libass分析6-源码分析-ASS_Renderer结构体分析，ass文件数据是如何存放的

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Author: wencoo
Blog：https://wencoo.blog.csdn.net/
Date: 01/03/2024
Email: jianwen056@aliyun.com
Wechat：wencoo824
QQ：1419440391
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正文 或 背景

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ASS_Renderer结构体原型

struct ass_renderer {ASS_Library *library;       //ass库指针FT_Library ftlibrary;       //字体库ASS_FontSelector *fontselect;   //字体选择结构体size_t num_emfonts;             //字体编号？？ASS_Settings settings;          //ass设置类int render_id;                  //渲染样式索引 idASS_Image *images_root;     // rendering result is stored here  渲染结果存储在这里ASS_Image *prev_images_root;    //上一帧的渲染结果存储EventImages *eimg;          // temporary buffer for sorting rendered events  用于排序呈现事件的临时缓冲区int eimg_size;              // allocated buffer size  分配的缓冲区大小// frame-global dataint width, height;          // screen dimensions (the whole frame from ass_set_frame_size)  屏幕尺寸(来自ass_set_frame_size的整个帧)int frame_content_height;   // content frame height ( = screen height - API margins )       内容框架高度(=屏幕高度- API边距)int frame_content_width;    // content frame width ( = screen width - API margins )         内容框架宽度(=屏幕宽度- API边距)double fit_height;          // content frame height without zoom & pan (fit to screen & letterboxed)    不缩放和平移的内容框架高度(适合屏幕和信箱)double fit_width;           // content frame width without zoom & pan (fit to screen & letterboxed)     没有缩放和平移的内容框架宽度(适合屏幕和信箱)ASS_Track *track;long long time;             // frame's timestamp, ms   帧的时间戳，msdouble par_scale_x;         // x scale applied to all glyphs to preserve text aspect ratio   X比例适用于所有字形，以保持文本长宽比RenderContext state;        // reader的状态机？TextInfo text_info;CacheStore cache;const BitmapEngine *engine;ASS_Style user_override_style;
};

先来看看ASS_FontSelector结构体存储了那种信息

ASS_FontSelector结构体原型

struct font_selector {ASS_Library *library;FT_Library ftlibrary;// uid counter  uid计数器int uid;// fallbacks  两个回调函数char *family_default;       //字体族函数回调char *path_default;         //路径回到int index_default;// font databaseint n_font;                 //???int alloc_font;             //???ASS_FontInfo *font_infos;   //字体信息ASS_FontProvider *default_provider;     //默认程序ASS_FontProvider *embedded_provider;    //嵌入程序
};

先依照顺序来看ASS_FontInfo结构

ASS_FontInfo结构体原型

// internal font database element  内部字体数据库元素
// all strings are utf-8        所有字符串都是utf-8
struct font_info {int uid;            // unique font face id  唯一的字体idchar **families;    // family name  字体族名称列表char **fullnames;   // list of localized fullnames (e.g. Arial Bold Italic) 本地化的全名列表(例如Arial Bold Italic)int n_family;       //列表索引int n_fullname;     //列表索引int slant;          // 倾斜角度？int weight;         // TrueType scale, 100-900   TrueType量表，100-900int width;// how to access this face  如何访问这张脸？char *path;            // absolute path  绝对路径int index;             // font index inside font collections   字体集合内的字体索引char *postscript_name; // can be used as an alternative to index to  可以用作索引的替代品吗// identify a font inside a collection    识别集合中的字体char *extended_family;  //扩展字体族// font source  字体来源???ASS_FontProvider *provider;// private data for callbacks   回调的私有数据void *priv;
};

这里还有一个ASS_FontProvider的结构，也来看一下吧

ASS_FontProvider结构体原型

struct font_provider {ASS_FontSelector *parent;       //字体选择结构ASS_FontProviderFuncs funcs;    //回调函数的结构体集合void *priv;                     //回调函数的私有数据
};

