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610 lines
22 KiB
610 lines
22 KiB
unit imjdmainct;
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{ This file is part of the Independent JPEG Group's software.
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For conditions of distribution and use, see the accompanying README file.
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This file contains the main buffer controller for decompression.
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The main buffer lies between the JPEG decompressor proper and the
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post-processor; it holds downsampled data in the JPEG colorspace.
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Note that this code is bypassed in raw-data mode, since the application
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supplies the equivalent of the main buffer in that case. }
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{ Original: jdmainct.c ; Copyright (C) 1994-1996, Thomas G. Lane. }
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{ In the current system design, the main buffer need never be a full-image
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buffer; any full-height buffers will be found inside the coefficient or
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postprocessing controllers. Nonetheless, the main controller is not
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trivial. Its responsibility is to provide context rows for upsampling/
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rescaling, and doing this in an efficient fashion is a bit tricky.
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Postprocessor input data is counted in "row groups". A row group
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is defined to be (v_samp_factor * DCT_scaled_size / min_DCT_scaled_size)
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sample rows of each component. (We require DCT_scaled_size values to be
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chosen such that these numbers are integers. In practice DCT_scaled_size
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values will likely be powers of two, so we actually have the stronger
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condition that DCT_scaled_size / min_DCT_scaled_size is an integer.)
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Upsampling will typically produce max_v_samp_factor pixel rows from each
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row group (times any additional scale factor that the upsampler is
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applying).
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The coefficient controller will deliver data to us one iMCU row at a time;
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each iMCU row contains v_samp_factor * DCT_scaled_size sample rows, or
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exactly min_DCT_scaled_size row groups. (This amount of data corresponds
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to one row of MCUs when the image is fully interleaved.) Note that the
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number of sample rows varies across components, but the number of row
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groups does not. Some garbage sample rows may be included in the last iMCU
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row at the bottom of the image.
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Depending on the vertical scaling algorithm used, the upsampler may need
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access to the sample row(s) above and below its current input row group.
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The upsampler is required to set need_context_rows TRUE at global
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selection
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time if so. When need_context_rows is FALSE, this controller can simply
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obtain one iMCU row at a time from the coefficient controller and dole it
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out as row groups to the postprocessor.
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When need_context_rows is TRUE, this controller guarantees that the buffer
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passed to postprocessing contains at least one row group's worth of samples
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above and below the row group(s) being processed. Note that the context
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rows "above" the first passed row group appear at negative row offsets in
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the passed buffer. At the top and bottom of the image, the required
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context rows are manufactured by duplicating the first or last real sample
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row; this avoids having special cases in the upsampling inner loops.
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The amount of context is fixed at one row group just because that's a
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convenient number for this controller to work with. The existing
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upsamplers really only need one sample row of context. An upsampler
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supporting arbitrary output rescaling might wish for more than one row
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group of context when shrinking the image; tough, we don't handle that.
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(This is justified by the assumption that downsizing will be handled mostly
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by adjusting the DCT_scaled_size values, so that the actual scale factor at
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the upsample step needn't be much less than one.)
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To provide the desired context, we have to retain the last two row groups
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of one iMCU row while reading in the next iMCU row. (The last row group
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can't be processed until we have another row group for its below-context,
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and so we have to save the next-to-last group too for its above-context.)
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We could do this most simply by copying data around in our buffer, but
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that'd be very slow. We can avoid copying any data by creating a rather
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strange pointer structure. Here's how it works. We allocate a workspace
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consisting of M+2 row groups (where M = min_DCT_scaled_size is the number
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of row groups per iMCU row). We create two sets of redundant pointers to
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the workspace. Labeling the physical row groups 0 to M+1, the synthesized
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pointer lists look like this:
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M+1 M-1
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master pointer --> 0 master pointer --> 0
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1 1
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... ...
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M-3 M-3
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M-2 M
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M-1 M+1
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M M-2
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M+1 M-1
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0 0
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We read alternate iMCU rows using each master pointer; thus the last two
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row groups of the previous iMCU row remain un-overwritten in the workspace.
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The pointer lists are set up so that the required context rows appear to
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be adjacent to the proper places when we pass the pointer lists to the
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upsampler.
