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Unit JDataDst;
{ This file contains compression data destination routines for the case of
emitting JPEG data to a file (or any stdio stream). While these routines
are sufficient for most applications, some will want to use a different
destination manager.
IMPORTANT: we assume that fwrite() will correctly transcribe an array of
JOCTETs into 8-bit-wide elements on external storage. If char is wider
than 8 bits on your machine, you may need to do some tweaking. }
{ Original : jdatadst.c ; Copyright (C) 1994-1996, Thomas G. Lane. }
interface
{$I jconfig.inc}
{ this is not a core library module, so it doesn't define JPEG_INTERNALS }
uses
jmorecfg,
jpeglib,
jinclude,
jdeferr,
jerror;
{ Prepare for output to a stdio stream.
The caller must have already opened the stream, and is responsible
for closing it after finishing compression. }
{GLOBAL}
procedure jpeg_stdio_dest (cinfo : j_compress_ptr; outfile : FILEptr);
implementation
{ Expanded data destination object for stdio output }
type
my_dest_ptr = ^my_destination_mgr;
my_destination_mgr = record
pub : jpeg_destination_mgr; { public fields }
outfile : FILEPTR; { target stream }
buffer : JOCTET_FIELD_PTR; { start of buffer }
end; {my_destination_mgr;}
const
OUTPUT_BUF_SIZE = 4096; { choose an efficiently fwrite'able size }
{ Initialize destination --- called by jpeg_start_compress
before any data is actually written. }
{METHODDEF}
procedure init_destination (cinfo : j_compress_ptr); far;
var
dest : my_dest_ptr;
begin
dest := my_dest_ptr(cinfo^.dest);
{ Allocate the output buffer --- it will be released when done with image }
dest^.buffer := JOCTET_FIELD_PTR(
cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
OUTPUT_BUF_SIZE * SIZEOF(JOCTET)) );
dest^.pub.next_output_byte := JOCTETptr(dest^.buffer);
dest^.pub.free_in_buffer := OUTPUT_BUF_SIZE;
end;
{ Empty the output buffer --- called whenever buffer fills up.
In typical applications, this should write the entire output buffer
(ignoring the current state of next_output_byte & free_in_buffer),
reset the pointer & count to the start of the buffer, and return TRUE
indicating that the buffer has been dumped.
In applications that need to be able to suspend compression due to output
overrun, a FALSE return indicates that the buffer cannot be emptied now.
In this situation, the compressor will return to its caller (possibly with
an indication that it has not accepted all the supplied scanlines). The
application should resume compression after it has made more room in the
output buffer. Note that there are substantial restrictions on the use of
suspension --- see the documentation.
When suspending, the compressor will back up to a convenient restart point
(typically the start of the current MCU). next_output_byte & free_in_buffer
indicate where the restart point will be if the current call returns FALSE.
Data beyond this point will be regenerated after resumption, so do not
write it out when emptying the buffer externally. }
{METHODDEF}
function empty_output_buffer (cinfo : j_compress_ptr) : boolean; far;
var
dest : my_dest_ptr;
begin
dest := my_dest_ptr(cinfo^.dest);
if (JFWRITE(dest^.outfile, dest^.buffer, OUTPUT_BUF_SIZE) <>
size_t(OUTPUT_BUF_SIZE)) then
ERREXIT(j_common_ptr(cinfo), JERR_FILE_WRITE);
dest^.pub.next_output_byte := JOCTETptr(dest^.buffer);
dest^.pub.free_in_buffer := OUTPUT_BUF_SIZE;
empty_output_buffer := TRUE;
end;
{ Terminate destination --- called by jpeg_finish_compress
after all data has been written. Usually needs to flush buffer.
NB: *not* called by jpeg_abort or jpeg_destroy; surrounding
application must deal with any cleanup that should happen even
for error exit. }
{METHODDEF}
procedure term_destination (cinfo : j_compress_ptr); far;
var
dest : my_dest_ptr;
datacount : size_t;
begin
dest := my_dest_ptr (cinfo^.dest);
datacount := OUTPUT_BUF_SIZE - dest^.pub.free_in_buffer;
{ Write any data remaining in the buffer }
if (datacount > 0) then
begin
if (JFWRITE(dest^.outfile, dest^.buffer, datacount) <> datacount) then
ERREXIT(j_common_ptr(cinfo), JERR_FILE_WRITE);
end;
{fflush(dest^.outfile^);}
{ Make sure we wrote the output file OK }
{if (ferror(dest^.outfile))
ERREXIT(cinfo, JERR_FILE_WRITE);}
if IOresult <> 0 then
ERREXIT(j_common_ptr(cinfo), JERR_FILE_WRITE);
end;
{ Prepare for output to a stdio stream.
The caller must have already opened the stream, and is responsible
for closing it after finishing compression. }
{GLOBAL}
procedure jpeg_stdio_dest (cinfo : j_compress_ptr; outfile : FILEptr);
var
dest : my_dest_ptr;
begin
{ The destination object is made permanent so that multiple JPEG images
can be written to the same file without re-executing jpeg_stdio_dest.
This makes it dangerous to use this manager and a different destination
manager serially with the same JPEG object, because their private object
sizes may be different. Caveat programmer. }
if (cinfo^.dest = NIL) then
begin { first time for this JPEG object? }
cinfo^.dest := jpeg_destination_mgr_ptr(
cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_PERMANENT,
SIZEOF(my_destination_mgr)) );
end;
dest := my_dest_ptr (cinfo^.dest);
dest^.pub.init_destination := init_destination;
dest^.pub.empty_output_buffer := empty_output_buffer;
dest^.pub.term_destination := term_destination;
dest^.outfile := outfile;
end;
end.
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