Add jpeg_skip_scanlines() API to libjpeg-turbo

jdmainct.c

 /*
  * jdmainct.c
  *
  * This file was part of the Independent JPEG Group's software:
  * Copyright (C) 1994-1996, Thomas G. Lane.
  * libjpeg-turbo Modifications:
  * Copyright (C) 2010, D. R. Commander.
  * 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"
-#include "jpegcomp.h"
+#include "jdmainct.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
@@ skipping 73 matching lines @@
  * 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,
@@ skipping 76 matching lines @@
      * 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_ptr = (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_ptr->xbuffer[0][ci];
-    xbuf1 = main_ptr->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_ptr = (my_main_ptr) cinfo->main;
   int ci, i, rgroup, iMCUheight, rows_left;
   jpeg_component_info *compptr;
   JSAMPARRAY xbuf;
@@ skipping 227 matching lines @@
   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_ptr->buffer[ci] = (*cinfo->mem->alloc_sarray)
                         ((j_common_ptr) cinfo, JPOOL_IMAGE,
                          compptr->width_in_blocks * compptr->_DCT_scaled_size,
                          (JDIMENSION) (rgroup * ngroups));
   }
 }