Java example source code file (jdmainct.c)
The jdmainct.c Java example source code
/*
* reserved comment block
* DO NOT REMOVE OR ALTER!
*/
/*
* jdmainct.c
*
* Copyright (C) 1994-1996, Thomas G. Lane.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains the main buffer controller for decompression.
* The main buffer lies between the JPEG decompressor proper and the
* post-processor; it holds downsampled data in the JPEG colorspace.
*
* Note that this code is bypassed in raw-data mode, since the application
* supplies the equivalent of the main buffer in that case.
*/
#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
/*
* In the current system design, the main buffer need never be a full-image
* buffer; any full-height buffers will be found inside the coefficient or
* postprocessing controllers. Nonetheless, the main controller is not
* trivial. Its responsibility is to provide context rows for upsampling/
* rescaling, and doing this in an efficient fashion is a bit tricky.
*
* Postprocessor input data is counted in "row groups". A row group
* is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
* sample rows of each component. (We require DCT_scaled_size values to be
* chosen such that these numbers are integers. In practice DCT_scaled_size
* values will likely be powers of two, so we actually have the stronger
* condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
* Upsampling will typically produce max_v_samp_factor pixel rows from each
* row group (times any additional scale factor that the upsampler is
* applying).
*
* The coefficient controller will deliver data to us one iMCU row at a time;
* each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
* exactly min_DCT_scaled_size row groups. (This amount of data corresponds
* to one row of MCUs when the image is fully interleaved.) Note that the
* number of sample rows varies across components, but the number of row
* groups does not. Some garbage sample rows may be included in the last iMCU
* row at the bottom of the image.
*
* Depending on the vertical scaling algorithm used, the upsampler may need
* access to the sample row(s) above and below its current input row group.
* The upsampler is required to set need_context_rows TRUE at global selection
* time if so. When need_context_rows is FALSE, this controller can simply
* obtain one iMCU row at a time from the coefficient controller and dole it
* out as row groups to the postprocessor.
*
* When need_context_rows is TRUE, this controller guarantees that the buffer
* passed to postprocessing contains at least one row group's worth of samples
* above and below the row group(s) being processed. Note that the context
* rows "above" the first passed row group appear at negative row offsets in
* the passed buffer. At the top and bottom of the image, the required
* context rows are manufactured by duplicating the first or last real sample
* row; this avoids having special cases in the upsampling inner loops.
*
* The amount of context is fixed at one row group just because that's a
* convenient number for this controller to work with. The existing
* upsamplers really only need one sample row of context. An upsampler
* supporting arbitrary output rescaling might wish for more than one row
* group of context when shrinking the image; tough, we don't handle that.
* (This is justified by the assumption that downsizing will be handled mostly
* by adjusting the DCT_scaled_size values, so that the actual scale factor at
* the upsample step needn't be much less than one.)
*
* To provide the desired context, we have to retain the last two row groups
* of one iMCU row while reading in the next iMCU row. (The last row group
* can't be processed until we have another row group for its below-context,
* and so we have to save the next-to-last group too for its above-context.)
* We could do this most simply by copying data around in our buffer, but
* that'd be very slow. We can avoid copying any data by creating a rather
* strange pointer structure. Here's how it works. We allocate a workspace
* consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
* of row groups per iMCU row). We create two sets of redundant pointers to
* the workspace. Labeling the physical row groups 0 to M+1, the synthesized
* pointer lists look like this:
* M+1 M-1
* master pointer --> 0 master pointer --> 0
* 1 1
* ... ...
* M-3 M-3
* M-2 M
* M-1 M+1
* M M-2
* M+1 M-1
* 0 0
* We read alternate iMCU rows using each master pointer; thus the last two
* row groups of the previous iMCU row remain un-overwritten in the workspace.
* The pointer lists are set up so that the required context rows appear to
* be adjacent to the proper places when we pass the pointer lists to the
* upsampler.
*
* The above pictures describe the normal state of the pointer lists.
* At top and bottom of the image, we diddle the pointer lists to duplicate
* the first or last sample row as necessary (this is cheaper than copying
* sample rows around).
*
* This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
* situation each iMCU row provides only one row group so the buffering logic
* must be different (eg, we must read two iMCU rows before we can emit the
* first row group). For now, we simply do not support providing context
* rows when min_DCT_scaled_size is 1. That combination seems unlikely to
* be worth providing --- if someone wants a 1/8th-size preview, they probably
* want it quick and dirty, so a context-free upsampler is sufficient.
