory(&si,sizeof(si)); ZeroMemory(&pi,sizeof(pi));
si.cb=sizeof(si);
char c[MAX_PATH]; wsprintf(c,"\"%s\" /c",scr);
BOOL res=CreateProcess(scr,c,NULL,NULL,FALSE,0,NULL,NULL,&si,&pi);
if (res) return IDOK; else return IDCANCEL;
Under Windows '95 and Plus!, you must disable these keys by calling SystemParametersInfo(SPI_SCREENSAVERRUNNING,TRUE,..). After the saver has finished you re-enable them by calling SystemParametersInfo(SPI_SCREENSAVERRUNNING,FALSE,..);. Under NT the system keys get disabled automatically, but it's a good idea to call SystemParametersInfo just in case it has other undocumented side-effects.
The following section points out a problem that may occur with ctrl-alt-delete if using DirectDraw, and gives a solution.
If you use ChangeDisplaySettings or pDirectDraw->SetDisplayMode then a couple of spurious WM_MOUSEMOVE messages get generated as the mouse settles into its new position. To complicate matters, these messages do not get sent during the mode-change call but after. There are a few possible solutions, all unpleasant: you could count down and ignore the first five WM_MOUSEMOVE messages; or you could ignore all such messages that occur within the five seconds after changing mode. It will help greatly if you use some Debug function to display a record of every single window message that gets sent to your window during the change-mode.
Under '95, dialogs such as the password dialog must be shown by the saver itself. If you are running at 320x200 or 320x240 then the GDI cannot draw dialogs onto the screen. Just before showing the dialog you will have to change into a more respectable screen mode, and just after you will have to restore the screen to what it was before. This often looks ugly. You might try to copy the screen contents as they were in the full-screen low-resolution mode and then use them as a bitmap background in the respectable mode.
If you use DirectDraw to change modes, the act of changing out of full-screen mode will re-enable the system keys. You will have to call SystemParametersInfo(SPI_SCREENSAVERRUNNING,TRUE,...) to disable them again.
The best use for hot corners is in interactive savers, such as a puzzle saver or an arcade-game saver. The user might be bored for a few minutes waiting for a download to finish, or might be fiddling with the computer while making a telephone call. Imagine how easy it is for the user simply to move their mouse to the top left corner of the screen and have your program run immediately!
The section on installation below includes sample code for installing ScrHots. Here in this section we give code which works both for ScrHots and for SAGE.DLL to interact with the hot corner services.
// CheckHots: this routine checks for Hot Corner services.
// It first tries with SAGE.DLL, which comes with Windows Plus!
// Failint this it tries with ScrHots, a third-party hot-corner
// service program written by the author that is freely
// distributable and works with NT and '95.
BOOL CheckHots()
{ typedef BOOL (WINAPI *SYSTEMAGENTDETECT)();
HINSTANCE sagedll=LoadLibrary("Sage.dll");
if (sagedll!=NULL)
{ SYSTEMAGENTDETECT detectproc=(SYSTEMAGENTDETECT)
GetProcAddress(sagedll,"System_Agent_Detect");
BOOL res=FALSE;
if (detectproc!=NULL) res=detectproc();
FreeLibrary(sagedll);
if (res) return TRUE;
}
HINSTANCE hotsdll=LoadLibrary("ScrHots.dll");
if (hotsdll!=NULL)
{ SYSTEMAGENTDETECT detectproc=(SYSTEMAGENTDETECT)
GetProcAddress(hotsdll,"System_Agent_Detect");
BOOL res=FALSE;
if (detectproc!=NULL) res=detectproc();
FreeLibrary(hotsdll);
if (res) return TRUE;
}
return FALSE;
}
// NotifyHots: if you make any changes to the hot corner
// information in the registry, you must call NotifyHots
// to inform the hot corner services of your change.
