jccoefct.pas

DELPHI版的JPEG文件解码源程序

  This amount of data is read from the source buffer, DCT'd and quantized,
  and saved into the virtual arrays.  We also generate suitable dummy blocks
  as needed at the right and lower edges.  (The dummy blocks are constructed
  in the virtual arrays, which have been padded appropriately.)  This makes
  it possible for subsequent passes not to worry about real vs. dummy blocks.

  We must also emit the data to the entropy encoder.  This is conveniently
  done by calling compress_output() after we've loaded the current strip
  of the virtual arrays.

  NB: input_buf contains a plane for each component in image.  All
  components are DCT'd and loaded into the virtual arrays in this pass.
  However, it may be that only a subset of the components are emitted to
  the entropy encoder during this first pass; be careful about looking
  at the scan-dependent variables (MCU dimensions, etc). }

{METHODDEF}
function compress_first_pass (cinfo : j_compress_ptr;
                              input_buf : JSAMPIMAGE) : boolean;
var
  coef : my_coef_ptr;
  last_iMCU_row : JDIMENSION;
  blocks_across, MCUs_across, MCUindex : JDIMENSION;
  bi, ci, h_samp_factor, block_row, block_rows, ndummy : int;
  lastDC : JCOEF;
  compptr : jpeg_component_info_ptr;
  buffer : JBLOCKARRAY;
  thisblockrow, lastblockrow : JBLOCKROW;
begin
  coef := my_coef_ptr (cinfo^.coef);
  last_iMCU_row := cinfo^.total_iMCU_rows - 1;

  compptr := jpeg_component_info_ptr(cinfo^.comp_info);
  for ci := 0 to pred(cinfo^.num_components) do
  begin
    { Align the virtual buffer for this component. }
    buffer := cinfo^.mem^.access_virt_barray
      (j_common_ptr(cinfo), coef^.whole_image[ci],
       coef^.iMCU_row_num * compptr^.v_samp_factor,
       JDIMENSION (compptr^.v_samp_factor), TRUE);
    { Count non-dummy DCT block rows in this iMCU row. }
    if (coef^.iMCU_row_num < last_iMCU_row) then
      block_rows := compptr^.v_samp_factor
    else
    begin
      { NB: can't use last_row_height here, since may not be set! }
      block_rows := int (compptr^.height_in_blocks mod compptr^.v_samp_factor);
      if (block_rows = 0) then
        block_rows := compptr^.v_samp_factor;
    end;
    blocks_across := compptr^.width_in_blocks;
    h_samp_factor := compptr^.h_samp_factor;
    { Count number of dummy blocks to be added at the right margin. }
    ndummy := int (blocks_across mod h_samp_factor);
    if (ndummy > 0) then
      ndummy := h_samp_factor - ndummy;
    { Perform DCT for all non-dummy blocks in this iMCU row.  Each call
      on forward_DCT processes a complete horizontal row of DCT blocks. }

    for block_row := 0 to pred(block_rows) do
    begin
      thisblockrow := buffer^[block_row];
      cinfo^.fdct^.forward_DCT (cinfo, compptr,
	                        input_buf^[ci],
                                thisblockrow,
				JDIMENSION (block_row * DCTSIZE),
				JDIMENSION (0),
                                blocks_across);
      if (ndummy > 0) then
      begin
	{ Create dummy blocks at the right edge of the image. }
	Inc(JBLOCK_PTR(thisblockrow), blocks_across); { => first dummy block }
	jzero_far({FAR}pointer(thisblockrow), ndummy * SIZEOF(JBLOCK));
	{lastDC := thisblockrow^[-1][0];}
        { work around Range Checking }
        Dec(JBLOCK_PTR(thisblockrow));
        lastDC := thisblockrow^[0][0];
        Inc(JBLOCK_PTR(thisblockrow));

	for bi := 0 to pred(ndummy) do
        begin
	  thisblockrow^[bi][0] := lastDC;
	end;
      end;
    end;
    { If at end of image, create dummy block rows as needed.
      The tricky part here is that within each MCU, we want the DC values
      of the dummy blocks to match the last real block's DC value.
      This squeezes a few more bytes out of the resulting file... }

    if (coef^.iMCU_row_num = last_iMCU_row) then
    begin
      Inc(blocks_across, ndummy);       { include lower right corner }
      MCUs_across := blocks_across div h_samp_factor;
      for block_row := block_rows to pred(compptr^.v_samp_factor) do
      begin
	thisblockrow := buffer^[block_row];
	lastblockrow := buffer^[block_row-1];
	jzero_far({FAR} pointer(thisblockrow),
		  size_t(blocks_across * SIZEOF(JBLOCK)));
	for MCUindex := 0 to pred(MCUs_across) do
        begin
	  lastDC := lastblockrow^[h_samp_factor-1][0];
	  for bi := 0 to pred(h_samp_factor) do
          begin
	    thisblockrow^[bi][0] := lastDC;
	  end;
	  Inc(JBLOCK_PTR(thisblockrow), h_samp_factor); { advance to next MCU in row }
	  Inc(JBLOCK_PTR(lastblockrow), h_samp_factor);
	end;
      end;
    end;
    Inc(compptr);
  end;
  { NB: compress_output will increment iMCU_row_num if successful.
    A suspension return will result in redoing all the work above next time.}


  { Emit data to the entropy encoder, sharing code with subsequent passes }
  compress_first_pass := compress_output(cinfo, input_buf);
end;


{ Process some data in subsequent passes of a multi-pass case.
  We process the equivalent of one fully interleaved MCU row ("iMCU" row)
  per call, ie, v_samp_factor block rows for each component in the scan.
  The data is obtained from the virtual arrays and fed to the entropy coder.
  Returns TRUE if the iMCU row is completed, FALSE if suspended.