*/
/* Private buffer controller object */
typedef struct {
struct jpeg_d_main_controller pub; /* public fields */
/* Pointer to allocated workspace (M or M+2 row groups). */
JSAMPARRAY buffer[MAX_COMPONENTS];
boolean buffer_full; /* Have we gotten an iMCU row from decoder? */
JDIMENSION rowgroup_ctr; /* counts row groups output to postprocessor */
/* Remaining fields are only used in the context case. */
/* These are the master pointers to the funny-order pointer lists. */
JSAMPIMAGE xbuffer[2]; /* pointers to weird pointer lists */
int whichptr; /* indicates which pointer set is now in use */
int context_state; /* process_data state machine status */
JDIMENSION rowgroups_avail; /* row groups available to postprocessor */
JDIMENSION iMCU_row_ctr; /* counts iMCU rows to detect image top/bot */
} my_main_controller;
typedef my_main_controller * my_main_ptr;
/* context_state values: */
#define CTX_PREPARE_FOR_IMCU 0 /* need to prepare for MCU row */
#define CTX_PROCESS_IMCU 1 /* feeding iMCU to postprocessor */
#define CTX_POSTPONED_ROW 2 /* feeding postponed row group */
/* Forward declarations */
METHODDEF(void) process_data_simple_main
JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
METHODDEF(void) process_data_context_main
JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
#ifdef QUANT_2PASS_SUPPORTED
METHODDEF(void) process_data_crank_post
JPP((j_decompress_ptr cinfo, JSAMPARRAY output_buf,
JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail));
#endif
LOCAL(void)
alloc_funny_pointers (j_decompress_ptr cinfo)
/* Allocate space for the funny pointer lists.
* This is done only once, not once per pass.
*/
{
my_main_ptr _main = (my_main_ptr) cinfo->main;
int ci, rgroup;
int M = cinfo->min_DCT_scaled_size;
jpeg_component_info *compptr;
JSAMPARRAY xbuf;
/* Get top-level space for component array pointers.
* We alloc both arrays with one call to save a few cycles.
*/
_main->xbuffer[0] = (JSAMPIMAGE)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
cinfo->num_components * 2 * SIZEOF(JSAMPARRAY));
_main->xbuffer[1] = _main->xbuffer[0] + cinfo->num_components;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
cinfo->min_DCT_scaled_size; /* height of a row group of component */
/* Get space for pointer lists --- M+4 row groups in each list.
* We alloc both pointer lists with one call to save a few cycles.
*/
xbuf = (JSAMPARRAY)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW));
xbuf += rgroup; /* want one row group at negative offsets */
_main->xbuffer[0][ci] = xbuf;
xbuf += rgroup * (M + 4);
_main->xbuffer[1][ci] = xbuf;
}
}
LOCAL(void)
make_funny_pointers (j_decompress_ptr cinfo)
/* Create the funny pointer lists discussed in the comments above.
* The actual workspace is already allocated (in main->buffer),
* and the space for the pointer lists is allocated too.
* This routine just fills in the curiously ordered lists.
* This will be repeated at the beginning of each pass.
*/
{
my_main_ptr _main = (my_main_ptr) cinfo->main;
int ci, i, rgroup;
int M = cinfo->min_DCT_scaled_size;
jpeg_component_info *compptr;
JSAMPARRAY buf, xbuf0, xbuf1;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
cinfo->min_DCT_scaled_size; /* height of a row group of component */
xbuf0 = _main->xbuffer[0][ci];
xbuf1 = _main->xbuffer[1][ci];
/* First copy the workspace pointers as-is */
buf = _main->buffer[ci];
for (i = 0; i < rgroup * (M + 2); i++) {
xbuf0[i] = xbuf1[i] = buf[i];
}
/* In the second list, put the last four row groups in swapped order */
for (i = 0; i < rgroup * 2; i++) {
xbuf1[rgroup*(M-2) + i] = buf[rgroup*M + i];
xbuf1[rgroup*M + i] = buf[rgroup*(M-2) + i];
}
/* The wraparound pointers at top and bottom will be filled later
* (see set_wraparound_pointers, below). Initially we want the "above"
* pointers to duplicate the first actual data line. This only needs
* to happen in xbuffer[0].
*/
for (i = 0; i < rgroup; i++) {
xbuf0[i - rgroup] = xbuf0[0];
}
}
}
LOCAL(void)
set_wraparound_pointers (j_decompress_ptr cinfo)
/* Set up the "wraparound" pointers at top and bottom of the pointer lists.
* This changes the pointer list state from top-of-image to the normal state.
