skia / third_party / freetype2 / 286e9e0d72ddc24d49adc4c6e59ec84d78dee1c2 / . / src / sdf / ftbsdf.c

/**************************************************************************** | |

* | |

* ftbsdf.c | |

* | |

* Signed Distance Field support for bitmap fonts (body only). | |

* | |

* Copyright (C) 2020 by | |

* David Turner, Robert Wilhelm, and Werner Lemberg. | |

* | |

* Written by Anuj Verma. | |

* | |

* 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. | |

* | |

*/ | |

#include <freetype/internal/ftobjs.h> | |

#include <freetype/internal/ftdebug.h> | |

#include <freetype/internal/ftmemory.h> | |

#include <freetype/fttrigon.h> | |

#include "ftsdf.h" | |

#include "ftsdferrs.h" | |

#include "ftsdfcommon.h" | |

/************************************************************************** | |

* | |

* A brief technical overview of how the BSDF rasterizer works | |

* ----------------------------------------------------------- | |

* | |

* [Notes]: | |

* * SDF stands for Signed Distance Field everywhere. | |

* | |

* * BSDF stands for Bitmap to Signed Distance Field rasterizer. | |

* | |

* * This renderer converts rasterized bitmaps to SDF. There is another | |

* renderer called 'sdf', which generates SDF directly from outlines; | |

* see file `ftsdf.c` for more. | |

* | |

* * The idea of generating SDF from bitmaps is taken from two research | |

* papers, where one is dependent on the other: | |

* | |

* - Per-Erik Danielsson: Euclidean Distance Mapping | |

* http://webstaff.itn.liu.se/~stegu/JFA/Danielsson.pdf | |

* | |

* From this paper we use the eight-point sequential Euclidean | |

* distance mapping (8SED). This is the heart of the process used | |

* in this rasterizer. | |

* | |

* - Stefan Gustavson, Robin Strand: Anti-aliased Euclidean distance transform. | |

