?? ftgrays.c
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/***************************************************************************/
/* */
/* ftgrays.c */
/* */
/* A new `perfect' anti-aliasing renderer (body). */
/* */
/* Copyright 2000-2001, 2002, 2003, 2005, 2006 by */
/* David Turner, Robert Wilhelm, and Werner Lemberg. */
/* */
/* This file is part of the FreeType project, and may only be used, */
/* modified, and distributed under the terms of the FreeType project */
/* license, LICENSE.TXT. By continuing to use, modify, or distribute */
/* this file you indicate that you have read the license and */
/* understand and accept it fully. */
/* */
/***************************************************************************/
/*************************************************************************/
/* */
/* This file can be compiled without the rest of the FreeType engine, by */
/* defining the _STANDALONE_ macro when compiling it. You also need to */
/* put the files `ftgrays.h' and `ftimage.h' into the current */
/* compilation directory. Typically, you could do something like */
/* */
/* - copy `src/smooth/ftgrays.c' (this file) to your current directory */
/* */
/* - copy `include/freetype/ftimage.h' and `src/smooth/ftgrays.h' to the */
/* same directory */
/* */
/* - compile `ftgrays' with the _STANDALONE_ macro defined, as in */
/* */
/* cc -c -D_STANDALONE_ ftgrays.c */
/* */
/* The renderer can be initialized with a call to */
/* `ft_gray_raster.raster_new'; an anti-aliased bitmap can be generated */
/* with a call to `ft_gray_raster.raster_render'. */
/* */
/* See the comments and documentation in the file `ftimage.h' for more */
/* details on how the raster works. */
/* */
/*************************************************************************/
/*************************************************************************/
/* */
/* This is a new anti-aliasing scan-converter for FreeType 2. The */
/* algorithm used here is _very_ different from the one in the standard */
/* `ftraster' module. Actually, `ftgrays' computes the _exact_ */
/* coverage of the outline on each pixel cell. */
/* */
/* It is based on ideas that I initially found in Raph Levien's */
/* excellent LibArt graphics library (see http://www.levien.com/libart */
/* for more information, though the web pages do not tell anything */
/* about the renderer; you'll have to dive into the source code to */
/* understand how it works). */
/* */
/* Note, however, that this is a _very_ different implementation */
/* compared to Raph's. Coverage information is stored in a very */
/* different way, and I don't use sorted vector paths. Also, it doesn't */
/* use floating point values. */
/* */
/* This renderer has the following advantages: */
/* */
/* - It doesn't need an intermediate bitmap. Instead, one can supply a */
/* callback function that will be called by the renderer to draw gray */
/* spans on any target surface. You can thus do direct composition on */
/* any kind of bitmap, provided that you give the renderer the right */
/* callback. */
/* */
/* - A perfect anti-aliaser, i.e., it computes the _exact_ coverage on */
/* each pixel cell. */
/* */
/* - It performs a single pass on the outline (the `standard' FT2 */
/* renderer makes two passes). */