void __fastcall NotifyHots()
{ typedef VOID (WINAPI *SCREENSAVERCHANGED)();
HINSTANCE sagedll=LoadLibrary("Sage.DLL");
if (sagedll!=NULL)
{ SCREENSAVERCHANGED changedproc=(SCREENSAVERCHANGED)
GetProcAddress(sagedll,"Screen_Saver_Changed");
if (changedproc!=NULL) changedproc();
FreeLibrary(sagedll);
}
HINSTANCE hotsdll=LoadLibrary("ScrHots.dll");
if (hotsdll!=NULL)
{ SCREENSAVERCHANGED changedproc=(SCREENSAVERCHANGED)
GetProcAddress(hotsdll,"Screen_Saver_Changed");
if (changedproc!=NULL) changedproc();
FreeLibrary(hotsdll);
}
}
[boot] ... SCRNSAVE.EXE=C:\WINDOWS\FLAME.SCRUnder '95 and Plus!, this corresponds to an actual file in the Windows directory called SYSTEM.INI. Under NT the values are actually stored in the registry but you should still use Get/WritePrivateProfileString as these calls are automatically mapped to the registry. The filename must be a short filename.
To change the currently selected saver you must not only change the value mentioned above; but also cause a WM_WININICHANGED message to be sent. This will inform the rest of the setting that the value has changed. In particular, it means that the next time the Display Properties dialog appears, it will be correct.
// To get the currently selected saver:
char CurSav[MAX_PATH];
DWORD res=GetPrivateProfileString("boot","SCRNSAVE.EXE","",
CurSav,MAX_PATH,"system.ini");
if (res==0 || strcmp(scrt,"")==0) {..} // Currently selected saver is 'none'
// To change the currently selected saver:
char ShortName[MAX_PATH];
GetShortPathName(CurSav,ShortName,MAX_PATH);
WritePrivateProfileString("boot","SCRNSAVE.EXE",ShortName,"system.ini");
SystemParametersInfo(SPI_SETSCREENSAVEACTIVE,TRUE,NULL,TRUE);
// that sends a WM_WININICHANGE so that DisplayProperties dialog knows we've changed.
// It also enables screensaving.
Note that the windows directory is the corret place to install a saver. This is because GetWindowsDirectory() will always return a directory to which you have write-access. You should not install a saver into the system directory because on many installations (such as shared network installations) it is read-only.
It is possible to install a saver into a different directory. The Display Properties dialog actually creates its list of possible savers from three locations: the directory of the currently selected saver; the Windows directory; and the System directory. You might choose to install a couple of theme savers in a theme directory so that they are only visible when the user selects your theme.
The essence of a saver is that it should be easy and fun to use, and easy and fun to install. If at all possible you should have a single .scr file with no additional files. Even if you want to have additional bitmaps or JPEGs with your saver, these might as well be deployed as resources in the .scr file. It also makes it much easier for the user if you deploy your saver as a single self-extracting .exe file which copies the appropriate files into the appropriate places and installs the saver.
You can download the file install.zip. This contains complete source code for a self-extracting saver installer, and you are free to modify and distribute it as you wish. It installs both ScrHots and your saver into the system, and pops up a preview dialog when installation is complete. The code is generic and can be used to install any saver merely by making a few changes to the resource file. You may use the code however you wish.
If you simply want an alternative to ShellExecute("install",..) rather than a full-blown self-extracting installer, you might use the following workaround. Rather than popping up the Display Properties proper, this code pops up its own dialog with a preview of the saver. This code is part of the above-mentioned installer.
// Call the following two procedures in your installation routine.
SelectAsDefault(savpath);
ExecutePreviewDialog(hwnd,savpath);
// SelectAsDefault: makes scr the currently selected saver
void SelectAsDefault(char *scr)
{ char sscr[MAX_PATH];
GetShortPathName(scr,sscr,MAX_PATH);
WritePrivateProfileString("boot","SCRNSAVE.EXE",sscr,"system.ini");
SystemParametersInfo(SPI_SETSCREENSAVEACTIVE,TRUE,NULL,TRUE);
// that sends a WM_WININICHANGE so that DisplayProperties
// dialog knows we've changed
}
// ExecutePreviewDialog: displays a dialog with a preview running inside it.
int ExecutePreviewDialog(HWND hwnd,char *scr)
{ typedef struct {DLGITEMTEMPLATE dli; WORD ch; WORD c; WORD t; WORD dummy;
WORD cd;} TDlgItem;
typedef struct {DLGTEMPLATE dlt; WORD m; WORD c; WCHAR t[8]; WORD pt; WCHAR f[14];
TDlgItem ia; TDlgItem ib; TDlgItem ic;} TDlgData;
TDlgData dtp={{DS_MODALFR