minhngoc25a
/
freetype2
mirror of git://git.savannah.gnu.org/freetype/freetype2.git
2
1
Fork 2
Code Issues 4 Releases Wiki Activity
freetype2/include/freetype/ftimage.h

1289 lines
41 KiB
C
Raw Blame History

/****************************************************************************
*
* ftimage.h
*
* FreeType glyph image formats and default raster interface
* (specification).
*
* Copyright (C) 1996-2023 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.
*
*/
/**************************************************************************
*
* Note: A 'raster' is simply a scan-line converter, used to render
* `FT_Outline`s into `FT_Bitmap`s.
*
*/
#ifndef FTIMAGE_H_
#define FTIMAGE_H_
FT_BEGIN_HEADER
/**************************************************************************
*
* @section:
* basic_types
*
*/
/**************************************************************************
*
* @type:
* FT_Pos
*
* @description:
* The type FT_Pos is used to store vectorial coordinates. Depending on
* the context, these can represent distances in integer font units, or
* 16.16, or 26.6 fixed-point pixel coordinates.
*/
typedef signed long FT_Pos;
/**************************************************************************
*
* @struct:
* FT_Vector
*
* @description:
* A simple structure used to store a 2D vector; coordinates are of the
* FT_Pos type.
*
* @fields:
* x ::
* The horizontal coordinate.
* y ::
* The vertical coordinate.
*/
typedef struct FT_Vector_
{
FT_Pos x;
FT_Pos y;
} FT_Vector;
/**************************************************************************
*
* @struct:
* FT_BBox
*
* @description:
* A structure used to hold an outline's bounding box, i.e., the
* coordinates of its extrema in the horizontal and vertical directions.
*
* @fields:
* xMin ::
* The horizontal minimum (left-most).
*
* yMin ::
* The vertical minimum (bottom-most).
*
* xMax ::
* The horizontal maximum (right-most).
*
* yMax ::
* The vertical maximum (top-most).
*
* @note:
* The bounding box is specified with the coordinates of the lower left
* and the upper right corner. In PostScript, those values are often
* called (llx,lly) and (urx,ury), respectively.
*
* If `yMin` is negative, this value gives the glyph's descender.
* Otherwise, the glyph doesn't descend below the baseline. Similarly,
* if `ymax` is positive, this value gives the glyph's ascender.
*
* `xMin` gives the horizontal distance from the glyph's origin to the
* left edge of the glyph's bounding box. If `xMin` is negative, the
* glyph extends to the left of the origin.
*/
typedef struct FT_BBox_
{
FT_Pos xMin, yMin;
FT_Pos xMax, yMax;
} FT_BBox;
/**************************************************************************
*
* @enum:
* FT_Pixel_Mode
*
* @description:
* An enumeration type used to describe the format of pixels in a given
* bitmap. Note that additional formats may be added in the future.
*
* @values:
* FT_PIXEL_MODE_NONE ::
* Value~0 is reserved.
*
* FT_PIXEL_MODE_MONO ::
* A monochrome bitmap, using 1~bit per pixel. Note that pixels are
* stored in most-significant order (MSB), which means that the
* left-most pixel in a byte has value 128.
*
* FT_PIXEL_MODE_GRAY ::
* An 8-bit bitmap, generally used to represent anti-aliased glyph
* images. Each pixel is stored in one byte. Note that the number of
* 'gray' levels is stored in the `num_grays` field of the @FT_Bitmap
* structure (it generally is 256).
*
* FT_PIXEL_MODE_GRAY2 ::
* A 2-bit per pixel bitmap, used to represent embedded anti-aliased
* bitmaps in font files according to the OpenType specification. We
* haven't found a single font using this format, however.
*
* FT_PIXEL_MODE_GRAY4 ::
* A 4-bit per pixel bitmap, representing embedded anti-aliased bitmaps
* in font files according to the OpenType specification. We haven't
* found a single font using this format, however.
*
* FT_PIXEL_MODE_LCD ::
* An 8-bit bitmap, representing RGB or BGR decimated glyph images used
* for display on LCD displays; the bitmap is three times wider than
* the original glyph image. See also @FT_RENDER_MODE_LCD.
*
* FT_PIXEL_MODE_LCD_V ::
* An 8-bit bitmap, representing RGB or BGR decimated glyph images used
* for display on rotated LCD displays; the bitmap is three times
* taller than the original glyph image. See also
* @FT_RENDER_MODE_LCD_V.
*
* FT_PIXEL_MODE_BGRA ::
* [Since 2.5] An image with four 8-bit channels per pixel,
* representing a color image (such as emoticons) with alpha channel.
* For each pixel, the format is BGRA, which means, the blue channel
* comes first in memory. The color channels are pre-multiplied and in
* the sRGB colorspace. For example, full red at half-translucent
* opacity will be represented as '00,00,80,80', not '00,00,FF,80'.
