// Create the wrapped-around downsampling input buffer needed for context mode.
static void create_context_buffer(jpeg_compress cinfo)
{
my_prep_controller prep = (my_prep_controller)cinfo.prep;
int rgroup_height = cinfo.max_v_samp_factor;
for (int ci = 0; ci < cinfo.num_components; ci++)
{
jpeg_component_info compptr = cinfo.comp_info[ci];
// Grab enough space for fake row pointers;
// we need five row groups' worth of pointers for each component.
byte[][] fake_buffer = new byte[5 * rgroup_height][];
// Allocate the actual buffer space (3 row groups) for this component.
// We make the buffer wide enough to allow the downsampler to edge-expand
// horizontally within the buffer, if it so chooses.
byte[][] true_buffer = alloc_sarray(cinfo,
(uint)(((int)compptr.width_in_blocks * cinfo.DCT_size * cinfo.max_h_samp_factor) / compptr.h_samp_factor),
(uint)(3 * rgroup_height));
// Copy true buffer row pointers into the middle of the fake row array
Array.Copy(true_buffer, 0, fake_buffer, rgroup_height, 3 * rgroup_height);
// Fill in the above and below wraparound pointers
for (int i = 0; i < rgroup_height; i++)
{
fake_buffer[i] = true_buffer[2 * rgroup_height + i];
fake_buffer[4 * rgroup_height + i] = true_buffer[i];
}
prep.color_buf[ci] = fake_buffer;
}
}
// Initialize preprocessing controller.
static void jinit_c_prep_controller(jpeg_compress cinfo, bool need_full_buffer)
{
if (need_full_buffer)
{
ERREXIT(cinfo, J_MESSAGE_CODE.JERR_BAD_BUFFER_MODE); // safety check
}
my_prep_controller prep = null;
try
{
prep = new my_prep_controller();
}
catch
{
ERREXIT1(cinfo, J_MESSAGE_CODE.JERR_OUT_OF_MEMORY, 4);
}
cinfo.prep = prep;
prep.start_pass = start_pass_prep;
// Allocate the color conversion buffer.
// We make the buffer wide enough to allow the downsampler to edge-expand
// horizontally within the buffer, if it so chooses.
if (cinfo.downsample.need_context_rows)
{
// Set up to provide context rows
#if CONTEXT_ROWS_SUPPORTED
prep.pre_process_data = pre_process_context;
create_context_buffer(cinfo);
#else
ERREXIT(cinfo, J_MESSAGE_CODE.JERR_NOT_COMPILED);
#endif
}
else
{
// No context, just make it tall enough for one row group
prep.pre_process_data = pre_process_data;
for (int ci = 0; ci < cinfo.num_components; ci++)
{
jpeg_component_info compptr = cinfo.comp_info[ci];
prep.color_buf[ci] = alloc_sarray(cinfo,
(uint)(((int)compptr.width_in_blocks * cinfo.DCT_size * cinfo.max_h_samp_factor) / compptr.h_samp_factor),
(uint)cinfo.max_v_samp_factor);
}
}
}
// Process some data in the simple no-context case.
//
// Preprocessor output data is counted in "row groups". A row group
// is defined to be v_samp_factor sample rows of each component.
// Downsampling will produce this much data from each max_v_samp_factor input rows.
static void pre_process_data(jpeg_compress cinfo, byte[][] input_buf, ref uint in_row_ctr, uint in_rows_avail, byte[][][] output_buf, ref uint out_row_group_ctr, uint out_row_groups_avail)
{
my_prep_controller prep = (my_prep_controller)cinfo.prep;
while (in_row_ctr < in_rows_avail && out_row_group_ctr < out_row_groups_avail)
{
// Do color conversion to fill the conversion buffer.
uint inrows = in_rows_avail - in_row_ctr;
int numrows = cinfo.max_v_samp_factor - prep.next_buf_row;
numrows = (int)Math.Min((uint)numrows, inrows);
cinfo.cconvert.color_convert(cinfo, input_buf, in_row_ctr, prep.color_buf, (uint)prep.next_buf_row, numrows);
in_row_ctr += (uint)numrows;
prep.next_buf_row += numrows;
prep.rows_to_go -= (uint)numrows;
// If at bottom of image, pad to fill the conversion buffer.
if (prep.rows_to_go == 0 && prep.next_buf_row < cinfo.max_v_samp_factor)
{
for (int ci = 0; ci < cinfo.num_components; ci++)
{
expand_bottom_edge(prep.color_buf[ci], cinfo.image_width, prep.next_buf_row, cinfo.max_v_samp_factor);
}
prep.next_buf_row = cinfo.max_v_samp_factor;
}
// If we've filled the conversion buffer, empty it.
if (prep.next_buf_row == cinfo.max_v_samp_factor)
{
cinfo.downsample.downsample(cinfo, prep.color_buf, 0, output_buf, out_row_group_ctr);
prep.next_buf_row = 0;
out_row_group_ctr++;
}
// If at bottom of image, pad the output to a full iMCU height.
// Note we assume the caller is providing a one-iMCU-height output buffer!
if (prep.rows_to_go == 0 && out_row_group_ctr < out_row_groups_avail)
{
for (int ci = 0; ci < cinfo.num_components; ci++)
{
jpeg_component_info compptr = cinfo.comp_info[ci];
expand_bottom_edge(output_buf[ci], compptr.width_in_blocks * cinfo.DCT_size, (int)(out_row_group_ctr * compptr.v_samp_factor), (int)(out_row_groups_avail * compptr.v_samp_factor));
}
out_row_group_ctr = out_row_groups_avail;
break; // can exit outer loop without test
}
} // while(...)