/* */
/* - It can easily be modified to render to _any_ number of gray levels */
/* cheaply. */
/* */
/* - For small (< 20) pixel sizes, it is faster than the standard */
/* renderer. */
/* */
/*************************************************************************/
/* experimental support for gamma correction within the rasterizer */
#define xxxGRAYS_USE_GAMMA
/*************************************************************************/
/* */
/* The macro FT_COMPONENT is used in trace mode. It is an implicit */
/* parameter of the FT_TRACE() and FT_ERROR() macros, used to print/log */
/* messages during execution. */
/* */
#undef FT_COMPONENT
#define FT_COMPONENT trace_smooth
#define ErrRaster_MemoryOverflow -4
#ifdef _STANDALONE_
#include <string.h> /* for ft_memcpy() */
#include <setjmp.h>
#include <limits.h>
#define FT_UINT_MAX UINT_MAX
#define ft_memset memset
#define ft_setjmp setjmp
#define ft_longjmp longjmp
#define ft_jmp_buf jmp_buf
#define ErrRaster_Invalid_Mode -2
#define ErrRaster_Invalid_Outline -1
#define FT_BEGIN_HEADER
#define FT_END_HEADER
#include "ftimage.h"
#include "ftgrays.h"
/* This macro is used to indicate that a function parameter is unused. */
/* Its purpose is simply to reduce compiler warnings. Note also that */
/* simply defining it as `(void)x' doesn't avoid warnings with certain */
/* ANSI compilers (e.g. LCC). */
#define FT_UNUSED( x ) (x) = (x)
/* Disable the tracing mechanism for simplicity -- developers can */
/* activate it easily by redefining these two macros. */
#ifndef FT_ERROR
#define FT_ERROR( x ) do ; while ( 0 ) /* nothing */
#endif
#ifndef FT_TRACE
#define FT_TRACE( x ) do ; while ( 0 ) /* nothing */
#endif
#else /* _STANDALONE_ */
#include <ft2build.h>
#include "ftgrays.h"
#include FT_INTERNAL_OBJECTS_H
#include FT_INTERNAL_DEBUG_H
#include FT_OUTLINE_H
#include "ftsmerrs.h"
#define ErrRaster_Invalid_Mode Smooth_Err_Cannot_Render_Glyph
#define ErrRaster_Invalid_Outline Smooth_Err_Invalid_Outline
#endif /* _STANDALONE_ */
#ifndef FT_MEM_SET
#define FT_MEM_SET( d, s, c ) ft_memset( d, s, c )
#endif
#ifndef FT_MEM_ZERO
#define FT_MEM_ZERO( dest, count ) FT_MEM_SET( dest, 0, count )
#endif
/* define this to dump debugging information */
#define xxxDEBUG_GRAYS
/* as usual, for the speed hungry :-) */
#ifndef FT_STATIC_RASTER
#define RAS_ARG PRaster raster
#define RAS_ARG_ PRaster raster,
#define RAS_VAR raster
#define RAS_VAR_ raster,
#define ras (*raster)
#else /* FT_STATIC_RASTER */
#define RAS_ARG /* empty */
#define RAS_ARG_ /* empty */
#define RAS_VAR /* empty */
#define RAS_VAR_ /* empty */
static TRaster ras;
#endif /* FT_STATIC_RASTER */
/* must be at least 6 bits! */
#define PIXEL_BITS 8
#define ONE_PIXEL ( 1L << PIXEL_BITS )
#define PIXEL_MASK ( -1L << PIXEL_BITS )
#define TRUNC( x ) ( (TCoord)((x) >> PIXEL_BITS) )
#define SUBPIXELS( x ) ( (TPos)(x) << PIXEL_BITS )
#define FLOOR( x ) ( (x) & -ONE_PIXEL )
#define CEILING( x ) ( ( (x) + ONE_PIXEL - 1 ) & -ONE_PIXEL )
#define ROUND( x ) ( ( (x) + ONE_PIXEL / 2 ) & -ONE_PIXEL )
#if PIXEL_BITS >= 6
#define UPSCALE( x ) ( (x) << ( PIXEL_BITS - 6 ) )
#define DOWNSCALE( x ) ( (x) >> ( PIXEL_BITS - 6 ) )
#else
#define UPSCALE( x ) ( (x) >> ( 6 - PIXEL_BITS ) )
#define DOWNSCALE( x ) ( (x) << ( 6 - PIXEL_BITS ) )
#endif