* See also @FT_LOAD_COLOR.
*/
typedef enum FT_Pixel_Mode_
{
FT_PIXEL_MODE_NONE = 0,
FT_PIXEL_MODE_MONO,
FT_PIXEL_MODE_GRAY,
FT_PIXEL_MODE_GRAY2,
FT_PIXEL_MODE_GRAY4,
FT_PIXEL_MODE_LCD,
FT_PIXEL_MODE_LCD_V,
FT_PIXEL_MODE_BGRA,
FT_PIXEL_MODE_MAX /* do not remove */
} FT_Pixel_Mode;
/* these constants are deprecated; use the corresponding `FT_Pixel_Mode` */
/* values instead. */
#define ft_pixel_mode_none FT_PIXEL_MODE_NONE
#define ft_pixel_mode_mono FT_PIXEL_MODE_MONO
#define ft_pixel_mode_grays FT_PIXEL_MODE_GRAY
#define ft_pixel_mode_pal2 FT_PIXEL_MODE_GRAY2
#define ft_pixel_mode_pal4 FT_PIXEL_MODE_GRAY4
/* */
/* For debugging, the @FT_Pixel_Mode enumeration must stay in sync */
/* with the `pixel_modes` array in file `ftobjs.c`. */
/**************************************************************************
*
* @struct:
* FT_Bitmap
*
* @description:
* A structure used to describe a bitmap or pixmap to the raster. Note
* that we now manage pixmaps of various depths through the `pixel_mode`
* field.
*
* @fields:
* rows ::
* The number of bitmap rows.
*
* width ::
* The number of pixels in bitmap row.
*
* pitch ::
* The pitch's absolute value is the number of bytes taken by one
* bitmap row, including padding. However, the pitch is positive when
* the bitmap has a 'down' flow, and negative when it has an 'up' flow.
* In all cases, the pitch is an offset to add to a bitmap pointer in
* order to go down one row.
*
* Note that 'padding' means the alignment of a bitmap to a byte
* border, and FreeType functions normally align to the smallest
* possible integer value.
*
* For the B/W rasterizer, `pitch` is always an even number.
*
* To change the pitch of a bitmap (say, to make it a multiple of 4),
* use @FT_Bitmap_Convert. Alternatively, you might use callback
* functions to directly render to the application's surface; see the
* file `example2.cpp` in the tutorial for a demonstration.
*
* buffer ::
* A typeless pointer to the bitmap buffer. This value should be
* aligned on 32-bit boundaries in most cases.
*
* num_grays ::
* This field is only used with @FT_PIXEL_MODE_GRAY; it gives the
* number of gray levels used in the bitmap.
*
* pixel_mode ::
* The pixel mode, i.e., how pixel bits are stored. See @FT_Pixel_Mode
* for possible values.
*
* palette_mode ::
* This field is intended for paletted pixel modes; it indicates how
* the palette is stored. Not used currently.
*
* palette ::
* A typeless pointer to the bitmap palette; this field is intended for
* paletted pixel modes. Not used currently.
*
* @note:
* `width` and `rows` refer to the *physical* size of the bitmap, not the
* *logical* one. For example, if @FT_Pixel_Mode is set to
* `FT_PIXEL_MODE_LCD`, the logical width is a just a third of the
* physical one.
*/
typedef struct FT_Bitmap_
{
unsigned int rows;
unsigned int width;
int pitch;
unsigned char* buffer;
unsigned short num_grays;
unsigned char pixel_mode;
unsigned char palette_mode;
void* palette;
} FT_Bitmap;
/**************************************************************************
*
* @section:
* outline_processing
*
*/
/**************************************************************************
*
* @struct:
* FT_Outline
*
* @description:
* This structure is used to describe an outline to the scan-line
* converter.
*
* @fields:
* n_contours ::
* The number of contours in the outline.
*
* n_points ::
* The number of points in the outline.
*
* points ::
* A pointer to an array of `n_points` @FT_Vector elements, giving the
* outline's point coordinates.
*
* tags ::
* A pointer to an array of `n_points` chars, giving each outline
* point's type.
*
* If bit~0 is unset, the point is 'off' the curve, i.e., a Bezier
* control point, while it is 'on' if set.
*
* Bit~1 is meaningful for 'off' points only. If set, it indicates a
* third-order Bezier arc control point; and a second-order control
* point if unset.
*
* If bit~2 is set, bits 5-7 contain the drop-out mode (as defined in
* the OpenType specification; the value is the same as the argument to
* the 'SCANMODE' instruction).
*
* Bits 3 and~4 are reserved for internal purposes.
*
* contours ::
* An array of `n_contours` shorts, giving the end point of each
* contour within the outline. For example, the first contour is
* defined by the points '0' to `contours[0]`, the second one is
* defined by the points `contours[0]+1` to `contours[1]`, etc.