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The above pictures describe the normal state of the pointer lists.
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At top and bottom of the image, we diddle the pointer lists to duplicate
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the first or last sample row as necessary (this is cheaper than copying
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sample rows around).
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This scheme breaks down if M < 2, ie, min_DCT_scaled_size is 1. In that
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situation each iMCU row provides only one row group so the buffering logic
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must be different (eg, we must read two iMCU rows before we can emit the
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first row group). For now, we simply do not support providing context
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rows when min_DCT_scaled_size is 1. That combination seems unlikely to
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be worth providing --- if someone wants a 1/8th-size preview, they probably
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want it quick and dirty, so a context-free upsampler is sufficient. }
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interface
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{$I imjconfig.inc}
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uses
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imjmorecfg,
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imjinclude,
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{$ifdef QUANT_2PASS_SUPPORTED}
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imjquant2,
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{$endif}
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imjdeferr,
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imjerror,
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imjpeglib;
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{GLOBAL}
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procedure jinit_d_main_controller (cinfo : j_decompress_ptr;
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need_full_buffer : boolean);
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implementation
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{ Private buffer controller object }
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type
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my_main_ptr = ^my_main_controller;
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my_main_controller = record
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pub : jpeg_d_main_controller; { public fields }
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{ Pointer to allocated workspace (M or M+2 row groups). }
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buffer : array[0..MAX_COMPONENTS-1] of JSAMPARRAY;
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buffer_full : boolean; { Have we gotten an iMCU row from decoder? }
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rowgroup_ctr : JDIMENSION ; { counts row groups output to postprocessor }
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{ Remaining fields are only used in the context case. }
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{ These are the master pointers to the funny-order pointer lists. }
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xbuffer : array[0..2-1] of JSAMPIMAGE; { pointers to weird pointer lists }
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whichptr : int; { indicates which pointer set is now in use }
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context_state : int; { process_data state machine status }
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rowgroups_avail : JDIMENSION; { row groups available to postprocessor }
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iMCU_row_ctr : JDIMENSION; { counts iMCU rows to detect image top/bot }
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end; { my_main_controller; }
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{ context_state values: }
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const
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CTX_PREPARE_FOR_IMCU = 0; { need to prepare for MCU row }
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CTX_PROCESS_IMCU = 1; { feeding iMCU to postprocessor }
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CTX_POSTPONED_ROW = 2; { feeding postponed row group }
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{ Forward declarations }
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{METHODDEF}
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procedure process_data_simple_main(cinfo : j_decompress_ptr;
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output_buf : JSAMPARRAY;
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var out_row_ctr : JDIMENSION;
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out_rows_avail : JDIMENSION); forward;
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{METHODDEF}
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procedure process_data_context_main (cinfo : j_decompress_ptr;
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output_buf : JSAMPARRAY;
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var out_row_ctr : JDIMENSION;
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out_rows_avail : JDIMENSION); forward;
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{$ifdef QUANT_2PASS_SUPPORTED}
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{METHODDEF}
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procedure process_data_crank_post (cinfo : j_decompress_ptr;
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output_buf : JSAMPARRAY;
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var out_row_ctr : JDIMENSION;
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out_rows_avail : JDIMENSION); forward;
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{$endif}
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{LOCAL}
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procedure alloc_funny_pointers (cinfo : j_decompress_ptr);
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{ Allocate space for the funny pointer lists.
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This is done only once, not once per pass. }
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var
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main : my_main_ptr;
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ci, rgroup : int;
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M : int;
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compptr : jpeg_component_info_ptr;
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xbuf : JSAMPARRAY;
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begin
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main := my_main_ptr (cinfo^.main);
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M := cinfo^.min_DCT_scaled_size;
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{ Get top-level space for component array pointers.
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We alloc both arrays with one call to save a few cycles. }
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main^.xbuffer[0] := JSAMPIMAGE (
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cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
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cinfo^.num_components * 2 * SIZEOF(JSAMPARRAY)) );
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main^.xbuffer[1] := JSAMPIMAGE(@( main^.xbuffer[0]^[cinfo^.num_components] ));
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compptr := jpeg_component_info_ptr(cinfo^.comp_info);
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for ci := 0 to pred(cinfo^.num_components) do
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begin
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rgroup := (compptr^.v_samp_factor * compptr^.DCT_scaled_size) div
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cinfo^.min_DCT_scaled_size; { height of a row group of component }
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{ Get space for pointer lists --- M+4 row groups in each list.
