Support X core font driver on cairo (Bug#28236)

* configure.ac (HAVE_X_WINDOWS): Add xfont.o to FONT_OBJ if HAVE_CAIRO.

* doc/lispref/frames.texi (Font and Color Parameters): Mention X core font
driver with Cairo drawing.

* src/font.c (syms_of_font) [HAVE_X_WINDOWS && USE_CAIRO]: Call syms_of_xfont.

* src/xfns.c (x_create_tip_frame) [USE_CAIRO]: Register xfont_driver.

* src/xterm.c (x_cr_gc_clip) [USE_CAIRO]: New function extracted from
x_begin_cr_clip.
(x_begin_cr_clip) [USE_CAIRO]: Use it.
(xlib_surface_key, saved_drawable_key) [USE_CAIRO]: New variables.
(x_cr_destroy_xlib_surface, x_try_cr_xlib_drawable)
(x_end_cr_xlib_drawable) [USE_CAIRO]: New functions.
(x_draw_composite_glyph_string_foreground)
(x_draw_glyph_string_foreground) [USE_CAIRO]: Get Xlib surface when drawing
text with X core fonts into bitmap surfaces.  Add fallback code for drawing
into outline surfaces.

5 files changed, 267 insertions, 90 deletions

diff --git a/configure.ac b/configure.ac
index bd51f54212c..5c96f4231ee 100644
--- a/configure.ac
+++ b/configure.ac
@@ -5261,7 +5261,7 @@ if test "${HAVE_X_WINDOWS}" = "yes" ; then
   XOBJ="xterm.o xfns.o xselect.o xrdb.o xsmfns.o xsettings.o"
   FONT_OBJ=xfont.o
   if test "$HAVE_CAIRO" = "yes"; then
-    FONT_OBJ="ftfont.o ftcrfont.o"
+    FONT_OBJ="$FONT_OBJ ftfont.o ftcrfont.o"
   elif test "$HAVE_XFT" = "yes"; then
     FONT_OBJ="$FONT_OBJ ftfont.o xftfont.o ftxfont.o"
   elif test "$HAVE_FREETYPE" = "yes"; then
diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index 336075a1ca2..629cec3c5fe 100644
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -2282,11 +2282,11 @@ drawing characters on the frame, in order of priority.  In Emacs built
 without Cairo drawing on X, there are currently three available font
 backends: @code{x} (the X core font driver), @code{xft} (the Xft font
 driver), and @code{xfthb} (the Xft font driver with HarfBuzz text
-shaping).  If built with the Cairo drawing, there are two available
-font backends on X: @code{ftcr} (the FreeType font driver on Cairo)
-and @code{ftcrhb} (the FreeType font driver on Cairo with HarfBuzz
-text shaping).  On MS-Windows, there are currently three available
-font backends: @code{gdi} (the core MS-Windows font driver),
+shaping).  If built with the Cairo drawing, there are also three
+available font backends on X: @code{x}, @code{ftcr} (the FreeType font
+driver on Cairo), and @code{ftcrhb} (the FreeType font driver on Cairo
+with HarfBuzz text shaping).  On MS-Windows, there are currently three
+available font backends: @code{gdi} (the core MS-Windows font driver),
 @code{uniscribe} (font driver for OTF and TTF fonts with text shaping
 by the Uniscribe engine), and @code{harfbuzz} (font driver for OTF and
 TTF fonts with HarfBuzz text shaping) (@pxref{Windows Fonts,,, emacs,
diff --git a/src/font.c b/src/font.c
index 6ab4923c3d2..5705758b99f 100644
--- a/src/font.c
+++ b/src/font.c
@@ -5497,10 +5497,10 @@ cause Xft crashes.  Only has an effect in Xft builds.  */);
 #ifdef HAVE_FREETYPE
   syms_of_ftfont ();
 #ifdef HAVE_X_WINDOWS
+  syms_of_xfont ();
 #ifdef USE_CAIRO
   syms_of_ftcrfont ();
 #else
-  syms_of_xfont ();
   syms_of_ftxfont ();
 #ifdef HAVE_XFT
   syms_of_xftfont ();
diff --git a/src/xfns.c b/src/xfns.c
index 460dd1316e6..46f19ff82ac 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -3794,8 +3794,8 @@ This function is an internal primitive--use `make-frame' instead.  */)
   register_font_driver (&ftxfont_driver, f);
 #endif  /* not HAVE_XFT */
 #endif  /* HAVE_FREETYPE */
-  register_font_driver (&xfont_driver, f);
 #endif  /* not USE_CAIRO */
+  register_font_driver (&xfont_driver, f);
 
