[FFmpeg-devel] [PATCH 1/2] avfilter/drawtext: support bitmap (including monochrome) fonts

[Yogeshwar Velingker]

Fix segfaults that occur when using a bitmap font. Do not free glyphs on
error in load_glyph - upon detecting a monochrome glyph, the function
would free it while leaving its corresponding node in the glyph tree,
resulting in invalid reads and double frees. Avoid calling
FT_Glyph_To_Bitmap on bitmap glyphs as this returns the same glyph
pointer, which is then stored in the glyph tree resulting in a double
free in uninit.

Also call ff_blend_mask with the appropriate bit depth so that
monochrome (and other pixel format) bitmaps can be drawn.

Signed-off-by: Yogeshwar Velingker <yogi at velingker.com>
---
 libavfilter/vf_drawtext.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/libavfilter/vf_drawtext.c b/libavfilter/vf_drawtext.c
index e4662f3a45..8bf5a3cd49 100644
--- a/libavfilter/vf_drawtext.c
+++ b/libavfilter/vf_drawtext.c
@@ -794,7 +794,7 @@ static int load_glyph(AVFilterContext *ctx, Glyph **glyph_ptr, uint32_t code, in
     }
 
     // Check if a bitmap is needed
-    if (shift_x64 >= 0 && shift_y64 >= 0) {
+    if (shift_x64 >= 0 && shift_y64 >= 0 && glyph->glyph->format != FT_GLYPH_FORMAT_BITMAP) {
         // Get the bitmap subpixel index (0 -> 15)
         int idx = get_subpixel_idx(shift_x64, shift_y64);
         shift.x = shift_x64;
@@ -807,11 +807,6 @@ static int load_glyph(AVFilterContext *ctx, Glyph **glyph_ptr, uint32_t code, in
                 goto error;
             }
             glyph->bglyph[idx] = (FT_BitmapGlyph)tmp_glyph;
-            if (glyph->bglyph[idx]->bitmap.pixel_mode == FT_PIXEL_MODE_MONO) {
-                av_log(ctx, AV_LOG_ERROR, "Monocromatic (1bpp) fonts are not supported.\n");
-                ret = AVERROR(EINVAL);
-                goto error;
-            }
         }
         if (s->borderw && !glyph->border_bglyph[idx]) {
             FT_Glyph tmp_glyph = glyph->border_glyph;
@@ -828,11 +823,6 @@ static int load_glyph(AVFilterContext *ctx, Glyph **glyph_ptr, uint32_t code, in
     return 0;
 
 error:
-    if (glyph && glyph->glyph)
-        FT_Done_Glyph(glyph->glyph);
-
-    av_freep(&glyph);
-    av_freep(&node);
     return ret;
 }
 
@@ -1282,7 +1272,7 @@ static int draw_glyphs(DrawTextContext *s, AVFrame *frame,
                        TextMetrics *metrics,
                        int x, int y, int borderw)
 {
-    int g, l, x1, y1, w1, h1, idx;
+    int g, l, x1, y1, w1, h1, idx, l2depth;
     int dx = 0, dy = 0, pdx = 0;
     GlyphInfo *info;
     Glyph dummy = { 0 }, *glyph;
@@ -1324,7 +1314,10 @@ static int draw_glyphs(DrawTextContext *s, AVFrame *frame,
             }
 
             idx = get_subpixel_idx(info->shift_x64, info->shift_y64);
-            b_glyph = borderw ? glyph->border_bglyph[idx] : glyph->bglyph[idx];
+            if (glyph->glyph->format != FT_GLYPH_FORMAT_BITMAP)
+                b_glyph = borderw ? glyph->border_bglyph[idx] : glyph->bglyph[idx];
+            else
+                b_glyph = (FT_BitmapGlyph)glyph->glyph;
             bitmap = b_glyph->bitmap;
             x1 = x + info->x + b_glyph->left;
             y1 = y + info->y - b_glyph->top + offset_y;
@@ -1357,8 +1350,18 @@ static int draw_glyphs(DrawTextContext *s, AVFrame *frame,
             w1 = FFMIN(clip_x - x1, w1 - dx);
             h1 = FFMIN(clip_y - y1, h1 - dy);
 
+            switch (bitmap.pixel_mode) {
+            case FT_PIXEL_MODE_GRAY: l2depth = 3; break;
+            case FT_PIXEL_MODE_MONO: l2depth = 0; break;
+            case FT_PIXEL_MODE_GRAY2: l2depth = 1; break;
+            case FT_PIXEL_MODE_GRAY4: l2depth = 2; break;
+            default:
+                av_log(s, AV_LOG_ERROR, "unsupported pixel format");
+                return AVERROR(EINVAL);
+            }
+
             ff_blend_mask(&s->dc, color, frame->data, frame->linesize, clip_x, clip_y,
-                bitmap.buffer + pdx, bitmap.pitch, w1, h1, 3, 0, x1, y1);
+                bitmap.buffer + pdx, bitmap.pitch, w1, h1, l2depth, 0, x1, y1);
         }
     }
 
-- 
2.47.2