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[truetype] Always use interpreter v35 for B/W rendering (#51051).

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* src/truetype/ttgload.c (tt_loader_init)
[TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL]: Adjust
`subpixel_hinting_lean', `grayscale_cleartype', and
`vertical_lcd_lean' accordingly.

* src/truetype/ttinterp.c (Ins_GETINFO): Updated.
(TT_RunIns): Update `backward_compatibility' flag.
This commit is contained in:
Nikolaus Waxweiler 2017-05-20 07:28:46 +02:00 committed by Werner Lemberg
parent ab2599ea3f
commit a0455468fd
4 changed files with 73 additions and 29 deletions
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12
ChangeLog
View File

@ -1,3 +1,15 @@
2017-05-20 Nikolaus Waxweiler <madigens@gmail.com>
[truetype] Always use interpreter v35 for B/W rendering (#51051).
* src/truetype/ttgload.c (tt_loader_init)
[TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL]: Adjust
`subpixel_hinting_lean', `grayscale_cleartype', and
`vertical_lcd_lean' accordingly.
* src/truetype/ttinterp.c (Ins_GETINFO): Updated.
(TT_RunIns): Update `backward_compatibility' flag.
2017-05-20 Alexei Podtelezhnikov <apodtele@gmail.com>
[smooth] Implement minimal dynamic padding for LCD filtering.

20
src/truetype/ttgload.c
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@ -2339,13 +2339,19 @@
#ifdef TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL
if ( driver->interpreter_version == TT_INTERPRETER_VERSION_40 )
{
subpixel_hinting_lean = TRUE;
grayscale_cleartype = !FT_BOOL( load_flags &
FT_LOAD_TARGET_LCD ||
load_flags &
FT_LOAD_TARGET_LCD_V );
exec->vertical_lcd_lean = FT_BOOL( load_flags &
FT_LOAD_TARGET_LCD_V );
subpixel_hinting_lean =
FT_BOOL( FT_LOAD_TARGET_MODE( load_flags ) !=
FT_RENDER_MODE_MONO );
grayscale_cleartype =
FT_BOOL( subpixel_hinting_lean &&
!( ( load_flags &
FT_LOAD_TARGET_LCD ) ||
( load_flags &
FT_LOAD_TARGET_LCD_V ) ) );
exec->vertical_lcd_lean =
FT_BOOL( subpixel_hinting_lean &&
( load_flags &
FT_LOAD_TARGET_LCD_V ) );
}
else
{

20
src/truetype/ttinterp.c
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@ -7345,7 +7345,7 @@
/* */
/* The only smoothing method FreeType supports unless someone sets */
/* FT_LOAD_TARGET_MONO. */
if ( ( args[0] & 2048 ) != 0 )
if ( ( args[0] & 2048 ) != 0 && exc->subpixel_hinting_lean )
K |= 1 << 18;
/********************************/
@ -7589,11 +7589,21 @@
#endif /* TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY */
#ifdef TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL
/* Toggle backward compatibility according to what font says, except */
/* when it's a `tricky' font that heavily relies on the interpreter to */
/* render glyphs correctly, e.g. DFKai-SB. Backward compatibility */
/* hacks may break it. */
/*
* Toggle backward compatibility according to what font wants, except
* when
*
* 1) we have a `tricky' font that heavily relies on the interpreter to
* render glyphs correctly, for example DFKai-SB, or
* 2) FT_RENDER_MODE_MONO (i.e, monochome rendering) is requested.
*
* In those cases, backward compatibility needs to be turned off to get
* correct rendering. The rendering is then completely up to the
* font's programming.
*
*/
if ( SUBPIXEL_HINTING_MINIMAL &&
exc->subpixel_hinting_lean &&
!FT_IS_TRICKY( &exc->face->root ) )
exc->backward_compatibility = !( exc->GS.instruct_control & 4 );
else

50
src/truetype/ttinterp.h
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@ -253,23 +253,38 @@ FT_BEGIN_HEADER
#ifdef TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL
/*
* Modern TrueType fonts are usually rendered through Microsoft's
* collection of rendering techniques called ClearType (e.g., subpixel
* rendering and subpixel hinting). When ClearType was introduced, most
* fonts were not ready. Microsoft decided to implement a backward
* compatibility mode that employed several simple to complicated
* assumptions and tricks that modified the interpretation of the
* bytecode contained in these fonts to make them look ClearType-y
* somehow. Most (web)fonts that were released since then have come to
* rely on these hacks to render correctly, even some of Microsoft's
* flagship ClearType fonts (Calibri, Cambria, Segoe UI).
* FreeType supports ClearType-like hinting of TrueType fonts through
* the version 40 interpreter. This is achieved through several hacks
* in the base (v35) interpreter, as detailed below.
*
* The minimal subpixel hinting code (interpreter version 40) employs a
* small list of font-agnostic hacks to bludgeon non-native-ClearType
* fonts (except tricky ones[1]) into submission. It will not try to
* toggle hacks for specific fonts for performance and complexity
* reasons. The focus is on modern (web)fonts rather than legacy fonts
* that were made for black-and-white rendering.
* ClearType is an umbrella term for several rendering techniques
* employed by Microsoft's various GUI and rendering toolkit
* implementations, most importantly: subpixel rendering for using the
* RGB subpixels of LCDs to approximately triple the perceived
* resolution on the x-axis and subpixel hinting for positioning stems
* on subpixel borders. TrueType programming is explicit, i.e., fonts
* must be programmed to take advantage of ClearType's possibilities.
*
* When ClearType was introduced, it seemed unlikely that all fonts
* would be reprogrammed, so Microsoft decided to implement a backward
* compatibility mode. It employs several simple to complicated
* assumptions and tricks, many of them font-dependent, that modify the
* interpretation of the bytecode contained in these fonts to retrofit
* them into a ClearType-y look. The quality of the results varies.
* Most (web)fonts that were released since then have come to rely on
* these hacks to render correctly, even some of Microsoft's flagship
* fonts (e.g., Calibri, Cambria, Segoe UI).
*
* FreeType's minimal subpixel hinting code (interpreter version 40)
* employs a small list of font-agnostic hacks loosely based on the
* public information available on Microsoft's compatibility mode[2].
* The focus is on modern (web)fonts rather than legacy fonts that were
* made for monochrome rendering. It will not match ClearType rendering
* exactly. Unlike the `Infinality' code (interpreter version 38) that
* came before, it will not try to toggle hacks for specific fonts for
* performance and complexity reasons. It will fall back to version 35
* behavior for tricky fonts[1] or when monochrome rendering is
* requested.
*
* Major hacks
*
@ -347,7 +362,8 @@ FT_BEGIN_HEADER
*
*/
/* Using v40 implies subpixel hinting. Used to detect interpreter */
/* Using v40 implies subpixel hinting, unless FT_RENDER_MODE_MONO has been
* requested. Used to detect interpreter */
/* version switches. `_lean' to differentiate from the Infinality */
/* `subpixel_hinting', which is managed differently. */
FT_Bool subpixel_hinting_lean;