path: root/gs/base/gxblend.c

/* Copyright (C) 2001-2006 Artifex Software, Inc.
   All Rights Reserved.

   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied, modified
   or distributed except as expressly authorized under the terms of that
   license.  Refer to licensing information at http://www.artifex.com/
   or contact Artifex Software, Inc.,  7 Mt. Lassen Drive - Suite A-134,
   San Rafael, CA  94903, U.S.A., +1(415)492-9861, for further information.
*/
/* $Id$ */
/* PDF 1.4 blending functions */

#include "memory_.h"
#include "gx.h"
#include "gstparam.h"
#include "gxblend.h"
#include "gxcolor2.h"
#include "gsicc_cache.h"
#include "gsicc_manage.h"

typedef int art_s32;

#if RAW_DUMP
extern unsigned int global_index;
extern unsigned int clist_band_count;
#endif

/* This function is used for mapping the SMask source to a
   monochrome luminosity value which basically is the alpha value
   Note, that separation colors are not allowed here.  Everything
   must be in CMYK, RGB or monochrome.  */

/* Note, data is planar */

void
smask_luminosity_mapping(int num_rows, int num_cols, int n_chan, int row_stride,
                         int plane_stride, byte *src, const byte *dst, bool isadditive,
                         gs_transparency_mask_subtype_t SMask_SubType)
{
    int x,y;
    int mask_alpha_offset,mask_C_offset,mask_M_offset,mask_Y_offset,mask_K_offset;
    int mask_R_offset,mask_G_offset,mask_B_offset;
    byte *dstptr;

#if RAW_DUMP
    dump_raw_buffer(num_rows, row_stride, n_chan,
                plane_stride, row_stride,
                "Raw_Mask", src);

    global_index++;
#endif
    dstptr = dst;
    /* If subtype is Luminosity then we should just grab the Y channel */
    if ( SMask_SubType == TRANSPARENCY_MASK_Luminosity ){
        memcpy(dst, &(src[plane_stride]), plane_stride);
        return;
    }
    /* If we are alpha type, then just grab that */
    /* We need to optimize this so that we are only drawing alpha in the rect fills */
    if ( SMask_SubType == TRANSPARENCY_MASK_Alpha ){
        mask_alpha_offset = (n_chan - 1) * plane_stride;
        memcpy(dst, &(src[mask_alpha_offset]), plane_stride);
        return;
    }
    /* To avoid the if statement inside this loop,
    decide on additive or subractive now */
    if (isadditive || n_chan == 2) {
        /* Now we need to split Gray from RGB */
        if( n_chan == 2 ) {
            /* Gray Scale case */
           mask_alpha_offset = (n_chan - 1) * plane_stride;
           mask_R_offset = 0;
            for ( y = 0; y < num_rows; y++ ) {
                for ( x = 0; x < num_cols; x++ ){
                    /* With the current design this will indicate if
                    we ever did a fill at this pixel. if not then move on.
                    This could have some serious optimization */
                    if (src[x + mask_alpha_offset] != 0x00) {
                        dstptr[x] = src[x + mask_R_offset];
                    }
                }
               dstptr += row_stride;
               mask_alpha_offset += row_stride;
               mask_R_offset += row_stride;
            }
        } else {
            /* RGB case */
           mask_R_offset = 0;
           mask_G_offset = plane_stride;
           mask_B_offset = 2 * plane_stride;
           mask_alpha_offset = (n_chan - 1) * plane_stride;
            for ( y = 0; y < num_rows; y++ ) {
               for ( x = 0; x < num_cols; x++ ){
                    /* With the current design this will indicate if
                    we ever did a fill at this pixel. if not then move on */
                    if (src[x + mask_alpha_offset] != 0x00) {
                        /* Get luminosity of Device RGB value */
                        float temp;
                        temp = ( 0.30 * src[x + mask_R_offset] +
                            0.59 * src[x + mask_G_offset] +
                            0.11 * src[x + mask_B_offset] );
                        temp = temp * (1.0 / 255.0 );  /* May need to be optimized */
                        dstptr[x] = float_color_to_byte_color(temp);
                    }
                }
               dstptr += row_stride;
               mask_alpha_offset += row_stride;
               mask_R_offset += row_stride;
               mask_G_offset += row_stride;
               mask_B_offset += row_stride;
            }
        }
    } else {
       /* CMYK case */
       mask_alpha_offset = (n_chan - 1) * plane_stride;
       mask_C_offset = 0;
       mask_M_offset = plane_stride;
       mask_Y_offset = 2 * plane_stride;
       mask_K_offset = 3 * plane_stride;
       for ( y = 0; y < num_rows; y++ ){
            for ( x = 0; x < num_cols; x++ ){
                /* With the current design this will indicate if
                we ever did a fill at this pixel. if not then move on */
                if (src[x + mask_alpha_offset] != 0x00){
                  /* PDF spec says to use Y = 0.30 (1 - C)(1 - K) +
                  0.59 (1 - M)(1 - K) + 0.11 (1 - Y)(1 - K) */
                    /* For device CMYK */
                    float temp;
                    temp = ( 0.30 * ( 0xff - src[x + mask_C_offset]) +
                        0.59 * ( 0xff - src[x + mask_M_offset]) +
                        0.11 * ( 0xff - src[x + mask_Y_offset]) ) *
                        ( 0xff - src[x + mask_K_offset]);
                    temp = temp * (1.0 / 65025.0 );  /* May need to be optimized */
                    dstptr[x] = float_color_to_byte_color(temp);
                }
            }
           dstptr += row_stride;
           mask_alpha_offset += row_stride;
           mask_C_offset += row_stride;
           mask_M_offset += row_stride;
           mask_Y_offset += row_stride;
           mask_K_offset += row_stride;
        }
    }
}

/* soft mask gray buffer should be blended with its transparency planar data
   during the pop for a luminosity case if we have a soft mask within a soft
   mask.  This situation is detected in the code so that we only do this
   blending in those rare situations */
void
smask_blend(byte *src, int width, int height, int rowstride,
                      int planestride)
{
    int x, y;
    int position;
    byte comp, a;
    int tmp;
    byte bg = 0;

    for (y = 0; y < height; y++) {
        position = y * rowstride;
        for (x = 0; x < width; x++) {
            a = src[position + planestride];
            if ((a + 1) & 0xfe) {
                a ^= 0xff;
                comp  = src[position];
                tmp = ((bg - comp) * a) + 0x80;
                comp += (tmp + (tmp >> 8)) >> 8;
                src[position] = comp;
            } else if (a == 0) {
                src[position] = 0;
            }
            position+=1;
        }
    }
}

void smask_copy(int num_rows, int num_cols, int row_stride,
                        byte *src, const byte *dst)
{
    int y;
    byte *dstptr,*srcptr;

    dstptr = dst;
    srcptr = src;
    for ( y = 0; y < num_rows; y++ ) {
        memcpy(dstptr,srcptr,num_cols);
        dstptr += row_stride;
        srcptr += row_stride;
    }
}

void smask_icc(gx_device *dev, int num_rows, int num_cols, int n_chan, 
               int row_stride, int plane_stride, byte *src, const byte *dst,
               gsicc_link_t *icclink)
{
    gsicc_bufferdesc_t input_buff_desc;
    gsicc_bufferdesc_t output_buff_desc;