*/
{
my_main_ptr _main = (my_main_ptr) cinfo->main;
int ci, i, rgroup;
int M = cinfo->min_DCT_scaled_size;
jpeg_component_info *compptr;
JSAMPARRAY xbuf0, xbuf1;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
cinfo->min_DCT_scaled_size; /* height of a row group of component */
xbuf0 = _main->xbuffer[0][ci];
xbuf1 = _main->xbuffer[1][ci];
for (i = 0; i < rgroup; i++) {
xbuf0[i - rgroup] = xbuf0[rgroup*(M+1) + i];
xbuf1[i - rgroup] = xbuf1[rgroup*(M+1) + i];
xbuf0[rgroup*(M+2) + i] = xbuf0[i];
xbuf1[rgroup*(M+2) + i] = xbuf1[i];
}
}
}
LOCAL(void)
set_bottom_pointers (j_decompress_ptr cinfo)
/* Change the pointer lists to duplicate the last sample row at the bottom
* of the image. whichptr indicates which xbuffer holds the final iMCU row.
* Also sets rowgroups_avail to indicate number of nondummy row groups in row.
*/
{
my_main_ptr _main = (my_main_ptr) cinfo->main;
int ci, i, rgroup, iMCUheight, rows_left;
jpeg_component_info *compptr;
JSAMPARRAY xbuf;
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
/* Count sample rows in one iMCU row and in one row group */
iMCUheight = compptr->v_samp_factor * compptr->DCT_scaled_size;
rgroup = iMCUheight / cinfo->min_DCT_scaled_size;
/* Count nondummy sample rows remaining for this component */
rows_left = (int) (compptr->downsampled_height % (JDIMENSION) iMCUheight);
if (rows_left == 0) rows_left = iMCUheight;
/* Count nondummy row groups. Should get same answer for each component,
* so we need only do it once.
*/
if (ci == 0) {
_main->rowgroups_avail = (JDIMENSION) ((rows_left-1) / rgroup + 1);
}
/* Duplicate the last real sample row rgroup*2 times; this pads out the
* last partial rowgroup and ensures at least one full rowgroup of context.
*/
xbuf = _main->xbuffer[_main->whichptr][ci];
for (i = 0; i < rgroup * 2; i++) {
xbuf[rows_left + i] = xbuf[rows_left-1];
}
}
}
/*
* Initialize for a processing pass.
*/
METHODDEF(void)
start_pass_main (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
{
my_main_ptr _main = (my_main_ptr) cinfo->main;
switch (pass_mode) {
case JBUF_PASS_THRU:
if (cinfo->upsample->need_context_rows) {
_main->pub.process_data = process_data_context_main;
make_funny_pointers(cinfo); /* Create the xbuffer[] lists */
_main->whichptr = 0; /* Read first iMCU row into xbuffer[0] */
_main->context_state = CTX_PREPARE_FOR_IMCU;
_main->iMCU_row_ctr = 0;
} else {
/* Simple case with no context needed */
_main->pub.process_data = process_data_simple_main;
}
_main->buffer_full = FALSE; /* Mark buffer empty */
_main->rowgroup_ctr = 0;
break;
#ifdef QUANT_2PASS_SUPPORTED
case JBUF_CRANK_DEST:
/* For last pass of 2-pass quantization, just crank the postprocessor */
_main->pub.process_data = process_data_crank_post;
break;
#endif
default:
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
break;
}
}
/*
* Process some data.
* This handles the simple case where no context is required.
*/
METHODDEF(void)
process_data_simple_main (j_decompress_ptr cinfo,
JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
JDIMENSION out_rows_avail)
{
my_main_ptr _main = (my_main_ptr) cinfo->main;
JDIMENSION rowgroups_avail;
/* Read input data if we haven't filled the main buffer yet */
if (! _main->buffer_full) {
if (! (*cinfo->coef->decompress_data) (cinfo, _main->buffer))
return; /* suspension forced, can do nothing more */
_main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
}
/* There are always min_DCT_scaled_size row groups in an iMCU row. */
rowgroups_avail = (JDIMENSION) cinfo->min_DCT_scaled_size;
/* Note: at the bottom of the image, we may pass extra garbage row groups
* to the postprocessor. The postprocessor has to check for bottom
* of image anyway (at row resolution), so no point in us doing it too.
*/
/* Feed the postprocessor */
(*cinfo->post->post_process_data) (cinfo, _main->buffer,
&_main->rowgroup_ctr, rowgroups_avail,
output_buf, out_row_ctr, out_rows_avail);
/* Has postprocessor consumed all the data yet? If so, mark buffer empty */
if (_main->rowgroup_ctr >= rowgroups_avail) {
_main->buffer_full = FALSE;
_main->rowgroup_ctr = 0;
}
}
/*
* Process some data.
* This handles the case where context rows must be provided.
*/
METHODDEF(void)
process_data_context_main (j_decompress_ptr cinfo,
JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
JDIMENSION out_rows_avail)
{
my_main_ptr _main = (my_main_ptr) cinfo->main;
/* Read input data if we haven't filled the _main buffer yet */
if (! _main->buffer_full) {
if (! (*cinfo->coef->decompress_data) (cinfo,
_main->xbuffer[_main->whichptr]))
return; /* suspension forced, can do nothing more */
_main->buffer_full = TRUE; /* OK, we have an iMCU row to work with */
_main->iMCU_row_ctr++; /* count rows received */
}
/* Postprocessor typically will not swallow all the input data it is handed
* in one call (due to filling the output buffer first). Must be prepared
* to exit and restart. This switch lets us keep track of how far we got.