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We alloc both pointer lists with one call to save a few cycles. }
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xbuf := JSAMPARRAY (
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cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
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2 * (rgroup * (M + 4)) * SIZEOF(JSAMPROW)) );
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Inc(JSAMPROW_PTR(xbuf), rgroup); { want one row group at negative offsets }
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main^.xbuffer[0]^[ci] := xbuf;
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Inc(JSAMPROW_PTR(xbuf), rgroup * (M + 4));
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main^.xbuffer[1]^[ci] := xbuf;
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Inc(compptr);
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end;
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end;
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{LOCAL}
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procedure make_funny_pointers (cinfo : j_decompress_ptr);
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{ Create the funny pointer lists discussed in the comments above.
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The actual workspace is already allocated (in main^.buffer),
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and the space for the pointer lists is allocated too.
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This routine just fills in the curiously ordered lists.
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This will be repeated at the beginning of each pass. }
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var
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main : my_main_ptr;
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ci, i, rgroup : int;
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M : int;
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compptr : jpeg_component_info_ptr;
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buf, xbuf0, xbuf1 : JSAMPARRAY;
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var
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help_xbuf0 : JSAMPARRAY; { work around negative offsets }
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begin
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main := my_main_ptr (cinfo^.main);
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M := cinfo^.min_DCT_scaled_size;
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compptr := jpeg_component_info_ptr(cinfo^.comp_info);
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for ci := 0 to pred(cinfo^.num_components) do
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begin
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rgroup := (compptr^.v_samp_factor * compptr^.DCT_scaled_size) div
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cinfo^.min_DCT_scaled_size; { height of a row group of component }
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xbuf0 := main^.xbuffer[0]^[ci];
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xbuf1 := main^.xbuffer[1]^[ci];
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{ First copy the workspace pointers as-is }
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buf := main^.buffer[ci];
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for i := 0 to pred(rgroup * (M + 2)) do
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begin
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xbuf0^[i] := buf^[i];
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xbuf1^[i] := buf^[i];
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end;
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{ In the second list, put the last four row groups in swapped order }
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for i := 0 to pred(rgroup * 2) do
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begin
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xbuf1^[rgroup*(M-2) + i] := buf^[rgroup*M + i];
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xbuf1^[rgroup*M + i] := buf^[rgroup*(M-2) + i];
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end;
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{ The wraparound pointers at top and bottom will be filled later
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(see set_wraparound_pointers, below). Initially we want the "above"
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pointers to duplicate the first actual data line. This only needs
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to happen in xbuffer[0]. }
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help_xbuf0 := xbuf0;
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Dec(JSAMPROW_PTR(help_xbuf0), rgroup);
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for i := 0 to pred(rgroup) do
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begin
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{xbuf0^[i - rgroup] := xbuf0^[0];}
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help_xbuf0^[i] := xbuf0^[0];
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end;
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Inc(compptr);
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end;
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end;
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{LOCAL}
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procedure set_wraparound_pointers (cinfo : j_decompress_ptr);
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{ Set up the "wraparound" pointers at top and bottom of the pointer lists.
