Re: [FFmpeg-devel] [PATCH] libavfilter/vf_drawtext: add letter_spacing as an evaluated parameter

[Paul B Mahol <onemda@gmail.com>]

On Mon, Jun 19, 2023 at 6:34 PM Mark Ren <mark.ren77@gmail.com> wrote:

> When enabled it will add pixels (or subtract if given a negative value)
> between each letters,
> set use_kerning to false,
> and add the pixels to text_w.
>

Conflicts with big drawtext filter set that will be pushed soon.


>
> Signed-off-by: Mark Ren <mark.ren77@gmail.com>
> ---
>  libavfilter/vf_drawtext.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
> index 71ab851462..ec8313820d 100644
> --- a/libavfilter/vf_drawtext.c
> +++ b/libavfilter/vf_drawtext.c
> @@ -183,6 +183,7 @@ typedef struct DrawTextContext {
>      unsigned int fontsize;          ///< font size to use
>      unsigned int default_fontsize;  ///< default font size to use
>
> +    int letter_spacing;             ///< letter spacing in pixels
>      int line_spacing;               ///< lines spacing in pixels
>      short int draw_box;             ///< draw box around text - true or
> false
>      int boxborderw;                 ///< box border width
> @@ -208,6 +209,8 @@ typedef struct DrawTextContext {
>      char   *a_expr;
>      AVExpr *a_pexpr;
>      int alpha;
> +    char* letter_spacing_expr;      ///< expression for letter spacing
> +    AVExpr* letter_spacing_pexpr;   ///< parsed expression for letter
> spacing
>      AVLFG  prng;                    ///< random
>      char       *tc_opt_string;      ///< specified timecode option string
>      AVRational  tc_rate;            ///< frame rate for timecode
> @@ -237,6 +240,7 @@ static const AVOption drawtext_options[]= {
>      {"shadowcolor", "set shadow color",     OFFSET(shadowcolor.rgba),
>  AV_OPT_TYPE_COLOR,  {.str="black"}, 0, 0, FLAGS},
>      {"box",         "set box",              OFFSET(draw_box),
>  AV_OPT_TYPE_BOOL,   {.i64=0},     0,        1       , FLAGS},
>      {"boxborderw",  "set box border width", OFFSET(boxborderw),
>  AV_OPT_TYPE_INT,    {.i64=0},     INT_MIN,  INT_MAX , FLAGS},
> +    {"letter_spacing", "set letter spacing in pixels",
> OFFSET(letter_spacing_expr), 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},
>      {"x",           "set x expression",     OFFSET(x_expr),
>  AV_OPT_TYPE_STRING, {.str="0"},   0, 0, FLAGS},
> @@ -812,7 +816,7 @@ static av_cold int init(AVFilterContext *ctx)
>                         FT_STROKER_LINEJOIN_ROUND, 0);
>      }
>
> -    s->use_kerning = FT_HAS_KERNING(s->face);
> +    s->use_kerning = FT_HAS_KERNING(s->face) && !s->letter_spacing;
>
>      /* load the fallback glyph with code 0 */
>      load_glyph(ctx, NULL, 0);
> @@ -857,8 +861,9 @@ static av_cold void uninit(AVFilterContext *ctx)
>      av_expr_free(s->y_pexpr);
>      av_expr_free(s->a_pexpr);
>      av_expr_free(s->fontsize_pexpr);
> +    av_expr_free(s->letter_spacing_pexpr);
>
> -    s->x_pexpr = s->y_pexpr = s->a_pexpr = s->fontsize_pexpr = NULL;
> +    s->x_pexpr = s->y_pexpr = s->a_pexpr = s->fontsize_pexpr =
> s->letter_spacing_pexpr = NULL;
>
>      av_freep(&s->positions);
>      s->nb_positions = 0;
> @@ -903,13 +908,16 @@ static int config_input(AVFilterLink *inlink)
>      av_expr_free(s->x_pexpr);
>      av_expr_free(s->y_pexpr);
>      av_expr_free(s->a_pexpr);
> -    s->x_pexpr = s->y_pexpr = s->a_pexpr = NULL;
> +    av_expr_free(s->letter_spacing_pexpr);
> +    s->x_pexpr = s->y_pexpr = s->a_pexpr = s->letter_spacing_pexpr = NULL;
>
>      if ((ret = av_expr_parse(&s->x_pexpr, expr = s->x_expr, var_names,
>                               NULL, NULL, fun2_names, fun2, 0, ctx)) < 0 ||
>          (ret = av_expr_parse(&s->y_pexpr, expr = s->y_expr, var_names,
>                               NULL, NULL, fun2_names, fun2, 0, ctx)) < 0 ||
>          (ret = av_expr_parse(&s->a_pexpr, expr = s->a_expr, var_names,
> +                             NULL, NULL, fun2_names, fun2, 0, ctx)) < 0 ||
> +        (ret = av_expr_parse(&s->letter_spacing_pexpr, expr =
> s->letter_spacing_expr, var_names,
>                               NULL, NULL, fun2_names, fun2, 0, ctx)) < 0) {
>          av_log(ctx, AV_LOG_ERROR, "Failed to parse expression: %s \n",
> expr);
>          return AVERROR(EINVAL);
> @@ -1525,6 +1533,9 @@ continue_on_invalid2:
>          dummy.fontsize = s->fontsize;
>          glyph = av_tree_find(s->glyphs, &dummy, glyph_cmp, NULL);
>
> +        /* letter spacing */
> +        x += s->letter_spacing;
> +
>          /* kerning */
>          if (s->use_kerning && prev_glyph && glyph->code) {
>              FT_Get_Kerning(s->face, prev_glyph->code, glyph->code,
> @@ -1539,7 +1550,12 @@ continue_on_invalid2:
>          else              x += glyph->advance;
>      }
>
> -    max_text_line_w = FFMAX(x, max_text_line_w);
> +    s->letter_spacing = av_expr_eval(s->letter_spacing_pexpr,
> s->var_values, &s->prng);
> +    if (s->letter_spacing < 0) {
> +        max_text_line_w = x+ s->letter_spacing;
> +    } else {
> +        max_text_line_w = FFMAX(x, max_text_line_w) + s->letter_spacing;
> +    }
>
>      s->var_values[VAR_TW] = s->var_values[VAR_TEXT_W] = max_text_line_w;
>      s->var_values[VAR_TH] = s->var_values[VAR_TEXT_H] = y +
> s->max_glyph_h;
> --
> 2.40.1
>
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