#if RAW_DUMP
    dump_raw_buffer(num_rows, row_stride, n_chan,
                plane_stride, row_stride,
                "Raw_Mask_ICC", src);
    global_index++;
#endif
/* Set up the buffer descriptors. Note that pdf14 always has
   the alpha channels at the back end (last planes).
   We will just handle that here and let the CMM know
   nothing about it */

    gsicc_init_buffer(&input_buff_desc, n_chan-1, 1,
                  false, false, true, plane_stride, row_stride,
                  num_rows, num_cols);
    gsicc_init_buffer(&output_buff_desc, 1, 1,
                  false, false, true, plane_stride,
                  row_stride, num_rows, num_cols);
    /* Transform the data */
    (icclink->procs.map_buffer)(dev, icclink, &input_buff_desc, &output_buff_desc, 
                                (void*) src, (void*) dst);
}

void
art_blend_luminosity_rgb_8(int n_chan, byte *dst, const byte *backdrop,
                           const byte *src)
{
    int rb = backdrop[0], gb = backdrop[1], bb = backdrop[2];
    int rs = src[0], gs = src[1], bs = src[2];
    int delta_y;
    int r, g, b;

    /*
     * From section 7.4 of the PDF 1.5 specification, for RGB, the luminosity
     * is:  Y = 0.30 R + 0.59 G + 0.11 B)
     */
    delta_y = ((rs - rb) * 77 + (gs - gb) * 151 + (bs - bb) * 28 + 0x80) >> 8;
    r = rb + delta_y;
    g = gb + delta_y;
    b = bb + delta_y;
    if ((r | g | b) & 0x100) {
        int y;
        int scale;

        y = (rs * 77 + gs * 151 + bs * 28 + 0x80) >> 8;
        if (delta_y > 0) {
            int max;

            max = r > g ? r : g;
            max = b > max ? b : max;
            scale = ((255 - y) << 16) / (max - y);
        } else {
            int min;

            min = r < g ? r : g;
            min = b < min ? b : min;
            scale = (y << 16) / (y - min);
        }
        r = y + (((r - y) * scale + 0x8000) >> 16);
        g = y + (((g - y) * scale + 0x8000) >> 16);
        b = y + (((b - y) * scale + 0x8000) >> 16);
    }
    dst[0] = r;
    dst[1] = g;
    dst[2] = b;
}

void
art_blend_luminosity_custom_8(int n_chan, byte *dst, const byte *backdrop,
                                const byte *src)
{
    int delta_y = 0, test = 0;
    int r[ART_MAX_CHAN];
    int i;

    /*
     * Since we do not know the details of the blending color space, we are
     * simply using the average as the luminosity.  First we need the
     * delta luminosity values.
     */
    for (i = 0; i < n_chan; i++)
        delta_y += src[i] - backdrop[i];
    delta_y = (delta_y + n_chan / 2) / n_chan;
    for (i = 0; i < n_chan; i++) {
        r[i] = backdrop[i] + delta_y;
        test |= r[i];
    }

    if (test & 0x100) {
        int y;
        int scale;

        /* Assume that the luminosity is simply the average of the backdrop. */
        y = src[0];
        for (i = 1; i < n_chan; i++)
            y += src[i];
        y = (y + n_chan / 2) / n_chan;

        if (delta_y > 0) {
            int max;

            max = r[0];
            for (i = 1; i < n_chan; i++)
                max = max(max, r[i]);
            scale = ((255 - y) << 16) / (max - y);
        } else {
            int min;

            min = r[0];
            for (i = 1; i < n_chan; i++)
                min = min(min, r[i]);
            scale = (y << 16) / (y - min);
        }
        for (i = 0; i < n_chan; i++)
            r[i] = y + (((r[i] - y) * scale + 0x8000) >> 16);
    }
    for (i = 0; i < n_chan; i++)
        dst[i] = r[i];
}

/*
 * The PDF 1.4 spec. does not give the details of the math involved in the
 * luminosity blending.  All we are given is:
 *   "Creates a color with the luminance of the source color and the hue
 *    and saturation of the backdrop color. This produces an inverse
 *    effect to that of the Color mode."
 * From section 7.4 of the PDF 1.5 specification, which is duscussing soft
 * masks, we are given that, for CMYK, the luminosity is:
 *    Y = 0.30 (1 - C)(1 - K) + 0.59 (1 - M)(1 - K) + 0.11 (1 - Y)(1 - K)
 * However the results of this equation do not match the results seen from
 * Illustrator CS.  Very different results are obtained if process gray
 * (.5, .5, .5, 0) is blended over pure cyan, versus gray (0, 0, 0, .5) over
 * the same pure cyan.  The first gives a medium cyan while the later gives a
 * medium gray.  This routine seems to match Illustrator's actions.  C, M and Y
 * are treated similar to RGB in the previous routine and black is treated
 * separately.
 *
 * Our component values have already been complemented, i.e. (1 - X).
 */
void
art_blend_luminosity_cmyk_8(int n_chan, byte *dst, const byte *backdrop,
                           const byte *src)
{
    int i;

    /* Treat CMY the same as RGB. */
    art_blend_luminosity_rgb_8(3, dst, backdrop, src);
    for (i = 3; i < n_chan; i++)
        dst[i] = src[i];
}

void
art_blend_saturation_rgb_8(int n_chan, byte *dst, const byte *backdrop,
                           const byte *src)
{
    int rb = backdrop[0], gb = backdrop[1], bb = backdrop[2];
    int rs = src[0], gs = src[1], bs = src[2];
    int minb, maxb;
    int mins, maxs;
    int y;
    int scale;
    int r, g, b;

    minb = rb < gb ? rb : gb;
    minb = minb < bb ? minb : bb;
    maxb = rb > gb ? rb : gb;
    maxb = maxb > bb ? maxb : bb;
    if (minb == maxb) {
        /* backdrop has zero saturation, avoid divide by 0 */
        dst[0] = gb;
        dst[1] = gb;
        dst[2] = gb;
        return;
    }

    mins = rs < gs ? rs : gs;
    mins = mins < bs ? mins : bs;
    maxs = rs > gs ? rs : gs;
    maxs = maxs > bs ? maxs : bs;