*
* flags ::
* A set of bit flags used to characterize the outline and give hints
* to the scan-converter and hinter on how to convert/grid-fit it. See
* @FT_OUTLINE_XXX.
*
* @note:
* The B/W rasterizer only checks bit~2 in the `tags` array for the first
* point of each contour. The drop-out mode as given with
* @FT_OUTLINE_IGNORE_DROPOUTS, @FT_OUTLINE_SMART_DROPOUTS, and
* @FT_OUTLINE_INCLUDE_STUBS in `flags` is then overridden.
*/
typedef struct FT_Outline_
{
short n_contours; /* number of contours in glyph */
short n_points; /* number of points in the glyph */
FT_Vector* points; /* the outline's points */
char* tags; /* the points flags */
short* contours; /* the contour end points */
int flags; /* outline masks */
} FT_Outline;
/* */
/* Following limits must be consistent with */
/* FT_Outline.{n_contours,n_points} */
#define FT_OUTLINE_CONTOURS_MAX SHRT_MAX
#define FT_OUTLINE_POINTS_MAX SHRT_MAX
/**************************************************************************
*
* @enum:
* FT_OUTLINE_XXX
*
* @description:
* A list of bit-field constants used for the flags in an outline's
* `flags` field.
*
* @values:
* FT_OUTLINE_NONE ::
* Value~0 is reserved.
*
* FT_OUTLINE_OWNER ::
* If set, this flag indicates that the outline's field arrays (i.e.,
* `points`, `flags`, and `contours`) are 'owned' by the outline
* object, and should thus be freed when it is destroyed.
*
* FT_OUTLINE_EVEN_ODD_FILL ::
* By default, outlines are filled using the non-zero winding rule. If
* set to 1, the outline will be filled using the even-odd fill rule
* (only works with the smooth rasterizer).
*
* FT_OUTLINE_REVERSE_FILL ::
* By default, outside contours of an outline are oriented in
* clock-wise direction, as defined in the TrueType specification.
* This flag is set if the outline uses the opposite direction
* (typically for Type~1 fonts). This flag is ignored by the scan
* converter.
*
* FT_OUTLINE_IGNORE_DROPOUTS ::
* By default, the scan converter will try to detect drop-outs in an
* outline and correct the glyph bitmap to ensure consistent shape
* continuity. If set, this flag hints the scan-line converter to
* ignore such cases. See below for more information.
*
* FT_OUTLINE_SMART_DROPOUTS ::
* Select smart dropout control. If unset, use simple dropout control.
* Ignored if @FT_OUTLINE_IGNORE_DROPOUTS is set. See below for more
* information.
*
* FT_OUTLINE_INCLUDE_STUBS ::
* If set, turn pixels on for 'stubs', otherwise exclude them. Ignored
* if @FT_OUTLINE_IGNORE_DROPOUTS is set. See below for more
* information.
*
* FT_OUTLINE_OVERLAP ::
* [Since 2.10.3] This flag indicates that this outline contains
* overlapping contours and the anti-aliased renderer should perform
* oversampling to mitigate possible artifacts. This flag should _not_
* be set for well designed glyphs without overlaps because it quadruples
* the rendering time.
*
* FT_OUTLINE_HIGH_PRECISION ::
* This flag indicates that the scan-line converter should try to
* convert this outline to bitmaps with the highest possible quality.
* It is typically set for small character sizes. Note that this is
* only a hint that might be completely ignored by a given
* scan-converter.
*
* FT_OUTLINE_SINGLE_PASS ::
* This flag is set to force a given scan-converter to only use a
* single pass over the outline to render a bitmap glyph image.
* Normally, it is set for very large character sizes. It is only a
* hint that might be completely ignored by a given scan-converter.
*
* @note:
* The flags @FT_OUTLINE_IGNORE_DROPOUTS, @FT_OUTLINE_SMART_DROPOUTS, and
* @FT_OUTLINE_INCLUDE_STUBS are ignored by the smooth rasterizer.
*
* There exists a second mechanism to pass the drop-out mode to the B/W
* rasterizer; see the `tags` field in @FT_Outline.
*
* Please refer to the description of the 'SCANTYPE' instruction in the
* OpenType specification (in file `ttinst1.doc`) how simple drop-outs,
* smart drop-outs, and stubs are defined.