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This changes the pointer list state from top-of-image to the normal state. }
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var
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main : my_main_ptr;
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ci, i, rgroup : int;
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M : int;
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compptr : jpeg_component_info_ptr;
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xbuf0, xbuf1 : JSAMPARRAY;
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var
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help_xbuf0,
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help_xbuf1 : JSAMPARRAY; { work around negative offsets }
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begin
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main := my_main_ptr (cinfo^.main);
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M := cinfo^.min_DCT_scaled_size;
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compptr := jpeg_component_info_ptr(cinfo^.comp_info);
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for ci := 0 to pred(cinfo^.num_components) do
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begin
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rgroup := (compptr^.v_samp_factor * compptr^.DCT_scaled_size) div
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cinfo^.min_DCT_scaled_size; { height of a row group of component }
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xbuf0 := main^.xbuffer[0]^[ci];
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xbuf1 := main^.xbuffer[1]^[ci];
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help_xbuf0 := xbuf0;
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Dec(JSAMPROW_PTR(help_xbuf0), rgroup);
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help_xbuf1 := xbuf1;
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Dec(JSAMPROW_PTR(help_xbuf1), rgroup);
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for i := 0 to pred(rgroup) do
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begin
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{xbuf0^[i - rgroup] := xbuf0^[rgroup*(M+1) + i];
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xbuf1^[i - rgroup] := xbuf1^[rgroup*(M+1) + i];}
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help_xbuf0^[i] := xbuf0^[rgroup*(M+1) + i];
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help_xbuf1^[i] := xbuf1^[rgroup*(M+1) + i];
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xbuf0^[rgroup*(M+2) + i] := xbuf0^[i];
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xbuf1^[rgroup*(M+2) + i] := xbuf1^[i];
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end;
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Inc(compptr);
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end;
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end;
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{LOCAL}
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procedure set_bottom_pointers (cinfo : j_decompress_ptr);
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{ Change the pointer lists to duplicate the last sample row at the bottom
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of the image. whichptr indicates which xbuffer holds the final iMCU row.
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Also sets rowgroups_avail to indicate number of nondummy row groups in row. }
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var
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main : my_main_ptr;
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ci, i, rgroup, iMCUheight, rows_left : int;
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compptr : jpeg_component_info_ptr;
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xbuf : JSAMPARRAY;
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begin
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main := my_main_ptr (cinfo^.main);
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compptr := jpeg_component_info_ptr(cinfo^.comp_info);
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for ci := 0 to pred(cinfo^.num_components) do
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begin
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{ Count sample rows in one iMCU row and in one row group }
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iMCUheight := compptr^.v_samp_factor * compptr^.DCT_scaled_size;
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rgroup := iMCUheight div cinfo^.min_DCT_scaled_size;
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{ Count nondummy sample rows remaining for this component }
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rows_left := int (compptr^.downsampled_height mod JDIMENSION (iMCUheight));
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if (rows_left = 0) then
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rows_left := iMCUheight;
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{ Count nondummy row groups. Should get same answer for each component,
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so we need only do it once. }
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if (ci = 0) then
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begin
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main^.rowgroups_avail := JDIMENSION ((rows_left-1) div rgroup + 1);
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end;
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{ Duplicate the last real sample row rgroup*2 times; this pads out the
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last partial rowgroup and ensures at least one full rowgroup of context. }
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xbuf := main^.xbuffer[main^.whichptr]^[ci];
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for i := 0 to pred(rgroup * 2) do
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begin
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xbuf^[rows_left + i] := xbuf^[rows_left-1];
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end;
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Inc(compptr);
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end;
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end;
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{ Initialize for a processing pass. }
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{METHODDEF}
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procedure start_pass_main (cinfo : j_decompress_ptr;
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pass_mode : J_BUF_MODE);
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var
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main : my_main_ptr;
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begin
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main := my_main_ptr (cinfo^.main);
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case (pass_mode) of
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JBUF_PASS_THRU:
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begin
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if (cinfo^.upsample^.need_context_rows) then
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begin
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main^.pub.process_data := process_data_context_main;
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make_funny_pointers(cinfo); { Create the xbuffer[] lists }
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main^.whichptr := 0; { Read first iMCU row into xbuffer[0] }
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main^.context_state := CTX_PREPARE_FOR_IMCU;
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main^.iMCU_row_ctr := 0;
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end
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else
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begin
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{ Simple case with no context needed }
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main^.pub.process_data := process_data_simple_main;
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end;
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main^.buffer_full := FALSE; { Mark buffer empty }
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main^.rowgroup_ctr := 0;
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end;
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{$ifdef QUANT_2PASS_SUPPORTED}
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JBUF_CRANK_DEST:
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{ For last pass of 2-pass quantization, just crank the postprocessor }
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main^.pub.process_data := process_data_crank_post;
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{$endif}
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else
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ERREXIT(j_common_ptr(cinfo), JERR_BAD_BUFFER_MODE);
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end;
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end;
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{ Process some data.
