ref: e9c50fa77de58b749b4b95706f7b55bfff0dd27f
dir: /src/truetype/ttinterp.h/
/****************************************************************************
*
* ttinterp.h
*
* TrueType bytecode interpreter (specification).
*
* Copyright (C) 1996-2021 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.
*
*/
#ifndef TTINTERP_H_
#define TTINTERP_H_
#include "ttobjs.h"
FT_BEGIN_HEADER
/**************************************************************************
*
* Rounding mode constants.
*/
#define TT_Round_Off 5
#define TT_Round_To_Half_Grid 0
#define TT_Round_To_Grid 1
#define TT_Round_To_Double_Grid 2
#define TT_Round_Up_To_Grid 4
#define TT_Round_Down_To_Grid 3
#define TT_Round_Super 6
#define TT_Round_Super_45 7
/**************************************************************************
*
* Function types used by the interpreter, depending on various modes
* (e.g. the rounding mode, whether to render a vertical or horizontal
* line etc).
*
*/
/* Rounding function */
typedef FT_F26Dot6
(*TT_Round_Func)( TT_ExecContext exc,
FT_F26Dot6 distance,
FT_Int color );
/* Point displacement along the freedom vector routine */
typedef void
(*TT_Move_Func)( TT_ExecContext exc,
TT_GlyphZone zone,
FT_UShort point,
FT_F26Dot6 distance );
/* Distance projection along one of the projection vectors */
typedef FT_F26Dot6
(*TT_Project_Func)( TT_ExecContext exc,
FT_Pos dx,
FT_Pos dy );
/* getting current ppem. Take care of non-square pixels if necessary */
typedef FT_Long
(*TT_Cur_Ppem_Func)( TT_ExecContext exc );
/* reading a cvt value. Take care of non-square pixels if necessary */
typedef FT_F26Dot6
(*TT_Get_CVT_Func)( TT_ExecContext exc,
FT_ULong idx );
/* setting or moving a cvt value. Take care of non-square pixels */
/* if necessary */
typedef void
(*TT_Set_CVT_Func)( TT_ExecContext exc,
FT_ULong idx,
FT_F26Dot6 value );
/**************************************************************************
*
* This structure defines a call record, used to manage function calls.
*/
typedef struct TT_CallRec_
{
FT_Int Caller_Range;
FT_Long Caller_IP;
FT_Long Cur_Count;
TT_DefRecord *Def; /* either FDEF or IDEF */
} TT_CallRec, *TT_CallStack;
#ifdef TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY
/**************************************************************************
*
* These structures define rules used to tweak subpixel hinting for
* various fonts. "", 0, "", NULL value indicates to match any value.
*/
#define SPH_MAX_NAME_SIZE 32
#define SPH_MAX_CLASS_MEMBERS 100
typedef struct SPH_TweakRule_
{
const char family[SPH_MAX_NAME_SIZE];
const FT_UInt ppem;
const char style[SPH_MAX_NAME_SIZE];
const FT_ULong glyph;
} SPH_TweakRule;
typedef struct SPH_ScaleRule_
{
const char family[SPH_MAX_NAME_SIZE];
const FT_UInt ppem;
const char style[SPH_MAX_NAME_SIZE];
const FT_ULong glyph;
const FT_ULong scale;
} SPH_ScaleRule;
typedef struct SPH_Font_Class_
{
const char name[SPH_MAX_NAME_SIZE];
const char member[SPH_MAX_CLASS_MEMBERS][SPH_MAX_NAME_SIZE];
} SPH_Font_Class;
#endif /* TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY */
/**************************************************************************
*
* The main structure for the interpreter which collects all necessary
* variables and states.