*/
#define FT_OUTLINE_NONE 0x0
#define FT_OUTLINE_OWNER 0x1
#define FT_OUTLINE_EVEN_ODD_FILL 0x2
#define FT_OUTLINE_REVERSE_FILL 0x4
#define FT_OUTLINE_IGNORE_DROPOUTS 0x8
#define FT_OUTLINE_SMART_DROPOUTS 0x10
#define FT_OUTLINE_INCLUDE_STUBS 0x20
#define FT_OUTLINE_OVERLAP 0x40
#define FT_OUTLINE_HIGH_PRECISION 0x100
#define FT_OUTLINE_SINGLE_PASS 0x200
/* these constants are deprecated; use the corresponding */
/* `FT_OUTLINE_XXX` values instead */
#define ft_outline_none FT_OUTLINE_NONE
#define ft_outline_owner FT_OUTLINE_OWNER
#define ft_outline_even_odd_fill FT_OUTLINE_EVEN_ODD_FILL
#define ft_outline_reverse_fill FT_OUTLINE_REVERSE_FILL
#define ft_outline_ignore_dropouts FT_OUTLINE_IGNORE_DROPOUTS
#define ft_outline_high_precision FT_OUTLINE_HIGH_PRECISION
#define ft_outline_single_pass FT_OUTLINE_SINGLE_PASS
/* */
#define FT_CURVE_TAG( flag ) ( flag & 0x03 )
/* see the `tags` field in `FT_Outline` for a description of the values */
#define FT_CURVE_TAG_ON 0x01
#define FT_CURVE_TAG_CONIC 0x00
#define FT_CURVE_TAG_CUBIC 0x02
#define FT_CURVE_TAG_HAS_SCANMODE 0x04
#define FT_CURVE_TAG_TOUCH_X 0x08 /* reserved for TrueType hinter */
#define FT_CURVE_TAG_TOUCH_Y 0x10 /* reserved for TrueType hinter */
#define FT_CURVE_TAG_TOUCH_BOTH ( FT_CURVE_TAG_TOUCH_X | \
FT_CURVE_TAG_TOUCH_Y )
/* values 0x20, 0x40, and 0x80 are reserved */
/* these constants are deprecated; use the corresponding */
/* `FT_CURVE_TAG_XXX` values instead */
#define FT_Curve_Tag_On FT_CURVE_TAG_ON
#define FT_Curve_Tag_Conic FT_CURVE_TAG_CONIC
#define FT_Curve_Tag_Cubic FT_CURVE_TAG_CUBIC
#define FT_Curve_Tag_Touch_X FT_CURVE_TAG_TOUCH_X
#define FT_Curve_Tag_Touch_Y FT_CURVE_TAG_TOUCH_Y
/**************************************************************************
*
* @functype:
* FT_Outline_MoveToFunc
*
* @description:
* A function pointer type used to describe the signature of a 'move to'
* function during outline walking/decomposition.
*
* A 'move to' is emitted to start a new contour in an outline.
*
* @input:
* to ::
* A pointer to the target point of the 'move to'.
*
* user ::
* A typeless pointer, which is passed from the caller of the
* decomposition function.
*
* @return:
* Error code. 0~means success.
*/
typedef int
(*FT_Outline_MoveToFunc)( const FT_Vector* to,
void* user );
#define FT_Outline_MoveTo_Func FT_Outline_MoveToFunc
/**************************************************************************
*
* @functype:
* FT_Outline_LineToFunc
*
* @description:
* A function pointer type used to describe the signature of a 'line to'
* function during outline walking/decomposition.
*
* A 'line to' is emitted to indicate a segment in the outline.
*
* @input:
* to ::
* A pointer to the target point of the 'line to'.
*
* user ::
* A typeless pointer, which is passed from the caller of the
* decomposition function.
*
* @return:
* Error code. 0~means success.
*/
typedef int
(*FT_Outline_LineToFunc)( const FT_Vector* to,
void* user );
#define FT_Outline_LineTo_Func FT_Outline_LineToFunc
/**************************************************************************
*
* @functype:
* FT_Outline_ConicToFunc
*
* @description:
* A function pointer type used to describe the signature of a 'conic to'
* function during outline walking or decomposition.
*
* A 'conic to' is emitted to indicate a second-order Bezier arc in the
* outline.
*
* @input:
* control ::
* An intermediate control point between the last position and the new
* target in `to`.
*
* to ::
* A pointer to the target end point of the conic arc.
*
* user ::
* A typeless pointer, which is passed from the caller of the
* decomposition function.
*
* @return:
* Error code. 0~means success.
*/
typedef int
(*FT_Outline_ConicToFunc)( const FT_Vector* control,
const FT_Vector* to,
void* user );
#define FT_Outline_ConicTo_Func FT_Outline_ConicToFunc
/**************************************************************************
*
* @functype:
* FT_Outline_CubicToFunc
*
* @description:
* A function pointer type used to describe the signature of a 'cubic to'
* function during outline walking or decomposition.
*
* A 'cubic to' is emitted to indicate a third-order Bezier arc.
*
* @input:
* control1 ::
* A pointer to the first Bezier control point.
*
* control2 ::
* A pointer to the second Bezier control point.