   image_cache_refcount =
     FRAME_IMAGE_CACHE (f) ? FRAME_IMAGE_CACHE (f)->refcount : 0;
diff --git a/src/xterm.c b/src/xterm.c
index e0edd9c1a40..3cd95b7a65d 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -357,6 +357,25 @@ x_cr_update_surface_desired_size (struct frame *f, int width, int height)
     }
 }
 
+static void
+x_cr_gc_clip (cairo_t *cr, struct frame *f, GC gc)
+{
+  if (gc)
+    {
+      struct x_gc_ext_data *gc_ext = x_gc_get_ext_data (f, gc, 0);
+
+      if (gc_ext && gc_ext->n_clip_rects)
+        {
+          for (int i = 0; i < gc_ext->n_clip_rects; i++)
+            cairo_rectangle (cr, gc_ext->clip_rects[i].x,
+                             gc_ext->clip_rects[i].y,
+                             gc_ext->clip_rects[i].width,
+                             gc_ext->clip_rects[i].height);
+          cairo_clip (cr);
+        }
+    }
+}
+
 cairo_t *
 x_begin_cr_clip (struct frame *f, GC gc)
 {
@@ -379,23 +398,7 @@ x_begin_cr_clip (struct frame *f, GC gc)
       cairo_surface_destroy (surface);
     }
   cairo_save (cr);
-
-  if (gc)
-    {
-      struct x_gc_ext_data *gc_ext = x_gc_get_ext_data (f, gc, 0);
-
-      if (gc_ext && gc_ext->n_clip_rects)
-        {
-          int i;
-
-          for (i = 0; i < gc_ext->n_clip_rects; i++)
-            cairo_rectangle (cr, gc_ext->clip_rects[i].x,
-                             gc_ext->clip_rects[i].y,
-                             gc_ext->clip_rects[i].width,
-                             gc_ext->clip_rects[i].height);
-          cairo_clip (cr);
-        }
-    }
+  x_cr_gc_clip (cr, f, gc);
 
   return cr;
 }
@@ -434,6 +437,116 @@ x_set_cr_source_with_gc_background (struct frame *f, GC gc)
                         color.green / 65535.0, color.blue / 65535.0);
 }
 
