Author: Jonas Bilinkevicius 

How to change the screen resolution programmatically

Answer:

Solve 1:

To change the screen resolution on a user's PC is bad programming style, but anyway:

1   { ... }
2   type
3     TDisplaySetting = record
4       dsWidth, dsHeight, dsBPP: Cardinal {DWORD};
5     end;
6     { ... }
7   
8   function ChangeDisplayMode(var Settings: TDisplaySetting): Boolean;
9   var
10    I: Integer;
11    DC: HDC;
12    DevMode: TDevMode;
13    Current: TDisplaySetting;
14  begin
15    Result := FALSE;
16    { Enumerate available display modes }
17    I := 0;
18    while EnumDisplaySettings(nil, I, DevMode) do
19    begin
20      { Check if this is desired settings }
21      if (DevMode.dmPelsWidth = Settings.dsWidth) and (DevMode.dmPelsHeight =
22        Settings.dsHeight)
23        and (DevMode.dmBitsPerPel = Settings.dsBPP) then
24      begin
25        { Get Current Display Settings }
26        DC := GetDC(0);
27        with Current do
28        begin
29          dsWidth := GetDeviceCaps(DC, HORZRES);
30          dsHeight := GetDeviceCaps(DC, VERTRES);
31          dsBPP := GetDeviceCaps(DC, BITSPIXEL);
32        end;
33        ReleaseDC(0, DC);
34        { Indicate what settings to change }
35        DevMode.dmFields := DM_BITSPERPEL or DM_PELSWIDTH or DM_PELSHEIGHT;
36        { Try to change settings }
37        if ChangeDisplaySettings(DevMode, 0) = DISP_CHANGE_SUCCESSFUL then
38        begin
39          Result := TRUE;
40          { Return previous settings if successful }
41          Settings := Current;
42        end;
43        Break;
44      end;
45      Inc(I);
46    end;
47  end;
48  
49  //Used like this:
50  
51  var
52    DS: TDisplaySettings;
53  begin
54    DS.dsWidth := 800;
55    DS.dsHeight := 600;
56    DS.dsBPP := 24;
57    { Change display mode }
58    if ChangeDisplayMode(DS) then
59    begin
60      { DS now stores previous settings }
61      { ... }
62      { Restore original settings }
63      ChangeDisplayMode(DS);
64    end;
65  end;



Solve 2:

Here's a method I built to force 1024x768:

66  function SetDisplay1024x768: Boolean;
67  var
68    DevMode: TDeviceMode;
69  begin
70    EnumDisplaySettings(nil, 0, DevMode);
71    DevMode.dmFields := DM_PELSWIDTH or DM_PELSHEIGHT;
72    DevMode.dmPelsWidth := 1024;
73    DevMode.dmPelsHeight := 768;
74    Result := ChangeDisplaySettings(DevMode, CDS_UPDATEREGISTRY)
75      = DISP_CHANGE_SUCCESSFUL;
76  end;



Answer 3:
77  
78  function ChangeRes(X, Y, Frequency, ColorDepth: Cardinal): boolean;
79  var
80    RetCode: Integer;
81    MyDevMode: TDeviceMode;
82  begin
83    EnumDisplaySettings(nil, 0, MyDevMode);
84    MyDevMode.dmDisplayFrequency := Frequency;
85    MyDevMode.dmPelsWidth := X;
86    MyDevMode.dmPelsHeight := Y;
87    MyDevMode.dmBitsPerPel := ColorDepth;
88    MyDevMode.dmFields := DM_PELSWIDTH or DM_PELSHEIGHT or DM_BITSPERPEL
89      or DM_DISPLAYFREQUENCY;
90    RetCode := ChangeDisplaySettings(MyDevMode, CDS_UPDATEREGISTRY);
91    case RetCode of
92      DISP_CHANGE_SUCCESSFUL, DISP_CHANGE_RESTART: Result := true;
93    else
94      Result := false;
95    end;
96    case RetCode of
97      DISP_CHANGE_SUCCESSFUL:
98        Writeln('DISP_CHANGE_SUCCESSFUL');
99      DISP_CHANGE_RESTART:
100       Writeln('DISP_CHANGE_RESTART');
101     DISP_CHANGE_FAILED:
102       Writeln('DISP_CHANGE_FAILED');
103     DISP_CHANGE_BADMODE:
104       Writeln('DISP_CHANGE_BADMODE');
105     DISP_CHANGE_NOTUPDATED:
106       Writeln('DISP_CHANGE_NOTUPDATED');
107     DISP_CHANGE_BADFLAGS:
108       Writeln('DISP_CHANGE_BADFLAGS');
109     DISP_CHANGE_BADPARAM:
110       Writeln('DISP_CHANGE_BADPARAM');
111   else
112     Writeln('DISP_CHANGE_OTHER_ERROR');
113   end;
114 end;