*
* to ::
* A pointer to the target end point.
*
* user ::
* A typeless pointer, which is passed from the caller of the
* decomposition function.
*
* @return:
* Error code. 0~means success.
*/
typedef int
(*FT_Outline_CubicToFunc)( const FT_Vector* control1,
const FT_Vector* control2,
const FT_Vector* to,
void* user );
#define FT_Outline_CubicTo_Func FT_Outline_CubicToFunc
/**************************************************************************
*
* @struct:
* FT_Outline_Funcs
*
* @description:
* A structure to hold various function pointers used during outline
* decomposition in order to emit segments, conic, and cubic Beziers.
*
* @fields:
* move_to ::
* The 'move to' emitter.
*
* line_to ::
* The segment emitter.
*
* conic_to ::
* The second-order Bezier arc emitter.
*
* cubic_to ::
* The third-order Bezier arc emitter.
*
* shift ::
* The shift that is applied to coordinates before they are sent to the
* emitter.
*
* delta ::
* The delta that is applied to coordinates before they are sent to the
* emitter, but after the shift.
*
* @note:
* The point coordinates sent to the emitters are the transformed version
* of the original coordinates (this is important for high accuracy
* during scan-conversion). The transformation is simple:
*
* ```
* x' = (x << shift) - delta
* y' = (y << shift) - delta
* ```
*
* Set the values of `shift` and `delta` to~0 to get the original point
* coordinates.
*/
typedef struct FT_Outline_Funcs_
{
FT_Outline_MoveToFunc move_to;
FT_Outline_LineToFunc line_to;
FT_Outline_ConicToFunc conic_to;
FT_Outline_CubicToFunc cubic_to;
int shift;
FT_Pos delta;
} FT_Outline_Funcs;
/**************************************************************************
*
* @section:
* basic_types
*
*/
/**************************************************************************
*
* @macro:
* FT_IMAGE_TAG
*
* @description:
* This macro converts four-letter tags to an unsigned long type.
*
* @note:
* Since many 16-bit compilers don't like 32-bit enumerations, you should
* redefine this macro in case of problems to something like this:
*
* ```
* #define FT_IMAGE_TAG( value, _x1, _x2, _x3, _x4 ) value
* ```
*
* to get a simple enumeration without assigning special numbers.
*/
#ifndef FT_IMAGE_TAG
#define FT_IMAGE_TAG( value, _x1, _x2, _x3, _x4 ) \
value = ( ( FT_STATIC_BYTE_CAST( unsigned long, _x1 ) << 24 ) | \
( FT_STATIC_BYTE_CAST( unsigned long, _x2 ) << 16 ) | \
( FT_STATIC_BYTE_CAST( unsigned long, _x3 ) << 8 ) | \
FT_STATIC_BYTE_CAST( unsigned long, _x4 ) )
#endif /* FT_IMAGE_TAG */
/**************************************************************************
*
* @enum:
* FT_Glyph_Format
*
* @description:
* An enumeration type used to describe the format of a given glyph
* image. Note that this version of FreeType only supports two image
* formats, even though future font drivers will be able to register
* their own format.
*
* @values:
* FT_GLYPH_FORMAT_NONE ::
* The value~0 is reserved.
*
* FT_GLYPH_FORMAT_COMPOSITE ::
* The glyph image is a composite of several other images. This format
* is _only_ used with @FT_LOAD_NO_RECURSE, and is used to report
* compound glyphs (like accented characters).
*
* FT_GLYPH_FORMAT_BITMAP ::
* The glyph image is a bitmap, and can be described as an @FT_Bitmap.
* You generally need to access the `bitmap` field of the
* @FT_GlyphSlotRec structure to read it.
*
* FT_GLYPH_FORMAT_OUTLINE ::
* The glyph image is a vectorial outline made of line segments and
* Bezier arcs; it can be described as an @FT_Outline; you generally
* want to access the `outline` field of the @FT_GlyphSlotRec structure
* to read it.
*
* FT_GLYPH_FORMAT_PLOTTER ::
* The glyph image is a vectorial path with no inside and outside
* contours. Some Type~1 fonts, like those in the Hershey family,
* contain glyphs in this format. These are described as @FT_Outline,
* but FreeType isn't currently capable of rendering them correctly.
*
* FT_GLYPH_FORMAT_SVG ::
* [Since 2.12] The glyph is represented by an SVG document in the
* 'SVG~' table.
