truetype: Don't write glyph if num_contours == 0

According to the Opentype spec, num_contours in a glyf table entry can
be > 0 (single glyph) or < 0 (composite glyph).  num_contours == 0 is
undefined.

The embedded font in the test case for this bug contained a space
glyph with num_contours == 0. This was failing on some printers.
According to the spec, glyphs with no outlines such as space are
required to have a 0 size entry in the loca table.

https://bugs.freedesktop.org/show_bug.cgi?id=79897

1 files changed, 24 insertions, 6 deletions

diff --git a/src/cairo-truetype-subset.c b/src/cairo-truetype-subset.c
index 3aa637d6f..f47b966a5 100644
--- a/src/cairo-truetype-subset.c
+++ b/src/cairo-truetype-subset.c
@@ -652,16 +652,34 @@ cairo_truetype_font_write_glyf_table (cairo_truetype_font_t *font,
 	if (unlikely (status))
 	    goto FAIL;
 
-        if (size != 0) {
-            status = font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
+	if (size > 1) {
+	    tt_glyph_data_t *glyph_data;
+	    int num_contours;
+
+	    status = font->backend->load_truetype_table (font->scaled_font_subset->scaled_font,
 							 TT_TAG_glyf, begin, buffer, &size);
 	    if (unlikely (status))
 		goto FAIL;
 
-            status = cairo_truetype_font_remap_composite_glyph (font, buffer, size);
-	    if (unlikely (status))
-		goto FAIL;
-        }
+	    glyph_data = (tt_glyph_data_t *) buffer;
+	    num_contours = (int16_t)be16_to_cpu (glyph_data->num_contours);
+	    if (num_contours < 0) {
+		status = cairo_truetype_font_remap_composite_glyph (font, buffer, size);
+		if (unlikely (status))
+		    goto FAIL;
+	    } else if (num_contours == 0) {
+		/* num_contours == 0 is undefined in the Opentype
+		 * spec. There are some embedded fonts that have a
+		 * space glyph with num_contours = 0 that fails on
+		 * some printers. The spec requires glyphs without
+		 * contours to have a 0 size glyph entry in the loca
+		 * table.
+		 *
+		 * If num_contours == 0, truncate the glyph to 0 size.
+		 */
+		_cairo_array_truncate (&font->output, _cairo_array_num_elements (&font->output) - size);
+	    }
+	}
     }
 
     status = cairo_truetype_font_align_output (font, &next);