libass 不支持subtitle字幕Underline问题
libass中本身有Underline支持字体下画线参数的，但怎么设置也不正常，我跟踪了一下它的源代码，也没有找到其根本原因，我想mplayer中有它的插件，于是对比了一下它的mplayer中的区别,主要是增加了两个函数(事实上只要一个)即可解决；计划在视频转换软件thinkvd的 effect 功能中加上它
测试效果图如下：
附上相关代码：（调用部分参考mplayer需要自己更改）
/*
* Strike a glyph with a horizontal line; it's possible to underline it
* and/or strike through it. For the line's position and size, truetype
* tables are consulted. Obviously this relies on the data in the tables
* being accurate.
*
*/
static int ass_strike_outline_glyph(FT_Face face, ass_font_t *font,
FT_Glyph glyph, int under, int through)
{
TT_OS2 *os2 = FT_Get_Sfnt_Table(face, ft_sfnt_os2);
TT_Postscript *ps = FT_Get_Sfnt_Table(face, ft_sfnt_post);
FT_Outline *ol = &((FT_OutlineGlyph) glyph)->outline;
int bear, advance, y_scale, i, dir;
if (!under && !through)
return 0;
// Grow outline
i = (under ? 4 : 0) + (through ? 4 : 0);
ol->points = realloc(ol->points, sizeof(FT_Vector) *
(ol->n_points + i));
ol->tags = realloc(ol->tags, ol->n_points + i);
i = !!under + !!through;
ol->contours = realloc(ol->contours, sizeof(short) *
(ol->n_contours + i));
// If the bearing is negative, the glyph starts left of the current
// pen position
bear = FFMIN(face->glyph->metrics.horiBearingX, 0);
// We're adding half a pixel to avoid small gaps
advance = d16_to_d6(glyph->advance.x) + 32;
y_scale = face->size->metrics.y_scale;
// Reverse drawing direction for non-truetype fonts
dir = FT_Outline_Get_Orientation(ol);
// Add points to the outline
if (under && ps) {
int pos, size;
pos = FT_MulFix(ps->underlinePosition, y_scale * font->scale_y);
size = FT_MulFix(ps->underlineThickness,
y_scale * font->scale_y / 2);
if (pos > 0 || size <= 0)
return 1;
FT_Vector points[4] = {
{.x = bear, .y = pos + size},
{.x = advance, .y = pos + size},
{.x = advance, .y = pos - size},
{.x = bear, .y = pos - size},
};
if (dir == FT_ORIENTATION_TRUETYPE) {
for (i = 0; i < 4; i++) {
ol->points[ol->n_points] = points[i];
ol->tags[ol->n_points++] = 1;
}
} else {
for (i = 3; i >= 0; i--) {
ol->points[ol->n_points] = points[i];
ol->tags[ol->n_points++] = 1;
}
}
ol->contours[ol->n_contours++] = ol->n_points - 1;
}
if (through && os2) {
int pos, size;
pos = FT_MulFix(os2->yStrikeoutPosition, y_scale * font->scale_y);
size = FT_MulFix(os2->yStrikeoutSize, y_scale * font->scale_y / 2);
if (pos < 0 || size <= 0)
return 1;
FT_Vector points[4] = {
{.x = bear, .y = pos + size},
{.x = advance, .y = pos + size},
{.x = advance, .y = pos - size},
{.x = bear, .y = pos - size},
};
if (dir == FT_ORIENTATION_TRUETYPE) {
for (i = 0; i < 4; i++) {
ol->points[ol->n_points] = points[i];
ol->tags[ol->n_points++] = 1;
}
} else {
for (i = 3; i >= 0; i--) {
ol->points[ol->n_points] = points[i];
ol->tags[ol->n_points++] = 1;
}
}
ol->contours[ol->n_contours++] = ol->n_points - 1;
}
return 0;
}
/**
* Slightly embold a glyph without touching its metrics
*/
static void ass_glyph_embolden(FT_GlyphSlot slot)
{
int str;