*/
typedef enum FT_Glyph_Format_
{
FT_IMAGE_TAG( FT_GLYPH_FORMAT_NONE, 0, 0, 0, 0 ),
FT_IMAGE_TAG( FT_GLYPH_FORMAT_COMPOSITE, 'c', 'o', 'm', 'p' ),
FT_IMAGE_TAG( FT_GLYPH_FORMAT_BITMAP, 'b', 'i', 't', 's' ),
FT_IMAGE_TAG( FT_GLYPH_FORMAT_OUTLINE, 'o', 'u', 't', 'l' ),
FT_IMAGE_TAG( FT_GLYPH_FORMAT_PLOTTER, 'p', 'l', 'o', 't' ),
FT_IMAGE_TAG( FT_GLYPH_FORMAT_SVG, 'S', 'V', 'G', ' ' )
} FT_Glyph_Format;
/* these constants are deprecated; use the corresponding */
/* `FT_Glyph_Format` values instead. */
#define ft_glyph_format_none FT_GLYPH_FORMAT_NONE
#define ft_glyph_format_composite FT_GLYPH_FORMAT_COMPOSITE
#define ft_glyph_format_bitmap FT_GLYPH_FORMAT_BITMAP
#define ft_glyph_format_outline FT_GLYPH_FORMAT_OUTLINE
#define ft_glyph_format_plotter FT_GLYPH_FORMAT_PLOTTER
/*************************************************************************/
/*************************************************************************/
/*************************************************************************/
/***** *****/
/***** R A S T E R D E F I N I T I O N S *****/
/***** *****/
/*************************************************************************/
/*************************************************************************/
/*************************************************************************/
/**************************************************************************
*
* @section:
* raster
*
* @title:
* Scanline Converter
*
* @abstract:
* How vectorial outlines are converted into bitmaps and pixmaps.
*
* @description:
* A raster or a rasterizer is a scan converter in charge of producing a
* pixel coverage bitmap that can be used as an alpha channel when
* compositing a glyph with a background. FreeType comes with two
* rasterizers: bilevel `raster1` and anti-aliased `smooth` are two
* separate modules. They are usually called from the high-level
* @FT_Load_Glyph or @FT_Render_Glyph functions and produce the entire
* coverage bitmap at once, while staying largely invisible to users.
*
* Instead of working with complete coverage bitmaps, it is also possible
* to intercept consecutive pixel runs on the same scanline with the same
* coverage, called _spans_, and process them individually. Only the
* `smooth` rasterizer permits this when calling @FT_Outline_Render with
* @FT_Raster_Params as described below.
*
* Working with either complete bitmaps or spans it is important to think
* of them as colorless coverage objects suitable as alpha channels to
* blend arbitrary colors with a background. For best results, it is
* recommended to use gamma correction, too.
*
* This section also describes the public API needed to set up alternative
* @FT_Renderer modules.
*
* @order:
* FT_Span
* FT_SpanFunc
* FT_Raster_Params
* FT_RASTER_FLAG_XXX
*
* FT_Raster
* FT_Raster_NewFunc
* FT_Raster_DoneFunc
* FT_Raster_ResetFunc
* FT_Raster_SetModeFunc
* FT_Raster_RenderFunc
* FT_Raster_Funcs
*
*/
/**************************************************************************
*
* @struct:
* FT_Span
*
* @description:
* A structure to model a single span of consecutive pixels when
* rendering an anti-aliased bitmap.
*
* @fields:
* x ::
* The span's horizontal start position.
*
* len ::
* The span's length in pixels.
*
* coverage ::
* The span color/coverage, ranging from 0 (background) to 255
* (foreground).
*
* @note:
* This structure is used by the span drawing callback type named
* @FT_SpanFunc that takes the y~coordinate of the span as a parameter.
*
* The anti-aliased rasterizer produces coverage values from 0 to 255,
* that is, from completely transparent to completely opaque.
*/
typedef struct FT_Span_
{
short x;
unsigned short len;
unsigned char coverage;
} FT_Span;
/**************************************************************************
*
* @functype:
* FT_SpanFunc
*
* @description:
* A function used as a call-back by the anti-aliased renderer in order
* to let client applications draw themselves the pixel spans on each
* scan line.
*
* @input:
* y ::
* The scanline's upward y~coordinate.
*
* count ::
* The number of spans to draw on this scanline.
*
* spans ::
* A table of `count` spans to draw on the scanline.
*
* user ::
* User-supplied data that is passed to the callback.
*
* @note:
* This callback allows client applications to directly render the spans
* of the anti-aliased bitmap to any kind of surfaces.
*
* This can be used to write anti-aliased outlines directly to a given
* background bitmap using alpha compositing. It can also be used for
* oversampling and averaging.
*/
typedef void
(*FT_SpanFunc)( int y,
int count,
const FT_Span* spans,
void* user );
#define FT_Raster_Span_Func FT_SpanFunc
/**************************************************************************
*
* @functype:
* FT_Raster_BitTest_Func
*
* @description:
* Deprecated, unimplemented.