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This handles the simple case where no context is required. }
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{METHODDEF}
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procedure process_data_simple_main (cinfo : j_decompress_ptr;
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output_buf : JSAMPARRAY;
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var out_row_ctr : JDIMENSION;
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out_rows_avail : JDIMENSION);
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var
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main : my_main_ptr;
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rowgroups_avail : JDIMENSION;
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var
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main_buffer_ptr : JSAMPIMAGE;
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begin
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main := my_main_ptr (cinfo^.main);
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main_buffer_ptr := JSAMPIMAGE(@(main^.buffer));
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{ Read input data if we haven't filled the main buffer yet }
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if (not main^.buffer_full) then
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begin
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if (cinfo^.coef^.decompress_data (cinfo, main_buffer_ptr)=0) then
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exit; { suspension forced, can do nothing more }
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main^.buffer_full := TRUE; { OK, we have an iMCU row to work with }
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end;
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{ There are always min_DCT_scaled_size row groups in an iMCU row. }
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rowgroups_avail := JDIMENSION (cinfo^.min_DCT_scaled_size);
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{ Note: at the bottom of the image, we may pass extra garbage row groups
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to the postprocessor. The postprocessor has to check for bottom
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of image anyway (at row resolution), so no point in us doing it too. }
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{ Feed the postprocessor }
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cinfo^.post^.post_process_data (cinfo, main_buffer_ptr,
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main^.rowgroup_ctr, rowgroups_avail,
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output_buf, out_row_ctr, out_rows_avail);
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{ Has postprocessor consumed all the data yet? If so, mark buffer empty }
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if (main^.rowgroup_ctr >= rowgroups_avail) then
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begin
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main^.buffer_full := FALSE;
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main^.rowgroup_ctr := 0;
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end;
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end;
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{ Process some data.
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This handles the case where context rows must be provided. }
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{METHODDEF}
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procedure process_data_context_main (cinfo : j_decompress_ptr;
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output_buf : JSAMPARRAY;
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var out_row_ctr : JDIMENSION;
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out_rows_avail : JDIMENSION);
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var
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main : my_main_ptr;
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begin
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main := my_main_ptr (cinfo^.main);
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{ Read input data if we haven't filled the main buffer yet }
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if (not main^.buffer_full) then
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begin
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if (cinfo^.coef^.decompress_data (cinfo,
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main^.xbuffer[main^.whichptr])=0) then
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exit; { suspension forced, can do nothing more }
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main^.buffer_full := TRUE; { OK, we have an iMCU row to work with }
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Inc(main^.iMCU_row_ctr); { count rows received }
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end;
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{ Postprocessor typically will not swallow all the input data it is handed
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in one call (due to filling the output buffer first). Must be prepared
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to exit and restart. This switch lets us keep track of how far we got.
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Note that each case falls through to the next on successful completion. }
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case (main^.context_state) of
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CTX_POSTPONED_ROW:
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begin
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{ Call postprocessor using previously set pointers for postponed row }
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cinfo^.post^.post_process_data (cinfo, main^.xbuffer[main^.whichptr],
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main^.rowgroup_ctr, main^.rowgroups_avail,
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output_buf, out_row_ctr, out_rows_avail);
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if (main^.rowgroup_ctr < main^.rowgroups_avail) then
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exit; { Need to suspend }
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main^.context_state := CTX_PREPARE_FOR_IMCU;
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if (out_row_ctr >= out_rows_avail) then
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exit; { Postprocessor exactly filled output buf }
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end;
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end;
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case (main^.context_state) of
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CTX_POSTPONED_ROW,
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CTX_PREPARE_FOR_IMCU: {FALLTHROUGH}
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begin
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{ Prepare to process first M-1 row groups of this iMCU row }
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main^.rowgroup_ctr := 0;
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main^.rowgroups_avail := JDIMENSION (cinfo^.min_DCT_scaled_size - 1);
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{ Check for bottom of image: if so, tweak pointers to "duplicate"
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the last sample row, and adjust rowgroups_avail to ignore padding rows. }
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if (main^.iMCU_row_ctr = cinfo^.total_iMCU_rows) then
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set_bottom_pointers(cinfo);