/* Define this if you want to use a more compact storage scheme. This */
/* increases the number of cells available in the render pool but slows */
/* down the rendering a bit. It is useful if you have a really tiny */
/* render pool. */
#undef GRAYS_COMPACT
/*************************************************************************/
/* */
/* TYPE DEFINITIONS */
/* */
/* don't change the following types to FT_Int or FT_Pos, since we might */
/* need to define them to "float" or "double" when experimenting with */
/* new algorithms */
typedef int TCoord; /* integer scanline/pixel coordinate */
typedef long TPos; /* sub-pixel coordinate */
/* determine the type used to store cell areas. This normally takes at */
/* least PIXEL_BITS*2 + 1 bits. On 16-bit systems, we need to use */
/* `long' instead of `int', otherwise bad things happen */
#if PIXEL_BITS <= 7
typedef int TArea;
#else /* PIXEL_BITS >= 8 */
/* approximately determine the size of integers using an ANSI-C header */
#if FT_UINT_MAX == 0xFFFFU
typedef long TArea;
#else
typedef int TArea;
#endif
#endif /* PIXEL_BITS >= 8 */
/* maximal number of gray spans in a call to the span callback */
#define FT_MAX_GRAY_SPANS 32
#ifdef GRAYS_COMPACT
typedef struct TCell_
{
short x : 14;
short y : 14;
int cover : PIXEL_BITS + 2;
int area : PIXEL_BITS * 2 + 2;
} TCell, *PCell;
#else /* GRAYS_COMPACT */
typedef struct TCell_
{
TCoord x;
TCoord y;
int cover;
TArea area;
} TCell, *PCell;
#endif /* GRAYS_COMPACT */
typedef struct TRaster_
{
PCell cells;
int max_cells;
int num_cells;
TPos min_ex, max_ex;
TPos min_ey, max_ey;
TArea area;
int cover;
int invalid;
TCoord ex, ey;
TCoord cx, cy;
TPos x, y;
TPos last_ey;
FT_Vector bez_stack[32 * 3 + 1];
int lev_stack[32];
FT_Outline outline;
FT_Bitmap target;
FT_BBox clip_box;
FT_Span gray_spans[FT_MAX_GRAY_SPANS];
int num_gray_spans;
FT_Raster_Span_Func render_span;
void* render_span_data;
int span_y;
int band_size;
int band_shoot;
int conic_level;
int cubic_level;
void* memory;
ft_jmp_buf jump_buffer;
#ifdef GRAYS_USE_GAMMA
unsigned char gamma[257];
#endif
} TRaster, *PRaster;
/*************************************************************************/
/* */
/* Initialize the cells table. */
/* */
static void
gray_init_cells( RAS_ARG_ void* buffer,
long byte_size )
{
ras.cells = (PCell)buffer;
ras.max_cells = (int)( byte_size / sizeof ( TCell ) );
ras.num_cells = 0;
ras.area = 0;
ras.cover = 0;
ras.invalid = 1;
}
/*************************************************************************/
/* */
/* Compute the outline bounding box. */
/* */
static void
gray_compute_cbox( RAS_ARG )
{
FT_Outline* outline = &ras.outline;
FT_Vector* vec = outline->points;
FT_Vector* limit = vec + outline->n_points;
if ( outline->n_points <= 0 )
{
ras.min_ex = ras.max_ex = 0;
ras.min_ey = ras.max_ey = 0;
return;
}
ras.min_ex = ras.max_ex = vec->x;
ras.min_ey = ras.max_ey = vec->y;
vec++;
for ( ; vec < limit; vec++ )
{
TPos x = vec->x;
TPos y = vec->y;
if ( x < ras.min_ex ) ras.min_ex = x;
if ( x > ras.max_ex ) ras.max_ex = x;
if ( y < ras.min_ey ) ras.min_ey = y;
if ( y > ras.max_ey ) ras.max_ey = y;
}
/* truncate the bounding box to integer pixels */
ras.min_ex = ras.min_ex >> 6;
ras.min_ey = ras.min_ey >> 6;
ras.max_ex = ( ras.max_ex + 63 ) >> 6;
ras.max_ey = ( ras.max_ey + 63 ) >> 6;
