WM_DISPLAYCHANGE // recognize a different screen resolution
lazarus / 34-Windows

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RAW · 2018-02-10 06:57

Maybe this is useful for anybody.... 

This is working for me...
EDIT: Instead of "ShowMessage" I use now "Color" in this example... As
GetMem mentioned "ShowMessage" is a bad idea inside a WndProc.
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i UNIT
Unit1;{$MODE OBJFPC}{$H+}{$J-} Interface USES  Windows, Classes,
Forms, Dialogs;  TYPE  TForm1 = Class(TForm)   Procedure FormCreate
(Sender: TObject);   Procedure FormClick  (Sender: TObject);    
PRIVATE     oldProc: Windows.WndProc;  End;  VAR  Form1:
TForm1; Implementation{$R *.LFM}  Function WndCallback  (MyWND: HWND;
uMSG: UINT; wParam: WPARAM; lParam: LPARAM): LRESULT; StdCall; Begin 
If (uMSG = WM_DISPLAYCHANGE)  Then Form1.Color:= RGB(0, 80, 255);  
Result:= CallWindowProc(Form1.oldProc, MyWND, uMSG, wParam,
lParam); End;  Procedure TForm1.FormCreate(Sender: TObject); Begin 
oldProc:= Windows.WndProc(GetWindowLongPtr(Handle, GWL_WNDPROC)); 
SetWindowLongPtr(Handle, GWL_WNDPROC,
PtrInt(@WndCallback)); End;  Procedure TForm1.FormClick(Sender:
TObject); Begin  Color:= RGB(0, 187, 0); End; END.

// not working for me...
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
unit1;{$mode objfpc}{$H+} interface uses Windows, Classes, SysUtils,
Forms, Dialogs; type  TForm1 = class(TForm)  private   procedure
WMDisplayChange(var msg: TMessage); message WM_DISPLAYCHANGE; 
end; var  Form1: TForm1; implementation {$R *.lfm} procedure
TForm1.WMDisplayChange(var msg: TMessage);begin showmessage('Display
Changed');end; end.
WndProc (standard way) isn't working for me either...

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balazsszekely · 2018-02-10 07:39

@RAW
The ShowMessage inside WndCallback is wrong, I mean fundamentally
wrong. You cannot block the message chain with a function like
ShowMessage. I know you put it there only for testing purposes, still
be careful with blocking functions.

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RAW · 2018-02-10 08:05

@GetMem
Yeah, I added some info lines regarding this... Thanks...

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taazz · 2018-02-10 09:39

Quote from: RAW on February 10, 2018, 07:57:47 am
// not working for me...
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
unit1;{$mode objfpc}{$H+} interface uses Windows, Classes, SysUtils,
Forms, Dialogs; type  TForm1 = class(TForm)  private   procedure
WMDisplayChange(var msg: TMessage); message WM_DISPLAYCHANGE; 
end; var  Form1: TForm1; implementation {$R *.lfm} procedure
TForm1.WMDisplayChange(var msg: TMessage);begin showmessage('Display
Changed');end; end.
WndProc (standard way) isn't working for me either...
that is because the default handler filters unsupported messages out
from the internal message loop. You should use the getwindowlong (look
the default handler proc for info) to get the attached wincontrol
instead of relying on a global variable that might or might not be
valid.

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RAW · 2018-02-11 20:16

@taazz
Thanks for the info...
What do you mean? Something like this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Procedure
TForm1.FormCreate(Sender: TObject); Begin  oldProc:=
Windows.WndProc(GetWindowLongPtr(Handle, GWL_WNDPROC)); 
SetWindowLongPtr(Handle, GWL_WNDPROC, PtrInt(@WndCallback)); End; ...
is working good too... 

But I heard it's better to use this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i  TYPE 
TSubClassProc = Function   (hWnd: HWND; uMSG: UINT; wParam: WPARAM;
lParam: LPARAM;    uIDSubclass: UINT_PTR; dwRefData: DWORD_PTR):
LRESULT; StdCall; ........................  Function
SetWindowSubclass  (hWnd: HWND; pfnSubclass: TSubClassProc;
uIDSubclass: UINT_PTR;   dwRefData: DWORD_PTR): BOOL; StdCall;
External 'ComCtl32.dll';  Function RemoveWindowSubclass  (hWnd: HWND;
pfnSubclass: TSubClassProc; uIDSubclass: UINT_PTR): BOOL;   StdCall;
External 'ComCtl32.dll';  Function DefSubclassProc  (hWnd: HWND; uMSG:
UINT; wParam: WPARAM; lParam: LPARAM): LRESULT;   StdCall; External
'ComCtl32.dll';  I'm working on it...

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taazz · 2018-02-11 20:40

Quote from: RAW on February 11, 2018, 09:16:47 pm@taazz
Thanks for the info...
What do you mean? Something like this:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Procedure
TForm1.FormCreate(Sender: TObject); Begin  oldProc:=
Windows.WndProc(GetWindowLongPtr(Handle, GWL_WNDPROC)); 
SetWindowLongPtr(Handle, GWL_WNDPROC, PtrInt(@WndCallback)); End; No I
mean

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i UNIT
Unit1;{$MODE OBJFPC}{$H+}{$J-} Interface USES  Windows, Classes,
Forms, Dialogs;  TYPE  TForm1 = Class(TForm)  Procedure FormCreate
(Sender: TObject);   PRIVATE    PrevWndProc: Windows.WNDPROC; 
End;  VAR  Form1: TForm1; Implementation{$R *.LFM}  Function
WndCallback (MyHWND: HWND; uMSG: UINT; wParam: WParam; lParam:
LParam): LRESULT; StdCall;var  WindowInfo: PWin32WindowInfo;Begin 
WindowInfo := GetWin32WindowInfo(Window); //<---- step one  If (uMSG =
WM_DISPLAYCHANGE)  Then ShowMessage('Display Changed') // only for
testing purposes...  Else Form1.Color:= RGB(0, 170, 0);  // don't use
this in real world apps, take                                      //
a look at the following post from GetMem   if WindowInfo^.WinControl
is TForm1 then //Eliminate form1 global variable for safer handling. 
Result:= CallWindowProc(TForm1(WindowInfo^.WinControl).PrevWndProc,
MyHWND, uMSG, WParam, LParam); End;  Procedure
TForm1.FormCreate(Sender: TObject); Begin  PrevWndProc:=
Windows.WNDPROC  (SetWindowLongPtr(Handle, GWL_WNDPROC,
PtrInt(@WndCallback))); End; END.
Take a closer look on WindowProc in the file win32callback.inc it has
all the information you need.