Reading the Joystick Interface

Most Intel PCs have one or two joystick ports. Usually, these are located on the sound card.

Under DOS, it was possible to directly access these ports. However, Windows 95 and above forbid direct hardware access. Therefore, this page exists to help get around windows.

Visual Basic | Delphi | C++ Builder | Java | Windows API

Generic References

Windows provides two ways to read the joystick, an input only device.

winmm.dll - 10 functions including joyGetPos and joyGetDevCaps.
DirectX

A basic overview (in very broken English)

Visual Basic 6.0

Delphi

Delphi 5 does not supply joystick support via the vcl.
Windows API support is defined in rtl\win\mmsystem.pas

The following code snipet is from The Unofficial Delphi Developers FAQ.

uses
  ... , mmSystem;

var
  myjoy: tjoyinfo;
begin
  joygetpos(joystickid1,@myjoy);
  trackbar1.position := myjoy.wypos;
  trackbar2.position := myjoy.wxpos;
  radiobutton1.checked := (myjoy.wbuttons and joy_button1)>0;
  radiobutton2.checked := (myjoy.wbuttons and joy_button2)>0;
end;

This snippet is pretty good, but only one radio button can be set at a time. Also note that the position range is 0 to 65,535 when calibrated. Be sure to set the trackbar max values appropriately. (On my test system, the center position is 38,500 x 26,900.)

Using a Message Handler

mmsystem.pas does a pretty good job of encapsulating the Windows joystick interface - all the functions in the Windows SDK Help file appear to be available. The only thing missing is a record definition so that you can use a message handler. This is the one I use.

type
  TMMJoyStick  = packed record
    Msg:     Cardinal;  // The message ID
    Buttons: Longint;   // The wParam
    XPos:    word;      // The lParam
    YPos:    word;
    Result:  Longint;
end;

There is one interesting inconsistency

The x and y positions are passed to a message handler as unsigned words (16 bits), but the associated Max and Min values in TJoyCaps and the x/y values in TJoyInfo are 32 bits (UINT).

The following code implements a message handler.

procedure MMJOY1BUTTONDOWN (var LocMessage: TMMJoyStick); message MM_JOY1BUTTONDOWN;
procedure MMJOY1BUTTONUP   (var LocMessage: TMMJoyStick); message MM_JOY1BUTTONUP;
procedure MMJOY1MOVE       (var LocMessage: TMMJoyStick); message MM_JOY1MOVE;

  // ButtonDown and Move are not shown, they just call ButtonUp
procedure TForm1.MMJOY1BUTTONUP (var LocMessage: TMMJoyStick);
begin
  trackbar1.position := LocMessage.ypos;
  trackbar2.position := LocMessage.xpos;
  Edit1.Text := IntToStr(LocMessage.ypos);  // so you can see 
  Edit2.Text := IntToStr(LocMessage.xpos);  //   what is happening
  CheckBox1.checked := (LocMessage.Buttons and joy_button1)>0;
  CheckBox2.checked := (LocMessage.Buttons and joy_button2)>0;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
  myJoyCaps: TJoyCaps;
begin
 joyGetDevCaps(joystickid1,@myJoyCaps, sizeof(myJoyCaps)); // for test
 joySetCapture(self.Handle, joystickid1, 100, true);
end;

procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  joyReleaseCapture(joystickid1);
end;

Several free and shareware components are available via Torry's Delphi Pages.

C++ Builder

Java

Windows API

Search the Windows SDK for Joystick. The following functions are listed under Multimedia Joystick Functions

joyGetDevCaps
joyGetNumDevs
joyGetPos
joyGetPosEx
joyGetThreshold
joyReleaseCapture
joySetCapture
joySetThreshold

Author: Robert Clemenzi - clemenzi@cpcug.org