*/
typedef struct TT_ExecContextRec_
{
TT_Face face;
TT_Size size;
FT_Memory memory;
/* instructions state */
FT_Error error; /* last execution error */
FT_Long top; /* top of exec. stack */
FT_Long stackSize; /* size of exec. stack */
FT_Long* stack; /* current exec. stack */
FT_Long args;
FT_Long new_top; /* new top after exec. */
TT_GlyphZoneRec zp0, /* zone records */
zp1,
zp2,
pts,
twilight;
FT_Long pointSize; /* in 26.6 format */
FT_Size_Metrics metrics;
TT_Size_Metrics tt_metrics; /* size metrics */
TT_GraphicsState GS; /* current graphics state */
FT_Int curRange; /* current code range number */
FT_Byte* code; /* current code range */
FT_Long IP; /* current instruction pointer */
FT_Long codeSize; /* size of current range */
FT_Byte opcode; /* current opcode */
FT_Int length; /* length of current opcode */
FT_Bool step_ins; /* true if the interpreter must */
/* increment IP after ins. exec */
FT_ULong cvtSize;
FT_Long* cvt;
FT_UInt glyphSize; /* glyph instructions buffer size */
FT_Byte* glyphIns; /* glyph instructions buffer */
FT_UInt numFDefs; /* number of function defs */
FT_UInt maxFDefs; /* maximum number of function defs */
TT_DefArray FDefs; /* table of FDefs entries */
FT_UInt numIDefs; /* number of instruction defs */
FT_UInt maxIDefs; /* maximum number of ins defs */
TT_DefArray IDefs; /* table of IDefs entries */
FT_UInt maxFunc; /* maximum function index */
FT_UInt maxIns; /* maximum instruction index */
FT_Int callTop, /* top of call stack during execution */
callSize; /* size of call stack */
TT_CallStack callStack; /* call stack */
FT_UShort maxPoints; /* capacity of this context's `pts' */
FT_Short maxContours; /* record, expressed in points and */
/* contours. */
TT_CodeRangeTable codeRangeTable; /* table of valid code ranges */
/* useful for the debugger */
FT_UShort storeSize; /* size of current storage */
FT_Long* storage; /* storage area */
FT_F26Dot6 period; /* values used for the */
FT_F26Dot6 phase; /* `SuperRounding' */
FT_F26Dot6 threshold;
FT_Bool instruction_trap; /* If `True', the interpreter will */
/* exit after each instruction */
TT_GraphicsState default_GS; /* graphics state resulting from */
/* the prep program */
FT_Bool is_composite; /* true if the glyph is composite */
FT_Bool pedantic_hinting; /* true if pedantic interpretation */
/* latest interpreter additions */
FT_Long F_dot_P; /* dot product of freedom and projection */
/* vectors */
TT_Round_Func func_round; /* current rounding function */
TT_Project_Func func_project, /* current projection function */
func_dualproj, /* current dual proj. function */
func_freeProj; /* current freedom proj. func */
TT_Move_Func func_move; /* current point move function */
TT_Move_Func func_move_orig; /* move original position function */
TT_Cur_Ppem_Func func_cur_ppem; /* get current proj. ppem value */
TT_Get_CVT_Func func_read_cvt; /* read a cvt entry */
TT_Set_CVT_Func func_write_cvt; /* write a cvt entry (in pixels) */
TT_Set_CVT_Func func_move_cvt; /* incr a cvt entry (in pixels) */
FT_Bool grayscale; /* bi-level hinting and */
/* grayscale rendering */
#ifdef TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL
/*
* 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.
*
* 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
* `Direct_Move_X'). This has the smallest code footprint and single
* biggest effect. The ClearType way to increase resolution is
* supersampling the x axis, the FreeType way is ignoring instructions
* on the x axis, which gives the same result in the majority of
* cases.
*
* - Points are not moved post-IUP (neither on the x nor on the y axis),
* except the x component of diagonal moves post-IUP (cf.
* `Direct_Move', `Direct_Move_Y', `Move_Zp2_Point'). Post-IUP
* changes are commonly used to `fix' pixel patterns which has little
* use outside monochrome rendering.