ASS_FontProviderFuncs是一个回调函数的结构体集合，里面有各种回调函数的结构，使用的时候，只需要指定具体的函数即可。看一下ASS_FontProviderFuncs的结构体原型

typedef struct font_provider_funcs {GetDataFunc         get_data;               /* optional/mandatory 这个意思应该是必须要实现的*/CheckPostscriptFunc check_postscript;       /* mandatory */CheckGlyphFunc      check_glyph;            /* mandatory */DestroyFontFunc     destroy_font;           /* optional */DestroyProviderFunc destroy_provider;       /* optional */MatchFontsFunc      match_fonts;            /* optional */SubstituteFontFunc  get_substitutions;      /* optional */GetFallbackFunc     get_fallback;           /* optional */GetFontIndex        get_font_index;         /* optional */
} ASS_FontProviderFuncs;

具体每个回调有哪些参数，我们先不去看，到了后面用的时候再细细研究。

ASS_Settings结构体原型

typedef struct {int frame_width;            //帧宽int frame_height;           //帧高int storage_width;          // video width before any rescaling     任何重新缩放之前的视频宽度int storage_height;         // video height before any rescaling    任何重新缩放之前的视频高度double font_size_coeff;     // font size multiplier  字体倍增器double line_spacing;        // additional line spacing (in frame pixels)  额外的行间距(以帧像素为单位)double line_position;       // vertical position for subtitles, 0-100 (0 = no change)   字幕的垂直位置，0-100(0 =不变)  int top_margin;             // height of top margin. Video frame is shifted down by top_margin.  上边距的高度。视频帧通过top_margin向下移动。int bottom_margin;          // height of bottom margin. (frame_height - top_margin - bottom_margin) is original video height.  底边距的高度。(frame_height - top_margin - bottom_margin)为原始视频高度。int left_margin;int right_margin;int use_margins;            // 0 - place all subtitles inside original frame    0 -将所有字幕放在原始帧内// 1 - place subtitles (incl. toptitles) in full display frame incl. margins    1 -将副标题(包括标题)放在完整的显示框中，包括页边距double par;                 // user defined pixel aspect ratio (0 = unset)      用户自定义像素宽高比(0 =未设置)ASS_Hinting hinting;        //ass 微调？ASS_ShapingLevel shaper;    //成形等级？？？int selective_style_overrides; // ASS_OVERRIDE_* flagschar *default_font;					//默认字体char *default_family;				//默认字体族
} ASS_Settings;

ASS_Hinting结构体原型

/** Hinting type. (see ass_set_hinting below) 提示类型。(参见下面的ass_set_hint)** Setting hinting to anything but ASS_HINTING_NONE will put libass in a mode  将提示设置为ASS_HINTING_NONE以外的任何值将使libass进入模式* that reduces compatibility with vsfilter and many ASS scripts. The main  这会降低与vsfilter和许多ASS脚本的兼容性。* problem is that hinting conflicts with smooth scaling, which precludes  这个主要问题是暗示与平滑缩放相冲突，这就排除了动画和精确定位* animations and precise positioning.** In other words, enabling hinting might break some scripts severely.  换句话说，启用提示可能会严重破坏某些脚本。** FreeType's native hinter is still buggy sometimes and it is recommended* to use the light autohinter, ASS_HINTING_LIGHT, instead.  For best* compatibility with problematic fonts, disable hinting.FreeType的本地提示有时仍然有bug，建议使用它使用轻自动提示，ASS_HINTING_LIGHT，而不是。最佳兼容有问题的字体，禁用提示。*/
typedef enum {ASS_HINTING_NONE = 0,ASS_HINTING_LIGHT,ASS_HINTING_NORMAL,ASS_HINTING_NATIVE
} ASS_Hinting;

ASS_ShapingLevel结构体原型

/*** \brief Text shaping levels.  文本塑形级别。** SIMPLE is a fast, font-agnostic shaper that can do only substitutions.   SIMPLE是一个快速的、与字体无关的整形器，它只能进行替换。* COMPLEX is a slower shaper using OpenType for substitutions and positioning.  COMPLEX是使用OpenType进行替换和定位的较慢的整形器。** libass uses the best shaper available by default.  Libass默认使用最好的形状器。*/
typedef enum {ASS_SHAPING_SIMPLE = 0,ASS_SHAPING_COMPLEX
} ASS_ShapingLevel;