* http://weber.itn.liu.se/~stegu/aadist/edtaa_preprint.pdf | |

* | |

* The original 8SED algorithm discards the pixels' alpha values, | |

* which can contain information about the actual outline of the | |

* glyph. This paper takes advantage of those alpha values and | |

* approximates outline pretty accurately. | |

* | |

* * This rasterizer also works for monochrome bitmaps. However, the | |

* result is not as accurate since we don't have any way to | |

* approximate outlines from binary bitmaps. | |

* | |

* ======================================================================== | |

* | |

* Generating SDF from bitmap is done in several steps. | |

* | |

* (1) The only information we have is the bitmap itself. It can | |

* be monochrome or anti-aliased. If it is anti-aliased, pixel values | |

* are nothing but coverage values. These coverage values can be used | |

* to extract information about the outline of the image. For | |

* example, if the pixel's alpha value is 0.5, then we can safely | |

* assume that the outline passes through the center of the pixel. | |

* | |

* (2) Find edge pixels in the bitmap (see `bsdf_is_edge` for more). For | |

* all edge pixels we use the Anti-aliased Euclidean distance | |

* transform algorithm and compute approximate edge distances (see | |

* `compute_edge_distance` and/or the second paper for more). | |

* | |

* (3) Now that we have computed approximate distances for edge pixels we | |

* use the 8SED algorithm to basically sweep the entire bitmap and | |

* compute distances for the rest of the pixels. (Since the algorithm | |

* is pretty convoluted it is only explained briefly in a comment to | |

* function `edt8`. To see the actual algorithm refer to the first | |

* paper.) | |

* | |

* (4) Finally, compute the sign for each pixel. This is done in function | |

* `finalize_sdf`. The basic idea is that if a pixel's original | |

* alpha/coverage value is greater than 0.5 then it is 'inside' (and | |

* 'outside' otherwise). | |

* | |

* Pseudo Code: | |

* | |

* ``` | |

* b = source bitmap; | |

* t = target bitmap; | |

* dm = list of distances; // dimension equal to b | |

* | |

* foreach grid_point (x, y) in b: | |

* { | |

* if (is_edge(x, y)): | |

* dm = approximate_edge_distance(b, x, y); | |

* | |

* // do the 8SED on the distances | |

* edt8(dm); | |

* | |

* // determine the signs | |

* determine_signs(dm): | |

* | |

* // copy SDF data to the target bitmap | |

* copy(dm to t); | |

* } | |

* | |

*/ | |

/************************************************************************** | |

* | |

* 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 bsdf | |

/************************************************************************** | |

* | |

* useful macros | |

* | |

*/ | |

#define ONE 65536 /* 1 in 16.16 */ | |

/************************************************************************** | |

* | |

* structs | |

* | |

*/ | |

/************************************************************************** | |

* | |

* @Struct: | |

* BSDF_TRaster | |

* | |

* @Description: | |

* This struct is used in place of @FT_Raster and is stored within the | |

* internal FreeType renderer struct. While rasterizing this is passed | |

* to the @FT_Raster_RenderFunc function, which then can be used however | |

* we want. | |

* | |

* @Fields: | |

* memory :: | |

* Used internally to allocate intermediate memory while raterizing. | |

* | |

*/ | |

typedef struct BSDF_TRaster_ | |

{ | |

FT_Memory memory; | |

} BSDF_TRaster; | |

/************************************************************************** | |

* | |

* @Struct: | |

* ED | |

* | |

* @Description: | |

* Euclidean distance. It gets used for Euclidean distance transforms; | |

* it can also be interpreted as an edge distance. | |

* | |

* @Fields: | |

* dist :: | |

* Vector length of the `near` parameter. Can be squared or absolute | |

* depending on the `USE_SQUARED_DISTANCES` macro defined in file | |

* `ftsdfcommon.h`. | |

* | |

* near :: | |

* Vector to the nearest edge. Can also be interpreted as shortest | |

* distance of a point. | |

* | |

* alpha :: | |

* Alpha value of the original bitmap from which we generate SDF. | |

* Needed for computing the gradient and determining the proper sign | |

* of a pixel. | |

* | |

*/ | |

typedef struct ED_ | |

{ | |

FT_16D16 dist; | |

FT_16D16_Vec near; | |

FT_Byte alpha; | |

} ED; | |

/************************************************************************** | |

* | |

* @Struct: | |

* BSDF_Worker | |

* | |

* @Description: | |

* A convenience struct that is passed to functions while generating | |

