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

[Francesco Carusi <klimklim@tiscali.it>]

You can find an overview of the changes here:

https://github.com/yethie/FFmpeg/blob/master/drawtext/CHANGES.md

and the new code here:

https://github.com/yethie/FFmpeg/blob/master/libavfilter/vf_drawtext.c


On 19/06/2023 19:56, Mark Ren wrote:
> Ah alright I see. When might that push come through and is there somewhere
> I can look at the kind of changes in the meantime?
>
> On Mon, Jun 19, 2023 at 12:39 PM Paul B Mahol <onemda@gmail.com> wrote:
>
>>
>> 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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