  NB: input_buf is ignored; it is likely to be a NIL pointer. }

{METHODDEF}
function compress_output (cinfo : j_compress_ptr;
                          input_buf : JSAMPIMAGE) : boolean;
var
  coef : my_coef_ptr;
  MCU_col_num : JDIMENSION;	{ index of current MCU within row }
  blkn, ci, xindex, yindex, yoffset : int;
  start_col : JDIMENSION;
  buffer : array[0..MAX_COMPS_IN_SCAN-1] of JBLOCKARRAY;
  buffer_ptr : JBLOCKROW;
  compptr : jpeg_component_info_ptr;
begin
  coef := my_coef_ptr (cinfo^.coef);

  { Align the virtual buffers for the components used in this scan.
    NB: during first pass, this is safe only because the buffers will
    already be aligned properly, so jmemmgr.c won't need to do any I/O. }

  for ci := 0 to pred(cinfo^.comps_in_scan) do
  begin
    compptr := cinfo^.cur_comp_info[ci];
    buffer[ci] := cinfo^.mem^.access_virt_barray (
       j_common_ptr(cinfo), coef^.whole_image[compptr^.component_index],
       coef^.iMCU_row_num * compptr^.v_samp_factor,
       JDIMENSION (compptr^.v_samp_factor), FALSE);
  end;

  { Loop to process one whole iMCU row }
  for yoffset := coef^.MCU_vert_offset to pred(coef^.MCU_rows_per_iMCU_row) do
  begin
    for MCU_col_num := coef^.mcu_ctr to pred(cinfo^.MCUs_per_row) do
    begin
      { Construct list of pointers to DCT blocks belonging to this MCU }
      blkn := 0;			{ index of current DCT block within MCU }
      for ci := 0 to pred(cinfo^.comps_in_scan) do
      begin
	compptr := cinfo^.cur_comp_info[ci];
	start_col := MCU_col_num * compptr^.MCU_width;
	for yindex := 0 to pred(compptr^.MCU_height) do
        begin
	  buffer_ptr := JBLOCKROW(@ buffer[ci]^[yindex+yoffset]^[start_col]);
	  for xindex := 0 to pred(compptr^.MCU_width) do
          begin
	    coef^.MCU_buffer[blkn] := buffer_ptr;
	    Inc(blkn);
            Inc(JBLOCK_PTR(buffer_ptr));
	  end;
	end;
      end;
      { Try to write the MCU. }
      if (not cinfo^.entropy^.encode_mcu (cinfo, coef^.MCU_buffer)) then
      begin
	{ Suspension forced; update state counters and exit }
	coef^.MCU_vert_offset := yoffset;
	coef^.mcu_ctr := MCU_col_num;
	compress_output := FALSE;
        exit;
      end;
    end;
    { Completed an MCU row, but perhaps not an iMCU row }
    coef^.mcu_ctr := 0;
  end;
  { Completed the iMCU row, advance counters for next one }
  Inc(coef^.iMCU_row_num);
  start_iMCU_row(cinfo);
  compress_output := TRUE;
end;

{$endif} { FULL_COEF_BUFFER_SUPPORTED }


{ Initialize coefficient buffer controller. }

{GLOBAL}
procedure jinit_c_coef_controller (cinfo : j_compress_ptr;
                                   need_full_buffer : boolean);
var
  coef : my_coef_ptr;
var
  buffer : JBLOCKROW;
  i : int;
var
  ci : int;
  compptr : jpeg_component_info_ptr;
begin
  coef := my_coef_ptr (
    cinfo^.mem^.alloc_small (j_common_ptr(cinfo), JPOOL_IMAGE,
				SIZEOF(my_coef_controller)) );
  cinfo^.coef := jpeg_c_coef_controller_ptr(coef);
  coef^.pub.start_pass := start_pass_coef;

  { Create the coefficient buffer. }
  if (need_full_buffer) then
  begin
{$ifdef FULL_COEF_BUFFER_SUPPORTED}
    { Allocate a full-image virtual array for each component, }
    { padded to a multiple of samp_factor DCT blocks in each direction. }

    compptr := jpeg_component_info_ptr(cinfo^.comp_info);
    for ci := 0 to pred(cinfo^.num_components) do
    begin
      coef^.whole_image[ci] := cinfo^.mem^.request_virt_barray
	(j_common_ptr(cinfo), JPOOL_IMAGE, FALSE,
	 JDIMENSION (jround_up( long (compptr^.width_in_blocks),
				long (compptr^.h_samp_factor) )),
	 JDIMENSION (jround_up(long (compptr^.height_in_blocks),
				long (compptr^.v_samp_factor))),
	 JDIMENSION (compptr^.v_samp_factor));
      Inc(compptr);
    end;
{$else}
    ERREXIT(j_common_ptr(cinfo), JERR_BAD_BUFFER_MODE);
{$endif}
  end
  else
  begin
    { We only need a single-MCU buffer. }
    buffer := JBLOCKROW (
      cinfo^.mem^.alloc_large (j_common_ptr(cinfo), JPOOL_IMAGE,
				  C_MAX_BLOCKS_IN_MCU * SIZEOF(JBLOCK)) );
    for i := 0 to pred(C_MAX_BLOCKS_IN_MCU) do
    begin
      coef^.MCU_buffer[i] := JBLOCKROW(@ buffer^[i]);
    end;
    coef^.whole_image[0] := NIL; { flag for no virtual arrays }
  end;
end;

end.