Scroller: C++Builder Version

In C++Builder programs, we achieve the animation-based message loop through an OnIdle event handler:

void __fastcall TForm1::OnIdle(TObject *Sender, bool &Done)
{
   Scroll();
   Done = False;
}

An Idle event occurs whenever there are no other events occurring, meaning the OnIdle event handler will essentially just be called over and over. Because Idle events are associated with the application and not a form, we must explicitly set up the OnIdle handler just as we set up the application's OnActivate handler in all C++Builder examples:

Application->OnIdle = OnIdle;

Our OnIdle event handler does nothing more than call our Scroll() function to perform one iteration of the scroll.

/****************************************************************************\
*                                                                            *
*  Scroller.cpp                                                              *
*  ScrollerU.cpp                                                             *
*                                                                            *
*  This program demonstrates circular scrolling within a virtual buffer.     *
*                                                                            *
*  Because fg_scroll() requires a "hidden" virtual buffer to save and then   *
*  restore portions of the area being scrolled, we create a second virtual   *
*  buffer for this purpose.                                                  *
*                                                                            *
\****************************************************************************/
#include 
#pragma hdrstop
#include "ScrollerU.h"
//---------------------------------------------------------------------------
#pragma resource "*.dfm"
TForm1 *Form1;
//---------------------------------------------------------------------------
__fastcall TForm1::TForm1(TComponent* Owner)
   : TForm(Owner)
{
}
//---------------------------------------------------------------------------
void __fastcall TForm1::OnIdle(TObject *Sender, bool &Done)
{
   Scroll();
   Done = False;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormActivate(TObject *Sender)
{
   fg_realize(hPal);
   Invalidate();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormCreate(TObject *Sender)
{
   hDC = GetDC(Form1->Handle);
   fg_setdc(hDC);
   hPal = fg_defpal();
   fg_realize(hPal);
   fg_vbinit();
   hVB1 = fg_vballoc(vbWidth,vbHeight);
   hVB2 = fg_vballoc(vbWidth,vbHeight);
   fg_vbopen(hVB2);
   fg_vbcolors();
   fg_vbopen(hVB1);
   fg_vbcolors();
   fg_sethpage(hVB2);
   fg_setcolor(19);
   fg_fillpage();
   fg_setcolor(25);
   fg_rect(132,188,50,150);
   fg_setcolor(20);
   fg_move(160,67);
   fg_draw(175,107);
   fg_draw(140,82);
   fg_draw(180,82);
   fg_draw(145,107);
   fg_draw(160,67);
   fg_paint(160,77);
   fg_paint(150,87);
   fg_paint(160,87);
   fg_paint(170,87);
   fg_paint(155,97);
   fg_paint(165,97);
   Application->OnActivate = OnActivate;
   Application->OnIdle = OnIdle;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormPaint(TObject *Sender)
{
   fg_vbscale(0,vbWidth-1,0,vbHeight-1,0,cxClient-1,0,cyClient-1);
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormResize(TObject *Sender)
{
   cxClient = ClientWidth;
   cyClient = ClientHeight;
   Invalidate();
}
//---------------------------------------------------------------------------
void __fastcall TForm1::FormDestroy(TObject *Sender)
{
   fg_vbclose();
   fg_vbfree(hVB1);
   fg_vbfree(hVB2);
   fg_vbfin();
   DeleteObject(hPal);
   ReleaseDC(Form1->Handle,hDC);
}
/****************************************************************************\
*                                                                            *
*  Scroll()                                                                  *
*                                                                            *
*  The Scroll() function moves the scrolling region up four pixels in a      *
*  circular manner. It is called from the OnIdle event handler.              *
*                                                                            *
\****************************************************************************/
void __fastcall TForm1::Scroll()
{
   fg_scroll(136,184,50,150,-4,0);
   fg_vbscale(0,vbWidth-1,0,vbHeight-1,0,cxClient-1,0,cyClient-1);
}