xref: /plan9/sys/src/cmd/gs/src/gxbitmap.h (revision 593dc095aefb2a85c828727bbfa9da139a49bdf4)

/* Copyright (C) 1989, 1993, 1996, 1997, 1998, 1999 Aladdin Enterprises.  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 the license contained in the file LICENSE in this distribution.

  For more information about licensing, please refer to
  http://www.ghostscript.com/licensing/. For information on
  commercial licensing, go to http://www.artifex.com/licensing/ or
  contact Artifex Software, Inc., 101 Lucas Valley Road #110,
  San Rafael, CA  94903, U.S.A., +1(415)492-9861.
*/

/* $Id: gxbitmap.h,v 1.6 2002/03/05 16:56:33 lpd Exp $ */
/* Definitions for stored bitmaps for Ghostscript */

#ifndef gxbitmap_INCLUDED
#  define gxbitmap_INCLUDED

#include "gstypes.h"		/* for gs_id */
#include "gsbitmap.h"

/* Define the gx version of a bitmap identifier. */
typedef gs_bitmap_id gx_bitmap_id;

/* Define the gx version of the "no identifier" value. */
#define gx_no_bitmap_id gs_no_bitmap_id

/*
 * Most graphics library procedures that process bitmap data (such as, for
 * example, the "device" procedures in gdevm*.c) impose two requirements
 * on such data: an alignment requirement, and a padding requirement.
 * Both requirements arise from the fact that these library procedures
 * attempt to process the bits in units of align_bitmap_mod bytes.
 *
 * The alignment requirement is that each scan line must start at an
 * address that is 0 mod align_bitmap_mod.  This requirement is only for
 * the benefit of the hardware (which may, for example, require that
 * instructions fetching or storing a 'long' quantity only do so at an
 * address that is long-aligned), but it must be respected in all
 * platform-independent code.  More precisely, platform-independent code
 * can *assume* that Ghostscript allocators return blocks that are adequately
 * aligned, and then must *ensure* that that alignment is not lost.  (The
 * assumption is not true in some MSVC implementations, but even in those
 * implementations, the alignment is sufficient to satisfy the hardware.
 * See gsmemraw.h for more information about this.)
 *
 * The padding requirement is that if the last data byte being operated on
 * is at offset B relative to the start of the scan line, bytes up to and
 * including offset ROUND_UP(B + 1, align_bitmap_mod) - 1 may be accessed,
 * and therefore must be allocated (not cause hardware-level access faults).
 */
/* We assume arch_align_long_mod is 1-4 or 8. */
#if arch_align_long_mod <= 4
#  define log2_align_bitmap_mod 2
#else
#if arch_align_long_mod == 8
#  define log2_align_bitmap_mod 3
#endif
#endif
#define align_bitmap_mod (1 << log2_align_bitmap_mod)
#define bitmap_raster(width_bits)\
  ((uint)((((width_bits) + (align_bitmap_mod * 8 - 1))\
    >> (log2_align_bitmap_mod + 3)) << log2_align_bitmap_mod))

/*
 * Define the gx analogue of the basic bitmap structure.  Note that since
 * all scan lines must be aligned, the requirement on raster is:
 *      If size.y > 1,
 *          raster >= bitmap_raster(size.x * depth)
 *          raster % align_bitmap_mod = 0
 */
#define gx_bitmap_common(data_type) gs_bitmap_common(data_type)
typedef struct gx_bitmap_s {
    gx_bitmap_common(byte);
} gx_bitmap;
typedef struct gx_const_bitmap_s {
    gx_bitmap_common(const byte);
} gx_const_bitmap;

/*
 * Define the gx analogue of the tile bitmap structure.  Note that if
 * shift != 0 (for strip bitmaps, see below), size.y and rep_height
 * mean something slightly different: see below for details.
 */
#define gx_tile_bitmap_common(data_type) gs_tile_bitmap_common(data_type)
typedef struct gx_tile_bitmap_s {
    gx_tile_bitmap_common(byte);
} gx_tile_bitmap;
typedef struct gx_const_tile_bitmap_s {
    gx_tile_bitmap_common(const byte);
} gx_const_tile_bitmap;

/*
 * For halftones at arbitrary angles, we provide for storing the halftone
 * data as a strip that must be shifted in X for different values of Y.  For
 * an ordinary (non-shifted) halftone that has a repetition width of W and a
 * repetition height of H, the pixel at coordinate (X,Y) corresponds to
 * halftone pixel (X mod W, Y mod H), ignoring phase; for a strip halftone
 * with strip shift S and strip height H, the pixel at (X,Y) corresponds to
 * halftone pixel ((X + S * floor(Y/H)) mod W, Y mod H).  In other words,
 * each Y increment of H shifts the strip left by S pixels.
 *
 * As for non-shifted tiles, a strip bitmap may include multiple copies
 * in X or Y to reduce loop overhead.  In this case, we must distinguish:
 *      - The height of an individual strip, which is the same as
 *      the height of the bitmap being replicated (rep_height, H);
 *      - The height of the entire bitmap (size.y).
 * Similarly, we must distinguish:
 *      - The shift per strip (rep_shift, S);
 *      - The shift for the entire bitmap (shift).
 * Note that shift = (rep_shift * size.y / rep_height) mod rep_width,
 * so the shift member of the structure is only an accelerator.  It is,
 * however, an important one, since it indicates whether the overall
 * bitmap requires shifting or not.
 *
 * Note that for shifted tiles, size.y is the size of the stored bitmap
 * (1 or more strips), and NOT the height of the actual tile.  The latter
 * is not stored in the structure at all: it can be computed as H * W /
 * gcd(S, W).
 *
 * If the bitmap consists of a multiple of W / gcd(S, W) copies in Y, the
 * effective shift is zero, reducing it to a tile.  For simplicity, we
 * require that if shift is non-zero, the bitmap height be less than H * W /
 * gcd(S, W).  I.e., we don't allow strip bitmaps that are large enough to
 * include a complete tile but that don't include an integral number of
 * tiles.  Requirements:
 *      rep_shift < rep_width
 *      shift = (rep_shift * (size.y / rep_height)) % rep_width
 */
#define gx_strip_bitmap_common(data_type)\
	gx_tile_bitmap_common(data_type);\
	ushort rep_shift;\
	ushort shift
typedef struct gx_strip_bitmap_s {
    gx_strip_bitmap_common(byte);
} gx_strip_bitmap;
typedef struct gx_const_strip_bitmap_s {
    gx_strip_bitmap_common(const byte);
} gx_const_strip_bitmap;

extern_st(st_gx_strip_bitmap);
#define public_st_gx_strip_bitmap()	/* in gspcolor.c */\
  gs_public_st_suffix_add0_local(st_gx_strip_bitmap, gx_strip_bitmap,\
    "gx_strip_bitmap", bitmap_enum_ptrs, bitmap_reloc_ptrs,\
    st_gs_tile_bitmap)
#define st_gx_strip_bitmap_max_ptrs 1

#endif /* gxbitmap_INCLUDED */