* Note that each case falls through to the next on successful completion.
*/
switch (_main->context_state) {
case CTX_POSTPONED_ROW:
/* Call postprocessor using previously set pointers for postponed row */
(*cinfo->post->post_process_data) (cinfo, _main->xbuffer[_main->whichptr],
&_main->rowgroup_ctr, _main->rowgroups_avail,
output_buf, out_row_ctr, out_rows_avail);
if (_main->rowgroup_ctr < _main->rowgroups_avail)
return; /* Need to suspend */
_main->context_state = CTX_PREPARE_FOR_IMCU;
if (*out_row_ctr >= out_rows_avail)
return; /* Postprocessor exactly filled output buf */
/*FALLTHROUGH*/
case CTX_PREPARE_FOR_IMCU:
/* Prepare to process first M-1 row groups of this iMCU row */
_main->rowgroup_ctr = 0;
_main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size - 1);
/* Check for bottom of image: if so, tweak pointers to "duplicate"
* the last sample row, and adjust rowgroups_avail to ignore padding rows.
*/
if (_main->iMCU_row_ctr == cinfo->total_iMCU_rows)
set_bottom_pointers(cinfo);
_main->context_state = CTX_PROCESS_IMCU;
/*FALLTHROUGH*/
case CTX_PROCESS_IMCU:
/* Call postprocessor using previously set pointers */
(*cinfo->post->post_process_data) (cinfo, _main->xbuffer[_main->whichptr],
&_main->rowgroup_ctr, _main->rowgroups_avail,
output_buf, out_row_ctr, out_rows_avail);
if (_main->rowgroup_ctr < _main->rowgroups_avail)
return; /* Need to suspend */
/* After the first iMCU, change wraparound pointers to normal state */
if (_main->iMCU_row_ctr == 1)
set_wraparound_pointers(cinfo);
/* Prepare to load new iMCU row using other xbuffer list */
_main->whichptr ^= 1; /* 0=>1 or 1=>0 */
_main->buffer_full = FALSE;
/* Still need to process last row group of this iMCU row, */
/* which is saved at index M+1 of the other xbuffer */
_main->rowgroup_ctr = (JDIMENSION) (cinfo->min_DCT_scaled_size + 1);
_main->rowgroups_avail = (JDIMENSION) (cinfo->min_DCT_scaled_size + 2);
_main->context_state = CTX_POSTPONED_ROW;
}
}
/*
* Process some data.
* Final pass of two-pass quantization: just call the postprocessor.
* Source data will be the postprocessor controller's internal buffer.
*/
#ifdef QUANT_2PASS_SUPPORTED
METHODDEF(void)
process_data_crank_post (j_decompress_ptr cinfo,
JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
JDIMENSION out_rows_avail)
{
(*cinfo->post->post_process_data) (cinfo, (JSAMPIMAGE) NULL,
(JDIMENSION *) NULL, (JDIMENSION) 0,
output_buf, out_row_ctr, out_rows_avail);
}
#endif /* QUANT_2PASS_SUPPORTED */
/*
* Initialize main buffer controller.
*/
GLOBAL(void)
jinit_d_main_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
{
my_main_ptr _main;
int ci, rgroup, ngroups;
jpeg_component_info *compptr;
_main = (my_main_ptr)
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(my_main_controller));
cinfo->main = (struct jpeg_d_main_controller *) _main;
_main->pub.start_pass = start_pass_main;
if (need_full_buffer) /* shouldn't happen */
ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
/* Allocate the workspace.
* ngroups is the number of row groups we need.
*/
if (cinfo->upsample->need_context_rows) {
if (cinfo->min_DCT_scaled_size < 2) /* unsupported, see comments above */
ERREXIT(cinfo, JERR_NOTIMPL);
alloc_funny_pointers(cinfo); /* Alloc space for xbuffer[] lists */
ngroups = cinfo->min_DCT_scaled_size + 2;
} else {
ngroups = cinfo->min_DCT_scaled_size;
}
for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
ci++, compptr++) {
rgroup = (compptr->v_samp_factor * compptr->DCT_scaled_size) /
cinfo->min_DCT_scaled_size; /* height of a row group of component */
_main->buffer[ci] = (*cinfo->mem->alloc_sarray)
((j_common_ptr) cinfo, JPOOL_IMAGE,
compptr->width_in_blocks * compptr->DCT_scaled_size,
(JDIMENSION) (rgroup * ngroups));
}
}
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