* SDF; most of those functions require the same parameters. | |

* | |

* @Fields: | |

* distance_map :: | |

* A one-dimensional array that gets interpreted as two-dimensional | |

* one. It contains the Euclidean distances of all points of the | |

* bitmap. | |

* | |

* width :: | |

* Width of the above `distance_map`. | |

* | |

* rows :: | |

* Number of rows in the above `distance_map`. | |

* | |

* params :: | |

* Internal parameters and properties required by the rasterizer. See | |

* file `ftsdf.h` for more. | |

* | |

*/ | |

typedef struct BSDF_Worker_ | |

{ | |

ED* distance_map; | |

FT_Int width; | |

FT_Int rows; | |

SDF_Raster_Params params; | |

} BSDF_Worker; | |

/************************************************************************** | |

* | |

* initializer | |

* | |

*/ | |

static const ED zero_ed = { 0, { 0, 0 }, 0 }; | |

/************************************************************************** | |

* | |

* rasterizer functions | |

* | |

*/ | |

/************************************************************************** | |

* | |

* @Function: | |

* bsdf_is_edge | |

* | |

* @Description: | |

* Check whether a pixel is an edge pixel, i.e., whether it is | |

* surrounded by a completely black pixel (zero alpha), and the current | |

* pixel is not a completely black pixel. | |

* | |

* @Input: | |

* dm :: | |

* Array of distances. The parameter must point to the current | |

* pixel, i.e., the pixel that is to be checked for being an edge. | |

* | |

* x :: | |

* The x position of the current pixel. | |

* | |

* y :: | |

* The y position of the current pixel. | |

* | |

* w :: | |

* Width of the bitmap. | |

* | |

* r :: | |

* Number of rows in the bitmap. | |

* | |

* @Return: | |

* 1~if the current pixel is an edge pixel, 0~otherwise. | |

* | |

*/ | |

#ifdef CHECK_NEIGHBOR | |

#undef CHECK_NEIGHBOR | |

#endif | |

#define CHECK_NEIGHBOR( x_offset, y_offset ) \ | |

if ( x + x_offset >= 0 && x + x_offset < w && \ | |

y + y_offset >= 0 && y + y_offset < r ) \ | |

{ \ | |

num_neighbors++; \ | |

\ | |

to_check = dm + y_offset * w + x_offset; \ | |

if ( to_check->alpha == 0 ) \ | |

{ \ | |

is_edge = 1; \ | |

goto Done; \ | |

} \ | |

} | |

static FT_Bool | |

bsdf_is_edge( ED* dm, /* distance map */ | |

FT_Int x, /* x index of point to check */ | |

FT_Int y, /* y index of point to check */ | |

FT_Int w, /* width */ | |

FT_Int r ) /* rows */ | |

{ | |

FT_Bool is_edge = 0; | |

ED* to_check = NULL; | |

FT_Int num_neighbors = 0; | |

if ( dm->alpha == 0 ) | |

goto Done; | |

if ( dm->alpha > 0 && dm->alpha < 255 ) | |

{ | |

is_edge = 1; | |

goto Done; | |

} | |

/* up */ | |

CHECK_NEIGHBOR( 0, -1 ); | |

/* down */ | |

CHECK_NEIGHBOR( 0, 1 ); | |

/* left */ | |

CHECK_NEIGHBOR( -1, 0 ); | |

/* right */ | |

CHECK_NEIGHBOR( 1, 0 ); | |

/* up left */ | |

CHECK_NEIGHBOR( -1, -1 ); | |

/* up right */ | |

CHECK_NEIGHBOR( 1, -1 ); | |

/* down left */ | |

CHECK_NEIGHBOR( -1, 1 ); | |

/* down right */ | |

CHECK_NEIGHBOR( 1, 1 ); | |

if ( num_neighbors != 8 ) | |

is_edge = 1; | |

Done: | |

return is_edge; | |

} | |

#undef CHECK_NEIGHBOR | |

/************************************************************************** | |

* | |

* @Function: | |

* compute_edge_distance | |

* | |

* @Description: | |

* Approximate the outline and compute the distance from `current` | |

* to the approximated outline. | |

* | |

* @Input: | |

* current :: | |

* Array of Euclidean distances. `current` must point to the position | |

* for which the distance is to be caculated. We treat this array as | |

* a two-dimensional array mapped to a one-dimensional array. | |

* | |

* x :: | |

* The x coordinate of the `current` parameter in the array. | |

* | |

* y :: | |

* The y coordinate of the `current` parameter in the array. | |

* | |

* w :: | |

* The width of the distances array. | |

* | |

* r :: | |

* Number of rows in the distances array. | |

* | |

* @Return: | |

* A vector pointing to the approximate edge distance. | |

* | |

* @Note: | |

* This is a computationally expensive function. Try to reduce the | |

* number of calls to this function. Moreover, this must only be used | |

* for edge pixel positions. | |

* | |

*/ | |

static FT_16D16_Vec | |

compute_edge_distance( ED* current, | |

FT_Int x, | |

FT_Int y, | |

FT_Int w, | |

FT_Int r ) | |

{ | |

/* | |

* This function, based on the paper presented by Stefan Gustavson and | |

* Robin Strand, gets used to approximate edge distances from | |

* anti-aliased bitmaps. | |

* | |

* The algorithm is as follows. | |