*
* - SHPIX and DELTAP don't execute unless moving a composite on the
* y axis or moving a previously y touched point. SHPIX additionally
* denies movement on the x axis (cf. `Ins_SHPIX' and `Ins_DELTAP').
* Both instructions are commonly used to `fix' pixel patterns for
* monochrome or Windows's GDI rendering but make little sense for
* FreeType rendering. Both can distort the outline. See [2] for
* details.
*
* - The hdmx table and modifications to phantom points are ignored.
* Bearings and advance widths remain unchanged (except rounding them
* outside the interpreter!), cf. `compute_glyph_metrics' and
* `TT_Hint_Glyph'. Letting non-native-ClearType fonts modify spacing
* might mess up spacing.
*
* Minor hacks
*
* - FLIPRGON, FLIPRGOFF, and FLIPPT don't execute post-IUP. This
* prevents dents in e.g. Arial-Regular's `D' and `G' glyphs at
* various sizes.
*
* (Post-IUP is the state after both IUP[x] and IUP[y] have been
* executed.)
*
* The best results are achieved for fonts that were from the outset
* designed with ClearType in mind, meaning they leave the x axis mostly
* alone and don't mess with the `final' outline to produce more
* pleasing pixel patterns. The harder the designer tried to produce
* very specific patterns (`superhinting') for pre-ClearType-displays,
* the worse the results.
*
* Microsoft defines a way to turn off backward compatibility and
* interpret instructions as before (called `native ClearType')[2][3].
* The font designer then regains full control and is responsible for
* making the font work correctly with ClearType without any
* hand-holding by the interpreter or rasterizer[4]. The v40
* interpreter assumes backward compatibility by default, which can be
* turned off the same way by executing the following in the control
* program (cf. `Ins_INSTCTRL').
*
* #PUSH 4,3
* INSTCTRL[]
*
* [1] Tricky fonts as FreeType defines them rely on the bytecode
* interpreter to display correctly. Hacks can interfere with them,
* so they get treated like native ClearType fonts (v40 with
* backward compatibility turned off). Cf. `TT_RunIns'.
*
* [2] Proposed by Microsoft's Greg Hitchcock in
* https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx
*
* [3] Beat Stamm describes it in more detail:
* http://rastertragedy.com/RTRCh4.htm#Sec12.
*
* [4] The list of `native ClearType' fonts is small at the time of this
* writing; I found the following on a Windows 10 Update 1511
* installation: Constantia, Corbel, Sitka, Malgun Gothic, Microsoft
* JhengHei (Bold and UI Bold), Microsoft YaHei (Bold and UI Bold),
* SimSun, NSimSun, and Yu Gothic.
*
*/
/* 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;
/* Long side of a LCD subpixel is vertical (e.g., screen is rotated). */
/* `_lean' to differentiate from the Infinality `vertical_lcd', which */
/* is managed differently. */
FT_Bool vertical_lcd_lean;
/* Default to backward compatibility mode in v40 interpreter. If */
/* this is false, it implies the interpreter is in v35 or in native */
/* ClearType mode. */
FT_Bool backward_compatibility;
/* Useful for detecting and denying post-IUP trickery that is usually */
/* used to fix pixel patterns (`superhinting'). */
FT_Bool iupx_called;
FT_Bool iupy_called;
/* ClearType hinting and grayscale rendering, as used by Universal */
/* Windows Platform apps (Windows 8 and above). Like the standard */
/* colorful ClearType mode, it utilizes a vastly increased virtual */
/* resolution on the x axis. Different from bi-level hinting and */
/* grayscale rendering, the old mode from Win9x days that roughly */
/* adheres to the physical pixel grid on both axes. */