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main^.context_state := CTX_PROCESS_IMCU;
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end;
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end;
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case (main^.context_state) of
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CTX_POSTPONED_ROW,
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CTX_PREPARE_FOR_IMCU, {FALLTHROUGH}
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CTX_PROCESS_IMCU:
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begin
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{ Call postprocessor using previously set pointers }
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cinfo^.post^.post_process_data (cinfo, main^.xbuffer[main^.whichptr],
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main^.rowgroup_ctr, main^.rowgroups_avail,
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output_buf, out_row_ctr, out_rows_avail);
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if (main^.rowgroup_ctr < main^.rowgroups_avail) then
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exit; { Need to suspend }
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{ After the first iMCU, change wraparound pointers to normal state }
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if (main^.iMCU_row_ctr = 1) then
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set_wraparound_pointers(cinfo);
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{ Prepare to load new iMCU row using other xbuffer list }
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main^.whichptr := main^.whichptr xor 1; { 0=>1 or 1=>0 }
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main^.buffer_full := FALSE;
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{ Still need to process last row group of this iMCU row, }
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{ which is saved at index M+1 of the other xbuffer }
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main^.rowgroup_ctr := JDIMENSION (cinfo^.min_DCT_scaled_size + 1);
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main^.rowgroups_avail := JDIMENSION (cinfo^.min_DCT_scaled_size + 2);
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main^.context_state := CTX_POSTPONED_ROW;
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end;
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end;
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end;
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{ Process some data.
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Final pass of two-pass quantization: just call the postprocessor.
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Source data will be the postprocessor controller's internal buffer. }
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{$ifdef QUANT_2PASS_SUPPORTED}
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{METHODDEF}
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procedure process_data_crank_post (cinfo : j_decompress_ptr;
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output_buf : JSAMPARRAY;
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var out_row_ctr : JDIMENSION;
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out_rows_avail : JDIMENSION);
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var
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in_row_group_ctr : JDIMENSION;
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begin
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in_row_group_ctr := 0;
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cinfo^.post^.post_process_data (cinfo, JSAMPIMAGE (NIL),
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in_row_group_ctr,
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JDIMENSION(0),
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output_buf,
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out_row_ctr,
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out_rows_avail);
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end;
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{$endif} { QUANT_2PASS_SUPPORTED }
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{ Initialize main buffer controller. }
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{GLOBAL}
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procedure jinit_d_main_controller (cinfo : j_decompress_ptr;
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need_full_buffer : boolean);
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var
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main : my_main_ptr;
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ci, rgroup, ngroups : int;
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compptr : jpeg_component_info_ptr;
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begin
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main := my_main_ptr(
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cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
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SIZEOF(my_main_controller)) );
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cinfo^.main := jpeg_d_main_controller_ptr(main);
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main^.pub.start_pass := start_pass_main;
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if (need_full_buffer) then { shouldn't happen }
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ERREXIT(j_common_ptr(cinfo), JERR_BAD_BUFFER_MODE);
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{ Allocate the workspace.
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ngroups is the number of row groups we need.}
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if (cinfo^.upsample^.need_context_rows) then
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begin
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if (cinfo^.min_DCT_scaled_size < 2) then { unsupported, see comments above }
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ERREXIT(j_common_ptr(cinfo), JERR_NOTIMPL);
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alloc_funny_pointers(cinfo); { Alloc space for xbuffer[] lists }
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ngroups := cinfo^.min_DCT_scaled_size + 2;
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end
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else
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begin
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ngroups := cinfo^.min_DCT_scaled_size;
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end;
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compptr := jpeg_component_info_ptr(cinfo^.comp_info);
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for ci := 0 to pred(cinfo^.num_components) do
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begin
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rgroup := (compptr^.v_samp_factor * compptr^.DCT_scaled_size) div
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cinfo^.min_DCT_scaled_size; { height of a row group of component }
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main^.buffer[ci] := cinfo^.mem^.alloc_sarray
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(j_common_ptr(cinfo), JPOOL_IMAGE,
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compptr^.width_in_blocks * LongWord(compptr^.DCT_scaled_size),
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JDIMENSION (rgroup * ngroups));
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Inc(compptr);
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end;
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end;
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end.
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