+static const cairo_user_data_key_t xlib_surface_key, saved_drawable_key;
+
+static void
+x_cr_destroy_xlib_surface (cairo_surface_t *xlib_surface)
+{
+  if (xlib_surface)
+    {
+      XFreePixmap (cairo_xlib_surface_get_display (xlib_surface),
+                   cairo_xlib_surface_get_drawable (xlib_surface));
+      cairo_surface_destroy (xlib_surface);
+    }
+}
+
+static bool
+x_try_cr_xlib_drawable (struct frame *f, GC gc)
+{
+  cairo_t *cr = FRAME_CR_CONTEXT (f);
+  if (!cr)
+    return true;
+
+  cairo_surface_t *surface = cairo_get_target (cr);
+  switch (cairo_surface_get_type (surface))
+    {
+    case CAIRO_SURFACE_TYPE_XLIB:
+      cairo_surface_flush (surface);
+      return true;
+
+    case CAIRO_SURFACE_TYPE_IMAGE:
+      break;
+
+    default:
+      return false;
+    }
+
+  /* FRAME_CR_CONTEXT (f) is an image surface we can not draw into
+     directly with Xlib.  Set up a Pixmap so we can copy back the
+     result later in x_end_cr_xlib_drawable.  */
+  cairo_surface_t *xlib_surface = cairo_get_user_data (cr, &xlib_surface_key);
+  int width = FRAME_CR_SURFACE_DESIRED_WIDTH (f);
+  int height = FRAME_CR_SURFACE_DESIRED_HEIGHT (f);
+  Pixmap pixmap;
+  if (xlib_surface
+      && cairo_xlib_surface_get_width (xlib_surface) == width
+      && cairo_xlib_surface_get_height (xlib_surface) == height)
+    pixmap = cairo_xlib_surface_get_drawable (xlib_surface);
+  else
+    {
+      pixmap = XCreatePixmap (FRAME_X_DISPLAY (f), FRAME_X_RAW_DRAWABLE (f),
+                              width, height,
+                              DefaultDepthOfScreen (FRAME_X_SCREEN (f)));
+      xlib_surface = cairo_xlib_surface_create (FRAME_X_DISPLAY (f),
+                                                pixmap, FRAME_X_VISUAL (f),
+                                                width, height);
+      cairo_set_user_data (cr, &xlib_surface_key, xlib_surface,
+                           (cairo_destroy_func_t) x_cr_destroy_xlib_surface);
+    }
+
+  cairo_t *buf = cairo_create (xlib_surface);
+  cairo_set_source_surface (buf, surface, 0, 0);
+  cairo_matrix_t matrix;
+  cairo_get_matrix (cr, &matrix);
+  cairo_pattern_set_matrix (cairo_get_source (cr), &matrix);
+  cairo_set_operator (buf, CAIRO_OPERATOR_SOURCE);
+  x_cr_gc_clip (buf, f, gc);
+  cairo_paint (buf);
+  cairo_destroy (buf);
+
+  cairo_set_user_data (cr, &saved_drawable_key,
+                       (void *) (uintptr_t) FRAME_X_RAW_DRAWABLE (f), NULL);
+  FRAME_X_RAW_DRAWABLE (f) = pixmap;
+  cairo_surface_flush (xlib_surface);
+
+  return true;
+}
+
+static void
+x_end_cr_xlib_drawable (struct frame *f, GC gc)
+{
+  cairo_t *cr = FRAME_CR_CONTEXT (f);
+  if (!cr)
+    return;
+
+  Drawable saved_drawable
+    = (uintptr_t) cairo_get_user_data (cr, &saved_drawable_key);
+  cairo_surface_t *surface = (saved_drawable
+                              ? cairo_get_user_data (cr, &xlib_surface_key)
+                              : cairo_get_target (cr));
+  struct x_gc_ext_data *gc_ext = x_gc_get_ext_data (f, gc, 0);
+  if (gc_ext && gc_ext->n_clip_rects)
+    for (int i = 0; i < gc_ext->n_clip_rects; i++)
+      cairo_surface_mark_dirty_rectangle (surface, gc_ext->clip_rects[i].x,
+                                          gc_ext->clip_rects[i].y,
+                                          gc_ext->clip_rects[i].width,
+                                          gc_ext->clip_rects[i].height);
+  else
+    cairo_surface_mark_dirty (surface);
+  if (!saved_drawable)
+    return;
+
+  cairo_save (cr);
+  cairo_set_source_surface (cr, surface, 0, 0);
+  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
+  x_cr_gc_clip (cr, f, gc);
+  cairo_paint (cr);
+  cairo_restore (cr);
+
+  FRAME_X_RAW_DRAWABLE (f) = saved_drawable;
+  cairo_set_user_data (cr, &saved_drawable_key, NULL, NULL);
+}
+
 /* Fringe bitmaps.  */
 
 static int max_fringe_bmp = 0;
@@ -1732,20 +1845,65 @@ x_draw_glyph_string_foreground (struct glyph_string *s)
   else
     {
       struct font *font = s->font;
-      int boff = font->baseline_offset;
-      int y;
+#ifdef USE_CAIRO
+      if (!EQ (font->driver->type, Qx)
+          || x_try_cr_xlib_drawable (s->f, s->gc))
+        {
+#endif  /* USE_CAIRO */
+          int boff = font->baseline_offset;
+          int y;
 