RenderContext结构体原型

// Renderer state.
// Values like current font face, color, screen position, clipping and so on are stored here.
// 像当前字体、颜色、屏幕位置、剪辑等值都存储在这里。
struct render_context {ASS_Renderer *renderer;     //渲染器指针TextInfo *text_info;        //字形结构信息ASS_Shaper *shaper;         //ass字形，第三方库接入处理RasterizerData rasterizer;  //光栅化程序数据ASS_Event *event;           //事件参数ASS_Style *style;           //风格参数ASS_Font *font;             //字体库的指针存储结构double font_size;           //字体大小int parsed_tags;            //解析标识int flags;                  // decoration flags (underline/strike-through) 装饰旗帜(下划线/划线)int alignment;              // alignment overrides go here; if zero, style value will be used  对齐覆盖到这里;如果为零，则使用样式值int justify;                // justify instructions  证明的说明？？？这个翻译看不懂double frx, fry, frz;       // 一个什么数据的x,y,z值double fax, fay;            // text shearing  文本剪切double pos_x, pos_y;        // position     位置坐标double org_x, org_y;        // origin       原点坐标double scale_x, scale_y;    // 缩放的x，y坐标double hspacing;            // distance between letters, in pixels  字母之间的距离，以像素为单位double border_x;            // outline width  轮廓宽度double border_y;enum {EVENT_NORMAL = 0,       // "normal" top-, sub- or mid- title  “普通”标题，副标题或中标题EVENT_POSITIONED = 1,   // happens after \pos or \move, margins are ignored  发生在\pos或\move之后，忽略边距EVENT_HSCROLL = 2,      // "Banner" transition effect, text_width is unlimited  “Banner”的过渡效果，text_width是无限制的EVENT_VSCROLL = 4       // "Scroll up", "Scroll down" transition effects  “向上滚动”，“向下滚动”的过渡效果} evt_type;int border_style;           //边框风格uint32_t c[4];              // colors(Primary, Secondary, so on) in RGBAint clip_x0, clip_y0, clip_x1, clip_y1;     //裁剪坐标char have_origin;           // origin is explicitly defined; if 0, get_base_point() is used   明确定义了原点;如果为0，则使用get_base_point()char clip_mode;             // 1 = iclip    裁剪模式char detect_collisions;     //碰撞检测char be;                    // blur edges  边缘模糊int fade;                   // alpha from \fad  和fad效果值一样，从fad的设置来double blur;                // gaussian blur    高斯模糊double shadow_x;            //窗口xdouble shadow_y;            //窗口ydouble pbo;                 // drawing baseline offset  绘制基线偏移量ASS_StringView clip_drawing_text;  // 裁剪绘制文本？？？// used to store RenderContext.style when doing selective style overrides   用于存储RenderContext。在进行选择性样式重写时ASS_Style override_style_temp_storage;int drawing_scale;          // currently reading: regular text if 0, drawing otherwise  当前读取:如果为0，则为常规文本，否则为绘图int clip_drawing_scale;     // 裁剪绘制缩放？？？int clip_drawing_mode;      // 0 = regular clip, 1 = inverse clip  0 =正夹，1 =逆夹Effect effect_type;         //特效类型int32_t effect_timing;      //特效的生效时间int32_t effect_skip_timing; //特效跳过时间bool reset_effect;          //重置特效标志enum {SCROLL_LR,              // left-to-rightSCROLL_RL,SCROLL_TB,              // top-to-bottomSCROLL_BT} scroll_direction;         // for EVENT_HSCROLL, EVENT_VSCROLL  滚动方向的枚举double scroll_shift;        //循环滚动int scroll_y0, scroll_y1;   //滚动的两个坐标？？// face properties    字体属性相关？ASS_StringView family;      //unsigned bold;              //粗体unsigned italic;            //斜体int treat_family_as_pattern;int wrap_style;             //环绕风格？int font_encoding;          //字体编码// combination of ASS_OVERRIDE_BIT_* flags that apply right now  现在应用的ASS_OVERRIDE_BIT_*标志的组合unsigned overrides;// whether to apply font_scale  是否应用font_scaleint apply_font_scale;// whether this is assumed to be explicitly positioned  是否假定它被显式定位int explicit;double screen_scale_x;      //屏幕缩放xdouble screen_scale_y;      //屏幕缩放ydouble border_scale_x;      //边框缩放xdouble border_scale_y;double blur_scale_x;        //模糊缩放xdouble blur_scale_y;
};

