Author: wencoo
Blog：https://wencoo.blog.csdn.net/
Date: 01/03/2024
Email: jianwen056@aliyun.com
Wechat：wencoo824
QQ：1419440391
Details:
文章目录
- 目录
- 正文 或 背景
- ASS_Renderer结构体原型
- ASS_FontSelector结构体原型
- ASS_FontInfo结构体原型
- ASS_FontProvider结构体原型
- ASS_Settings结构体原型
- ASS_Hinting结构体原型
- ASS_ShapingLevel结构体原型
- RenderContext结构体原型
- ASS_Shaper结构体原型
- RasterizerData结构体原型
- ASS_Font结构体原型
- TextInfo结构体原型
- CacheStore结构体原型
- ASS_Style结构体原型
- 总结
- 参考
- 技术交流
目录
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。
参考
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