* | |

* (1) In anti-aliased images, the pixel's alpha value is the coverage | |

* of the pixel by the outline. For example, if the alpha value is | |

* 0.5f we can assume that the outline passes through the center of | |

* the pixel. | |

* | |

* (2) For this reason we can use that alpha value to approximate the real | |

* distance of the pixel to edge pretty accurately. A simple | |

* approximation is `(0.5f - alpha)`, assuming that the outline is | |

* parallel to the x or y~axis. However, in this algorithm we use a | |

* different approximation which is quite accurate even for | |

* non-axis-aligned edges. | |

* | |

* (3) The only remaining piece of information that we cannot | |

* approximate directly from the alpha is the direction of the edge. | |

* This is where we use Sobel's operator to compute the gradient of | |

* the pixel. The gradient give us a pretty good approximation of | |

* the edge direction. We use a 3x3 kernel filter to compute the | |

* gradient. | |

* | |

* (4) After the above two steps we have both the direction and the | |

* distance to the edge which is used to generate the Signed | |

* Distance Field. | |

* | |

* References: | |

* | |

* - Anti-Aliased Euclidean Distance Transform: | |

* http://weber.itn.liu.se/~stegu/aadist/edtaa_preprint.pdf | |

* - Sobel Operator: | |

* https://en.wikipedia.org/wiki/Sobel_operator | |

*/ | |

FT_16D16_Vec g = { 0, 0 }; | |

FT_16D16 dist, current_alpha; | |

FT_16D16 a1, temp; | |

FT_16D16 gx, gy; | |

FT_16D16 alphas[9]; | |

/* Since our spread cannot be 0, this condition */ | |

/* can never be true. */ | |

if ( x <= 0 || x >= w - 1 || | |

y <= 0 || y >= r - 1 ) | |

return g; | |

/* initialize the alphas */ | |

alphas[0] = 256 * (FT_16D16)current[-w - 1].alpha; | |

alphas[1] = 256 * (FT_16D16)current[-w ].alpha; | |

alphas[2] = 256 * (FT_16D16)current[-w + 1].alpha; | |

alphas[3] = 256 * (FT_16D16)current[ -1].alpha; | |

alphas[4] = 256 * (FT_16D16)current[ 0].alpha; | |

alphas[5] = 256 * (FT_16D16)current[ 1].alpha; | |

alphas[6] = 256 * (FT_16D16)current[ w - 1].alpha; | |

alphas[7] = 256 * (FT_16D16)current[ w ].alpha; | |

alphas[8] = 256 * (FT_16D16)current[ w + 1].alpha; | |

current_alpha = alphas[4]; | |

/* Compute the gradient using the Sobel operator. */ | |

/* In this case we use the following 3x3 filters: */ | |

/* */ | |

/* For x: | -1 0 -1 | */ | |

/* | -root(2) 0 root(2) | */ | |

/* | -1 0 1 | */ | |

/* */ | |

/* For y: | -1 -root(2) -1 | */ | |

/* | 0 0 0 | */ | |

/* | 1 root(2) 1 | */ | |

/* */ | |

/* [Note]: 92681 is root(2) in 16.16 format. */ | |

g.x = -alphas[0] - | |

FT_MulFix( alphas[3], 92681 ) - | |

alphas[6] + | |

alphas[2] + | |

FT_MulFix( alphas[5], 92681 ) + | |

alphas[8]; | |

g.y = -alphas[0] - | |

FT_MulFix( alphas[1], 92681 ) - | |

alphas[2] + | |

alphas[6] + | |

FT_MulFix( alphas[7], 92681 ) + | |

alphas[8]; | |

FT_Vector_NormLen( &g ); | |

/* The gradient gives us the direction of the */ | |

/* edge for the current pixel. Once we have the */ | |

/* approximate direction of the edge, we can */ | |

/* approximate the edge distance much better. */ | |

if ( g.x == 0 || g.y == 0 ) | |

dist = ONE / 2 - alphas[4]; | |

else | |

{ | |

gx = g.x; | |

gy = g.y; | |

gx = FT_ABS( gx ); | |

gy = FT_ABS( gy ); | |

if ( gx < gy ) | |

{ | |

temp = gx; | |

gx = gy; | |

gy = temp; | |

} | |

a1 = FT_DivFix( gy, gx ) / 2; | |

if ( current_alpha < a1 ) | |

dist = ( gx + gy ) / 2 - | |

square_root( 2 * FT_MulFix( gx, | |

FT_MulFix( gy, | |

current_alpha ) ) ); | |

else if ( current_alpha < ( ONE - a1 ) ) | |

dist = FT_MulFix( ONE / 2 - current_alpha, gx ); | |

else | |

dist = -( gx + gy ) / 2 + | |

square_root( 2 * FT_MulFix( gx, | |

FT_MulFix( gy, | |

ONE - current_alpha ) ) ); | |

} | |

g.x = FT_MulFix( g.x, dist ); | |

g.y = FT_MulFix( g.y, dist ); | |

return g; | |

} | |

/************************************************************************** | |

* | |

* @Function: | |

* bsdf_approximate_edge | |

* | |

* @Description: | |

* Loops over all the pixels and call `compute_edge_distance` only for | |

* edge pixels. This maked the process a lot faster since | |

* `compute_edge_distance` uses functions such as `FT_Vector_NormLen', | |

* which are quite slow. | |

* | |

* @InOut: | |

* worker :: | |

* Contains the distance map as well as all the relevant parameters | |

* required by the function. | |

* | |

* @Return: | |

* FreeType error, 0 means success. | |

* | |

* @Note: | |

* The function directly manipulates `worker->distance_map`. | |

* | |

*/ | |

static FT_Error | |

bsdf_approximate_edge( BSDF_Worker* worker ) | |

