# dlib C++ Library - jdpostct.c

    /*
     * jdpostct.c
     *
     * Copyright (C) 1994-1996, Thomas G. Lane.
     * This file is part of the Independent JPEG Group's software.
     * For conditions of distribution and use, see the accompanying README file.
     *
     * This file contains the decompression postprocessing controller.
     * This controller manages the upsampling, color conversion, and color
     * quantization/reduction steps; specifically, it controls the buffering
     * between upsample/color conversion and color quantization/reduction.
     *
     * If no color quantization/reduction is required, then this module has no
     * work to do, and it just hands off to the upsample/color conversion code.
     * An integrated upsample/convert/quantize process would replace this module
     * entirely.
     */

    #define JPEG_INTERNALS
    #include "jinclude.h"
    #include "jpeglib.h"

    /* Private buffer controller object */

    typedef struct {
      struct jpeg_d_post_controller pub; /* public fields */

      /* Color quantization source buffer: this holds output data from
       * the upsample/color conversion step to be passed to the quantizer.
       * For two-pass color quantization, we need a full-image buffer;
       * for one-pass operation, a strip buffer is sufficient.
       */
      jvirt_sarray_ptr whole_image;	/* virtual array, or NULL if one-pass */
      JSAMPARRAY buffer;		/* strip buffer, or current strip of virtual */
      JDIMENSION strip_height;	/* buffer size in rows */
      /* for two-pass mode only: */
      JDIMENSION starting_row;	/* row # of first row in current strip */
      JDIMENSION next_row;		/* index of next row to fill/empty in strip */
    } my_post_controller;

    typedef my_post_controller * my_post_ptr;

    /* Forward declarations */
    METHODDEF(void) post_process_1pass
    	JPP((j_decompress_ptr cinfo,
    	     JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    	     JDIMENSION in_row_groups_avail,
    	     JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    	     JDIMENSION out_rows_avail));
    #ifdef QUANT_2PASS_SUPPORTED
    METHODDEF(void) post_process_prepass
    	JPP((j_decompress_ptr cinfo,
    	     JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    	     JDIMENSION in_row_groups_avail,
    	     JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    	     JDIMENSION out_rows_avail));
    METHODDEF(void) post_process_2pass
    	JPP((j_decompress_ptr cinfo,
    	     JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    	     JDIMENSION in_row_groups_avail,
    	     JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    	     JDIMENSION out_rows_avail));
    #endif

    /*
     * Initialize for a processing pass.
     */

    METHODDEF(void)
    start_pass_dpost (j_decompress_ptr cinfo, J_BUF_MODE pass_mode)
    {
      my_post_ptr post = (my_post_ptr) cinfo->post;

      switch (pass_mode) {
      case JBUF_PASS_THRU:
        if (cinfo->quantize_colors) {
          /* Single-pass processing with color quantization. */
          post->pub.post_process_data = post_process_1pass;
          /* We could be doing buffered-image output before starting a 2-pass
           * color quantization; in that case, jinit_d_post_controller did not
           * allocate a strip buffer.  Use the virtual-array buffer as workspace.
           */
          if (post->buffer == NULL) {
    	post->buffer = (*cinfo->mem->access_virt_sarray)
    	  ((j_common_ptr) cinfo, post->whole_image,
    	   (JDIMENSION) 0, post->strip_height, TRUE);
          }
        } else {
          /* For single-pass processing without color quantization,
           * I have no work to do; just call the upsampler directly.
           */
          post->pub.post_process_data = cinfo->upsample->upsample;
        }
        break;
    #ifdef QUANT_2PASS_SUPPORTED
      case JBUF_SAVE_AND_PASS:
        /* First pass of 2-pass quantization */
        if (post->whole_image == NULL)
          ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
        post->pub.post_process_data = post_process_prepass;
        break;
      case JBUF_CRANK_DEST:
        /* Second pass of 2-pass quantization */
        if (post->whole_image == NULL)
          ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
        post->pub.post_process_data = post_process_2pass;
        break;
    #endif /* QUANT_2PASS_SUPPORTED */
      default:
        ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
        break;
      }
      post->starting_row = post->next_row = 0;
    }

    /*
     * Process some data in the one-pass (strip buffer) case.
     * This is used for color precision reduction as well as one-pass quantization.
     */

    METHODDEF(void)
    post_process_1pass (j_decompress_ptr cinfo,
    		    JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    		    JDIMENSION in_row_groups_avail,
    		    JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    		    JDIMENSION out_rows_avail)
    {
      my_post_ptr post = (my_post_ptr) cinfo->post;
      JDIMENSION num_rows, max_rows;

      /* Fill the buffer, but not more than what we can dump out in one go. */
      /* Note we rely on the upsampler to detect bottom of image. */
      max_rows = out_rows_avail - *out_row_ctr;
      if (max_rows > post->strip_height)
        max_rows = post->strip_height;
      num_rows = 0;
      (*cinfo->upsample->upsample) (cinfo,
    		input_buf, in_row_group_ctr, in_row_groups_avail,
    		post->buffer, &num_rows, max_rows);
      /* Quantize and emit data. */
      (*cinfo->cquantize->color_quantize) (cinfo,
    		post->buffer, output_buf + *out_row_ctr, (int) num_rows);
      *out_row_ctr += num_rows;
    }