ASS_Shaper结构体原型

struct ass_shaper {ASS_ShapingLevel shaping_level;// FriBidi log2visint n_glyphs, n_pars;FriBidiChar *event_text; // just a reference, owned by text_info  只是一个引用，属于text_infoFriBidiCharType *ctypes;FriBidiLevel *emblevels;FriBidiStrIndex *cmap;FriBidiParType *pbase_dir;FriBidiParType base_direction;// OpenType features   特色功能int n_features;hb_feature_t *features;hb_language_t language;// Glyph metrics cache, to speed up shaping   字形指标缓存，以加快塑造Cache *metrics_cache;#ifdef USE_FRIBIDI_EX_APIFriBidiBracketType *btypes;bool bidi_brackets;
#endifchar whole_text_layout;
};

该结构体使用了fribidi库，fribidi库主要用来转换不同语系中存在的文本方向问题，例如右向左的文本， 翻转后为左向右顺序的文本。

RasterizerData结构体原型

typedef struct {int outline_error;  // acceptable error (in 1/64 pixel units) 可接受误差(1/64像素单位)// usable after rasterizer_set_outline  在rasterizer_set_outline之后可用ASS_Rect bbox;// internal buffers   内部缓冲区struct segment *linebuf[2];size_t size[2], capacity[2];size_t n_first;uint8_t *tile;
} RasterizerData;

ASS_Font结构体原型

struct ass_font {ASS_FontDesc desc;                      //一个解码的结构体ASS_Library *library;FT_Library ftlibrary;                   //ft库的结构体int faces_uid[ASS_FONT_MAX_FACES];FT_Face faces[ASS_FONT_MAX_FACES];      //ASS_ShaperFontData *shaper_priv;        //字形数据int n_faces;double size;
};

TextInfo结构体原型

typedef struct {GlyphInfo *glyphs;              //字形结构指针FriBidiChar *event_text;        //文字事件char *breaks;int length;                     //长度LineInfo *lines;                //行信息int n_lines;                    //行索引CombinedBitmapInfo *combined_bitmaps;   //组合位图？？？unsigned n_bitmaps;                     //位图索引double height;int border_top;             //边框顶int border_bottom;          //边框底int border_x;               //边框x位置int max_glyphs;             //最大字形数int max_lines;              //最大行数unsigned max_bitmaps;       //最大位图数
} TextInfo;

CacheStore结构体原型

缓存存储结构，Cache结构体是一个链表结构

typedef struct {Cache *font_cache;              //字体缓存Cache *outline_cache;           //轮廓缓存Cache *bitmap_cache;            //位图缓存Cache *composite_cache;         //合成图缓存Cache *metrics_cache;           //度量缓存？size_t glyph_max;               //字形最大值size_t bitmap_max_size;         //位图最大值size_t composite_max_size;      //合成最大值
} CacheStore;

ASS_Style结构体原型

已在别处分析过了，这里就不贴了

总结

我们现在整体细致的分析了ass_renderer结构的数据内容，发现里面结构体很多，并且不同的结构体里面有相同的字段，目前还不清楚两个不同结构体中相同字段是否一样，有没有什么不同，下一篇文章继续慢慢分析。

由于笔者的水平有限， 加之编写的同时还要参与开发工作，文中难免会出现一些错误或者不准确的地方，恳请读者批评指正。如果读者有任何宝贵意见，可以加我微信 wencoo824。QQ：1419440391。

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