{ | |

FT_Error error = FT_Err_Ok; | |

FT_Int i, j; | |

FT_Int index; | |

ED* ed; | |

if ( !worker || !worker->distance_map ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

ed = worker->distance_map; | |

for ( j = 0; j < worker->rows; j++ ) | |

{ | |

for ( i = 0; i < worker->width; i++ ) | |

{ | |

index = j * worker->width + i; | |

if ( bsdf_is_edge( worker->distance_map + index, | |

i, j, | |

worker->width, | |

worker->rows ) ) | |

{ | |

/* approximate the edge distance for edge pixels */ | |

ed[index].near = compute_edge_distance( ed + index, | |

i, j, | |

worker->width, | |

worker->rows ); | |

ed[index].dist = VECTOR_LENGTH_16D16( ed[index].near ); | |

} | |

else | |

{ | |

/* for non-edge pixels assign far away distances */ | |

ed[index].dist = 400 * ONE; | |

ed[index].near.x = 200 * ONE; | |

ed[index].near.y = 200 * ONE; | |

} | |

} | |

} | |

Exit: | |

return error; | |

} | |

/************************************************************************** | |

* | |

* @Function: | |

* bsdf_init_distance_map | |

* | |

* @Description: | |

* Initialize the distance map according to the '8-point sequential | |

* Euclidean distance mapping' (8SED) algorithm. Basically it copies | |

* the `source` bitmap alpha values to the `distance_map->alpha` | |

* parameter of `worker`. | |

* | |

* @Input: | |

* source :: | |

* Source bitmap to copy the data from. | |

* | |

* @Output: | |

* worker :: | |

* Target distance map to copy the data to. | |

* | |

* @Return: | |

* FreeType error, 0 means success. | |

* | |

*/ | |

static FT_Error | |

bsdf_init_distance_map( const FT_Bitmap* source, | |

BSDF_Worker* worker ) | |

{ | |

FT_Error error = FT_Err_Ok; | |

FT_Int x_diff, y_diff; | |

FT_Int t_i, t_j, s_i, s_j; | |

FT_Byte* s; | |

ED* t; | |

/* again check the parameters (probably unnecessary) */ | |

if ( !source || !worker ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

/* Because of the way we convert a bitmap to SDF, */ | |

/* i.e., aligning the source to the center of the */ | |

/* target, the target's width and rows must be */ | |

/* checked before copying. */ | |

if ( worker->width < (FT_Int)source->width || | |

worker->rows < (FT_Int)source->rows ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

/* check pixel mode */ | |

if ( source->pixel_mode == FT_PIXEL_MODE_NONE ) | |

{ | |

FT_ERROR(( "bsdf_copy_source_to_target:" | |

" Invalid pixel mode of source bitmap" )); | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

#ifdef FT_DEBUG_LEVEL_TRACE | |

if ( source->pixel_mode == FT_PIXEL_MODE_MONO ) | |

{ | |

FT_TRACE0(( "bsdf_copy_source_to_target:" | |

" The `bsdf' renderer can convert monochrome\n" )); | |

FT_TRACE0(( " " | |

" bitmaps to SDF but the results are not perfect\n" )); | |

FT_TRACE0(( " " | |

" because there is no way to approximate actual\n" )); | |

FT_TRACE0(( " " | |

" outlines from monochrome bitmaps. Consider\n" )); | |

FT_TRACE0(( " " | |

" using an anti-aliased bitmap instead.\n" )); | |

} | |

#endif | |

/* Calculate the width and row differences */ | |

/* between target and source. */ | |

x_diff = worker->width - source->width; | |

y_diff = worker->rows - source->rows; | |

x_diff /= 2; | |

y_diff /= 2; | |

t = (ED*)worker->distance_map; | |

s = source->buffer; | |

/* For now we only support pixel mode `FT_PIXEL_MODE_MONO` */ | |

/* and `FT_PIXEL_MODE_GRAY`. More will be added later. */ | |

/* */ | |

/* [NOTE]: We can also use @FT_Bitmap_Convert to convert */ | |

/* bitmap to 8bpp. To avoid extra allocation and */ | |

/* since the target bitmap can be 16bpp we manually */ | |

/* convert the source bitmap to the desired bpp. */ | |

switch ( source->pixel_mode ) | |

{ | |

case FT_PIXEL_MODE_MONO: | |

{ | |

FT_Int t_width = worker->width; | |

FT_Int t_rows = worker->rows; | |

FT_Int s_width = source->width; | |

FT_Int s_rows = source->rows; | |

for ( t_j = 0; t_j < t_rows; t_j++ ) | |

{ | |

for ( t_i = 0; t_i < t_width; t_i++ ) | |

{ | |

FT_Int t_index = t_j * t_width + t_i; | |

FT_Int s_index; | |

FT_Int div, mod; | |

FT_Byte pixel, byte; | |

t[t_index] = zero_ed; | |

s_i = t_i - x_diff; | |

s_j = t_j - y_diff; | |

/* Assign 0 to padding similar to */ | |

/* the source bitmap. */ | |

if ( s_i < 0 || s_i >= s_width || | |

s_j < 0 || s_j >= s_rows ) | |

continue; | |

if ( worker->params.flip_y ) | |

s_index = ( s_rows - s_j - 1 ) * source->pitch; | |

else | |

s_index = s_j * source->pitch; | |

div = s_index + s_i / 8; | |

mod = 7 - s_i % 8; | |

pixel = s[div]; | |

byte = 1 << mod; | |

t[t_index].alpha = pixel & byte ? 255 : 0; | |