    scale = ((maxs - mins) << 16) / (maxb - minb);
    y = (rb * 77 + gb * 151 + bb * 28 + 0x80) >> 8;
    r = y + ((((rb - y) * scale) + 0x8000) >> 16);
    g = y + ((((gb - y) * scale) + 0x8000) >> 16);
    b = y + ((((bb - y) * scale) + 0x8000) >> 16);

    if ((r | g | b) & 0x100) {
        int scalemin, scalemax;
        int min, max;

        min = r < g ? r : g;
        min = min < b ? min : b;
        max = r > g ? r : g;
        max = max > b ? max : b;

        if (min < 0)
            scalemin = (y << 16) / (y - min);
        else
            scalemin = 0x10000;

        if (max > 255)
            scalemax = ((255 - y) << 16) / (max - y);
        else
            scalemax = 0x10000;

        scale = scalemin < scalemax ? scalemin : scalemax;
        r = y + (((r - y) * scale + 0x8000) >> 16);
        g = y + (((g - y) * scale + 0x8000) >> 16);
        b = y + (((b - y) * scale + 0x8000) >> 16);
    }

    dst[0] = r;
    dst[1] = g;
    dst[2] = b;
}

void
art_blend_saturation_custom_8(int n_chan, byte *dst, const byte *backdrop,
                           const byte *src)
{
    int minb, maxb;
    int mins, maxs;
    int y;
    int scale;
    int r[ART_MAX_CHAN];
    int test = 0;
    int temp, i;

    /* Determine min and max of the backdrop */
    minb = maxb = temp = backdrop[0];
    for (i = 1; i < n_chan; i++) {
        temp = backdrop[i];
        minb = min(minb, temp);
        maxb = max(maxb, temp);
    }

    if (minb == maxb) {
        /* backdrop has zero saturation, avoid divide by 0 */
        for (i = 0; i < n_chan; i++)
            dst[i] = temp;
        return;
    }

    /* Determine min and max of the source */
    mins = maxs = src[0];
    for (i = 1; i < n_chan; i++) {
        temp = src[i];
        mins = min(minb, temp);
        maxs = max(minb, temp);
    }

    scale = ((maxs - mins) << 16) / (maxb - minb);

    /* Assume that the saturation is simply the average of the backdrop. */
    y = backdrop[0];
    for (i = 1; i < n_chan; i++)
        y += backdrop[i];
    y = (y + n_chan / 2) / n_chan;

    /* Calculate the saturated values */
    for (i = 0; i < n_chan; i++) {
        r[i] = y + ((((backdrop[i] - y) * scale) + 0x8000) >> 16);
        test |= r[i];
    }

    if (test & 0x100) {
        int scalemin, scalemax;
        int min, max;

        /* Determine min and max of our blended values */
        min = max = temp = r[0];
        for (i = 1; i < n_chan; i++) {
            temp = src[i];
            min = min(min, temp);
            max = max(max, temp);
        }

        if (min < 0)
            scalemin = (y << 16) / (y - min);
        else
            scalemin = 0x10000;

        if (max > 255)
            scalemax = ((255 - y) << 16) / (max - y);
        else
            scalemax = 0x10000;

        scale = scalemin < scalemax ? scalemin : scalemax;
        for (i = 0; i < n_chan; i++)
            r[i] = y + (((r[i] - y) * scale + 0x8000) >> 16);
    }

    for (i = 0; i < n_chan; i++)
        dst[i] = r[i];
}

/* Our component values have already been complemented, i.e. (1 - X). */
void
art_blend_saturation_cmyk_8(int n_chan, byte *dst, const byte *backdrop,
                           const byte *src)
{
    int i;

    /* Treat CMY the same as RGB */
    art_blend_saturation_rgb_8(3, dst, backdrop, src);
    for (i = 3; i < n_chan; i++)
        dst[i] = backdrop[i];
}

/* This array consists of floor ((x - x * x / 255.0) * 65536 / 255 +
   0.5) for x in [0..255]. */
const unsigned int art_blend_sq_diff_8[256] = {
    0, 256, 510, 762, 1012, 1260, 1506, 1750, 1992, 2231, 2469, 2705,
    2939, 3171, 3401, 3628, 3854, 4078, 4300, 4519, 4737, 4953, 5166,
    5378, 5588, 5795, 6001, 6204, 6406, 6606, 6803, 6999, 7192, 7384,
    7573, 7761, 7946, 8129, 8311, 8490, 8668, 8843, 9016, 9188, 9357,
    9524, 9690, 9853, 10014, 10173, 10331, 10486, 10639, 10790, 10939,
    11086, 11232, 11375, 11516, 11655, 11792, 11927, 12060, 12191, 12320,
    12447, 12572, 12695, 12816, 12935, 13052, 13167, 13280, 13390, 13499,
    13606, 13711, 13814, 13914, 14013, 14110, 14205, 14297, 14388, 14477,
    14564, 14648, 14731, 14811, 14890, 14967, 15041, 15114, 15184, 15253,
    15319, 15384, 15446, 15507, 15565, 15622, 15676, 15729, 15779, 15827,
    15874, 15918, 15960, 16001, 16039, 16075, 16110, 16142, 16172, 16200,
    16227, 16251, 16273, 16293, 16311, 16327, 16341, 16354, 16364, 16372,
    16378, 16382, 16384, 16384, 16382, 16378, 16372, 16364, 16354, 16341,
    16327, 16311, 16293, 16273, 16251, 16227, 16200, 16172, 16142, 16110,
    16075, 16039, 16001, 15960, 15918, 15874, 15827, 15779, 15729, 15676,
    15622, 15565, 15507, 15446, 15384, 15319, 15253, 15184, 15114, 15041,
    14967, 14890, 14811, 14731, 14648, 14564, 14477, 14388, 14297, 14205,
    14110, 14013, 13914, 13814, 13711, 13606, 13499, 13390, 13280, 13167,
    13052, 12935, 12816, 12695, 12572, 12447, 12320, 12191, 12060, 11927,
    11792, 11655, 11516, 11375, 11232, 11086, 10939, 10790, 10639, 10486,
    10331, 10173, 10014, 9853, 9690, 9524, 9357, 9188, 9016, 8843, 8668,
    8490, 8311, 8129, 7946, 7761, 7573, 7384, 7192, 6999, 6803, 6606,
    6406, 6204, 6001, 5795, 5588, 5378, 5166, 4953, 4737, 4519, 4300,
    4078, 3854, 3628, 3401, 3171, 2939, 2705, 2469, 2231, 1992, 1750,
    1506, 1260, 1012, 762, 510, 256, 0
};

/* This array consists of SoftLight (x, 255) - x, for values of x in
   the range [0..255] (normalized to [0..255 range). The original
   values were directly sampled from Adobe Illustrator 9. I've fit a
   quadratic spline to the SoftLight (x, 1) function as follows
   (normalized to [0..1] range):

