PRODUCT  :  Borland C++                           NUMBER  :  1045
  VERSION  :  3.1
       OS  :  DOS
     DATE  :  October 19, 1993                         PAGE  :  1/5

    TITLE  :  Switching Video Mode without clearing Video Memory.





  /* ----------------------------------------------------------- *\
  | The purpose of this program is to demonstrate how to switch   |
  | from graphics mode to text mode and back without having all of|
  | the video memory being cleared.                               |
  |                                                               |
  | If bit 7 of the AX register is set then video memory is not   |
  | cleared when function 0 of interrupt 10 is called.            |
  |                                                               |
  | The top portion of the graphics screen may be corrupted by    |
  | switching to text mode.  The function getimage is used to     |
  | preserve this area of the screen.                             |
  |                                                               |
  | If you are running this in the IDE be sure to allocate enough |
  | memory for Program heap size: Under Options-Debugger.         |
  \* ----------------------------------------------------------- */

  #include <alloc.h>
  #include <graphics.h>
  #include <iostream.h>
  #include <stdlib.h>
  #include <conio.h>


  void   totext (unsigned char&);
  void   textfunction (void);
  void   tographics (unsigned char&);

  // For holding a copy of the top portion of the graphics screen.
  void far*  image = NULL;



  // Display prompt #1
  void displayprompt1 ()
  {
       // Display prompt
       settextjustify (CENTER_TEXT,CENTER_TEXT);
       outtextxy (getmaxx()/2,getmaxy()/2,
                 "In graphics mode.  Press any key");
       getch ();

       // Erase the text so that it won't be displayed upon













  PRODUCT  :  Borland C++                           NUMBER  :  1046
  VERSION  :  3.1
       OS  :  DOS
     DATE  :  October 19, 1993                         PAGE  :  2/5

    TITLE  :  Switching Video Mode without clearing Video Memory.




       // returning to graphics mode.
       setfillstyle (SOLID_FILL,0);
       bar (1,getmaxy()/2 - 10, getmaxx()-1, getmaxy()/2+10);

  }    // displayprompt1



  // Display prompt #2
  void displayprompt2 ()
  {
       outtextxy (getmaxx()/2,getmaxy()/2,
                 "Back in graphics mode.  Press any key to exit.");
       getch ();
  } // displayprompt2



  // Purpose:  Switch to text mode without clearing video memory
  //
  // oldgrmode is needed so that the graphics mode can be restored.
  // image will hold the image of the first ROW_SAVE rows upon exit
  // of totext.
  void totext (unsigned char& oldgrmode)
  {
       // The value of ROW_SAVE was determined by trial and error.
       // 110 is a a little beyond the rows that get corrupted when
       // the switch to text mode is made.  The 110 was found for
       // 640 x 480 mode.
       const ROW_SAVE = 110;

       // Need the size of the image
       unsigned imgsize = imagesize (0,0,getmaxx(),ROW_SAVE);

       image = farmalloc (imgsize);

       // Check that memory allocation was successful
       // If you are running this in the IDE be sure to allocate
       // enough memory for Program heap size: Under
       // Options-Debugger.
       if (!image)
       {
            closegraph ();













  PRODUCT  :  Borland C++                           NUMBER  :  1046
  VERSION  :  3.1
       OS  :  DOS
     DATE  :  October 19, 1993                         PAGE  :  3/5

    TITLE  :  Switching Video Mode without clearing Video Memory.




            cout << "Error: Could not allocate memory for "
                    "the image." << endl;
            exit (1);
       } // if

       // Store the image
       getimage (0,0,getmaxx(),110,image);

       displayprompt1 ();

       // Get the current graphics mode from the BIOS
       _AX= 0x0f00;
       asm  int 10h

       // Save the mode #
       oldgrmode = _AL;

       // Set bit 7 of AX to prevent video memory from being
       // cleared during mode switch.
       _AX = 0x0080;

       // Video mode #3 which is a text mode.
       _AX |= 0x0003;

       // Switch modes.
       asm  int 10h
  }    // totext



  // Purpose:  To return to graphics mode without clearing video
  // memory oldgrmode holds the graphics mode the system was in
  // before switching to text mode.
  // image holds the image of top portion of the screen.
  void tographics (unsigned char& oldgrmode)
  {
       // _AX will hold the the video mode that will be entered.
       _AX = (int) oldgrmode;

       // Set bit 7 of AX to prevent video memory from being
       // cleared.
       _AX |= 0x0080;














  PRODUCT  :  Borland C++                           NUMBER  :  1046
  VERSION  :  3.1
       OS  :  DOS
     DATE  :  October 19, 1993                         PAGE  :  4/5

    TITLE  :  Switching Video Mode without clearing Video Memory.




       // Switch modes
       asm  int 10h

       // Restore the image to the screen.
       putimage (0,0,image,COPY_PUT);

       displayprompt2 ();

       farfree (image);
  }    // tographics



  // Perfom output in text mode.
  void textfunction ()
  {
       clrscr ();
       gotoxy (0,12);
       cout << "\n\n\n\n\n\n\n\n\n\n";
       cout.fill (' ');
       cout.width (55);
       cout << "Now in text mode.  Press any key.";
       getch ();
  }    // textfunction



  int main(void)
  {
       /* request auto detection */
       int gdriver = DETECT, gmode, errorcode;

       /* initialize graphics mode */
       initgraph(&gdriver, &gmode, "");

       /* read result of initialization */
       errorcode = graphresult();

       if (errorcode != grOk)  /* an error occurred */
       {
            cout << "Graphics error: " << grapherrormsg(errorcode)
                 << endl;
            cout << "Press any key to halt:";













  PRODUCT  :  Borland C++                           NUMBER  :  1046
  VERSION  :  3.1
       OS  :  DOS
     DATE  :  October 19, 1993                         PAGE  :  5/5

    TITLE  :  Switching Video Mode without clearing Video Memory.




            getch();
            clrscr ();
            exit(1);             /* return with error code */
       }

       setcolor (getmaxcolor());
       // Draw a full screen image
       for (int i=0;i<getmaxx()/2; i+=2)
       {
            line (i,0,0,getmaxy()/2-i);
            line (i,getmaxy(),0,getmaxy()/2+i);
            line (getmaxx()-i,0,getmaxx(),getmaxy()/2-i);
            line (getmaxx()-i,getmaxy(),getmaxx(),getmaxy()/2+i);
       }

       // This holds the graphics mode that system is in.
       unsigned char oldgrmode;

       totext (oldgrmode);
       textfunction ();
       tographics (oldgrmode);

       closegraph ();
       return( 0 );
  }



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