pixel = 0; | |

} | |

} | |

} | |

break; | |

case FT_PIXEL_MODE_GRAY: | |

{ | |

FT_Int t_width = worker->width; | |

FT_Int t_rows = worker->rows; | |

FT_Int s_width = source->width; | |

FT_Int s_rows = source->rows; | |

/* loop over all pixels and assign pixel values from source */ | |

for ( t_j = 0; t_j < t_rows; t_j++ ) | |

{ | |

for ( t_i = 0; t_i < t_width; t_i++ ) | |

{ | |

FT_Int t_index = t_j * t_width + t_i; | |

FT_Int s_index; | |

t[t_index] = zero_ed; | |

s_i = t_i - x_diff; | |

s_j = t_j - y_diff; | |

/* Assign 0 to padding similar to */ | |

/* the source bitmap. */ | |

if ( s_i < 0 || s_i >= s_width || | |

s_j < 0 || s_j >= s_rows ) | |

continue; | |

if ( worker->params.flip_y ) | |

s_index = ( s_rows - s_j - 1 ) * s_width + s_i; | |

else | |

s_index = s_j * s_width + s_i; | |

/* simply copy the alpha values */ | |

t[t_index].alpha = s[s_index]; | |

} | |

} | |

} | |

break; | |

default: | |

FT_ERROR(( "bsdf_copy_source_to_target:" | |

" unsopported pixel mode of source bitmap\n" )); | |

error = FT_THROW( Unimplemented_Feature ); | |

break; | |

} | |

Exit: | |

return error; | |

} | |

/************************************************************************** | |

* | |

* @Function: | |

* compare_neighbor | |

* | |

* @Description: | |

* Compare neighbor pixel (which is defined by the offset) and update | |

* `current` distance if the new distance is shorter than the original. | |

* | |

* @Input: | |

* x_offset :: | |

* X offset of the neighbor to be checked. The offset is relative to | |

* the `current`. | |

* | |

* y_offset :: | |

* Y offset of the neighbor to be checked. The offset is relative to | |

* the `current`. | |

* | |

* width :: | |

* Width of the `current` array. | |

* | |

* @InOut: | |

* current :: | |

* Pointer into array of distances. This parameter must point to the | |

* position whose neighbor is to be checked. The array is treated as | |

* a two-dimensional array. | |

* | |

*/ | |

static void | |

compare_neighbor( ED* current, | |

FT_Int x_offset, | |

FT_Int y_offset, | |

FT_Int width ) | |

{ | |

ED* to_check; | |

FT_16D16 dist; | |

FT_16D16_Vec dist_vec; | |

to_check = current + ( y_offset * width ) + x_offset; | |

/* | |

* While checking for the nearest point we first approximate the | |

* distance of `current` by adding the deviation (which is sqrt(2) at | |

* most). Only if the new value is less than the current value we | |

* calculate the actual distances using `FT_Vector_Length`. This last | |

* step can be omitted by using squared distances. | |

*/ | |

/* | |

* Approximate the distance. We subtract 1 to avoid precision errors, | |

* which could happen because the two directions can be opposite. | |

*/ | |

dist = to_check->dist - ONE; | |

if ( dist < current->dist ) | |

{ | |

dist_vec = to_check->near; | |

dist_vec.x += x_offset * ONE; | |

dist_vec.y += y_offset * ONE; | |

dist = VECTOR_LENGTH_16D16( dist_vec ); | |

if ( dist < current->dist ) | |

{ | |

current->dist = dist; | |

current->near = dist_vec; | |

} | |

} | |

} | |

/************************************************************************** | |

* | |

* @Function: | |

* first_pass | |

* | |

* @Description: | |

* First pass of the 8SED algorithm. Loop over the bitmap from top to | |

* bottom and scan each row left to right, updating the distances in | |

* `worker->distance_map`. | |

* | |

* @InOut: | |

* worker:: | |

* Contains all the relevant parameters. | |

* | |

*/ | |

static void | |

first_pass( BSDF_Worker* worker ) | |

{ | |

FT_Int i, j; /* iterators */ | |

FT_Int w, r; /* width, rows */ | |

ED* dm; /* distance map */ | |

dm = worker->distance_map; | |

w = worker->width; | |

r = worker->rows; | |

/* Start scanning from top to bottom and sweep each */ | |

/* row back and forth comparing the distances of the */ | |

/* neighborhood. Leave the first row as it has no top */ | |

/* neighbor; it will be covered in the second scan of */ | |

/* the image (from bottom to top). */ | |

for ( j = 1; j < r; j++ ) | |

{ | |

FT_Int index; | |

ED* current; | |

/* Forward pass of rows (left -> right). Leave the first */ | |

/* column, which gets covered in the backward pass. */ | |

for ( i = 1; i < w; i++ ) | |

{ | |

index = j * w + i; | |

current = dm + index; | |

/* left-up */ | |

compare_neighbor( current, -1, -1, w ); | |

/* up */ | |

compare_neighbor( current, 0, -1, w ); | |

/* up-right */ | |

compare_neighbor( current, 1, -1, w ); | |

/* left */ | |

compare_neighbor( current, -1, 0, w ); | |

} | |

/* Backward pass of rows (right -> left). Leave the last */ | |