FT_Bool grayscale_cleartype;
#endif /* TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL */
#ifdef TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY
TT_Round_Func func_round_sphn; /* subpixel rounding function */
FT_Bool subpixel_hinting; /* Using subpixel hinting? */
FT_Bool ignore_x_mode; /* Standard rendering mode for */
/* subpixel hinting. On if gray */
/* or subpixel hinting is on. */
/* The following 6 aren't fully implemented but here for MS rasterizer */
/* compatibility. */
FT_Bool compatible_widths; /* compatible widths? */
FT_Bool symmetrical_smoothing; /* symmetrical_smoothing? */
FT_Bool bgr; /* bgr instead of rgb? */
FT_Bool vertical_lcd; /* long side of LCD subpixel */
/* rectangles is horizontal */
FT_Bool subpixel_positioned; /* subpixel positioned */
/* (DirectWrite ClearType)? */
FT_Bool gray_cleartype; /* ClearType hinting but */
/* grayscale rendering */
FT_Int rasterizer_version; /* MS rasterizer version */
FT_Bool iup_called; /* IUP called for glyph? */
FT_ULong sph_tweak_flags; /* flags to control */
/* hint tweaks */
FT_ULong sph_in_func_flags; /* flags to indicate if in */
/* special functions */
#endif /* TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY */
/* We maintain two counters (in addition to the instruction counter) */
/* that act as loop detectors for LOOPCALL and jump opcodes with */
/* negative arguments. */
FT_ULong loopcall_counter;
FT_ULong loopcall_counter_max;
FT_ULong neg_jump_counter;
FT_ULong neg_jump_counter_max;
} TT_ExecContextRec;
extern const TT_GraphicsState tt_default_graphics_state;
#ifdef TT_USE_BYTECODE_INTERPRETER
FT_LOCAL( void )
TT_Goto_CodeRange( TT_ExecContext exec,
FT_Int range,
FT_Long IP );
FT_LOCAL( void )
TT_Set_CodeRange( TT_ExecContext exec,
FT_Int range,
void* base,
FT_Long length );
FT_LOCAL( void )
TT_Clear_CodeRange( TT_ExecContext exec,
FT_Int range );
FT_LOCAL( FT_Error )
Update_Max( FT_Memory memory,
FT_ULong* size,
FT_ULong multiplier,
void* _pbuff,
FT_ULong new_max );
#endif /* TT_USE_BYTECODE_INTERPRETER */
/**************************************************************************
*
* @Function:
* TT_New_Context
*
* @Description:
* Queries the face context for a given font. Note that there is
* now a _single_ execution context in the TrueType driver which is
* shared among faces.
*
* @Input:
* face ::
* A handle to the source face object.
*
* @Return:
* A handle to the execution context. Initialized for `face'.
*
* @Note:
* Only the glyph loader and debugger should call this function.
* (And right now only the glyph loader uses it.)
*/
FT_EXPORT( TT_ExecContext )
TT_New_Context( TT_Driver driver );
#ifdef TT_USE_BYTECODE_INTERPRETER
FT_LOCAL( void )
TT_Done_Context( TT_ExecContext exec );
FT_LOCAL( FT_Error )
TT_Load_Context( TT_ExecContext exec,
TT_Face face,
TT_Size size );
FT_LOCAL( void )
TT_Save_Context( TT_ExecContext exec,
TT_Size ins );
FT_LOCAL( FT_Error )
TT_Run_Context( TT_ExecContext exec );
#endif /* TT_USE_BYTECODE_INTERPRETER */
/**************************************************************************
*
* @Function:
* TT_RunIns
*
* @Description:
* Executes one or more instruction in the execution context. This
* is the main function of the TrueType opcode interpreter.
*
* @Input:
* exec ::
* A handle to the target execution context.
*
* @Return:
* FreeType error code. 0 means success.
*
* @Note:
* Only the object manager and debugger should call this function.
*
* This function is publicly exported because it is directly
* invoked by the TrueType debugger.
*/
FT_EXPORT( FT_Error )
TT_RunIns( TT_ExecContext exec );
FT_END_HEADER
#endif /* TTINTERP_H_ */
/* END */