Edit
kc3-lang/freetype/src/truetype/ttinterp.h
Werner Lemberg
- src/truetype/ttinterp.h
-
/**************************************************************************** * * ttinterp.h * * TrueType bytecode interpreter (specification). * * Copyright (C) 1996-2020 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_F26Dot6 compensation ); /* 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 */