[xlib] Discard clip if larger than glyph extents

Implement cheap calculation of glyph extents to see whether we can discard
the clip region. This is effective around 50% of the time for firefox (and
makes the xtrace so much neater).

3 files changed, 65 insertions, 0 deletions

diff --git a/src/cairo-scaled-font.c b/src/cairo-scaled-font.c
index 74a2c88c..199ad39e 100644
--- a/src/cairo-scaled-font.c
+++ b/src/cairo-scaled-font.c
@@ -2021,6 +2021,42 @@ _cairo_scaled_font_glyph_device_extents (cairo_scaled_font_t	 *scaled_font,
     return CAIRO_STATUS_SUCCESS;
 }
 
+void
+_cairo_scaled_font_glyph_approximate_extents (cairo_scaled_font_t	 *scaled_font,
+					      const cairo_glyph_t	 *glyphs,
+					      int                      num_glyphs,
+					      cairo_rectangle_int_t   *extents)
+{
+    double x0 = HUGE_VAL, x1 = -HUGE_VAL;
+    double y0 = HUGE_VAL, y1 = -HUGE_VAL;
+    int i;
+
+    for (i = 0; i < num_glyphs; i++) {
+	double g;
+
+	g = glyphs[i].x;
+	if (g < x0) x0 = g;
+	if (g > x1) x1 = g;
+
+	g = glyphs[i].y;
+	if (g < y0) y0 = g;
+	if (g > y1) y1 = g;
+    }
+
+    if (x0 <= x1 && y0 <= y1) {
+	extents->x = floor (x0 - scaled_font->extents.max_x_advance);
+	extents->width = ceil (x1 + scaled_font->extents.max_x_advance);
+	extents->width -= extents->x;
+
+	extents->y = floor (y0 - scaled_font->extents.ascent);
+	extents->height = ceil (y1 + scaled_font->extents.descent);
+	extents->height -= extents->y;
+    } else {
+	extents->x = extents->y = 0;
+	extents->width = extents->height = 0;
+    }
+}
+
 cairo_status_t
 _cairo_scaled_font_show_glyphs (cairo_scaled_font_t	*scaled_font,
 				cairo_operator_t	 op,
diff --git a/src/cairo-xlib-surface.c b/src/cairo-xlib-surface.c
index 375c6605..2b5b801b 100644
--- a/src/cairo-xlib-surface.c
+++ b/src/cairo-xlib-surface.c
@@ -4413,6 +4413,29 @@ _cairo_xlib_surface_show_glyphs (void                *abstract_dst,
     if (! _cairo_xlib_surface_owns_font (dst, scaled_font))
 	return UNSUPPORTED ("unowned font");
 
+    if (clip_region != NULL &&
+	cairo_region_num_rectangles (clip_region) == 1)
+    {
+	cairo_rectangle_int_t glyph_extents;
+	const cairo_rectangle_int_t *clip_extents;
+
+	/* Can we do without the clip?
+	 * Around 50% of the time the clip is redundant (firefox).
+	 */
+	_cairo_scaled_font_glyph_approximate_extents (scaled_font,
+						      glyphs, num_glyphs,
+						      &glyph_extents);
+
+	clip_extents = &clip->path->extents;
+	if (clip_extents->x <= glyph_extents.x &&
+	    clip_extents->y <= glyph_extents.y &&
+	    clip_extents->x + clip_extents->width  >= glyph_extents.x + glyph_extents.width &&
+	    clip_extents->y + clip_extents->height >= glyph_extents.y + glyph_extents.height)
+	{
+	    clip_region = NULL;
+	}
+    }
+
     status = _cairo_xlib_surface_set_clip_region (dst, clip_region);
     if (unlikely (status))
 	return status;
diff --git a/src/cairoint.h b/src/cairoint.h
index f6a45596..8b82454f 100644
--- a/src/cairoint.h
+++ b/src/cairoint.h
@@ -1726,6 +1726,12 @@ _cairo_scaled_font_glyph_device_extents (cairo_scaled_font_t	 *scaled_font,
 					 cairo_rectangle_int_t   *extents,
 					 cairo_bool_t		 *overlap);
 
+cairo_private void
+_cairo_scaled_font_glyph_approximate_extents (cairo_scaled_font_t	 *scaled_font,
+					      const cairo_glyph_t	 *glyphs,
+					      int                      num_glyphs,
+					      cairo_rectangle_int_t   *extents);
+
 cairo_private cairo_status_t
 _cairo_scaled_font_show_glyphs (cairo_scaled_font_t *scaled_font,
 				cairo_operator_t     op,