if (slot->format != FT_GLYPH_FORMAT_OUTLINE)
return;
str = FT_MulFix(slot->face->units_per_EM,
slot->face->size->metrics.y_scale) / 64;
FT_Outline_Embolden(&slot->outline, str);
}
/**
* /brief Get a glyph
* /param ch character code
**/
FT_Glyph ass_font_get_glyph(void* fontconfig_priv, ass_font_t* font, uint32_t ch, ass_hinting_t hinting, int deco)
{
int error;
int index = 0;
int i;
FT_Glyph glyph;
FT_Face face = 0;
int flags = 0;
int vertical = font->desc.vertical;
if (ch < 0x20)
return 0;
// Handle NBSP like a regular space when rendering the glyph
if (ch == 0xa0)
ch = ' ';
if (font->n_faces == 0)
return 0;
for (i = 0; i < font->n_faces; ++i) {
face = font->faces[i];
index = FT_Get_Char_Index(face, ch);
if (index)
break;
}
#ifdef CONFIG_FONTCONFIG
if (index == 0) {
int face_idx;
mp_msg(MSGT_ASS, MSGL_INFO, MSGTR_LIBASS_GlyphNotFoundReselectingFont,
ch, font->desc.family, font->desc.bold, font->desc.italic);
face_idx = add_face(fontconfig_priv, font, ch);
if (face_idx >= 0) {
face = font->faces[face_idx];
index = FT_Get_Char_Index(face, ch);
if (index == 0) {
mp_msg(MSGT_ASS, MSGL_ERR, MSGTR_LIBASS_GlyphNotFound,
ch, font->desc.family, font->desc.bold, font->desc.italic);
}
}
}
#endif
switch (hinting) {
case ASS_HINTING_NONE: flags = FT_LOAD_NO_HINTING; break;
case ASS_HINTING_LIGHT: flags = FT_LOAD_FORCE_AUTOHINT | FT_LOAD_TARGET_LIGHT; break;
case ASS_HINTING_NORMAL: flags = FT_LOAD_FORCE_AUTOHINT; break;
case ASS_HINTING_NATIVE: flags = 0; break;
}
error = FT_Load_Glyph(face, index, FT_LOAD_NO_BITMAP | flags);
if (error) {
mp_msg(MSGT_ASS, MSGL_WARN, MSGTR_LIBASS_ErrorLoadingGlyph);
return 0;
}
#if (FREETYPE_MAJOR > 2) || /
((FREETYPE_MAJOR == 2) && (FREETYPE_MINOR >= 2)) || /
((FREETYPE_MAJOR == 2) && (FREETYPE_MINOR == 1) && (FREETYPE_PATCH >= 10))
// FreeType >= 2.1.10 required
if (!(face->style_flags & FT_STYLE_FLAG_ITALIC) &&
(font->desc.italic > 55)) {
FT_GlyphSlot_Oblique(face->glyph);
}
#endif
if (!(face->style_flags & FT_STYLE_FLAG_BOLD) &&
(font->desc.bold > 80)) {
ass_glyph_embolden(face->glyph);
}
error = FT_Get_Glyph(face->glyph, &glyph);
if (error) {
mp_msg(MSGT_ASS, MSGL_WARN, MSGTR_LIBASS_ErrorLoadingGlyph);
return 0;
}
// Rotate glyph, if needed
/*if (vertical && ch >= VERTICAL_LOWER_BOUND) {
FT_Matrix m = { 0, double_to_d16(-1.0), double_to_d16(1.0), 0 };
FT_Outline_Transform(&((FT_OutlineGlyph) glyph)->outline, &m);
FT_Outline_Translate(&((FT_OutlineGlyph) glyph)->outline,
face->glyph->metrics.vertAdvance,
0);
glyph->advance.x = face->glyph->linearVertAdvance;
}*/
// Apply scaling and shift
FT_Matrix scale = { double_to_d16(font->scale_x), 0, 0,
double_to_d16(font->scale_y) };
FT_Outline *outl = &((FT_OutlineGlyph) glyph)->outline;
FT_Outline_Transform(outl, &scale);
FT_Outline_Translate(outl, font->v.x, font->v.y);
glyph->advance.x *= font->scale_x;
ass_strike_outline_glyph(face, font, glyph, deco & DECO_UNDERLINE,
deco & DECO_STRIKETHROUGH);
return glyph;
}