Add a new libjpeg API function (jpeg_skip_scanlines()) to allow for partially decoding a JPEG image.
git-svn-id: svn+ssh://svn.code.sf.net/p/libjpeg-turbo/code/trunk@1582 632fc199-4ca6-4c93-a231-07263d6284db
diff --git a/jdcoefct.h b/jdcoefct.h
new file mode 100644
index 0000000..2f7bbe5
--- /dev/null
+++ b/jdcoefct.h
@@ -0,0 +1,82 @@
+/*
+ * jdcoefct.h
+ *
+ * This file was part of the Independent JPEG Group's software:
+ * Copyright (C) 1994-1997, Thomas G. Lane.
+ * libjpeg-turbo Modifications:
+ * Copyright 2009 Pierre Ossman <ossman@cendio.se> for Cendio AB
+ * For conditions of distribution and use, see the accompanying README file.
+ */
+
+#define JPEG_INTERNALS
+#include "jinclude.h"
+#include "jpeglib.h"
+
+
+/* Block smoothing is only applicable for progressive JPEG, so: */
+#ifndef D_PROGRESSIVE_SUPPORTED
+#undef BLOCK_SMOOTHING_SUPPORTED
+#endif
+
+
+/* Private buffer controller object */
+
+typedef struct {
+ struct jpeg_d_coef_controller pub; /* public fields */
+
+ /* These variables keep track of the current location of the input side. */
+ /* cinfo->input_iMCU_row is also used for this. */
+ JDIMENSION MCU_ctr; /* counts MCUs processed in current row */
+ int MCU_vert_offset; /* counts MCU rows within iMCU row */
+ int MCU_rows_per_iMCU_row; /* number of such rows needed */
+
+ /* The output side's location is represented by cinfo->output_iMCU_row. */
+
+ /* In single-pass modes, it's sufficient to buffer just one MCU.
+ * We allocate a workspace of D_MAX_BLOCKS_IN_MCU coefficient blocks,
+ * and let the entropy decoder write into that workspace each time.
+ * In multi-pass modes, this array points to the current MCU's blocks
+ * within the virtual arrays; it is used only by the input side.
+ */
+ JBLOCKROW MCU_buffer[D_MAX_BLOCKS_IN_MCU];
+
+ /* Temporary workspace for one MCU */
+ JCOEF * workspace;
+
+#ifdef D_MULTISCAN_FILES_SUPPORTED
+ /* In multi-pass modes, we need a virtual block array for each component. */
+ jvirt_barray_ptr whole_image[MAX_COMPONENTS];
+#endif
+
+#ifdef BLOCK_SMOOTHING_SUPPORTED
+ /* When doing block smoothing, we latch coefficient Al values here */
+ int * coef_bits_latch;
+#define SAVED_COEFS 6 /* we save coef_bits[0..5] */
+#endif
+} my_coef_controller;
+
+typedef my_coef_controller * my_coef_ptr;
+
+
+LOCAL(void)
+start_iMCU_row (j_decompress_ptr cinfo)
+/* Reset within-iMCU-row counters for a new row (input side) */
+{
+ my_coef_ptr coef = (my_coef_ptr) cinfo->coef;
+
+ /* In an interleaved scan, an MCU row is the same as an iMCU row.
+ * In a noninterleaved scan, an iMCU row has v_samp_factor MCU rows.
+ * But at the bottom of the image, process only what's left.
+ */
+ if (cinfo->comps_in_scan > 1) {
+ coef->MCU_rows_per_iMCU_row = 1;
+ } else {
+ if (cinfo->input_iMCU_row < (cinfo->total_iMCU_rows-1))
+ coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->v_samp_factor;
+ else
+ coef->MCU_rows_per_iMCU_row = cinfo->cur_comp_info[0]->last_row_height;
+ }
+
+ coef->MCU_ctr = 0;
+ coef->MCU_vert_offset = 0;
+}