[FFmpeg-devel] [PATCH] avfilter/drawtext - implement fix_bounds

[Gyan Doshi]

The no-op commit e496c45 from Libav introduced an option which allowed 
the user to relocate text to fit within the frame if it was going out of 
bounds.

For some reason, when the merge commit b479e01 was applied, the option 
was added but the code fragment which implemented it, was not. So the 
option was dead on arrival, and has remained impotent (since Feb 2012).

Attached patch implements option. Text styling elements like shadow or 
box are also kept within bounds. Default value changed to false so that 
filter outcome doesn't change in existing scripts.

Regards,
Gyan
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From d74b718d75db0ab6724ca807e2af1c1e756f7c56 Mon Sep 17 00:00:00 2001
From: Gyan Doshi <gyandoshi at gmail.com>
Date: Thu, 11 Jan 2018 18:30:16 +0530
Subject: [PATCH] avfilter/drawtext - implement fix_bounds

When enabled, text, including effects like shadow or box, will be
completely bound within the video frame.

Default value changed to false to keep continuity of behaviour.

Fixes #6960.
---
 libavfilter/vf_drawtext.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
index f6151443bb..f97a741b50 100644
--- a/libavfilter/vf_drawtext.c
+++ b/libavfilter/vf_drawtext.c
@@ -238,7 +238,7 @@ static const AVOption drawtext_options[]= {
     {"rate",            "set rate (timecode only)",         OFFSET(tc_rate),       AV_OPT_TYPE_RATIONAL, {.dbl=0},           0,  INT_MAX, FLAGS},
     {"reload",     "reload text file for each frame",                       OFFSET(reload),     AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     { "alpha",       "apply alpha while rendering", OFFSET(a_expr),      AV_OPT_TYPE_STRING, { .str = "1"     },          .flags = FLAGS },
-    {"fix_bounds", "check and fix text coords to avoid clipping", OFFSET(fix_bounds), AV_OPT_TYPE_BOOL, {.i64=1}, 0, 1, FLAGS},
+    {"fix_bounds", "check and fix text coords to avoid clipping", OFFSET(fix_bounds), AV_OPT_TYPE_BOOL, {.i64=0}, 0, 1, FLAGS},
     {"start_number", "start frame number for n/frame_num variable", OFFSET(start_number), AV_OPT_TYPE_INT, {.i64=0}, 0, INT_MAX, FLAGS},
 
 #if CONFIG_LIBFRIBIDI
@@ -1401,6 +1401,32 @@ static int draw_text(AVFilterContext *ctx, AVFrame *frame,
     box_w = FFMIN(width - 1 , max_text_line_w);
     box_h = FFMIN(height - 1, y + s->max_glyph_h);
 
+    if (s->fix_bounds) {
+
+        /* calculate footprint of text effects */
+        int boxoffset     = s->draw_box ? FFMAX(s->boxborderw, 0) : 0;
+        int borderoffset  = s->borderw  ? FFMAX(s->borderw, 0) : 0;
+
+        int offsetleft = FFMAX3(boxoffset, borderoffset,
+                                (s->shadowx < 0 ? FFABS(s->shadowx) : 0));
+        int offsettop = FFMAX3(boxoffset, borderoffset,
+                                (s->shadowy < 0 ? FFABS(s->shadowy) : 0));
+
+        int offsetright = FFMAX3(boxoffset, borderoffset,
+                                 (s->shadowx > 0 ? s->shadowx : 0));
+        int offsetbottom = FFMAX3(boxoffset, borderoffset,
+                                  (s->shadowy > 0 ? s->shadowy : 0));
+
+
+        if (s->x - offsetleft < 0) s->x = offsetleft;
+        if (s->y - offsettop < 0)  s->y = offsettop;
+
+        if (s->x + box_w + offsetright > width)
+            s->x = FFMAX(width - box_w - offsetright, 0);
+        if (s->y + box_h + offsetbottom > height)
+            s->y = FFMAX(height - box_h - offsetbottom, 0);
+    }
+
     /* draw box */
     if (s->draw_box)
         ff_blend_rectangle(&s->dc, &boxcolor,
-- 
2.11.1.windows.1