-      if (font->vertical_centering)
-        boff = VCENTER_BASELINE_OFFSET (font, s->f) - boff;
+          if (font->vertical_centering)
+            boff = VCENTER_BASELINE_OFFSET (font, s->f) - boff;
 
-      y = s->ybase - boff;
-      if (s->for_overlaps
-          || (s->background_filled_p && s->hl != DRAW_CURSOR))
-        font->driver->draw (s, 0, s->nchars, x, y, false);
+          y = s->ybase - boff;
+          if (s->for_overlaps
+              || (s->background_filled_p && s->hl != DRAW_CURSOR))
+            font->driver->draw (s, 0, s->nchars, x, y, false);
+          else
+            font->driver->draw (s, 0, s->nchars, x, y, true);
+          if (s->face->overstrike)
+            font->driver->draw (s, 0, s->nchars, x + 1, y, false);
+#ifdef USE_CAIRO
+          if (EQ (font->driver->type, Qx))
+            x_end_cr_xlib_drawable (s->f, s->gc);
+        }
       else
-        font->driver->draw (s, 0, s->nchars, x, y, true);
-      if (s->face->overstrike)
-        font->driver->draw (s, 0, s->nchars, x + 1, y, false);
+        {
+          /* Fallback for the case that no Xlib Drawable is available
+             for drawing text with X core fonts.  */
+          if (!(s->for_overlaps
+                || (s->background_filled_p && s->hl != DRAW_CURSOR)))
+            {
+              int box_line_width = max (s->face->box_line_width, 0);
+
+              if (s->stippled_p)
+                {
+                  Display *display = FRAME_X_DISPLAY (s->f);
+
+                  /* Fill background with a stipple pattern.  */
+                  XSetFillStyle (display, s->gc, FillOpaqueStippled);
+                  x_fill_rectangle (s->f, s->gc, s->x,
+                                    s->y + box_line_width,
+                                    s->background_width,
+                                    s->height - 2 * box_line_width);
+                  XSetFillStyle (display, s->gc, FillSolid);
+                }
+              else
+                x_clear_glyph_string_rect (s, s->x, s->y + box_line_width,
+                                           s->background_width,
+                                           s->height - 2 * box_line_width);
+            }
+          for (i = 0; i < s->nchars; ++i)
+            {
+              struct glyph *g = s->first_glyph + i;
+              x_draw_rectangle (s->f,
+                                s->gc, x, s->y, g->pixel_width - 1,
+                                s->height - 1);
+              x += g->pixel_width;
+            }
+        }
+#endif  /* USE_CAIRO */
     }
 }
 
@@ -1778,65 +1936,84 @@ x_draw_composite_glyph_string_foreground (struct glyph_string *s)
         x_draw_rectangle (s->f, s->gc, x, s->y,
                         s->width - 1, s->height - 1);
     }
-  else if (! s->first_glyph->u.cmp.automatic)
-    {
-      int y = s->ybase;
-
-      for (i = 0, j = s->cmp_from; i < s->nchars; i++, j++)
-        /* TAB in a composition means display glyphs with padding
-           space on the left or right.  */
-        if (COMPOSITION_GLYPH (s->cmp, j) != '\t')
-          {
-            int xx = x + s->cmp->offsets[j * 2];
-            int yy = y - s->cmp->offsets[j * 2 + 1];
-
-            font->driver->draw (s, j, j + 1, xx, yy, false);
-            if (s->face->overstrike)
-              font->driver->draw (s, j, j + 1, xx + 1, yy, false);
-          }
-    }
   else
-    {
-      Lisp_Object gstring = composition_gstring_from_id (s->cmp_id);
-      Lisp_Object glyph;
-      int y = s->ybase;
-      int width = 0;
-
-      for (i = j = s->cmp_from; i < s->cmp_to; i++)
-        {
-          glyph = LGSTRING_GLYPH (gstring, i);
-          if (NILP (LGLYPH_ADJUSTMENT (glyph)))
-            width += LGLYPH_WIDTH (glyph);
-          else
-            {
-              int xoff, yoff, wadjust;
+#ifdef USE_CAIRO
+    if (!EQ (font->driver->type, Qx)
+        || x_try_cr_xlib_drawable (s->f, s->gc))
+      {
+#endif  /* USE_CAIRO */
+        if (! s->first_glyph->u.cmp.automatic)
+          {
+            int y = s->ybase;
 
