int vga_drawline(int x1, int y1, int x2, int y2);
draws a line from (x1, y1) to (x2, y2) on the screen. If you exchange start and end of the line you should not expect the exactly identical set of pixel be covered by the line.
This function is very inefficient as is does a bunch of vga_drawpixel(3) calls, you should consider using gl_line(3) which is very efficient, or doing direct screen access instead or use vga_drawscansegment(3) to handle more than one pixel.
The color drawn is set with vga_setcolor(3) or vga_setrgbcolor(3) resp.
The function always returns 0 (on which you should probably not really rely).
svgalib(7), vgagl(7), libvga.config(5), gl_line(3) vga_clear(3), vga_setcolor(3), vga_setrgbcolor(3), vga_getpixel(3), vga_drawline(3), vga_drawscanline(3), vga_drawscansegment(3), vga_getscansegment(3)
This manual page was edited by Michael Weller <firstname.lastname@example.org>. The exact source of the referenced function as well as of the original documentation is unknown. This Page was modified by Don Secrest <email@example.com>
It is very likely that both are at least to some extent are due to Harm Hanemaayer <H.Hanemaayer@inter.nl.net>.
Occasionally this might be wrong. I hereby asked to be excused by the original author and will happily accept any additions or corrections to this first version of the svgalib manual.
svgalib(7), vga_clear(3), vga_drawpixel(3), vga_drawscanline(3), vga_drawscansegment(3), vga_getpixel(3), vga_getscansegment(3), vga_runinbackground(3), vga_setcolor(3), vga_setegacolor(3), vga_setrgbcolor(3).