ref: a0455468fdb8dd1959596d0c8c8a3ff07ee495a3
parent: ab2599ea3f09ba8da4f50b877021d23241d22609
author: Nikolaus Waxweiler <[email protected]>
date: Sat May 20 03:28:46 EDT 2017
[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.
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2017-05-20 Nikolaus Waxweiler <[email protected]>
+
+ [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 <[email protected]>
[smooth] Implement minimal dynamic padding for LCD filtering.
--- a/src/truetype/ttgload.c
+++ b/src/truetype/ttgload.c
@@ -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
{--- a/src/truetype/ttinterp.c
+++ b/src/truetype/ttinterp.c
@@ -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
--- a/src/truetype/ttinterp.h
+++ b/src/truetype/ttinterp.h
@@ -253,24 +253,39 @@
#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
*
* - Any point movement on the x axis is ignored (cf. `Direct_Move' and
@@ -347,7 +362,8 @@
*
*/
- /* 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;