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avfilter/vf_drawtext: implement text alignment

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Text can now be aligned vertically (top, middle, bottom) and horizontally (left, center, right)
relative to the background box.
pull/389/head
yethie 1 year ago committed by Paul B Mahol
parent 01d843f6d0
commit 5f2d907de2
2 changed files with 56 additions and 1 deletions
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  1. 6
      doc/filters.texi
  2. 51
      libavfilter/vf_drawtext.c

6
doc/filters.texi
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@ -12384,6 +12384,12 @@ The default value of @var{boxcolor} is "white".
@item line_spacing
Set the line spacing in pixels. The default value of @var{line_spacing} is 0.
@item text_align
Set the vertical and horizontal alignment of the text with respect to the box boundaries.
The value must contain exactly two letters, one for the vertical alignment (T=top,
M=middle, B=bottom) and one for the horizontal alignment (L=left, C=center, R=right).
Please note that tab characters are only supported with the left horizontal alignment.
@item borderw
Set the width of the border to be drawn around the text using @var{bordercolor}.
The default value of @var{borderw} is 0.

51
libavfilter/vf_drawtext.c
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@ -309,12 +309,14 @@ typedef struct DrawTextContext {
int boxw; ///< the value of the boxw parameter
int boxh; ///< the value of the boxh parameter
uint8_t *text_align; ///< the horizontal and vertical text alignment
TextLine *lines; ///< computed information about text lines
int line_count; ///< the number of text lines
uint32_t *tab_clusters; ///< the position of tab characters in the text
int tab_count; ///< the number of tab characters
int blank_advance64; ///< the size of the space character
int tab_warning_printed; ///< ensure the tab warning to be printed only once
} DrawTextContext;
#define OFFSET(x) offsetof(DrawTextContext, x)
@ -333,6 +335,7 @@ static const AVOption drawtext_options[]= {
{"boxborderw", "set box borders width", OFFSET(boxborderw), AV_OPT_TYPE_STRING, {.str="0"}, 0, 0, FLAGS},
{"line_spacing", "set line spacing in pixels", OFFSET(line_spacing), AV_OPT_TYPE_INT, {.i64=0}, INT_MIN, INT_MAX, FLAGS},
{"fontsize", "set font size", OFFSET(fontsize_expr), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, FLAGS},
{"text_align", "set text alignment", OFFSET(text_align), AV_OPT_TYPE_STRING, {.str="TL"}, 0, 0, FLAGS},
{"x", "set x expression", OFFSET(x_expr), AV_OPT_TYPE_STRING, {.str="0"}, 0, 0, FLAGS},
{"y", "set y expression", OFFSET(y_expr), AV_OPT_TYPE_STRING, {.str="0"}, 0, 0, FLAGS},
{"boxw", "set box width", OFFSET(boxw), AV_OPT_TYPE_INT, {.i64=0}, 0, INT_MAX, FLAGS},
@ -851,6 +854,19 @@ static int string_to_array(const char *source, int *result, int result_size)
return counter;
}
static int validate_text_align(char* text_align)
{
int err = 0;
if (strlen(text_align) != 2
|| strchr("LCRTMB", text_align[0]) == NULL || strchr("LCRTMB", text_align[1]) == NULL
|| (strchr("TMB", text_align[0]) != NULL && strchr("LCR", text_align[1]) == NULL)
|| (strchr("LCR", text_align[0]) != NULL && strchr("TMB", text_align[1]) == NULL)) {
err = AVERROR(EINVAL);
}
return err;
}
static av_cold int init(AVFilterContext *ctx)
{
int err;
@ -916,6 +932,14 @@ static av_cold int init(AVFilterContext *ctx)
return AVERROR(EINVAL);
}
if ((err = validate_text_align(s->text_align))) {
av_log(ctx, AV_LOG_ERROR,
"The value provided for parameter 'text_align' is not valid,\n");
av_log(ctx, AV_LOG_ERROR,
"please specify a two characters string containing only one letter for horizontal alignment ('LCR') and one for vertical alignment ('TMB')\n");
return err;
}
#if CONFIG_LIBFRIBIDI
if (s->text_shaping)
if ((err = shape_text(ctx)) < 0)
@ -1486,13 +1510,32 @@ static int draw_glyphs(DrawTextContext *s, AVFrame *frame,
Glyph dummy = { 0 }, *glyph;
FT_Bitmap bitmap;
FT_BitmapGlyph b_glyph;
uint8_t j_center = 0, j_right = 0, j_middle = 0, j_bottom = 0;
int line_w, offset_y = 0;
int clip_x = 0, clip_y = 0;
j_center = strstr(s->text_align, "C") > 0;
j_right = strstr(s->text_align, "R") > 0;
j_middle = strstr(s->text_align, "M") > 0;
j_bottom = strstr(s->text_align, "B") > 0;
if (j_middle) {
offset_y = (s->box_height - metrics->height) / 2;
} else if (j_bottom) {
offset_y = s->box_height - metrics->height;
}
if ((j_right || j_center) && !s->tab_warning_printed && s->tab_count > 0) {
s->tab_warning_printed = 1;
av_log(s, AV_LOG_WARNING, "Tab characters are only supported with left horizontal alignment\n");
}
clip_x = FFMIN(metrics->rect_x + s->box_width + s->bb_right, frame->width);
clip_y = FFMIN(metrics->rect_y + s->box_height + s->bb_bottom, frame->height);
for (l = 0; l < s->line_count; ++l) {
TextLine *line = &s->lines[l];
line_w = POS_CEIL(line->width64, 64);
for (g = 0; g < line->hb_data.glyph_count; ++g) {
info = &line->glyphs[g];
dummy.fontsize = s->fontsize;
@ -1506,10 +1549,16 @@ static int draw_glyphs(DrawTextContext *s, AVFrame *frame,
b_glyph = borderw ? glyph->border_bglyph[idx] : glyph->bglyph[idx];
bitmap = b_glyph->bitmap;
x1 = x + info->x + b_glyph->left;
y1 = y + info->y - b_glyph->top;
y1 = y + info->y - b_glyph->top + offset_y;
w1 = bitmap.width;
h1 = bitmap.rows;
if (j_center) {
x1 += (s->box_width - line_w) / 2;
} else if (j_right) {
x1 += s->box_width - line_w;
}
// Offset of the glyph's bitmap in the visible region
dx = dy = 0;
if (x1 < metrics->rect_x - s->bb_left) {

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