Implementing event functions InitializeWizard while using ISSI (to add background image) in Inno Setup: Duplicate identifier 'INITIALIZEWIZARD'

I'm trying to put a background image to Inno Setup installer using ISSI along with a song using the "BASS audio library", but I can only keep one of them active since I get this compiler error:

Duplicate identifier 'INITIALIZEWIZARD'

Would I have another way to get a full-screen background image so I can use the BASS audio library?

Inno Setup code:

; Script generated by the Inno Setup Script Wizard.
; SEE THE DOCUMENTATION FOR DETAILS ON CREATING INNO SETUP SCRIPT FILES!

#define ISSI_BackgroundImage "E:\Instalador\file.bmp"

#define ISSI_BackgroundImage_BGColor "clWhite"

#define ISSI_IncludePath "C:\ISSI"
#include ISSI_IncludePath+"\_issi.isi"

[Files]
Source: "Bass.dll"; Flags: dontcopy
Source: "AudioFile.mp3"; Flags: dontcopy

[Code]
const
  BASS_SAMPLE_LOOP = 4;
  BASS_UNICODE = $80000000;
  BASS_CONFIG_GVOL_STREAM = 5;
const
  #ifndef UNICODE
    EncodingFlag = 0;
  #else
    EncodingFlag = BASS_UNICODE;
  #endif
type
  HSTREAM = DWORD;

function BASS_Init(device: LongInt; freq, flags: DWORD;
  win: HWND; clsid: Cardinal): BOOL;
  external 'BASS_Init@files:bass.dll stdcall';
function BASS_StreamCreateFile(mem: BOOL; f: string; offset1: DWORD;
  offset2: DWORD; length1: DWORD; length2: DWORD; flags: DWORD): HSTREAM;
  external 'BASS_StreamCreateFile@files:bass.dll stdcall';
function BASS_ChannelPlay(handle: DWORD; restart: BOOL): BOOL;
  external 'BASS_ChannelPlay@files:bass.dll stdcall';
function BASS_SetConfig(option: DWORD; value: DWORD ): BOOL;
  external 'BASS_SetConfig@files:bass.dll stdcall';
function BASS_Free: BOOL;
  external 'BASS_Free@files:bass.dll stdcall';

procedure InitializeWizard;
var
  StreamHandle: HSTREAM;
begin
  ExtractTemporaryFile('AudioFile.mp3');
  if BASS_Init(-1, 44100, 0, 0, 0) then
  begin
    StreamHandle := BASS_StreamCreateFile(False,
      ExpandConstant('{tmp}\AudioFile.mp3'), 0, 0, 0, 0,
      EncodingFlag or BASS_SAMPLE_LOOP);
    BASS_SetConfig(BASS_CONFIG_GVOL_STREAM, 2500);
    BASS_ChannelPlay(StreamHandle, False);
  end;
end;

procedure DeinitializeSetup;
begin
  BASS_Free;
end;

Who can help me, I'm really grateful.

Solution

In Inno Setup 6, with its support for event attributes, see Merging event function (InitializeWizard) implementations from different sources.

[Code]

<event('InitializeWizard')>
procedure InitializeWizard2;
begin
  { Your BASS code goes here }
end;

For older versions of Inno Setup:

Inno Setup Script #Includes (ISSI) may implement some Inno Setup event functions, like InitializeWizard, InitializeSetup, CurPageChanged, BackButtonClick, NextButtonClick and DeinitializeSetup for its own purposes. Not all event functions are necessarily defined, it depends on ISSI features you are using. In your case, it's the ISSI_BackgroundImage that causes implementation of InitializeWizard event function.

If you need to run your own code in some of these event functions, ISSI implementation of event function can call your user defined function, when you define an appropriate preprocessor symbol. The symbol name is like ISSI_EventFunctionName and the user defined function must have the same name. The function/procedure also must have the same signature as the original Inno Setup event function.

Both the symbol and the user function must be defined before you include _issi.isi.

An example for InitializeWizard:

[Code]

procedure ISSI_InitializeWizard;
begin
  { Your BASS code goes here }
end;

#define ISSI_InitializeWizard

#define ISSI_IncludePath "C:\ISSI"
#include ISSI_IncludePath+"\_issi.isi"