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avfilter/vf_drawtext: add expression variables to control font ascent/descent

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The following new variables can be used in the x and y expressions: font_a, font_d, top_a, bottom_d.
This commit is contained in:
yethie 2023-05-26 12:46:10 +02:00 committed by Paul B Mahol
parent fac7bb06d8
commit 01d843f6d0
2 changed files with 24 additions and 0 deletions
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12
doc/filters.texi
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@ -12597,6 +12597,18 @@ contained in the rendered text, it is equivalent to @var{ascent} -
maximum glyph width, that is the maximum width for all the glyphs
contained in the rendered text
@item font_a
the ascent size defined in the font metrics
@item font_d
the descent size defined in the font metrics
@item top_a
the maximum ascender of the glyphs of the first text line
@item bottom_d
the maximum descender of the glyphs of the last text line
@item n
the number of input frame, starting from 0

12
libavfilter/vf_drawtext.c
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@ -89,6 +89,10 @@ static const char *const var_names[] = {
"max_glyph_d", "descent", ///< min glyph descender
"max_glyph_h", ///< max glyph height
"max_glyph_w", ///< max glyph width
"font_a", ///< font-defined ascent
"font_d", ///< font-defined descent
"top_a", ///< max glyph ascender of the top line
"bottom_d", ///< max glyph descender of the bottom line
"n", ///< number of frame
"sar",
"t", ///< timestamp expressed in seconds
@ -136,6 +140,10 @@ enum var_name {
VAR_MAX_GLYPH_D, VAR_DESCENT,
VAR_MAX_GLYPH_H,
VAR_MAX_GLYPH_W,
VAR_FONT_A,
VAR_FONT_D,
VAR_TOP_A,
VAR_BOTTOM_D,
VAR_N,
VAR_SAR,
VAR_T,
@ -1800,8 +1808,12 @@ static int draw_text(AVFilterContext *ctx, AVFrame *frame)
s->var_values[VAR_MAX_GLYPH_W] = s->max_glyph_w;
s->var_values[VAR_MAX_GLYPH_H] = s->max_glyph_h;
s->var_values[VAR_MAX_GLYPH_A] = s->var_values[VAR_ASCENT] = POS_CEIL(metrics.max_y64, 64);
s->var_values[VAR_FONT_A] = s->face->size->metrics.ascender / 64;
s->var_values[VAR_MAX_GLYPH_D] = s->var_values[VAR_DESCENT] = POS_CEIL(metrics.min_y64, 64);
s->var_values[VAR_FONT_D] = -s->face->size->metrics.descender / 64;
s->var_values[VAR_TOP_A] = POS_CEIL(metrics.offset_top64, 64);
s->var_values[VAR_BOTTOM_D] = -POS_CEIL(metrics.offset_bottom64, 64);
s->var_values[VAR_LINE_H] = s->var_values[VAR_LH] = metrics.line_height64 / 64.;
if (s->text_source == AV_FRAME_DATA_DETECTION_BBOXES) {