svgalib question, gl_putbox

svgalib question, gl_putbox

Post by ADAM P JENKI » Thu, 02 Feb 1995 14:40:28

I don't understand a problem I'm having with using gl_putbox, from the
libvgagl functions.  If I create a solid color bitmap, and then write
it to the screen with gl_putbox, it doesn't come out solid, but is
filled with evenly spaced vertical lines that are the background
color.  This doesn't happen if the putbox command is the first drawing
command, but if I put "gl_clearscreen" first, or any other writes to
the screen, than "putbox" has this problem. Here is the relevant code,
(a simplified version).

#include <vga.h>
#include <vgagl.h>

  void *buffer;
  GraphicsContext savedcontext;
  int x, y, width, height, color;


  width = 128;                  /* width of the bitmap */
  height = 256;                 /* height of the bitmap */

  /* allocate memory for a bitmap */
  buffer = (void *)malloc(width * height * BYTESPERPIXEL);

  /* use temporary virtual context to create a bitmap */
  gl_setcontextvirtual(width, height, BYTESPERPIXEL, BITSPERPIXEL, buffer);

  color = 50;
  /* make each pixel in the bitmap one color (50) */
  for (y = 0; y < height; y++)
    for (x = 0; x < width; x++)
      gl_setpixel(x, y, color);

  /* restore the saved context */

  gl_clearscreen(2);            /* if this isn't here first, no problem */

  x = 264;
  y = 100;
   * put the bitmap on the sceen, around the middle.
   * This is the box that seems like it should be solid, but it has lines
   * throught it.
  gl_putbox(x, y, width, height, buffer);

  /* press 'q' to exit */
  while (vga_getkey() != 'q')



        If you just comment out the "gl_clearscreen" line, it will
draw a solid box, otherwise it will have vertical lines through it. I
saw mentioned in "aligned putbox".  Can you not put a box
anywhere on the screen?  Does it have anything to do with the graphics
mode?  I would appreciate any help on this.  Thank you.  (The above
code will compile if you want to test it, with "gcc test.c -lvgagl -lvga")

Adam P. Jenkins

Adam P. Jenkins


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