}
// Initialize for a processing pass.
static void start_pass_prep(jpeg_compress cinfo, J_BUF_MODE pass_mode)
{
my_prep_controller prep = (my_prep_controller)cinfo.prep;
if (pass_mode != J_BUF_MODE.JBUF_PASS_THRU)
{
ERREXIT(cinfo, J_MESSAGE_CODE.JERR_BAD_BUFFER_MODE);
}
// Initialize total-height counter for detecting bottom of image
prep.rows_to_go = cinfo.image_height;
// Mark the conversion buffer empty
prep.next_buf_row = 0;
#if CONTEXT_ROWS_SUPPORTED
// Preset additional state variables for context mode.
// These aren't used in non-context mode, so we needn't test which mode.
prep.this_row_group = 0;
// Set next_buf_stop to stop after two row groups have been read in.
prep.next_buf_stop = 2 * cinfo.max_v_samp_factor;
#endif
}
// Initialize preprocessing controller.
static void jinit_c_prep_controller(jpeg_compress cinfo, bool need_full_buffer)
{
if(need_full_buffer) ERREXIT(cinfo, J_MESSAGE_CODE.JERR_BAD_BUFFER_MODE); // safety check
my_prep_controller prep=null;
try
{
prep=new my_prep_controller();
}
catch
{
ERREXIT1(cinfo, J_MESSAGE_CODE.JERR_OUT_OF_MEMORY, 4);
}
cinfo.prep=prep;
prep.start_pass=start_pass_prep;
// Allocate the color conversion buffer.
// We make the buffer wide enough to allow the downsampler to edge-expand
// horizontally within the buffer, if it so chooses.
if(cinfo.downsample.need_context_rows)
{
// Set up to provide context rows
#if CONTEXT_ROWS_SUPPORTED
prep.pre_process_data=pre_process_context;
create_context_buffer(cinfo);
#else
ERREXIT(cinfo, J_MESSAGE_CODE.JERR_NOT_COMPILED);
#endif
}
else
{
// No context, just make it tall enough for one row group
prep.pre_process_data=pre_process_data;
for(int ci=0; ci<cinfo.num_components; ci++)
{
jpeg_component_info compptr=cinfo.comp_info[ci];
prep.color_buf[ci]=alloc_sarray(cinfo,
(uint)(((int)compptr.width_in_blocks*cinfo.DCT_size*cinfo.max_h_samp_factor)/compptr.h_samp_factor),
(uint)cinfo.max_v_samp_factor);
}
}
}
// Process some data in the context case.
static void pre_process_context(jpeg_compress cinfo, byte[][] input_buf, ref uint in_row_ctr, uint in_rows_avail, byte[][][] output_buf, ref uint out_row_group_ctr, uint out_row_groups_avail)
{
my_prep_controller prep = (my_prep_controller)cinfo.prep;
int buf_height = cinfo.max_v_samp_factor * 3;
int rgroup_height = cinfo.max_v_samp_factor;
while (out_row_group_ctr < out_row_groups_avail)
{
if (in_row_ctr < in_rows_avail)
{
// Do color conversion to fill the conversion buffer.
uint inrows = in_rows_avail - in_row_ctr;
int numrows = prep.next_buf_stop - prep.next_buf_row;
numrows = (int)Math.Min((uint)numrows, inrows);
cinfo.cconvert.color_convert(cinfo, input_buf, in_row_ctr, prep.color_buf, (uint)rgroup_height + (uint)prep.next_buf_row, numrows);
// Pad at top of image, if first time through
if (prep.rows_to_go == cinfo.image_height)
{
for (int ci = 0; ci < cinfo.num_components; ci++)
{
for (int row = 1; row <= cinfo.max_v_samp_factor; row++)
{
jcopy_sample_rows(prep.color_buf[ci], rgroup_height, prep.color_buf[ci], rgroup_height - row, 1, cinfo.image_width);
}
}
}
in_row_ctr += (uint)numrows;
prep.next_buf_row += numrows;
prep.rows_to_go -= (uint)numrows;
}
else
{
// Return for more data, unless we are at the bottom of the image.
if (prep.rows_to_go != 0)
{
break;
}
// When at bottom of image, pad to fill the conversion buffer.
if (prep.next_buf_row < prep.next_buf_stop)
{
for (int ci = 0; ci < cinfo.num_components; ci++)
{
expand_bottom_edge(prep.color_buf[ci], cinfo.image_width, rgroup_height + prep.next_buf_row, rgroup_height + prep.next_buf_stop);
}
prep.next_buf_row = prep.next_buf_stop;
}
}
// If we've gotten enough data, downsample a row group.
if (prep.next_buf_row == prep.next_buf_stop)
{
cinfo.downsample.downsample(cinfo, prep.color_buf, (uint)rgroup_height + (uint)prep.this_row_group, output_buf, out_row_group_ctr);
out_row_group_ctr++;
// Advance pointers with wraparound as necessary.
prep.this_row_group += cinfo.max_v_samp_factor;
if (prep.this_row_group >= buf_height)
{
prep.this_row_group = 0;
}
if (prep.next_buf_row >= buf_height)
{
prep.next_buf_row = 0;
}
prep.next_buf_stop = prep.next_buf_row + cinfo.max_v_samp_factor;
}
} // while(...)
}