/* column, which was already covered in the forward pass. */ | |

for ( i = w - 2; i >= 0; i-- ) | |

{ | |

index = j * w + i; | |

current = dm + index; | |

/* right */ | |

compare_neighbor( current, 1, 0, w ); | |

} | |

} | |

} | |

/************************************************************************** | |

* | |

* @Function: | |

* second_pass | |

* | |

* @Description: | |

* Second pass of the 8SED algorithm. Loop over the bitmap from bottom | |

* to top and scan each row left to right, updating the distances in | |

* `worker->distance_map`. | |

* | |

* @InOut: | |

* worker:: | |

* Contains all the relevant parameters. | |

* | |

*/ | |

static void | |

second_pass( BSDF_Worker* worker ) | |

{ | |

FT_Int i, j; /* iterators */ | |

FT_Int w, r; /* width, rows */ | |

ED* dm; /* distance map */ | |

dm = worker->distance_map; | |

w = worker->width; | |

r = worker->rows; | |

/* Start scanning from bottom to top and sweep each */ | |

/* row back and forth comparing the distances of the */ | |

/* neighborhood. Leave the last row as it has no down */ | |

/* neighbor; it is already covered in the first scan */ | |

/* of the image (from top to bottom). */ | |

for ( j = r - 2; j >= 0; j-- ) | |

{ | |

FT_Int index; | |

ED* current; | |

/* Forward pass of rows (left -> right). Leave the first */ | |

/* column, which gets covered in the backward pass. */ | |

for ( i = 1; i < w; i++ ) | |

{ | |

index = j * w + i; | |

current = dm + index; | |

/* left-up */ | |

compare_neighbor( current, -1, 1, w ); | |

/* up */ | |

compare_neighbor( current, 0, 1, w ); | |

/* up-right */ | |

compare_neighbor( current, 1, 1, w ); | |

/* left */ | |

compare_neighbor( current, -1, 0, w ); | |

} | |

/* Backward pass of rows (right -> left). Leave the last */ | |

/* column, which was already covered in the forward pass. */ | |

for ( i = w - 2; i >= 0; i-- ) | |

{ | |

index = j * w + i; | |

current = dm + index; | |

/* right */ | |

compare_neighbor( current, 1, 0, w ); | |

} | |

} | |

} | |

/************************************************************************** | |

* | |

* @Function: | |

* edt8 | |

* | |

* @Description: | |

* Compute the distance map of the a bitmap. Execute both first and | |

* second pass of the 8SED algorithm. | |

* | |

* @InOut: | |

* worker:: | |

* Contains all the relevant parameters. | |

* | |

* @Return: | |

* FreeType error, 0 means success. | |

* | |

*/ | |

static FT_Error | |

edt8( BSDF_Worker* worker ) | |

{ | |

FT_Error error = FT_Err_Ok; | |

if ( !worker || !worker->distance_map ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

/* first scan of the image */ | |

first_pass( worker ); | |

/* second scan of the image */ | |

second_pass( worker ); | |

Exit: | |

return error; | |

} | |

/************************************************************************** | |

* | |

* @Function: | |

* finalize_sdf | |

* | |

* @Description: | |

* Copy the SDF data from `worker->distance_map` to the `target` bitmap. | |

* Also transform the data to output format, (which is 6.10 fixed-point | |

* format at the moment). | |

* | |

* @Input: | |

* worker :: | |

* Contains source distance map and other SDF data. | |

* | |

* @Output: | |

* target :: | |

* Target bitmap to which the SDF data is copied to. | |

* | |

* @Return: | |

* FreeType error, 0 means success. | |

* | |

*/ | |

static FT_Error | |

finalize_sdf( BSDF_Worker* worker, | |

const FT_Bitmap* target ) | |

{ | |

FT_Error error = FT_Err_Ok; | |

FT_Int w, r; | |

FT_Int i, j; | |

FT_6D10* t_buffer; | |

FT_16D16 spread; | |

if ( !worker || !target ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

w = target->width; | |

r = target->rows; | |

t_buffer = (FT_6D10*)target->buffer; | |

if ( w != worker->width || | |

r != worker->rows ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

#if USE_SQUARED_DISTANCES | |

spread = FT_INT_16D16( worker->params.spread * | |

worker->params.spread ); | |

#else | |

spread = FT_INT_16D16( worker->params.spread ); | |

#endif | |

for ( j = 0; j < r; j++ ) | |

{ | |

for ( i = 0; i < w; i++ ) | |

{ | |

FT_Int index; | |

FT_16D16 dist; | |

FT_6D10 final_dist; | |

FT_Char sign; | |

index = j * w + i; | |

dist = worker->distance_map[index].dist; | |

if ( dist < 0 || dist > spread ) | |

dist = spread; | |

#if USE_SQUARED_DISTANCES | |

dist = square_root( dist ); | |

#endif | |

/* convert from 16.16 to 6.10 */ | |

dist /= 64; | |

final_dist = (FT_6D10)(dist & 0x0000FFFF); | |

/* We assume that if the pixel is inside a contour */ | |

/* its coverage value must be > 127. */ | |