}
/*************************************************************************/
/* */
/* Record the current cell in the table. */
/* */
static void
gray_record_cell( RAS_ARG )
{
PCell cell;
if ( !ras.invalid && ( ras.area | ras.cover ) )
{
if ( ras.num_cells >= ras.max_cells )
ft_longjmp( ras.jump_buffer, 1 );
cell = ras.cells + ras.num_cells++;
cell->x = (TCoord)(ras.ex - ras.min_ex);
cell->y = (TCoord)(ras.ey - ras.min_ey);
cell->area = ras.area;
cell->cover = ras.cover;
}
}
/*************************************************************************/
/* */
/* Set the current cell to a new position. */
/* */
static void
gray_set_cell( RAS_ARG_ TCoord ex,
TCoord ey )
{
int invalid, record, clean;
/* Move the cell pointer to a new position. We set the `invalid' */
/* flag to indicate that the cell isn't part of those we're interested */
/* in during the render phase. This means that: */
/* */
/* . the new vertical position must be within min_ey..max_ey-1. */
/* . the new horizontal position must be strictly less than max_ex */
/* */
/* Note that if a cell is to the left of the clipping region, it is */
/* actually set to the (min_ex-1) horizontal position. */
record = 0;
clean = 1;
invalid = ( ey < ras.min_ey || ey >= ras.max_ey || ex >= ras.max_ex );
if ( !invalid )
{
/* All cells that are on the left of the clipping region go to the */
/* min_ex - 1 horizontal position. */
if ( ex < ras.min_ex )
ex = (TCoord)(ras.min_ex - 1);
/* if our position is new, then record the previous cell */
if ( ex != ras.ex || ey != ras.ey )
record = 1;
else
clean = ras.invalid; /* do not clean if we didn't move from */
/* a valid cell */
}
/* record the previous cell if needed (i.e., if we changed the cell */
/* position, or changed the `invalid' flag) */
if ( ras.invalid != invalid || record )
gray_record_cell( RAS_VAR );
if ( clean )
{
ras.area = 0;
ras.cover = 0;
}
ras.invalid = invalid;
ras.ex = ex;
ras.ey = ey;
}
/*************************************************************************/
/* */
/* Start a new contour at a given cell. */
/* */
static void
gray_start_cell( RAS_ARG_ TCoord ex,
TCoord ey )
{
if ( ex < ras.min_ex )
ex = (TCoord)(ras.min_ex - 1);
ras.area = 0;
ras.cover = 0;
ras.ex = ex;
ras.ey = ey;
ras.last_ey = SUBPIXELS( ey );
ras.invalid = 0;
gray_set_cell( RAS_VAR_ ex, ey );
}
/*************************************************************************/
/* */
/* Render a scanline as one or more cells. */
/* */
static void
gray_render_scanline( RAS_ARG_ TCoord ey,
TPos x1,
TCoord y1,
TPos x2,
TCoord y2 )
{
TCoord ex1, ex2, fx1, fx2, delta;
long p, first, dx;
int incr, lift, mod, rem;
dx = x2 - x1;
ex1 = TRUNC( x1 ); /* if (ex1 >= ras.max_ex) ex1 = ras.max_ex-1; */
ex2 = TRUNC( x2 ); /* if (ex2 >= ras.max_ex) ex2 = ras.max_ex-1; */
fx1 = (TCoord)( x1 - SUBPIXELS( ex1 ) );
fx2 = (TCoord)( x2 - SUBPIXELS( ex2 ) );
/* trivial case. Happens often */
if ( y1 == y2 )
{
gray_set_cell( RAS_VAR_ ex2, ey );
return;
}
/* everything is located in a single cell. That is easy! */
/* */
if ( ex1 == ex2 )
{
delta = y2 - y1;
ras.area += (TArea)( fx1 + fx2 ) * delta;
ras.cover += delta;
return;
}
/* ok, we'll have to render a run of adjacent cells on the same */
/* scanline... */
/* */
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