   Anchor point (0, 0)
   Control point (0.0755, 0.302)
   Anchor point (0.18, 0.4245)
   Control point (0.4263, 0.7131)
   Anchor point (1, 1)

   I don't believe this is _exactly_ the function that Adobe uses,
   but it really should be close enough for all practical purposes.  */
const byte art_blend_soft_light_8[256] = {
    0, 3, 6, 9, 11, 14, 16, 19, 21, 23, 26, 28, 30, 32, 33, 35, 37, 39,
    40, 42, 43, 45, 46, 47, 48, 49, 51, 52, 53, 53, 54, 55, 56, 57, 57,
    58, 58, 59, 60, 60, 60, 61, 61, 62, 62, 62, 62, 63, 63, 63, 63, 63,
    63, 63, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 63, 62, 62, 62,
    62, 62, 62, 62, 61, 61, 61, 61, 61, 61, 60, 60, 60, 60, 60, 59, 59,
    59, 59, 59, 58, 58, 58, 58, 57, 57, 57, 57, 56, 56, 56, 56, 55, 55,
    55, 55, 54, 54, 54, 54, 53, 53, 53, 52, 52, 52, 51, 51, 51, 51, 50,
    50, 50, 49, 49, 49, 48, 48, 48, 47, 47, 47, 46, 46, 46, 45, 45, 45,
    44, 44, 43, 43, 43, 42, 42, 42, 41, 41, 40, 40, 40, 39, 39, 39, 38,
    38, 37, 37, 37, 36, 36, 35, 35, 35, 34, 34, 33, 33, 33, 32, 32, 31,
    31, 31, 30, 30, 29, 29, 28, 28, 28, 27, 27, 26, 26, 25, 25, 25, 24,
    24, 23, 23, 22, 22, 21, 21, 21, 20, 20, 19, 19, 18, 18, 17, 17, 16,
    16, 15, 15, 15, 14, 14, 13, 13, 12, 12, 11, 11, 10, 10, 9, 9, 8, 8, 7,
    7, 6, 6, 5, 5, 4, 4, 3, 3, 2, 2, 1, 1, 0, 0
};

void
art_blend_pixel_8(byte *dst, const byte *backdrop,
                const byte *src, int n_chan, gs_blend_mode_t blend_mode,
                const pdf14_nonseparable_blending_procs_t * pblend_procs)
{
    int i;
    byte b, s;
    bits32 t;

    switch (blend_mode) {
        case BLEND_MODE_Normal:
        case BLEND_MODE_Compatible:	/* todo */
            memcpy(dst, src, n_chan);
            break;
        case BLEND_MODE_Multiply:
            for (i = 0; i < n_chan; i++) {
                t = ((bits32) backdrop[i]) * ((bits32) src[i]);
                t += 0x80;
                t += (t >> 8);
                dst[i] = t >> 8;
            }
            break;
        case BLEND_MODE_Screen:
            for (i = 0; i < n_chan; i++) {
                t =
                    ((bits32) (0xff - backdrop[i])) *
                    ((bits32) (0xff - src[i]));
                t += 0x80;
                t += (t >> 8);
                dst[i] = 0xff - (t >> 8);
            }
            break;
        case BLEND_MODE_Overlay:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                if (b < 0x80)
                    t = 2 * ((bits32) b) * ((bits32) s);
                else
                    t = 0xfe01 -
                        2 * ((bits32) (0xff - b)) * ((bits32) (0xff - s));
                t += 0x80;
                t += (t >> 8);
                dst[i] = t >> 8;
            }
            break;
        case BLEND_MODE_SoftLight:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                if (s < 0x80) {
                    t = (0xff - (s << 1)) * art_blend_sq_diff_8[b];
                    t += 0x8000;
                    dst[i] = b - (t >> 16);
                } else {
                    t =
                        ((s << 1) -
                         0xff) * ((bits32) (art_blend_soft_light_8[b]));
                    t += 0x80;
                    t += (t >> 8);
                    dst[i] = b + (t >> 8);
                }
            }
            break;
        case BLEND_MODE_HardLight:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                if (s < 0x80)
                    t = 2 * ((bits32) b) * ((bits32) s);
                else
                    t = 0xfe01 -
                        2 * ((bits32) (0xff - b)) * ((bits32) (0xff - s));
                t += 0x80;
                t += (t >> 8);
                dst[i] = t >> 8;
            }
            break;
        case BLEND_MODE_ColorDodge:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = 0xff - src[i];
                if (b == 0)
                    dst[i] = 0;
                else if (b >= s)
                    dst[i] = 0xff;
                else
                    dst[i] = (0x1fe * b + s) / (s << 1);
            }
            break;
        case BLEND_MODE_ColorBurn:
            for (i = 0; i < n_chan; i++) {
                b = 0xff - backdrop[i];
                s = src[i];
                if (b == 0)
                    dst[i] = 0xff;
                else if (b >= s)
                    dst[i] = 0;
                else
                    dst[i] = 0xff - (0x1fe * b + s) / (s << 1);
            }
            break;
        case BLEND_MODE_Darken:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                dst[i] = b < s ? b : s;
            }
            break;
        case BLEND_MODE_Lighten:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                dst[i] = b > s ? b : s;
            }
            break;
        case BLEND_MODE_Difference:
            for (i = 0; i < n_chan; i++) {
                art_s32 tmp;

                tmp = ((art_s32) backdrop[i]) - ((art_s32) src[i]);
                dst[i] = tmp < 0 ? -tmp : tmp;
            }
            break;
        case BLEND_MODE_Exclusion:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                t = ((bits32) (0xff - b)) * ((bits32) s) +
                    ((bits32) b) * ((bits32) (0xff - s));
                t += 0x80;
                t += (t >> 8);
                dst[i] = t >> 8;
            }
            break;
        case BLEND_MODE_Luminosity:
            pblend_procs->blend_luminosity(n_chan, dst, backdrop, src);
            break;
        case BLEND_MODE_Color:
            pblend_procs->blend_luminosity(n_chan, dst, src, backdrop);
            break;
        case BLEND_MODE_Saturation:
            pblend_procs->blend_saturation(n_chan, dst, backdrop, src);
            break;
        case BLEND_MODE_Hue:
            {
                byte tmp[4];

                pblend_procs->blend_luminosity(n_chan, tmp, src, backdrop);
                pblend_procs->blend_saturation(n_chan, dst, tmp, backdrop);
            }
            break;
        default:
            dlprintf1("art_blend_pixel_8: blend mode %d not implemented\n",
                      blend_mode);
            memcpy(dst, src, n_chan);
            break;
    }
}

void
art_blend_pixel(ArtPixMaxDepth* dst, const ArtPixMaxDepth *backdrop,
                const ArtPixMaxDepth* src, int n_chan,
                gs_blend_mode_t blend_mode)
{
    int i;
    ArtPixMaxDepth b, s;
    bits32 t;