*/
typedef int
(*FT_Raster_BitTest_Func)( int y,
int x,
void* user );
/**************************************************************************
*
* @functype:
* FT_Raster_BitSet_Func
*
* @description:
* Deprecated, unimplemented.
*/
typedef void
(*FT_Raster_BitSet_Func)( int y,
int x,
void* user );
/**************************************************************************
*
* @enum:
* FT_RASTER_FLAG_XXX
*
* @description:
* A list of bit flag constants as used in the `flags` field of a
* @FT_Raster_Params structure.
*
* @values:
* FT_RASTER_FLAG_DEFAULT ::
* This value is 0.
*
* FT_RASTER_FLAG_AA ::
* This flag is set to indicate that an anti-aliased glyph image should
* be generated. Otherwise, it will be monochrome (1-bit).
*
* FT_RASTER_FLAG_DIRECT ::
* This flag is set to indicate direct rendering. In this mode, client
* applications must provide their own span callback. This lets them
* directly draw or compose over an existing bitmap. If this bit is
* _not_ set, the target pixmap's buffer _must_ be zeroed before
* rendering and the output will be clipped to its size.
*
* Direct rendering is only possible with anti-aliased glyphs.
*
* FT_RASTER_FLAG_CLIP ::
* This flag is only used in direct rendering mode. If set, the output
* will be clipped to a box specified in the `clip_box` field of the
* @FT_Raster_Params structure. Otherwise, the `clip_box` is
* effectively set to the bounding box and all spans are generated.
*
* FT_RASTER_FLAG_SDF ::
* This flag is set to indicate that a signed distance field glyph
* image should be generated. This is only used while rendering with
* the @FT_RENDER_MODE_SDF render mode.
*/
#define FT_RASTER_FLAG_DEFAULT 0x0
#define FT_RASTER_FLAG_AA 0x1
#define FT_RASTER_FLAG_DIRECT 0x2
#define FT_RASTER_FLAG_CLIP 0x4
#define FT_RASTER_FLAG_SDF 0x8
/* these constants are deprecated; use the corresponding */
/* `FT_RASTER_FLAG_XXX` values instead */
#define ft_raster_flag_default FT_RASTER_FLAG_DEFAULT
#define ft_raster_flag_aa FT_RASTER_FLAG_AA
#define ft_raster_flag_direct FT_RASTER_FLAG_DIRECT
#define ft_raster_flag_clip FT_RASTER_FLAG_CLIP
/**************************************************************************
*
* @struct:
* FT_Raster_Params
*
* @description:
* A structure to hold the parameters used by a raster's render function,
* passed as an argument to @FT_Outline_Render.
*
* @fields:
* target ::
* The target bitmap.
*
* source ::
* A pointer to the source glyph image (e.g., an @FT_Outline).
*
* flags ::
* The rendering flags.
*
* gray_spans ::
* The gray span drawing callback.
*
* black_spans ::
* Unused.
*
* bit_test ::
* Unused.
*
* bit_set ::
* Unused.
*
* user ::
* User-supplied data that is passed to each drawing callback.
*
* clip_box ::
* An optional span clipping box expressed in _integer_ pixels
* (not in 26.6 fixed-point units).
*
* prelines ::
* Pointer of type FT_PreLine, containing line data for a glyph
*
* @note:
* The @FT_RASTER_FLAG_AA bit flag must be set in the `flags` to
* generate an anti-aliased glyph bitmap, otherwise a monochrome bitmap
* is generated. The `target` should have appropriate pixel mode and its
* dimensions define the clipping region.
*
* If both @FT_RASTER_FLAG_AA and @FT_RASTER_FLAG_DIRECT bit flags
* are set in `flags`, the raster calls an @FT_SpanFunc callback
* `gray_spans` with `user` data as an argument ignoring `target`. This
* allows direct composition over a pre-existing user surface to perform
* the span drawing and composition. To optionally clip the spans, set
* the @FT_RASTER_FLAG_CLIP flag and `clip_box`. The monochrome raster
* does not support the direct mode.
*
* The gray-level rasterizer always uses 256 gray levels. If you want
* fewer gray levels, you have to use @FT_RASTER_FLAG_DIRECT and reduce
* the levels in the callback function.
*/
typedef struct FT_Raster_Params_
{
const FT_Bitmap* target;
const void* source;
int flags;
FT_SpanFunc gray_spans;
FT_SpanFunc black_spans; /* unused */
FT_Raster_BitTest_Func bit_test; /* unused */
FT_Raster_BitSet_Func bit_set; /* unused */
void* user;
FT_BBox clip_box;
void* prelines;
} FT_Raster_Params;
/**************************************************************************
*
* @type:
* FT_Raster
*
* @description:
* An opaque handle (pointer) to a raster object. Each object can be
* used independently to convert an outline into a bitmap or pixmap.
*
* @note:
* In FreeType 2, all rasters are now encapsulated within specific
* @FT_Renderer modules and only used in their context.
