> > On 10/19/2009 11:16 PM, D. Zimmer wrote:
> > >>> Hello all,
> > >>>
> > >>> probably this has come up before, but I can't find it:
> > >>>
> > >>> my application has to display JPEG images, but does not load
> > >>> them from disk files. They come in as blobs from a remote database.
> > >>>
> > >>> Is there a way to load these into an Fl_JPEG_image?
> > >>>
> > >>> Right now I am reduced to writing them to a temp file, and then reading
> > >>> that into the image. But that is a bad solution: it assumes that I can
> > >>> write to disk in this application.
> > >>>
> > >>> I read the code (fltk 1.1.9), there doesn't seem to be a
> > >>> straightforward way, can't just hook up an istream, or something of
> > >>> that nature.
> > >>>
> > >>> Any advice?
> > >>>
> > >>>
> > >>
> > >> I expect you will have to modify Fl_JPEG_Image. FLTK 1.1.9 has
> > >> Fl_JPEG_Image(const char *jpeg) which is hard-coded to expect a
> > >> filename. Write a new constructor that takes your blob of JPEG data
> > >> instead, and base it on the existing code from Fl_JPEG_Image.
> > >>
> > >> I'm pretty sure this can be done, and I think you will need to make the
> > >> following changes:
> > >>
> > >> 1. get rid of references to the FILE pointer in the function
> > >> (declaration, fopen(), flose()).
> > >>
> > >> 2. replace the call to jpeg_stdio_src() with code to fill the
> > >> jpeg_decompress_struct with function pointers that will operate on your
> > >> blob of JPEG data rather than a FILE pointer.
> > >>
> > >> I've never done it, but I expect you should be able to find examples on
> > >> the internet... if not, how hard could it be (memcpy(), current position
> > >> pointer, etc.)? If you download the actual jpeglib full source, the
> > >> file djpeg.c provides function pointers for setting up the library to
> > >> handle FILE pointer streams... work from that.
> > >>
> > >> You're probably in for a a few hours coding and testing though.
> > >>
> > >> good luck,
> > >> Don.
> > >>
> > >>
> > >>
> > >
> > > sorry, not djpeg.c but jdatasrc.c, which is part of the jpeg library
> > > included with FLTK.
> > >
> >
> > Thanks Don,
> >
> > Yes I saw that. On first reading, it seems that jdatasrc.c needs to be
> > modified in maybe 2 lines of code. Where the data come from doesn't
> > seem to make much difference, except for 2 calls to read(). But I'll try
> > that in the day :)
> >
> > Probably I will make a new class, parallel to Fl_JPEG_image.
> > FL_JPEG_image only provides a constructor (at least in 1.1.9), nothing
> > else. That's reasonably clean. The uglier part is ending up with
> > something new that is more part of jpeglib than of fltk. Which is
> > probably why this hasn't been done yet, at least in public.
> >
> >
> > Bernd
> >
> >
> >
>
> I wouldn't think that the library would need to be changed... I think the
> library allows you to do what you want to achieve, as-is. I meant to use
> jdatasrc.c as a possible quide for your class.
>
> Don.
>
> Here is a quick modfication of code from jdatasrc.c, that you would add to
> your modified class, then just call jpeg_blob_src() in place of
> jpeg_stdio_src() in the constructor... never tested or compiled, or really
> thought out for that matter.
>
> // most comments striped
> #include "jinclude.h"
> #include "jpeglib.h"
> #include "jerror.h"
>
> typedef struct {
> struct jpeg_source_mgr pub; /* public fields */
> void *blob; /* address of blob */
> size_t size; /* size into blob */
> size_t pos; /* index into blob */
> JOCTET * buffer; /* start of buffer */
> boolean start_of_file; /* have we gotten any data yet? */
> } my_source_mgr;
>
> typedef my_source_mgr * my_src_ptr;
>
> #define INPUT_BUF_SIZE 4096 /* choose an efficiently fread'able size */
>
> static void init_source (j_decompress_ptr cinfo)
> {
> my_src_ptr src = (my_src_ptr) cinfo->src;
> src->start_of_file = TRUE;
> }
>
> static boolean fill_input_buffer (j_decompress_ptr cinfo)
> {
> my_src_ptr src = (my_src_ptr) cinfo->src;
> size_t nbytes;
>
> nbytes = MAX(src->size - src->pos, INPUT_BUF_SIZE);
> src->size -= nbytes;
>
> if (nbytes <= 0) {
> if (src->start_of_file) /* Treat empty input file as fatal error */
> ERREXIT(cinfo, JERR_INPUT_EMPTY);
> WARNMS(cinfo, JWRN_JPEG_EOF);
> /* Insert a fake EOI marker */
> src->buffer[0] = (JOCTET) 0xFF;
> src->buffer[1] = (JOCTET) JPEG_EOI;
> nbytes = 2;
> }
>
> src->pub.next_input_byte = src->buffer;
> src->pub.bytes_in_buffer = nbytes;
> src->start_of_file = FALSE;
>
> return TRUE;
> }
>
>
> static void skip_input_data (j_decompress_ptr cinfo, long num_bytes)
> {
> my_src_ptr src = (my_src_ptr) cinfo->src;
>
> if (num_bytes > 0) {
> while (num_bytes > (long) src->pub.bytes_in_buffer) {
> num_bytes -= (long) src->pub.bytes_in_buffer;
> (void) fill_input_buffer(cinfo);
> /* note we assume that fill_input_buffer will never return FALSE,
> * so suspension need not be handled.
> */
> }
> src->pub.next_input_byte += (size_t) num_bytes;
> src->pub.bytes_in_buffer -= (size_t) num_bytes;
> }
> }
>
>
> static void term_source (j_decompress_ptr cinfo)
> {
> /* no work necessary here */
> }
>
>
> extern void jpeg_blob_src (j_decompress_ptr cinfo, void *blob, size_t size)
> {
> my_src_ptr src;
>
> if (cinfo->src == NULL) { /* first time for this JPEG object? */
> cinfo->src = (struct jpeg_source_mgr *)
> (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
> SIZEOF(my_source_mgr));
> src = (my_src_ptr) cinfo->src;
> src->buffer = (JOCTET *)
> (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
> INPUT_BUF_SIZE * SIZEOF(JOCTET));
> }
>
> src = (my_src_ptr) cinfo->src;
> src->pub.init_source = init_source;
> src->pub.fill_input_buffer = fill_input_buffer;
> src->pub.skip_input_data = skip_input_data;
> src->pub.resync_to_restart = jpeg_resync_to_restart; /* use default method
> */
> src->pub.term_source = term_source;
> src->blob = blob;
> src->size = size;
> src->pos = 0;
> src->pub.bytes_in_buffer = 0; /* forces fill_input_buffer on first read */
> src->pub.next_input_byte = NULL; /* until buffer loaded */
> }
>
>
>
>
oops:
nbytes = MAX(src->size - src->pos, INPUT_BUF_SIZE);
//src->size -= nbytes;
src->pos += nbytes;
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