ggiDBGetNumBuffers(3) GGI ggiDBGetNumBuffers(3)NAME
ggiDBGetNumBuffers, ggiDBGetBuffer : Get DirectBuffers from a visual
SYNOPSIS
#include <ggi/ggi.h>
int ggiDBGetNumBuffers(ggi_visual_t vis);
const ggi_directbuffer *ggiDBGetBuffer(ggi_visual_t vis, int bufnum);
DESCRIPTION
Dependent on the visual and runtime environment found, applications may
be granted direct access to hardware and/or library internal buffers.
This may significantly enhance performance for certain pixel oriented
applications or libraries.
The DirectBuffer is a mechanism in which a LibGGI program can use to
determine all the characteristics of these buffers (typically the
framebuffer), including the method of addressing, the stride, alignment
requirements, and endianness.
However, use not conforming to this specification will have undefined
effects and may cause data loss or corruption, program malfunction or
abnormal program termination. So you don't really want to do this.
ggiDBGetNumBuffers returns the number of DirectBuffers available to the
application. ggiDBGetBuffer obtains the DirectBuffer at the specified
position.
Use ggiDBGetBuffer to obtain the DirectBuffers at 0 to n-1, where n is
the number returned by ggiDBGetNumBuffers.
Pixel-linear buffers have type==GGI_DB_SIMPLE_PLB | GGI_DB_NORMAL.
You're on your own now.
DirectBuffers where ggiResourceMustAcquire(3) is true need to be ggiRe‐
sourceAcquire(3) and is released by calling ggiResourceRelease(3).
Beware that the read, write and stride fields of the DirectBuffer may
be changed by an acquire, and that they may be NULL or invalid when the
DirectBuffer is not acquired.
RETURN VALUEggiDBGetNumBuffers returns the number of DirectBuffers available. 0
indicates that no DirectBuffers are available.
ggiDBGetBuffer returns a pointer to a DirectBuffer structure.
TYPES OF BUFFERS
Only the framebuffer is defined currently. Other types of buffers, such
as stencil, z will be defined by appropriate GGI extensions.
A frame buffer may be organized as several distinct buffers. Each buf‐
fer may have a different layout. This means both the addressing scheme
to be used as well as the addressing parameters may differ from buffer
to buffer.
A framebuffer is denoted by ggi_directbuffer.type`==`GGI_DB_NORMAL.
Each frame has its own buffer, and its number is indicated in
ggi_directbuffer.frame.
EXAMPLES
How to obtain a DirectBuffer:
ggi_visual_t vis;
ggi_mode mode;
int i;
/* Framebuffer info */
unsigned char *fbptr[2];
int stride[2];
int numbufs;
mode.frames = 2; /* Double-buffering */
mode.visible.x = 640; /* Screen res */
mode.visible.y = 480;
mode.virt.x = GGI_AUTO; /* Any virtual resolution. Will usually be set */
mode.virt.y = GGI_AUTO; /* to be the same as visible but some targets */
/* may have restrictions on virtual size. */
mode.graphtype = GT_8BIT; /* Depend on 8-bit palette. */
mode.dpp.x = mode.dpp.y = GGI_AUTO; /* Always 1x1 but we don't care. */
if(ggiInit()) {
/* Failed to initialize library. Bomb out. */
}
vis = ggiOpen(NULL);
if(!vis) {
/* Opening default visual failed, quit. */
}
if(ggiSetMode(vis, &mode)) {
/* Set mode has failed, should check if suggested mode
is o.k. for us, and try the call again. */
}
numbufs = ggiDBGetNumBuffers(vis);
for(i = 0; i < numbufs; i++) {
ggi_directbuffer *db;
int frameno;
db = ggiDBGetBuffer(vis, i);
if(!(db->type & GGI_DB_SIMPLE_PLB))
{
/* We don't handle anything but simple pixel-linear buffers.
Fall back to ggiPutBox() or something. */
continue;
}
frameno = db->frame;
if(readptr[frameno] != NULL &&
(db->buffer.plb.pixelformat->flags & GGI_PF_REVERSE_ENDIAN))
{
continue;
}
fbptr[frameno] = db->write; /* read == write for simple plbs */
/* Stride of framebuffer (in bytes). */
stride[frameno] = db->buffer.plb.stride;
/* Check pixel format, be portable... */
SEE ALSOggi_directbuffer(3), ggiResourceAcquire(3)libggi-2.2.x 2006-12-30 ggiDBGetNumBuffers(3)
