SvgaLib/doc/man3/vga_setmode.3

.TH vga_setmode 3 "28 Jul 1999" "Svgalib 1.4.1" "Svgalib User Manual"
.SH NAME
vga_setmode \- sets a video mode
.SH SYNOPSIS

.B "#include <vga.h>"

.BI "int vga_setmode(int " mode );

.SH DESCRIPTION
.BI "vga_setmode(int " mode )
selects the video
.I mode
given and clears the screen (if it was a graphics mode).
Basically this should be the first action of your application after calling
.BR vga_init (3)
and finding out which mode to use.
Prior to exiting your application should call
.B vga_setmode(TEXT).

.B vga_setmode()
returns 0 on success and -1 if this mode is not available.

From svgalib-1.4.1, if 
.I mode
is -1 then vga_setmode() returns the current svgalib version, in BCD format, so 
svgalib 1.4.1 returns 0x1410.

.I mode
should be one of the following, predefined values, or generally a value in range
.B 1 <=
.I mode
.B <= vga_lastmodenumber()
where
.BR vga_modeinfo (3)
returned details about this mode. Instead of trying to set the mode,
.BR vga_hasmode (3)
determines if the mode would actually be supported. It is also possible to use
the numeric values given below though this is discouraged. They are commonly used as values
for the
.B SVGALIB_DEFAULT_MODE
environment variable to set the
.BR vga_getdefaultmode (3).

Here are the predefined values for
.IR mode .
.SS Text mode
.BR TEXT (0)
restores textmode and falls back to ordinary text console handling. All other calls switch to a
graphics mode. You should set this mode prior to exiting an svgalib application.
.SS VGA compatible graphics modes
In general, for all modes following, the first number is the amount of x pixels, the second
the amount of y pixels, the third the number of colors, with shortcuts 32K, 64K, 16M, 16M4
for 32768, 65536, and 1677721. Those with 2 or more than 256 colors use fixed color mappings
(either black and white or some RGB true/high color) the others make use of a color lookup
table.

Memory layout for the VGA modes is weird. Too weird to be explained here, but you can check
the usual VGA literature.
.BR vga_setmodeX (3)
has a short explanation which is valid for all 256 color modes.

.BR G320x200x16  (1),
.BR G640x200x16  (2),
.BR G640x350x16  (3),
.BR G640x480x16  (4),
.BR G320x200x256 (5),
.BR G320x240x256 (6),
.BR G320x400x256 (7),
.BR G360x480x256 "(8), and "
.BR G640x480x2 (9)

.SS Basic SVGA modes
These use linear 256 color memory layouts similar to
.BR G320x200x256 .

.BR G640x480x256 (10),
.BR G800x600x256 (11),
.BR G1024x768x256 "(12), and "
.BR G1280x1024x256 (13)

.SS High color SVGA modes
These also use linear memory layouts, but for 32K & 64K each pixel occupies two bytes and
three for 16M. For 32K, each 16 bit word is divided into 555 bit portions refering to 5
bit red, green, blue part. The most significant bit is ignored by the card. For 64K the
division is 565 allowing to specify green in a little bit more detail (Human eyes are more
sensitive to green. People joke this is because our ancestors lived in trees where light was
filtered through green leaves).

For the 16M modes, from low to high addresses the 3 bytes are named BGR and specify the
blue, green, red parts of the pixel value.

.BR G320x200x32K (14),
.BR G320x200x64K (15),
.BR G320x200x16M (16),
.BR G640x480x32K (17),
.BR G640x480x64K (18),
.BR G640x480x16M (19),
.BR G800x600x32K (20),
.BR G800x600x64K (21),
.BR G800x600x16M (22),
.BR G1024x768x32K (23),
.BR G1024x768x64K (24),
.BR G1024x768x16M (25),
.BR G1280x1024x32K (26),
.BR G1280x1024x64K "(27), and "
.BR G1280x1024x16M (28)

.SS High resolutions with less color numbers.
Memory layout is probably one nibble per pixel, two pixels per byte in a linear fashion where
the most significant nibble is the left most pixel.

.BR G800x600x16 (29),
.BR G1024x768x16 "(30), and "
.BR G1280x1024x16 (31)

.SS Hercules emulation mode
Again check out the ordinary VGA literature for the memory layout.

.BR G720x348x2 (32)

.SS 32-bit per pixel modes
These are similar to 16M but each pixel uses four bytes. The first three are similar to
16M but the fourth is left empty and ignored by the VGA card (you can store own status there).

This eases pixel address calculations on the screen and drawing operations. However, 1/3 more
data has to be moved to the screen. Experiments show that usually the higher memory bandwidth
used outweighs the effects of the simplified algorithms by far.

.BR G320x200x16M32 (33),
.BR G640x480x16M32 (34),
.BR G800x600x16M32 (35),
.BR G1024x768x16M32 "(36), and "
.BR G1280x1024x16M32 (37)

.SS Some more resolutions
It should by now be clear how the modes will look.

.BR G1152x864x16 (38),
.BR G1152x864x256 (39),
.BR G1152x864x32K (40),
.BR G1152x864x64K (41),
.BR G1152x864x16M (42),
.BR G1152x864x16M32 (43),
.BR G1600x1200x16 (44),
.BR G1600x1200x256 (45),
.BR G1600x1200x32K (46),
.BR G1600x1200x64K (47),
.BR G1600x1200x16M "(48), and "
.BR G1600x1200x16M32 (49)

.PP
The 
.BR vgatest (6)
produces a list of supported modes for your hardware, prints some info on the modes and
allows you to try each of them.
.SH SEE ALSO

.BR svgalib (7),
.BR vgagl (7),
.BR libvga.config (5),
.BR vgatest (6),
.BR vga_hasmode (3),
.BR vga_init (3),
.BR vga_modeinfo (3),
.BR vga_getcurrentmode (3),
.BR vga_getdefaultmode (3),
.BR vga_lastmodenumber (3),
.BR vga_getmodename (3),
.BR vga_getmodenumber (3)
.SH AUTHOR

This manual page was edited by Michael Weller <eowmob@exp-math.uni-essen.de>. The
exact source of the referenced function as well as of the original documentation is
unknown.

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.