    switch (blend_mode) {
        case BLEND_MODE_Normal:
        case BLEND_MODE_Compatible:	/* todo */
            memcpy(dst, src, n_chan * sizeof(ArtPixMaxDepth));
            break;
        case BLEND_MODE_Multiply:
            for (i = 0; i < n_chan; i++) {
                t = ((bits32) backdrop[i]) * ((bits32) src[i]);
                t += 0x8000;
                t += (t >> 16);
                dst[i] = t >> 16;
            }
            break;
        case BLEND_MODE_Screen:
            for (i = 0; i < n_chan; i++) {
                t =
                    ((bits32) (0xffff - backdrop[i])) *
                    ((bits32) (0xffff - src[i]));
                t += 0x8000;
                t += (t >> 16);
                dst[i] = 0xffff - (t >> 16);
            }
            break;
        case BLEND_MODE_Overlay:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                if (b < 0x8000)
                    t = 2 * ((bits32) b) * ((bits32) s);
                else
                    t = 0xfffe0001u -
                        2 * ((bits32) (0xffff - b)) * ((bits32) (0xffff - s));
                t += 0x8000;
                t += (t >> 16);
                dst[i] = t >> 16;
            }
            break;
        case BLEND_MODE_HardLight:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                if (s < 0x8000)
                    t = 2 * ((bits32) b) * ((bits32) s);
                else
                    t = 0xfffe0001u -
                        2 * ((bits32) (0xffff - b)) * ((bits32) (0xffff - s));
                t += 0x8000;
                t += (t >> 16);
                dst[i] = t >> 16;
            }
            break;
        case BLEND_MODE_ColorDodge:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                if (b == 0)
                    dst[i] = 0;
                else if (s >= b)
                    dst[i] = 0xffff;
                else
                    dst[i] = (0x1fffe * s + b) / (b << 1);
            }
            break;
        case BLEND_MODE_ColorBurn:
            for (i = 0; i < n_chan; i++) {
                b = 0xffff - backdrop[i];
                s = src[i];
                if (b == 0)
                    dst[i] = 0xffff;
                else if (b >= s)
                    dst[i] = 0;
                else
                    dst[i] = 0xffff - (0x1fffe * b + s) / (s << 1);
            }
            break;
        case BLEND_MODE_Darken:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                dst[i] = b < s ? b : s;
            }
            break;
        case BLEND_MODE_Lighten:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                dst[i] = b > s ? b : s;
            }
            break;
        case BLEND_MODE_Difference:
            for (i = 0; i < n_chan; i++) {
                art_s32 tmp;

                tmp = ((art_s32) backdrop[i]) - ((art_s32) src[i]);
                dst[i] = tmp < 0 ? -tmp : tmp;
            }
            break;
        case BLEND_MODE_Exclusion:
            for (i = 0; i < n_chan; i++) {
                b = backdrop[i];
                s = src[i];
                t = ((bits32) (0xffff - b)) * ((bits32) s) +
                    ((bits32) b) * ((bits32) (0xffff - s));
                t += 0x8000;
                t += (t >> 16);
                dst[i] = t >> 16;
            }
            break;
        default:
            dlprintf1("art_blend_pixel: blend mode %d not implemented\n",
                      blend_mode);
            memcpy(dst, src, n_chan);
            break;
    }
}

byte
art_pdf_union_8(byte alpha1, byte alpha2)
{
    int tmp;

    tmp = (0xff - alpha1) * (0xff - alpha2) + 0x80;
    return 0xff - ((tmp + (tmp >> 8)) >> 8);
}

byte
art_pdf_union_mul_8(byte alpha1, byte alpha2, byte alpha_mask)
{
    int tmp;

    if (alpha_mask == 0xff) {
        tmp = (0xff - alpha1) * (0xff - alpha2) + 0x80;
        return 0xff - ((tmp + (tmp >> 8)) >> 8);
    } else {
        tmp = alpha2 * alpha_mask + 0x80;
        tmp = (tmp + (tmp >> 8)) >> 8;
        tmp = (0xff - alpha1) * (0xff - tmp) + 0x80;
        return 0xff - ((tmp + (tmp >> 8)) >> 8);
    }
}

void
art_pdf_composite_pixel_alpha_8(byte *dst, const byte *src, int n_chan,
        gs_blend_mode_t blend_mode,
        const pdf14_nonseparable_blending_procs_t * pblend_procs)
{
    byte a_b, a_s;
    unsigned int a_r;
    int tmp;
    int src_scale;
    int c_b, c_s;
    int i;

    a_s = src[n_chan];
    if (a_s == 0) {
        /* source alpha is zero, avoid all computations and possible
           divide by zero errors. */
        return;
    }

    a_b = dst[n_chan];
    if (a_b == 0) {
        /* backdrop alpha is zero, just copy source pixels and avoid
           computation. */

        /* this idiom is faster than memcpy (dst, src, n_chan + 1); for
           expected small values of n_chan. */
        for (i = 0; i <= n_chan >> 2; i++) {
            ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
        }

        return;
    }

    /* Result alpha is Union of backdrop and source alpha */
    tmp = (0xff - a_b) * (0xff - a_s) + 0x80;
    a_r = 0xff - (((tmp >> 8) + tmp) >> 8);
    /* todo: verify that a_r is nonzero in all cases */

    /* Compute a_s / a_r in 16.16 format */
    src_scale = ((a_s << 16) + (a_r >> 1)) / a_r;

    if (blend_mode == BLEND_MODE_Normal) {
        /* Do simple compositing of source over backdrop */
        for (i = 0; i < n_chan; i++) {
            c_s = src[i];
            c_b = dst[i];
            tmp = (c_b << 16) + src_scale * (c_s - c_b) + 0x8000;
            dst[i] = tmp >> 16;
        }
    } else {
        /* Do compositing with blending */
        byte blend[ART_MAX_CHAN];

        art_blend_pixel_8(blend, dst, src, n_chan, blend_mode, pblend_procs);
        for (i = 0; i < n_chan; i++) {
            int c_bl;		/* Result of blend function */
            int c_mix;		/* Blend result mixed with source color */

            c_s = src[i];
            c_b = dst[i];
            c_bl = blend[i];
            tmp = a_b * (c_bl - ((int)c_s)) + 0x80;
            c_mix = c_s + (((tmp >> 8) + tmp) >> 8);
            tmp = (c_b << 16) + src_scale * (c_mix - c_b) + 0x8000;
            dst[i] = tmp >> 16;
        }
    }
    dst[n_chan] = a_r;
}