-              if (j < i)
+            for (i = 0, j = s->cmp_from; i < s->nchars; i++, j++)
+              /* TAB in a composition means display glyphs with
+                 padding space on the left or right.  */
+              if (COMPOSITION_GLYPH (s->cmp, j) != '\t')
                 {
-                  font->driver->draw (s, j, i, x, y, false);
+                  int xx = x + s->cmp->offsets[j * 2];
+                  int yy = y - s->cmp->offsets[j * 2 + 1];
+
+                  font->driver->draw (s, j, j + 1, xx, yy, false);
                   if (s->face->overstrike)
-                    font->driver->draw (s, j, i, x + 1, y, false);
-                  x += width;
+                    font->driver->draw (s, j, j + 1, xx + 1, yy, false);
                 }
-              xoff = LGLYPH_XOFF (glyph);
-              yoff = LGLYPH_YOFF (glyph);
-              wadjust = LGLYPH_WADJUST (glyph);
-              font->driver->draw (s, i, i + 1, x + xoff, y + yoff, false);
-              if (s->face->overstrike)
-                font->driver->draw (s, i, i + 1, x + xoff + 1, y + yoff,
-                                    false);
-              x += wadjust;
-              j = i + 1;
-              width = 0;
-            }
-        }
-      if (j < i)
-        {
-          font->driver->draw (s, j, i, x, y, false);
-          if (s->face->overstrike)
-            font->driver->draw (s, j, i, x + 1, y, false);
-        }
-    }
+          }
+        else
+          {
+            Lisp_Object gstring = composition_gstring_from_id (s->cmp_id);
+            Lisp_Object glyph;
+            int y = s->ybase;
+            int width = 0;
+
+            for (i = j = s->cmp_from; i < s->cmp_to; i++)
+              {
+                glyph = LGSTRING_GLYPH (gstring, i);
+                if (NILP (LGLYPH_ADJUSTMENT (glyph)))
+                  width += LGLYPH_WIDTH (glyph);
+                else
+                  {
+                    int xoff, yoff, wadjust;
+
+                    if (j < i)
+                      {
+                        font->driver->draw (s, j, i, x, y, false);
+                        if (s->face->overstrike)
+                          font->driver->draw (s, j, i, x + 1, y, false);
+                        x += width;
+                      }
+                    xoff = LGLYPH_XOFF (glyph);
+                    yoff = LGLYPH_YOFF (glyph);
+                    wadjust = LGLYPH_WADJUST (glyph);
+                    font->driver->draw (s, i, i + 1, x + xoff, y + yoff, false);
+                    if (s->face->overstrike)
+                      font->driver->draw (s, i, i + 1, x + xoff + 1, y + yoff,
+                                          false);
+                    x += wadjust;
+                    j = i + 1;
+                    width = 0;
+                  }
+              }
+            if (j < i)
+              {
+                font->driver->draw (s, j, i, x, y, false);
+                if (s->face->overstrike)
+                  font->driver->draw (s, j, i, x + 1, y, false);
+              }
+          }
+#ifdef USE_CAIRO
+        if (EQ (font->driver->type, Qx))
+          x_end_cr_xlib_drawable (s->f, s->gc);
+      }
+    else
+      {
+        /* Fallback for the case that no Xlib Drawable is available
+           for drawing text with X core fonts.  */
+        if (s->cmp_from == 0)
+          x_draw_rectangle (s->f, s->gc, x, s->y,
+                            s->width - 1, s->height - 1);
+      }
+#endif  /* USE_CAIRO */
 }