e8b40f3c2b
The Gordian knot that 7fec5074f9 attempted
to unravel was caused by the fact that there are several
data-precision-dependent (JSAMPLE-dependent) fields and methods in the
exposed libjpeg API structures, and if you change the exposed libjpeg
API structures, then you have to change the whole API. If you change
the whole API, then you have to provide a whole new library to support
the new API, and that makes it difficult to support multiple data
precisions in the same application. (It is not impossible, as example.c
demonstrated, but using data-precision-dependent libjpeg API structures
would have made the cjpeg, djpeg, and jpegtran source code hard to read,
so it made more sense to build, install, and package 12-bit-specific
versions of those applications.)
Unfortunately, the result of that initial integration effort was an
unreadable and unmaintainable mess, which is a problem for a library
that is an ISO/ITU-T reference implementation. Also, as I dug into the
problem of lossless JPEG support, I realized that 16-bit lossless JPEG
images are a thing, and supporting yet another version of the libjpeg
API just for those images is untenable.
In fact, however, the touch points for JSAMPLE in the exposed libjpeg
API structures are minimal:
- The colormap and sample_range_limit fields in jpeg_decompress_struct
- The alloc_sarray() and access_virt_sarray() methods in
jpeg_memory_mgr
- jpeg_write_scanlines() and jpeg_write_raw_data()
- jpeg_read_scanlines() and jpeg_read_raw_data()
- jpeg_skip_scanlines() and jpeg_crop_scanline()
(This is subtle, but both of those functions use JSAMPLE-dependent
opaque structures behind the scenes.)
It is much more readable and maintainable to provide 12-bit-specific
versions of those six top-level API functions and to document that the
aforementioned methods and fields must be type-cast when using 12-bit
samples. Since that eliminates the need to provide a 12-bit-specific
version of the exposed libjpeg API structures, we can:
- Compile only the precision-dependent libjpeg modules (the
coefficient buffer controllers, the colorspace converters, the
DCT/IDCT managers, the main buffer controllers, the preprocessing
and postprocessing controller, the downsampler and upsamplers, the
quantizers, the integer DCT methods, and the IDCT methods) for
multiple data precisions.
- Introduce 12-bit-specific methods into the various internal
structures defined in jpegint.h.
- Create precision-independent data type, macro, method, field, and
function names that are prefixed by an underscore, and use an
internal header to convert those into precision-dependent data
type, macro, method, field, and function names, based on the value
of BITS_IN_JSAMPLE, when compiling the precision-dependent libjpeg
modules.
- Expose precision-dependent jinit*() functions for each of the
precision-dependent libjpeg modules.
- Abstract the precision-dependent libjpeg modules by calling the
appropriate precision-dependent jinit*() function, based on the
value of cinfo->data_precision, from top-level libjpeg API
functions.
299 lines
11 KiB
C
299 lines
11 KiB
C
/*
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* jdpostct.c
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*
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* This file was part of the Independent JPEG Group's software:
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* Copyright (C) 1994-1996, Thomas G. Lane.
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* libjpeg-turbo Modifications:
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* Copyright (C) 2022, D. R. Commander.
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* For conditions of distribution and use, see the accompanying README.ijg
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* file.
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*
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* This file contains the decompression postprocessing controller.
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* This controller manages the upsampling, color conversion, and color
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* quantization/reduction steps; specifically, it controls the buffering
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* between upsample/color conversion and color quantization/reduction.
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*
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* If no color quantization/reduction is required, then this module has no
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* work to do, and it just hands off to the upsample/color conversion code.
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* An integrated upsample/convert/quantize process would replace this module
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* entirely.
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*/
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#define JPEG_INTERNALS
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#include "jinclude.h"
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#include "jpeglib.h"
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#include "jsamplecomp.h"
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/* Private buffer controller object */
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typedef struct {
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struct jpeg_d_post_controller pub; /* public fields */
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/* Color quantization source buffer: this holds output data from
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* the upsample/color conversion step to be passed to the quantizer.
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* For two-pass color quantization, we need a full-image buffer;
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* for one-pass operation, a strip buffer is sufficient.