#if 0
/**
 * art_pdf_composite_pixel_knockout_8: Composite two pixels with knockout.
 * @dst: Where to store resulting pixel, also immediate backdrop.
 * @backdrop: Initial backdrop color.
 * @src: Source pixel color.
 * @n_chan: Number of channels.
 * @blend_mode: Blend mode.
 *
 * Composites two pixels using the compositing operation specialized
 * for knockout groups (Section 5.5). A few things to keep in mind:
 *
 * 1. This is a reference implementation, not a high-performance one.
 *
 * 2. All pixels are assumed to have a single alpha channel.
 *
 * 3. Zero is black, one is white.
 *
 * Also note that src and dst are expected to be allocated aligned to
 * 32 bit boundaries, ie bytes from [0] to [(n_chan + 3) & -4] may
 * be accessed.
 *
 * All pixel values have both alpha and shape channels, ie with those
 * included the total number of channels is @n_chan + 2.
 *
 * An invariant: shape >= alpha.
 **/
void
art_pdf_composite_pixel_knockout_8(byte *dst,
                                   const byte *backdrop, const byte *src,
                                   int n_chan, gs_blend_mode_t blend_mode)
{
    int i;
    byte ct[ART_MAX_CHAN + 1];
    byte src_shape;
    byte backdrop_alpha;
    byte dst_alpha;
    bits32 src_opacity;
    bits32 backdrop_weight, t_weight;
    int tmp;

    if (src[n_chan] == 0)
        return;
    if (src[n_chan + 1] == 255 && blend_mode == BLEND_MODE_Normal ||
        dst[n_chan] == 0) {
        /* this idiom is faster than memcpy (dst, src, n_chan + 2); for
           expected small values of n_chan. */
        for (i = 0; i <= (n_chan + 1) >> 2; i++) {
            ((bits32 *) dst)[i] = ((const bits32 *)src[i]);
        }

        return;
    }

    src_shape = src[n_chan + 1];	/* $fs_i$ */
    src_opacity = (255 * src[n_chan] + 0x80) / src_shape;	/* $qs_i$ */
#if 0
    for (i = 0; i < (n_chan + 3) >> 2; i++) {
        ((bits32 *) src_tmp)[i] = ((const bits32 *)src[i]);
    }
    src_tmp[n_chan] = src_opacity;

    for (i = 0; i <= n_chan >> 2; i++) {
        ((bits32 *) tmp)[i] = ((bits32 *) backdrop[i]);
    }
#endif

    backdrop_scale = if (blend_mode == BLEND_MODE_Normal) {
        /* Do simple compositing of source over backdrop */
        for (i = 0; i < n_chan; i++) {
            c_s = src[i];
            c_b = dst[i];
            tmp = (c_b << 16) + ct_scale * (c_s - c_b) + 0x8000;
            ct[i] = tmp >> 16;
        }
    } else {
        /* Do compositing with blending */
        byte blend[ART_MAX_CHAN];

        art_blend_pixel_8(blend, backdrop, src, n_chan, blend_mode, pblend_procs);
        for (i = 0; i < n_chan; i++) {
            int c_bl;		/* Result of blend function */
            int c_mix;		/* Blend result mixed with source color */

            c_s = src[i];
            c_b = dst[i];
            c_bl = blend[i];
            tmp = a_b * (((int)c_bl) - ((int)c_s)) + 0x80;
            c_mix = c_s + (((tmp >> 8) + tmp) >> 8);
            tmp = (c_b << 16) + ct_scale * (c_mix - c_b) + 0x8000;
            ct[i] = tmp >> 16;
        }
    }

    /* do weighted average of $Ct$ using relative alpha contribution as weight */
    backdrop_alpha = backdrop[n_chan];
    tmp = (0xff - blend_alpha) * (0xff - backdrop_alpha) + 0x80;
    dst_alpha = 0xff - (((tmp >> 8) + tmp) >> 8);
    dst[n_chan] = dst_alpha;
    t_weight = ((blend_alpha << 16) + 0x8000) / dst_alpha;
    for (i = 0; i < n_chan; i++) {

    }
}
#endif

void
art_pdf_uncomposite_group_8(byte *dst,
                            const byte *backdrop,
                            const byte *src, byte src_alpha_g, int n_chan)
{
    byte backdrop_alpha = backdrop[n_chan];
    int i;
    int tmp;
    int scale;

    dst[n_chan] = src_alpha_g;

    if (src_alpha_g == 0)
        return;

    scale = (backdrop_alpha * 255 * 2 + src_alpha_g) / (src_alpha_g << 1) -
        backdrop_alpha;
    for (i = 0; i < n_chan; i++) {
        int si, di;

        si = src[i];
        di = backdrop[i];
        tmp = (si - di) * scale + 0x80;
        tmp = si + ((tmp + (tmp >> 8)) >> 8);

        /* todo: it should be possible to optimize these cond branches */
        if (tmp < 0)
            tmp = 0;
        if (tmp > 255)
            tmp = 255;
        dst[i] = tmp;
    }

}

void
art_pdf_recomposite_group_8(byte *dst, byte *dst_alpha_g,
        const byte *src, byte src_alpha_g, int n_chan,
        byte alpha, gs_blend_mode_t blend_mode,
        const pdf14_nonseparable_blending_procs_t * pblend_procs)
{
    byte dst_alpha;
    int i;
    int tmp;
    int scale;

    if (src_alpha_g == 0)
        return;

    if (blend_mode == BLEND_MODE_Normal && alpha == 255) {
        /* In this case, uncompositing and recompositing cancel each
           other out. Note: if the reason that alpha == 255 is that
           there is no constant mask and no soft mask, then this
           operation should be optimized away at a higher level. */
        for (i = 0; i <= n_chan >> 2; i++)
            ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
        if (dst_alpha_g != NULL) {
            tmp = (255 - *dst_alpha_g) * (255 - src_alpha_g) + 0x80;
            *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
        }
        return;
    } else {
        /* "interesting" blend mode */
        byte ca[ART_MAX_CHAN + 1];	/* $C, \alpha$ */

        dst_alpha = dst[n_chan];
        if (src_alpha_g == 255 || dst_alpha == 0) {
            for (i = 0; i < (n_chan + 3) >> 2; i++)
                ((bits32 *) ca)[i] = ((const bits32 *)src)[i];
        } else {
            /* Uncomposite the color. In other words, solve
               "src = (ca, src_alpha_g) over dst" for ca */

            /* todo (maybe?): replace this code with call to
               art_pdf_uncomposite_group_8() to reduce code
               duplication. */

            scale = (dst_alpha * 255 * 2 + src_alpha_g) / (src_alpha_g << 1) -
                dst_alpha;
            for (i = 0; i < n_chan; i++) {
                int si, di;

                si = src[i];
                di = dst[i];
                tmp = (si - di) * scale + 0x80;
                tmp = si + ((tmp + (tmp >> 8)) >> 8);

