setactivepage

Syntax

#include <graphics.h>

void setactivepage(int page);

Description

setactivepage makes page the active graphics page. All subsequent graphics output will be directed to that graphics page.

The active graphics page might not be the one you see onscreen, depending on how many graphics pages are available on your system. Only the EGA, VGA, and Hercules graphics cards support multiple pages.

Return Value

None.

See also

setvisualpage

swapbuffers

Example

/* setactivepage example */ 



#include <graphics.h>

#include <stdlib.h>

#include <stdio.h>

#include <conio.h>



int main(void)

{

   /* select driver and mode that supports multiple pages */

   int gdriver = EGA, gmode = EGAHI, errorcode;

   int x, y, ht;



   /* initialize graphics and local variables */

   initgraph(&gdriver, &gmode, "");



   /* read result of initialization */

   errorcode = graphresult();

   if (errorcode != grOk)    /* an error occurred */

   {

      printf("Graphics error: %s\n", grapherrormsg(errorcode));



      printf("Press any key to halt:");

      getch();

      exit(1);               /* terminate with an error code */

   }



   x = getmaxx() / 2;

   y = getmaxy() / 2;

   ht = textheight("W");



   /*  select the off screen page for drawing */

   setactivepage(1);



   /* draw a line on page #1 */

   line(0, 0, getmaxx(), getmaxy());



   /* output a message on page #1 */

   settextjustify(CENTER_TEXT, CENTER_TEXT);

   outtextxy(x, y, "This is page #1:");

   outtextxy(x, y+ht, "Press any key to halt:");





   /* select drawing to page #0 */

   setactivepage(0);



   /* output a message  on page #0 */

   outtextxy(x, y, "This is page #0.");

   outtextxy(x, y+ht, "Press any key to view page #1:");

   getch();



   /* select page #1 as the visible page */

   setvisualpage(1);



   /* clean up */

   getch();

   closegraph();

   return 0;

}