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vgagl(7)                      Svgalib User Manual                     vgagl(7)



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  commu-
       nication (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 orga-
       nized, 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:

              vga_setmode(G320x200x256);
              gl_setcontextvga(G320x200x256);

       In this example, the context is set to the physical screen. The context can be saved (only the screen type, not
       the contents) into a variable, e.g.

              GraphicsContext physicalscreen;
              gl_getcontext(&physicalscreen).

       To define a virtual screen in system memory, use gl_setcontextvgavirtual(3):

              gl_setcontextvgavirtual(G320x200x256)

       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.


2. DESCRIPTION OF VGAGL FUNCTIONS
   Context management
       gl_getcontext(3), currentcontext(3)
              get the current graphics contents..
       gl_setcontext(3)
              set a previously saved context.
       gl_setcontextvga(3)
              set the context to the physical screen.
       gl_setcontextvgavirtual(3)
              set the context to a virtual mode.
       gl_setcontextvirtual(3)
              define a virtual context.
       gl_allocatecontext(3)
              allocate a graphics context.
       gl_freecontext(3)
              free a virtual screen.
       gl_setcontextwidth(3), gl_setcontextheight(3)
              set the dimension of a context.

   Drawing primitives
       gl_clearscreen(3)
              clear the screen.
       gl_rgbcolor(3)
              return pixel value corresponding to an rgb color.
       gl_setpixel(3), gl_setpixelrgb(3)
              draw a pixel.
       gl_getpixel(3)
              return the color of a pixel.
       gl_getpixelrgb(3)
              store color components of a pixel.
       gl_hline(3)
              draw a horizontal line.
       gl_line(3)
              draw a line.
       gl_circle(3)
              draw a circle.
       gl_fillbox(3)
              fill a rectangular area.

   Copying of screen buffers and page flipping
       gl_copyscreen(3)
              copy the screen contents of contexts.
       gl_setscreenoffset(3)
              set a memory offset for copyscreen.
       gl_setdisplaystart(3)
              set the start of the screen are displayed.
       gl_enablepageflipping(3)
              enables automatic page flipping.

   Clipping
       gl_disableclipping(3)
              disables clipping.
       gl_enableclipping(3)
              enables clipping.
       gl_setclippingwindow(3)
              set the clipping window.

   Text drawing primitives
       gl_setfont(3)
              set the text font to be used.
       gl_setfontcolors(3)
              set the font colors.
       gl_expandfont(3)
              expand a packed pixel font.
       gl_colorfont(3)
              change the color of a font.
       gl_setwritemode(3)
              set the font writemode flags.
       gl_write(3), gl_writen(3)
              write a text string.
       gl_printf(3)
              formatted output to the graphics screen.
       gl_font8x8(3)
              a packed 8x8 pixel font.

   Pix- and Bitmap drawing
       gl_getbox(3)
              copy a rectangular pixmap from the screen to a buffer.
       gl_copybox(3)
              copy a rectangular screen area.
       gl_copyboxfromcontext(3)
              copy rectangular area from another context.
       gl_copyboxtocontext(3)
              copy a rectangular area to another context.
       gl_putbox(3)
              copy a pixmap to a rectangular area.
       gl_putboxpart(3)
              copy a partial pixmap to a rectangular area.
       gl_putboxmask(3)
              copy a masked  pixmap to a rectangular area.
       gl_putboxmaskcompiled(3)
              copy a compiled masked pixmap to a rectangular area.
       gl_compileboxmask(3)
              compress a masked bitmap.
       gl_compiledboxmasksize(3)
              compute the size of a compiled masked box.
       gl_scalebox(3)
              scale a pixmap.

   Palette handling
       gl_getpalettecolor(3), gl_getpalettecolors(3), gl_getpalette(3)
              read the color palette.
       gl_setpalettecolor(3), gl_setpalettecolors(3), gl_setpalette(3)
              set the color palette.
       gl_setrgbpalette(3)
              set a 256-color RGB palette.

   Triangle primitives from threeDkit
       gl_striangle(3)
              draw a solid colored triangle.
       gl_triangle(3)
              draw a triangle with interpolated colors.
       gl_swtriangle(3)
              draw a solid pixmap mapped on a triangle.
       gl_wtriangle(3)
              draw a shadowed pixmap mapped on a triangle.
       gl_trisetcolorlookup(3), gl_trigetcolorlookup(3)
              manages a color lookup table for shadowing.
       gl_trisetdrawpoint(3)
              set a triangle drawing function.

3. MACROS DEFINED IN VGAGL.H:
       WIDTH  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 handled   by most functions, but you never know. It can be avoided by using a logical scan-
       line  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).  Alterna-
       tively, avoid those functions by using a virtual screen.


SEE ALSO
       svgalib(7),  libvga.config(5), testgl(6), threedkit(7), currentcontext(3), gl_allocatecontext(3), gl_circle(3),
       gl_clearscreen(3), gl_colorfont(3), gl_compileboxmask(3),  gl_compiledboxmasksize(3),  gl_copybox(3),  gl_copy-
       boxfromcontext(3),   gl_copyboxtocontext(3),   gl_copyscreen(3),  gl_disableclipping(3),  gl_enableclipping(3),
       gl_enablepageflipping(3),  gl_expandfont(3),  gl_fillbox(3),  gl_font8x8(3),  gl_freecontext(3),  gl_getbox(3),
       gl_getcontext(3), gl_getpalette(3), gl_getpalettecolor(3), gl_getpalettecolors(3), gl_getpixel(3), gl_getpixel-
       rgb(3), gl_hline(3), gl_line(3), gl_putbox(3),  gl_putboxmask(3),  gl_putboxmaskcompiled(3),  gl_putboxpart(3),
       gl_rgbcolor(3),  gl_scalebox(3),  gl_setclippingwindow(3), gl_setcontext(3), gl_setcontextheight(3), gl_setcon-
       textvga(3), gl_setcontextvgavirtual(3), gl_setcontextvirtual(3), gl_setcontextwidth(3),  gl_setdisplaystart(3),
       gl_setfont(3),  gl_setfontcolors(3),  gl_setpalette(3),  gl_setpalettecolor(3), gl_setpalettecolors(3), gl_set-
       pixel(3), gl_setpixelrgb(3), gl_setrgbpalette(3), gl_setscreenoffset(3),  gl_setwritemode(3),  gl_striangle(3),
       gl_swtriangle(3),   gl_triangle(3),  gl_trigetcolorlookup(3),  gl_trisetcolorlookup(3),  gl_trisetdrawpoint(3),
       gl_write(3), gl_writen(3), gl_wtriangle(3).


AUTHOR
       There are many authors of svgalib. This page was edited by Michael Weller <eowmobATexp-math.de>.   The
       original documentation and most of vgagl was done by Harm Hanemaayer <H.HanemaayerATinter.net> though.



Svgalib (>= 1.2.11)               2 Aug 1997                          vgagl(7)