*
*/
typedef struct FT_RasterRec_* FT_Raster;
/**************************************************************************
*
* @functype:
* FT_Raster_NewFunc
*
* @description:
* A function used to create a new raster object.
*
* @input:
* memory ::
* A handle to the memory allocator.
*
* @output:
* raster ::
* A handle to the new raster object.
*
* @return:
* Error code. 0~means success.
*
* @note:
* The `memory` parameter is a typeless pointer in order to avoid
* un-wanted dependencies on the rest of the FreeType code. In practice,
* it is an @FT_Memory object, i.e., a handle to the standard FreeType
* memory allocator. However, this field can be completely ignored by a
* given raster implementation.
*/
typedef int
(*FT_Raster_NewFunc)( void* memory,
FT_Raster* raster );
#define FT_Raster_New_Func FT_Raster_NewFunc
/**************************************************************************
*
* @functype:
* FT_Raster_DoneFunc
*
* @description:
* A function used to destroy a given raster object.
*
* @input:
* raster ::
* A handle to the raster object.
*/
typedef void
(*FT_Raster_DoneFunc)( FT_Raster raster );
#define FT_Raster_Done_Func FT_Raster_DoneFunc
/**************************************************************************
*
* @functype:
* FT_Raster_ResetFunc
*
* @description:
* FreeType used to provide an area of memory called the 'render pool'
* available to all registered rasterizers. This was not thread safe,
* however, and now FreeType never allocates this pool.
*
* This function is called after a new raster object is created.
*
* @input:
* raster ::
* A handle to the new raster object.
*
* pool_base ::
* Previously, the address in memory of the render pool. Set this to
* `NULL`.
*
* pool_size ::
* Previously, the size in bytes of the render pool. Set this to 0.
*
* @note:
* Rasterizers should rely on dynamic or stack allocation if they want to
* (a handle to the memory allocator is passed to the rasterizer
* constructor).
*/
typedef void
(*FT_Raster_ResetFunc)( FT_Raster raster,
unsigned char* pool_base,
unsigned long pool_size );
#define FT_Raster_Reset_Func FT_Raster_ResetFunc
/**************************************************************************
*
* @functype:
* FT_Raster_SetModeFunc
*
* @description:
* This function is a generic facility to change modes or attributes in a
* given raster. This can be used for debugging purposes, or simply to
* allow implementation-specific 'features' in a given raster module.
*
* @input:
* raster ::
* A handle to the new raster object.
*
* mode ::
* A 4-byte tag used to name the mode or property.
*
* args ::
* A pointer to the new mode/property to use.
*/
typedef int
(*FT_Raster_SetModeFunc)( FT_Raster raster,
unsigned long mode,
void* args );
#define FT_Raster_Set_Mode_Func FT_Raster_SetModeFunc
/**************************************************************************
*
* @functype:
* FT_Raster_RenderFunc
*
* @description:
* Invoke a given raster to scan-convert a given glyph image into a
* target bitmap.
*
* @input:
* raster ::
* A handle to the raster object.
*
* params ::
* A pointer to an @FT_Raster_Params structure used to store the
* rendering parameters.
*
* @return:
* Error code. 0~means success.
*
* @note:
* The exact format of the source image depends on the raster's glyph
* format defined in its @FT_Raster_Funcs structure. It can be an
* @FT_Outline or anything else in order to support a large array of
* glyph formats.
*
* Note also that the render function can fail and return a
* `FT_Err_Unimplemented_Feature` error code if the raster used does not
* support direct composition.
*/
typedef int
(*FT_Raster_RenderFunc)( FT_Raster raster,
const FT_Raster_Params* params );
#define FT_Raster_Render_Func FT_Raster_RenderFunc
/**************************************************************************
*
* @struct:
* FT_Raster_Funcs
*
* @description:
* A structure used to describe a given raster class to the library.
*
* @fields:
* glyph_format ::
* The supported glyph format for this raster.
*
* raster_new ::
* The raster constructor.
*
* raster_reset ::
* Used to reset the render pool within the raster.
*
* raster_render ::
* A function to render a glyph into a given bitmap.
*
* raster_done ::
* The raster destructor.
*/
typedef struct FT_Raster_Funcs_
{
FT_Glyph_Format glyph_format;
FT_Raster_NewFunc raster_new;
FT_Raster_ResetFunc raster_reset;
FT_Raster_SetModeFunc raster_set_mode;
FT_Raster_RenderFunc raster_render;
FT_Raster_DoneFunc raster_done;
} FT_Raster_Funcs;
/* */
FT_END_HEADER
#endif /* FTIMAGE_H_ */
/* END */
/* Local Variables: */
/* coding: utf-8 */
/* End: */
Reference in New Issue View Git Blame Copy Permalink