                /* todo: it should be possible to optimize these cond branches */
                if (tmp < 0)
                    tmp = 0;
                if (tmp > 255)
                    tmp = 255;
                ca[i] = tmp;
            }
        }

        tmp = src_alpha_g * alpha + 0x80;
        tmp = (tmp + (tmp >> 8)) >> 8;
        ca[n_chan] = tmp;
        if (dst_alpha_g != NULL) {
            tmp = (255 - *dst_alpha_g) * (255 - tmp) + 0x80;
            *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
        }
        art_pdf_composite_pixel_alpha_8(dst, ca, n_chan,
                                        blend_mode, pblend_procs);
    }
    /* todo: optimize BLEND_MODE_Normal buf alpha != 255 case */
}

void
art_pdf_composite_group_8(byte *dst, byte *dst_alpha_g,
        const byte *src, int n_chan, byte alpha, gs_blend_mode_t blend_mode,
        const pdf14_nonseparable_blending_procs_t * pblend_procs)
{
    byte src_alpha;		/* $\alpha g_n$ */
    byte src_tmp[ART_MAX_CHAN + 1];
    int i;
    int tmp;

    if (alpha == 255) {
        art_pdf_composite_pixel_alpha_8(dst, src, n_chan,
                                        blend_mode, pblend_procs);
        if (dst_alpha_g != NULL) {
            tmp = (255 - *dst_alpha_g) * (255 - src[n_chan]) + 0x80;
            *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
        }
    } else {
        src_alpha = src[n_chan];
        if (src_alpha == 0)
            return;
        for (i = 0; i < (n_chan + 3) >> 2; i++)
            ((bits32 *) src_tmp)[i] = ((const bits32 *)src)[i];
        tmp = src_alpha * alpha + 0x80;
        src_tmp[n_chan] = (tmp + (tmp >> 8)) >> 8;
        art_pdf_composite_pixel_alpha_8(dst, src_tmp, n_chan,
                                        blend_mode, pblend_procs);
        if (dst_alpha_g != NULL) {
            tmp = (255 - *dst_alpha_g) * (255 - src_tmp[n_chan]) + 0x80;
            *dst_alpha_g = 255 - ((tmp + (tmp >> 8)) >> 8);
        }
    }
}

/* A very simple case.  Knockout isolated group going to a parent that is not
   a knockout.  Simply copy over everwhere where we have a non-zero alpha value */
void
art_pdf_knockoutisolated_group_8(byte *dst, const byte *src, int n_chan)
{
    int i;
    byte src_alpha;

    src_alpha = src[n_chan];
    if (src_alpha == 0)
        return;
    for (i = 0; i <= n_chan >> 2; i++) {
        ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
    }
}

void
art_pdf_composite_knockout_simple_8(byte *dst,
                                    byte *dst_shape,
                                    byte *dst_tag,
                                    const byte *src,
                                    byte tag,
                                    int n_chan, byte opacity)
{
    byte src_shape = src[n_chan];
    int i;

    if (src_shape == 0)
        return;
    else if (src_shape == 255) {
        for (i = 0; i < (n_chan + 3) >> 2; i++)
            ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
        dst[n_chan] = opacity;
        if (dst_shape != NULL)
            *dst_shape = 255;
    } else {
        /* Use src_shape to interpolate (in premultiplied alpha space)
           between dst and (src, opacity). */
        int dst_alpha = dst[n_chan];
        byte result_alpha;
        int tmp;

        tmp = (opacity - dst_alpha) * src_shape + 0x80;
        result_alpha = dst_alpha + ((tmp + (tmp >> 8)) >> 8);

        if (result_alpha != 0)
            for (i = 0; i < n_chan; i++) {
                /* todo: optimize this - can strength-reduce so that
                   inner loop is a single interpolation */
                tmp = dst[i] * dst_alpha * (255 - src_shape) +
                    ((int)src[i]) * opacity * src_shape + (result_alpha << 7);
                dst[i] = tmp / (result_alpha * 255);
            }
        dst[n_chan] = result_alpha;

        /* union in dst_shape if non-null */
        if (dst_shape != NULL) {
            tmp = (255 - *dst_shape) * (255 - src_shape) + 0x80;
            *dst_shape = 255 - ((tmp + (tmp >> 8)) >> 8);
        }
    }
}

void
art_pdf_composite_knockout_isolated_8(byte *dst,
                                      byte *dst_shape,
                                      byte *dst_tag,
                                      const byte *src,
                                      int n_chan,
                                      byte shape,
                                      byte tag,
                                      byte alpha_mask, byte shape_mask)
{
    int tmp;
    int i;

    if (shape == 0)
        return;
    else if ((shape & shape_mask) == 255) {
        for (i = 0; i < (n_chan + 3) >> 2; i++)
            ((bits32 *) dst)[i] = ((const bits32 *)src)[i];
        tmp = src[n_chan] * alpha_mask + 0x80;
        dst[n_chan] = (tmp + (tmp >> 8)) >> 8;
        if (dst_shape != NULL)
            *dst_shape = 255;
        if (dst_tag != NULL)
            *dst_tag = tag;
    } else {
        /* Use src_shape to interpolate (in premultiplied alpha space)
           between dst and (src, opacity). */
        byte src_shape, src_alpha;
        int dst_alpha = dst[n_chan];
        byte result_alpha;
        int tmp;

        tmp = shape * shape_mask + 0x80;
        src_shape = (tmp + (tmp >> 8)) >> 8;

        tmp = src[n_chan] * alpha_mask + 0x80;
        src_alpha = (tmp + (tmp >> 8)) >> 8;

        tmp = (src_alpha - dst_alpha) * src_shape + 0x80;
        result_alpha = dst_alpha + ((tmp + (tmp >> 8)) >> 8);

        if (result_alpha != 0)
            for (i = 0; i < n_chan; i++) {
                /* todo: optimize this - can strength-reduce so that
                   inner loop is a single interpolation */
                tmp = dst[i] * dst_alpha * (255 - src_shape) +
                    ((int)src[i]) * src_alpha * src_shape +
                    (result_alpha << 7);
                dst[i] = tmp / (result_alpha * 255);
            }
        dst[n_chan] = result_alpha;