    #ifdef QUANT_2PASS_SUPPORTED

    /*
     * Process some data in the first pass of 2-pass quantization.
     */

    METHODDEF(void)
    post_process_prepass (j_decompress_ptr cinfo,
    		      JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    		      JDIMENSION in_row_groups_avail,
    		      JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    		      JDIMENSION out_rows_avail)
    {
      my_post_ptr post = (my_post_ptr) cinfo->post;
      JDIMENSION old_next_row, num_rows;

      /* Reposition virtual buffer if at start of strip. */
      if (post->next_row == 0) {
        post->buffer = (*cinfo->mem->access_virt_sarray)
    	((j_common_ptr) cinfo, post->whole_image,
    	 post->starting_row, post->strip_height, TRUE);
      }

      /* Upsample some data (up to a strip height's worth). */
      old_next_row = post->next_row;
      (*cinfo->upsample->upsample) (cinfo,
    		input_buf, in_row_group_ctr, in_row_groups_avail,
    		post->buffer, &post->next_row, post->strip_height);

      /* Allow quantizer to scan new data.  No data is emitted, */
      /* but we advance out_row_ctr so outer loop can tell when we're done. */
      if (post->next_row > old_next_row) {
        num_rows = post->next_row - old_next_row;
        (*cinfo->cquantize->color_quantize) (cinfo, post->buffer + old_next_row,
    					 (JSAMPARRAY) NULL, (int) num_rows);
        *out_row_ctr += num_rows;
      }

      /* Advance if we filled the strip. */
      if (post->next_row >= post->strip_height) {
        post->starting_row += post->strip_height;
        post->next_row = 0;
      }
    }

    /*
     * Process some data in the second pass of 2-pass quantization.
     */

    METHODDEF(void)
    post_process_2pass (j_decompress_ptr cinfo,
    		    JSAMPIMAGE input_buf, JDIMENSION *in_row_group_ctr,
    		    JDIMENSION in_row_groups_avail,
    		    JSAMPARRAY output_buf, JDIMENSION *out_row_ctr,
    		    JDIMENSION out_rows_avail)
    {
      my_post_ptr post = (my_post_ptr) cinfo->post;
      JDIMENSION num_rows, max_rows;

      /* Reposition virtual buffer if at start of strip. */
      if (post->next_row == 0) {
        post->buffer = (*cinfo->mem->access_virt_sarray)
    	((j_common_ptr) cinfo, post->whole_image,
    	 post->starting_row, post->strip_height, FALSE);
      }

      /* Determine number of rows to emit. */
      num_rows = post->strip_height - post->next_row; /* available in strip */
      max_rows = out_rows_avail - *out_row_ctr; /* available in output area */
      if (num_rows > max_rows)
        num_rows = max_rows;
      /* We have to check bottom of image here, can't depend on upsampler. */
      max_rows = cinfo->output_height - post->starting_row;
      if (num_rows > max_rows)
        num_rows = max_rows;

      /* Quantize and emit data. */
      (*cinfo->cquantize->color_quantize) (cinfo,
    		post->buffer + post->next_row, output_buf + *out_row_ctr,
    		(int) num_rows);
      *out_row_ctr += num_rows;

      /* Advance if we filled the strip. */
      post->next_row += num_rows;
      if (post->next_row >= post->strip_height) {
        post->starting_row += post->strip_height;
        post->next_row = 0;
      }
    }

    #endif /* QUANT_2PASS_SUPPORTED */

    /*
     * Initialize postprocessing controller.
     */

    GLOBAL(void)
    jinit_d_post_controller (j_decompress_ptr cinfo, boolean need_full_buffer)
    {
      my_post_ptr post;

      post = (my_post_ptr)
        (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
    				SIZEOF(my_post_controller));
      cinfo->post = (struct jpeg_d_post_controller *) post;
      post->pub.start_pass = start_pass_dpost;
      post->whole_image = NULL;	/* flag for no virtual arrays */
      post->buffer = NULL;		/* flag for no strip buffer */

      /* Create the quantization buffer, if needed */
      if (cinfo->quantize_colors) {
        /* The buffer strip height is max_v_samp_factor, which is typically
         * an efficient number of rows for upsampling to return.
         * (In the presence of output rescaling, we might want to be smarter?)
         */
        post->strip_height = (JDIMENSION) cinfo->max_v_samp_factor;
        if (need_full_buffer) {
          /* Two-pass color quantization: need full-image storage. */
          /* We round up the number of rows to a multiple of the strip height. */
    #ifdef QUANT_2PASS_SUPPORTED
          post->whole_image = (*cinfo->mem->request_virt_sarray)
    	((j_common_ptr) cinfo, JPOOL_IMAGE, FALSE,
    	 cinfo->output_width * cinfo->out_color_components,
    	 (JDIMENSION) jround_up((long) cinfo->output_height,
    				(long) post->strip_height),
    	 post->strip_height);
    #else
          ERREXIT(cinfo, JERR_BAD_BUFFER_MODE);
    #endif /* QUANT_2PASS_SUPPORTED */
        } else {
          /* One-pass color quantization: just make a strip buffer. */
          post->buffer = (*cinfo->mem->alloc_sarray)
    	((j_common_ptr) cinfo, JPOOL_IMAGE,
    	 cinfo->output_width * cinfo->out_color_components,
    	 post->strip_height);
        }
      }
    }