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*/
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jvirt_sarray_ptr whole_image; /* virtual array, or NULL if one-pass */
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_JSAMPARRAY buffer; /* strip buffer, or current strip of virtual */
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JDIMENSION strip_height; /* buffer size in rows */
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/* for two-pass mode only: */
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JDIMENSION starting_row; /* row # of first row in current strip */
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JDIMENSION next_row; /* index of next row to fill/empty in strip */
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} my_post_controller;
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typedef my_post_controller *my_post_ptr;
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/* Forward declarations */
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METHODDEF(void) post_process_1pass(j_decompress_ptr cinfo,
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_JSAMPIMAGE input_buf,
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JDIMENSION *in_row_group_ctr,
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JDIMENSION in_row_groups_avail,
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_JSAMPARRAY output_buf,
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JDIMENSION *out_row_ctr,
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JDIMENSION out_rows_avail);
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#ifdef QUANT_2PASS_SUPPORTED
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METHODDEF(void) post_process_prepass(j_decompress_ptr cinfo,
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_JSAMPIMAGE input_buf,
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JDIMENSION *in_row_group_ctr,
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JDIMENSION in_row_groups_avail,
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_JSAMPARRAY output_buf,
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JDIMENSION *out_row_ctr,
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JDIMENSION out_rows_avail);
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METHODDEF(void) post_process_2pass(j_decompress_ptr cinfo,
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_JSAMPIMAGE input_buf,
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JDIMENSION *in_row_group_ctr,
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JDIMENSION in_row_groups_avail,
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_JSAMPARRAY output_buf,
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JDIMENSION *out_row_ctr,
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JDIMENSION out_rows_avail);
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#endif
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/*
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* Initialize for a processing pass.
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*/
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METHODDEF(void)
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start_pass_dpost(j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
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{
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my_post_ptr post = (my_post_ptr)cinfo->post;
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switch (pass_mode) {
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case JBUF_PASS_THRU:
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if (cinfo->quantize_colors) {
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/* Single-pass processing with color quantization. */
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post->pub._post_process_data = post_process_1pass;
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/* We could be doing buffered-image output before starting a 2-pass
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* color quantization; in that case, jinit_d_post_controller did not
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* allocate a strip buffer. Use the virtual-array buffer as workspace.
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*/
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if (post->buffer == NULL) {
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post->buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
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((j_common_ptr)cinfo, post->whole_image,
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(JDIMENSION)0, post->strip_height, TRUE);
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}
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} else {
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/* For single-pass processing without color quantization,
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* I have no work to do; just call the upsampler directly.
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*/
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post->pub._post_process_data = cinfo->upsample->_upsample;
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}
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break;
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#ifdef QUANT_2PASS_SUPPORTED
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case JBUF_SAVE_AND_PASS:
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/* First pass of 2-pass quantization */
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if (post->whole_image == NULL)
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ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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post->pub._post_process_data = post_process_prepass;
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break;
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case JBUF_CRANK_DEST:
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/* Second pass of 2-pass quantization */
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if (post->whole_image == NULL)
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ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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post->pub._post_process_data = post_process_2pass;
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break;
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#endif /* QUANT_2PASS_SUPPORTED */
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default:
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ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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break;
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}
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post->starting_row = post->next_row = 0;
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}
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/*
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* Process some data in the one-pass (strip buffer) case.
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* This is used for color precision reduction as well as one-pass quantization.
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*/
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METHODDEF(void)
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post_process_1pass(j_decompress_ptr cinfo, _JSAMPIMAGE input_buf,
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JDIMENSION *in_row_group_ctr,
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JDIMENSION in_row_groups_avail, _JSAMPARRAY output_buf,
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JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
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{
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my_post_ptr post = (my_post_ptr)cinfo->post;
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JDIMENSION num_rows, max_rows;
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/* Fill the buffer, but not more than what we can dump out in one go. */
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/* Note we rely on the upsampler to detect bottom of image. */
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max_rows = out_rows_avail - *out_row_ctr;
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if (max_rows > post->strip_height)
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max_rows = post->strip_height;
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num_rows = 0;
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(*cinfo->upsample->_upsample) (cinfo, input_buf, in_row_group_ctr,
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in_row_groups_avail, post->buffer, &num_rows,
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max_rows);
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/* Quantize and emit data. */
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(*cinfo->cquantize->_color_quantize) (cinfo, post->buffer,
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output_buf + *out_row_ctr,
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(int)num_rows);
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*out_row_ctr += num_rows;
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}
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#ifdef QUANT_2PASS_SUPPORTED
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/*
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* Process some data in the first pass of 2-pass quantization.