        /* union in dst_shape if non-null */
        if (dst_shape != NULL) {
            tmp = (255 - *dst_shape) * (255 - src_shape) + 0x80;
            *dst_shape = 255 - ((tmp + (tmp >> 8)) >> 8);
        }
        if (dst_tag != NULL) {
            *dst_tag = (*dst_tag | tag) & ~GS_UNTOUCHED_TAG;
        }
    }
}

void
art_pdf_composite_knockout_8(byte *dst,
                byte *dst_alpha_g, const byte *backdrop, const byte *src,
                int n_chan, byte shape, byte alpha_mask,
                byte shape_mask, gs_blend_mode_t blend_mode,
                const pdf14_nonseparable_blending_procs_t * pblend_procs)
{
    /* This implementation follows the Adobe spec pretty closely, rather
       than trying to do anything clever. For example, in the case of a
       Normal blend_mode when the top group is non-isolated, uncompositing
       and recompositing is more work than needed. So be it. Right now,
       I'm more worried about manageability than raw performance. */
    byte alpha_t;
    byte src_alpha, src_shape;
    byte src_opacity;
    byte ct[ART_MAX_CHAN];
    byte backdrop_alpha;
    byte alpha_g_i_1, alpha_g_i, alpha_i;
    int tmp;
    int i;
    int scale_b;
    int scale_src;

    if (shape == 0 || shape_mask == 0)
        return;

    tmp = shape * shape_mask + 0x80;
    /* $f s_i$ */
    src_shape = (tmp + (tmp >> 8)) >> 8;

    tmp = src[n_chan] * alpha_mask + 0x80;
    src_alpha = (tmp + (tmp >> 8)) >> 8;

    /* $q s_i$ */
    src_opacity = (src_alpha * 510 + src_shape) / (2 * src_shape);

    /* $\alpha t$, \alpha g_b is always zero for knockout groups */
    alpha_t = src_opacity;

    /* $\alpha b$ */
    backdrop_alpha = backdrop[n_chan];

    tmp = (0xff - src_opacity) * backdrop_alpha;
    /* $(1 - q s_i) \cdot alpha_b$ scaled by 2^16 */
    scale_b = tmp + (tmp >> 7) + (tmp >> 14);

    /* $q s_i$ scaled by 2^16 */
    scale_src = (src_opacity << 8) + (src_opacity) + (src_opacity >> 7);

    /* Do simple compositing of source over backdrop */
    if (blend_mode == BLEND_MODE_Normal) {
        for (i = 0; i < n_chan; i++) {
            int c_s;
            int c_b;

            c_s = src[i];
            c_b = backdrop[i];
            tmp = (c_b << 16) * scale_b + (c_s - c_b) + scale_src + 0x8000;
            ct[i] = tmp >> 16;
        }
    } else {
        byte blend[ART_MAX_CHAN];

        art_blend_pixel_8(blend, backdrop, src, n_chan,
                                blend_mode, pblend_procs);
        for (i = 0; i < n_chan; i++) {
            int c_s;
            int c_b;
            int c_bl;		/* Result of blend function */
            int c_mix;		/* Blend result mixed with source color */

            c_s = src[i];
            c_b = backdrop[i];
            c_bl = blend[i];
            tmp = backdrop_alpha * (c_bl - ((int)c_s)) + 0x80;
            c_mix = c_s + (((tmp >> 8) + tmp) >> 8);
            tmp = (c_b << 16) * scale_b + (c_mix - c_b) + scale_src + 0x8000;
            ct[i] = tmp >> 16;
        }
    }

    /* $\alpha g_{i - 1}$ */
    alpha_g_i_1 = *dst_alpha_g;

    tmp = src_shape * (((int)alpha_t) - alpha_g_i_1) + 0x80;
    /* $\alpha g_i$ */
    alpha_g_i = alpha_g_i_1 + ((tmp + (tmp >> 8)) >> 8);

    tmp = (0xff - backdrop_alpha) * (0xff - alpha_g_i) + 0x80;
    /* $\alpha_i$ */
    alpha_i = 0xff - ((tmp + (tmp >> 8)) >> 8);

    if (alpha_i > 0) {
        int scale_dst;
        int scale_t;
        byte dst_alpha;

        /* $f s_i / \alpha_i$ scaled by 2^16 */
        scale_t = ((src_shape << 17) + alpha_i) / (2 * alpha_i);

        /* $\alpha_{i - 1}$ */
        dst_alpha = dst[n_chan];

        tmp = (1 - src_shape) * dst_alpha;
        tmp = (tmp << 9) + (tmp << 1) + (tmp >> 7) + alpha_i;
        scale_dst = tmp / (2 * alpha_i);

        for (i = 0; i < n_chan; i++) {
            tmp = dst[i] * scale_dst + ct[i] * scale_t + 0x8000;
            /* todo: clamp? */
            dst[i] = tmp >> 16;
        }
    }
    dst[n_chan] = alpha_i;
    *dst_alpha_g = alpha_g_i;
}

#if RAW_DUMP
/* Debug dump of buffer data from pdf14 device.  Saved in
   planar form with global indexing and tag information in
   file name */
void
dump_raw_buffer(int num_rows, int width, int n_chan,
                int plane_stride, int rowstride,
                char filename[],byte *Buffer)
{
    char full_file_name[50];
    FILE *fid;
    int z,y;
    byte *buff_ptr;
    int max_bands;

   /* clist_band_count is incremented at every pdf14putimage */
   /* Useful for catching this thing and only dumping */
   /* during a particular band if we have a large file */
   /* if (clist_band_count != 65) return; */
    buff_ptr = Buffer;
#ifdef RAW_DUMP_AS_PAM
    if ((n_chan == 4) || (n_chan == 5)) {
        int x;
        sprintf(full_file_name,"%d)%s.pam",global_index,filename);
        fid = fopen(full_file_name,"wb");
        fprintf(fid, "P7\nWIDTH %d\nHEIGHT %d\nDEPTH 4\nMAXVAL 255\nTUPLTYPE RGB_ALPHA\nENDHDR\n",
                width, num_rows);
        for(y=0; y<num_rows; y++)
            for(x=0; x<width; x++)
                for(z=0; z<4; z++)
                    fputc(Buffer[z*plane_stride + y*rowstride + x], fid);
        fclose(fid);
        if (n_chan == 5) {
            sprintf(full_file_name,"%d)%s_shape.pam",global_index,filename);
            fid = fopen(full_file_name,"wb");
            fprintf(fid, "P7\nWIDTH %d\nHEIGHT %d\nDEPTH 1\nMAXVAL 255\nTUPLTYPE GRAYSCALE\nENDHDR\n",
                    width, num_rows);
            for(y=0; y<num_rows; y++)
                for(x=0; x<width; x++)
                    fputc(Buffer[4*plane_stride + y*rowstride + x], fid);
        }
        fclose(fid);
        return;
    }
#endif
    max_bands = ( n_chan < 57 ? n_chan : 56);   /* Photoshop handles at most 56 bands */
    sprintf(full_file_name,"%d)%s_%dx%dx%d.raw",global_index,filename,width,num_rows,max_bands);
    fid = fopen(full_file_name,"wb");

    for (z = 0; z < max_bands; ++z) {
        /* grab pointer to the next plane */
        buff_ptr = &(Buffer[z*plane_stride]);
        for ( y = 0; y < num_rows; y++ ) {
            /* write out each row */
            fwrite(buff_ptr,sizeof(unsigned char),width,fid);
            buff_ptr += rowstride;
        }
    }
    fclose(fid);
}
#endif