sign = worker->distance_map[index].alpha < 127 ? -1 : 1; | |

/* flip the sign according to the property */ | |

if ( worker->params.flip_sign ) | |

sign = -sign; | |

t_buffer[index] = final_dist * sign; | |

} | |

} | |

Exit: | |

return error; | |

} | |

/************************************************************************** | |

* | |

* interface functions | |

* | |

*/ | |

/* called when adding a new module through @FT_Add_Module */ | |

static FT_Error | |

bsdf_raster_new( FT_Memory memory, | |

FT_Raster* araster ) | |

{ | |

FT_Error error = FT_Err_Ok; | |

BSDF_TRaster* raster = NULL; | |

*araster = 0; | |

if ( !FT_ALLOC( raster, sizeof ( BSDF_TRaster ) ) ) | |

{ | |

raster->memory = memory; | |

*araster = (FT_Raster)raster; | |

} | |

return error; | |

} | |

/* unused */ | |

static void | |

bsdf_raster_reset( FT_Raster raster, | |

unsigned char* pool_base, | |

unsigned long pool_size ) | |

{ | |

FT_UNUSED( raster ); | |

FT_UNUSED( pool_base ); | |

FT_UNUSED( pool_size ); | |

} | |

/* unused */ | |

static FT_Error | |

bsdf_raster_set_mode( FT_Raster raster, | |

unsigned long mode, | |

void* args ) | |

{ | |

FT_UNUSED( raster ); | |

FT_UNUSED( mode ); | |

FT_UNUSED( args ); | |

return FT_Err_Ok; | |

} | |

/* called while rendering through @FT_Render_Glyph */ | |

static FT_Error | |

bsdf_raster_render( FT_Raster raster, | |

const FT_Raster_Params* params ) | |

{ | |

FT_Error error = FT_Err_Ok; | |

FT_Memory memory = NULL; | |

const FT_Bitmap* source = NULL; | |

const FT_Bitmap* target = NULL; | |

BSDF_TRaster* bsdf_raster = (BSDF_TRaster*)raster; | |

BSDF_Worker worker; | |

const SDF_Raster_Params* sdf_params = (const SDF_Raster_Params*)params; | |

worker.distance_map = NULL; | |

/* check for valid parameters */ | |

if ( !raster || !params ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

/* check whether the flag is set */ | |

if ( sdf_params->root.flags != FT_RASTER_FLAG_SDF ) | |

{ | |

error = FT_THROW( Raster_Corrupted ); | |

goto Exit; | |

} | |

source = sdf_params->root.source; | |

target = sdf_params->root.target; | |

/* check source and target bitmap */ | |

if ( !source || !target ) | |

{ | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

memory = bsdf_raster->memory; | |

if ( !memory ) | |

{ | |

FT_TRACE0(( "bsdf_raster_render: Raster not set up properly,\n" )); | |

FT_TRACE0(( " unable to find memory handle.\n" )); | |

error = FT_THROW( Invalid_Handle ); | |

goto Exit; | |

} | |

/* check whether spread is set properly */ | |

if ( sdf_params->spread > MAX_SPREAD || | |

sdf_params->spread < MIN_SPREAD ) | |

{ | |

FT_TRACE0(( "bsdf_raster_render:" | |

" The `spread' field of `SDF_Raster_Params'\n" )); | |

FT_TRACE0(( " " | |

" is invalid; the value of this field must be\n" )); | |

FT_TRACE0(( " " | |

" within [%d, %d].\n", | |

MIN_SPREAD, MAX_SPREAD )); | |

FT_TRACE0(( " " | |

" Also, you must pass `SDF_Raster_Params'\n" )); | |

FT_TRACE0(( " " | |

" instead of the default `FT_Raster_Params'\n" )); | |

FT_TRACE0(( " " | |

" while calling this function and set the fields\n" )); | |

FT_TRACE0(( " " | |

" accordingly.\n" )); | |

error = FT_THROW( Invalid_Argument ); | |

goto Exit; | |

} | |

/* set up the worker */ | |

/* allocate the distance map */ | |

if ( FT_QALLOC_MULT( worker.distance_map, target->rows, | |

target->width * sizeof ( *worker.distance_map ) ) ) | |

goto Exit; | |

worker.width = target->width; | |

worker.rows = target->rows; | |

worker.params = *sdf_params; | |

FT_CALL( bsdf_init_distance_map( source, &worker ) ); | |

FT_CALL( bsdf_approximate_edge( &worker ) ); | |

FT_CALL( edt8( &worker ) ); | |

FT_CALL( finalize_sdf( &worker, target ) ); | |

FT_TRACE0(( "bsdf_raster_render: Total memory used = %ld\n", | |

worker.width * worker.rows * | |

sizeof ( *worker.distance_map ) )); | |

Exit: | |

if ( worker.distance_map ) | |

FT_FREE( worker.distance_map ); | |

return error; | |

} | |

/* called while deleting `FT_Library` only if the module is added */ | |

static void | |

bsdf_raster_done( FT_Raster raster ) | |

{ | |

FT_Memory memory = (FT_Memory)((BSDF_TRaster*)raster)->memory; | |

FT_FREE( raster ); | |

} | |

FT_DEFINE_RASTER_FUNCS( | |

ft_bitmap_sdf_raster, | |

FT_GLYPH_FORMAT_BITMAP, | |

(FT_Raster_New_Func) bsdf_raster_new, /* raster_new */ | |

(FT_Raster_Reset_Func) bsdf_raster_reset, /* raster_reset */ | |

(FT_Raster_Set_Mode_Func)bsdf_raster_set_mode, /* raster_set_mode */ | |

(FT_Raster_Render_Func) bsdf_raster_render, /* raster_render */ | |

(FT_Raster_Done_Func) bsdf_raster_done /* raster_done */ | |

) | |

/* END */ |