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*/
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METHODDEF(void)
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post_process_prepass(j_decompress_ptr cinfo, _JSAMPIMAGE input_buf,
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JDIMENSION *in_row_group_ctr,
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JDIMENSION in_row_groups_avail, _JSAMPARRAY output_buf,
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JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
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{
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my_post_ptr post = (my_post_ptr)cinfo->post;
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JDIMENSION old_next_row, num_rows;
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/* Reposition virtual buffer if at start of strip. */
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if (post->next_row == 0) {
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post->buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
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((j_common_ptr)cinfo, post->whole_image,
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post->starting_row, post->strip_height, TRUE);
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}
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/* Upsample some data (up to a strip height's worth). */
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old_next_row = post->next_row;
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(*cinfo->upsample->_upsample) (cinfo, input_buf, in_row_group_ctr,
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in_row_groups_avail, post->buffer,
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&post->next_row, post->strip_height);
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/* Allow quantizer to scan new data. No data is emitted, */
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/* but we advance out_row_ctr so outer loop can tell when we're done. */
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if (post->next_row > old_next_row) {
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num_rows = post->next_row - old_next_row;
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(*cinfo->cquantize->_color_quantize) (cinfo, post->buffer + old_next_row,
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(_JSAMPARRAY)NULL, (int)num_rows);
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*out_row_ctr += num_rows;
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}
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/* Advance if we filled the strip. */
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if (post->next_row >= post->strip_height) {
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post->starting_row += post->strip_height;
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post->next_row = 0;
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}
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}
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/*
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* Process some data in the second pass of 2-pass quantization.
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*/
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METHODDEF(void)
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post_process_2pass(j_decompress_ptr cinfo, _JSAMPIMAGE input_buf,
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JDIMENSION *in_row_group_ctr,
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JDIMENSION in_row_groups_avail, _JSAMPARRAY output_buf,
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JDIMENSION *out_row_ctr, JDIMENSION out_rows_avail)
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{
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my_post_ptr post = (my_post_ptr)cinfo->post;
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JDIMENSION num_rows, max_rows;
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/* Reposition virtual buffer if at start of strip. */
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if (post->next_row == 0) {
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post->buffer = (_JSAMPARRAY)(*cinfo->mem->access_virt_sarray)
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((j_common_ptr)cinfo, post->whole_image,
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post->starting_row, post->strip_height, FALSE);
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}
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/* Determine number of rows to emit. */
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num_rows = post->strip_height - post->next_row; /* available in strip */
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max_rows = out_rows_avail - *out_row_ctr; /* available in output area */
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if (num_rows > max_rows)
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num_rows = max_rows;
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/* We have to check bottom of image here, can't depend on upsampler. */
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max_rows = cinfo->output_height - post->starting_row;
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if (num_rows > max_rows)
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num_rows = max_rows;
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/* Quantize and emit data. */
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(*cinfo->cquantize->_color_quantize) (cinfo, post->buffer + post->next_row,
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output_buf + *out_row_ctr,
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(int)num_rows);
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*out_row_ctr += num_rows;
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/* Advance if we filled the strip. */
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post->next_row += num_rows;
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if (post->next_row >= post->strip_height) {
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post->starting_row += post->strip_height;
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post->next_row = 0;
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}
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}
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#endif /* QUANT_2PASS_SUPPORTED */
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/*
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* Initialize postprocessing controller.
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*/
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GLOBAL(void)
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_jinit_d_post_controller(j_decompress_ptr cinfo, boolean need_full_buffer)
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{
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my_post_ptr post;
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if (cinfo->data_precision != BITS_IN_JSAMPLE)
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ERREXIT1(cinfo, JERR_BAD_PRECISION, cinfo->data_precision);
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post = (my_post_ptr)
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(*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
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sizeof(my_post_controller));
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cinfo->post = (struct jpeg_d_post_controller *)post;
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post->pub.start_pass = start_pass_dpost;
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post->whole_image = NULL; /* flag for no virtual arrays */
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post->buffer = NULL; /* flag for no strip buffer */
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/* Create the quantization buffer, if needed */
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if (cinfo->quantize_colors) {
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/* The buffer strip height is max_v_samp_factor, which is typically
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* an efficient number of rows for upsampling to return.
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* (In the presence of output rescaling, we might want to be smarter?)
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*/
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post->strip_height = (JDIMENSION)cinfo->max_v_samp_factor;
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if (need_full_buffer) {
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/* Two-pass color quantization: need full-image storage. */
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/* We round up the number of rows to a multiple of the strip height. */
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#ifdef QUANT_2PASS_SUPPORTED
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post->whole_image = (*cinfo->mem->request_virt_sarray)
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((j_common_ptr)cinfo, JPOOL_IMAGE, FALSE,
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cinfo->output_width * cinfo->out_color_components,
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(JDIMENSION)jround_up((long)cinfo->output_height,
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(long)post->strip_height),
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post->strip_height);
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#else
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ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
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#endif /* QUANT_2PASS_SUPPORTED */
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} else {
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/* One-pass color quantization: just make a strip buffer. */
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post->buffer = (_JSAMPARRAY)(*cinfo->mem->alloc_sarray)
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((j_common_ptr)cinfo, JPOOL_IMAGE,
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cinfo->output_width * cinfo->out_color_components,
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post->strip_height);
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}
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}
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}
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