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vgagl (7)
>> vgagl (7) ( Linux man: Макропакеты и соглашения )
NAME
vgagl - a fast framebuffer-level graphics library based ion svgalib
TABLE OF CONTENTS
0. Introduction
1. How to use vgagl
2. Description of vgagl functions
3. Macros defined in vgagl.h
0. INTRODUCTION
This is a fast framebuffer-level graphics library for linear 1, 2, 3 and 4
byte-per-pixel modes (256-color, hicolor, truecolor). It uses a limited
number of functions from svgalib (libvga) for low-level hardware
communication (the library is included in the svgalib shared image).
In particular,
svgalib(7)
maps the 64K VGA frame buffer window, and this library
directly addresses the buffer. For SVGA modes that use more than 64K of
screen memory, SVGA paging is required when writing to the physical screen;
this is done automatically for most functions (at a certain cost).
Alternatively, any number of virtual screens of any type in system memory can
be used, which can then be copied to the physical screen. There is also
support for 4 bytes per pixel framebuffers (and copying them to a 3 bytes per
pixel context), and limited planar 256 color mode support (copyscreen,
aligned putbox).
The planar 256 color modes (available on all VGA cards) can now be used
with a virtual screen, which is copied to the physical screen (with optional
page-flipping).
Bitmaps are raw, with one (or more) bytes per pixel (like pixmaps in X),
stored in row-major order. They are usually manipulated with the getbox
and putbox functions.
vgagl
does also make use of the graphic cards accelerator
(if it is supported)
in some situations.
A graphics context is just a structure that holds the size of the associated
graphics screen, how it is organized, clipping status etc. You can define a
custom virtual (system memory) graphics context of any size with the
setcontextvirtual function. All operations work on the current context.
Any questions, bug-reports, additions, suggestions etc. are welcome.
1. HOW TO USE VGAGL
Programs that use
vgagl
must
#include <vgagl.h>.
Linking must be done with
-lvgagl -lvga.
Functions in the
vgagl
library have the prefix
gl_*.
To initialize
vgagl,
the graphics context must be set. Example:
which allocates space for a screen identical to 320x200x256 graphics mode,
and makes this virtual screen the current graphics context.
The virtual screen can now be copied to the physical screen as follows:
gl_copyscreen(&physicalscreen);
Note that with a virtual screen in system memory, it is possible to add
fast X-Window support to a program, using MITSHM to copy the framebuffer
to the screen window.
The width in pixels of the current graphics context.
HEIGHT
Height in pixels.
BYTESPERPIXEL
Number of bytes per pixel (1, 2, 3 or 4).
BYTEWIDTH
Width of a scanline in bytes.
COLORS
Number of colors.
BITSPERPIXEL
Number of significant color bits.
VBUF
Address of the framebuffer.
__clip
Clipping flag.
__clipx1
__clipy1
Top-left corner of clipping window.
__clipx2
__clipy2
Bottom-right corner of clipping window.
BUGS
For three bytes per pixel (true color) modes, it is possible that
pixels cross a SVGA segment boundary. This should be correctly
handledby most functions, but you never know. It can be avoided by using a logical
scanline length that is a divisor of 65536 (a power of 2), like 1024
(as opposed to 960) for 320x200 and 2048 (1920) for 640x480. For
800x600, this is impractical (4096 as opposed to 2400 doesn't fit in
2MB). Alternatively, avoid those functions by using a virtual screen.
There are many authors of svgalib. This page was edited by
Michael Weller <eowmob@exp-math.uni-essen.de>.
The original documentation and most of
vgagl
was done by Harm Hanemaayer <H.Hanemaayer@inter.nl.net> though.
