* src/sdf/ftsdf.c: Include `ftbitmap.h`. * src/sdf/ftsdfcommon.h: Move function bodies to `ftsdfcommon.c`. Include `ftobjs.h` to get definitions of `FT_LOCAL` and friends. * src/sdf/ftsdfcommon.c: New file. * src/sdf/rules.mk, src/sdf/sdf.c: Updated.wl/meson-logging
Werner Lemberg
4 years ago
parent
36ee71714f
commit
35b21c71e5
6 changed files with 175 additions and 113 deletions
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/****************************************************************************
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* |
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* ftsdfcommon.c |
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* |
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* Auxiliary data for Signed Distance Field support (body). |
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* |
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* Copyright (C) 2020-2021 by |
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* David Turner, Robert Wilhelm, and Werner Lemberg. |
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* |
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* Written by Anuj Verma. |
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* |
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* This file is part of the FreeType project, and may only be used, |
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* modified, and distributed under the terms of the FreeType project |
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* license, LICENSE.TXT. By continuing to use, modify, or distribute |
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* this file you indicate that you have read the license and |
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* understand and accept it fully. |
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* |
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*/ |
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#include <ftsdf.h> |
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#include <ftsdfcommon.h> |
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/**************************************************************************
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* |
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* common functions |
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* |
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*/ |
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/*
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* Original algorithm: |
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* |
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* https://github.com/chmike/fpsqrt
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* |
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* Use this to compute the square root of a 16.16 fixed point number. |
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*/ |
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FT_LOCAL_DEF( FT_16D16 ) |
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square_root( FT_16D16 val ) |
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{ |
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FT_ULong t, q, b, r; |
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r = (FT_ULong)val; |
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b = 0x40000000L; |
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q = 0; |
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while ( b > 0x40L ) |
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{ |
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t = q + b; |
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if ( r >= t ) |
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{ |
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r -= t; |
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q = t + b; |
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} |
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r <<= 1; |
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b >>= 1; |
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} |
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q >>= 8; |
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return (FT_16D16)q; |
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} |
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/**************************************************************************
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* |
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* format and sign manipulating functions |
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* |
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*/ |
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/*
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* Convert 16.16 fixed point values to the desired output format. |
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* In this case we reduce 16.16 fixed point values to normalized |
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* 8-bit values. |
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* |
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* The `max_value` in the parameter is the maximum value in the |
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* distance field map and is equal to the spread. We normalize |
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* the distances using this value instead of computing the maximum |
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* value for the entire bitmap. |
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* |
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* You can use this function to map the 16.16 signed values to any |
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* format required. Do note that the output buffer is 8-bit, so only |
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* use an 8-bit format for `FT_SDFFormat`, or increase the buffer size in |
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* `ftsdfrend.c`. |
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*/ |
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FT_LOCAL_DEF( FT_SDFFormat ) |
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map_fixed_to_sdf( FT_16D16 dist, |
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FT_16D16 max_value ) |
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{ |
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FT_SDFFormat out; |
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FT_16D16 udist; |
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/* normalize the distance values */ |
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dist = FT_DivFix( dist, max_value ); |
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udist = dist < 0 ? -dist : dist; |
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/* Reduce the distance values to 8 bits. */ |
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/* */ |
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/* Since +1/-1 in 16.16 takes the 16th bit, we right-shift */ |
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/* the number by 9 to make it fit into the 7-bit range. */ |
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/* */ |
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/* One bit is reserved for the sign. */ |
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udist >>= 9; |
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/* Since `char` can only store a maximum positive value */ |
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/* of 127 we need to make sure it does not wrap around and */ |
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/* give a negative value. */ |
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if ( dist > 0 && udist > 127 ) |
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udist = 127; |
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if ( dist < 0 && udist > 128 ) |
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udist = 128; |
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/* Output the data; negative values are from [0, 127] and positive */ |
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/* from [128, 255]. One important thing is that negative values */ |
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/* are inverted here, that means [0, 128] maps to [-128, 0] linearly. */ |
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/* More on that in `freetype.h` near the documentation of */ |
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/* `FT_RENDER_MODE_SDF`. */ |
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out = dist < 0 ? 128 - (FT_SDFFormat)udist |
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: (FT_SDFFormat)udist + 128; |
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return out; |
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} |
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/*
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* Invert the signed distance packed into the corresponding format. |
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* So if the values are negative they will become positive in the |
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* chosen format. |
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* |
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* [Note]: This function should only be used after converting the |
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* 16.16 signed distance values to `FT_SDFFormat`. If that |
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* conversion has not been done, then simply invert the sign |
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* and use the above function to pack the values. |
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*/ |
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FT_LOCAL_DEF( FT_SDFFormat ) |
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invert_sign( FT_SDFFormat dist ) |
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{ |
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return 255 - dist; |
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} |
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/* END */ |
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