1 /*
2  * jdtrans.c
3  *
4  * Copyright (C) 1995-1997, Thomas G. Lane.
5  * Modified 2000-2009 by Guido Vollbeding.
6  * This file is part of the Independent JPEG Group's software.
7  * For conditions of distribution and use, see the accompanying README file.
8  *
9  * This file contains library routines for transcoding decompression,
10  * that is, reading raw DCT coefficient arrays from an input JPEG file.
11  * The routines in jdapimin.c will also be needed by a transcoder.
12  */
13 
14 #define JPEG_INTERNALS
15 #include "jinclude.h"
16 #include "jpeglib.h"
17 
18 
19 /* Forward declarations */
20 LOCAL(void) transdecode_master_selection JPP((j_decompress_ptr cinfo));
21 
22 
23 /*
24  * Read the coefficient arrays from a JPEG file.
25  * jpeg_read_header must be completed before calling this.
26  *
27  * The entire image is read into a set of virtual coefficient-block arrays,
28  * one per component.  The return value is a pointer to the array of
29  * virtual-array descriptors.  These can be manipulated directly via the
30  * JPEG memory manager, or handed off to jpeg_write_coefficients().
31  * To release the memory occupied by the virtual arrays, call
32  * jpeg_finish_decompress() when done with the data.
33  *
34  * An alternative usage is to simply obtain access to the coefficient arrays
35  * during a buffered-image-mode decompression operation.  This is allowed
36  * after any jpeg_finish_output() call.  The arrays can be accessed until
37  * jpeg_finish_decompress() is called.  (Note that any call to the library
38  * may reposition the arrays, so don't rely on access_virt_barray() results
39  * to stay valid across library calls.)
40  *
41  * Returns NULL if suspended.  This case need be checked only if
42  * a suspending data source is used.
43  */
44 
45 GLOBAL(jvirt_barray_ptr *)
jpeg_read_coefficients(j_decompress_ptr cinfo)46 jpeg_read_coefficients (j_decompress_ptr cinfo)
47 {
48   if (cinfo->global_state == DSTATE_READY) {
49     /* First call: initialize active modules */
50     transdecode_master_selection(cinfo);
51     cinfo->global_state = DSTATE_RDCOEFS;
52   }
53   if (cinfo->global_state == DSTATE_RDCOEFS) {
54     /* Absorb whole file into the coef buffer */
55     for (;;) {
56       int retcode;
57       /* Call progress monitor hook if present */
58       if (cinfo->progress != NULL)
59 	(*cinfo->progress->progress_monitor) ((j_common_ptr) cinfo);
60       /* Absorb some more input */
61       retcode = (*cinfo->inputctl->consume_input) (cinfo);
62       if (retcode == JPEG_SUSPENDED)
63 	return NULL;
64       if (retcode == JPEG_REACHED_EOI)
65 	break;
66       /* Advance progress counter if appropriate */
67       if (cinfo->progress != NULL &&
68 	  (retcode == JPEG_ROW_COMPLETED || retcode == JPEG_REACHED_SOS)) {
69 	if (++cinfo->progress->pass_counter >= cinfo->progress->pass_limit) {
70 	  /* startup underestimated number of scans; ratchet up one scan */
71 	  cinfo->progress->pass_limit += (long) cinfo->total_iMCU_rows;
72 	}
73       }
74     }
75     /* Set state so that jpeg_finish_decompress does the right thing */
76     cinfo->global_state = DSTATE_STOPPING;
77   }
78   /* At this point we should be in state DSTATE_STOPPING if being used
79    * standalone, or in state DSTATE_BUFIMAGE if being invoked to get access
80    * to the coefficients during a full buffered-image-mode decompression.
81    */
82   if ((cinfo->global_state == DSTATE_STOPPING ||
83        cinfo->global_state == DSTATE_BUFIMAGE) && cinfo->buffered_image) {
84     return cinfo->coef->coef_arrays;
85   }
86   /* Oops, improper usage */
87   ERREXIT1(cinfo, JERR_BAD_STATE, cinfo->global_state);
88   return NULL;			/* keep compiler happy */
89 }
90 
91 
92 /*
93  * Master selection of decompression modules for transcoding.
94  * This substitutes for jdmaster.c's initialization of the full decompressor.
95  */
96 
97 LOCAL(void)
transdecode_master_selection(j_decompress_ptr cinfo)98 transdecode_master_selection (j_decompress_ptr cinfo)
99 {
100   /* This is effectively a buffered-image operation. */
101   cinfo->buffered_image = TRUE;
102 
103   /* Compute output image dimensions and related values. */
104   jpeg_core_output_dimensions(cinfo);
105 
106   /* Entropy decoding: either Huffman or arithmetic coding. */
107   if (cinfo->arith_code)
108     jinit_arith_decoder(cinfo);
109   else {
110     jinit_huff_decoder(cinfo);
111   }
112 
113   /* Always get a full-image coefficient buffer. */
114   jinit_d_coef_controller(cinfo, TRUE);
115 
116   /* We can now tell the memory manager to allocate virtual arrays. */
117   (*cinfo->mem->realize_virt_arrays) ((j_common_ptr) cinfo);
118 
119   /* Initialize input side of decompressor to consume first scan. */
120   (*cinfo->inputctl->start_input_pass) (cinfo);
121 
122   /* Initialize progress monitoring. */
123   if (cinfo->progress != NULL) {
124     int nscans;
125     /* Estimate number of scans to set pass_limit. */
126     if (cinfo->progressive_mode) {
127       /* Arbitrarily estimate 2 interleaved DC scans + 3 AC scans/component. */
128       nscans = 2 + 3 * cinfo->num_components;
129     } else if (cinfo->inputctl->has_multiple_scans) {
130       /* For a nonprogressive multiscan file, estimate 1 scan per component. */
131       nscans = cinfo->num_components;
132     } else {
133       nscans = 1;
134     }
135     cinfo->progress->pass_counter = 0L;
136     cinfo->progress->pass_limit = (long) cinfo->total_iMCU_rows * nscans;
137     cinfo->progress->completed_passes = 0;
138     cinfo->progress->total_passes = 1;
139   }
140 }
141