[gtk+/wip/matthiasc/gskpango: 1/3] Add a Pango renderer



commit 893e8750fe88c9eb7e66011f7e012f7efc8a98b9
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Aug 30 11:12:50 2017 -0400

    Add a Pango renderer
    
    Copy the PangoCairoRenderer into GTK+, rename it to GskPangoRenderer,
    and strip it down far enough to build without private pango apis.
    This means we currently don't support hexboxes or shapes.
    
    Currently, this lives in gtk, but it might be nicer to put it
    in gsk eventually.

 gtk/gskpango.c  |  858 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 gtk/gskpango.h  |   43 +++
 gtk/meson.build |    1 +
 3 files changed, 902 insertions(+), 0 deletions(-)
---
diff --git a/gtk/gskpango.c b/gtk/gskpango.c
new file mode 100644
index 0000000..643af01
--- /dev/null
+++ b/gtk/gskpango.c
@@ -0,0 +1,858 @@
+/*
+ * Copyright (C) 2017 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+
+#include "config.h"
+
+#include "gskpango.h"
+
+#include <math.h>
+
+#include <pango/pango.h>
+#include <cairo/cairo.h>
+
+typedef struct _PangoCairoFontHexBoxInfo             PangoCairoFontHexBoxInfo;
+
+struct _PangoCairoFontHexBoxInfo
+{
+  PangoCairoFont *font;
+  int rows;
+  double digit_width;
+  double digit_height;
+  double pad_x;
+  double pad_y;
+  double line_width;
+  double box_descent;
+  double box_height;
+};
+
+#define GSK_PANGO_RENDERER_CLASS(klass)    (G_TYPE_CHECK_CLASS_CAST ((klass), GSK_TYPE_PANGO_RENDERER, 
GskPangoRendererClass))
+#define GSK_IS_PANGO_RENDERER_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), GSK_TYPE_PANGO_RENDERER))
+#define GSK_PANGO_RENDERER_GET_CLASS(obj)  (G_TYPE_INSTANCE_GET_CLASS ((obj), GSK_TYPE_PANGO_RENDERER, 
GskPangoRendererClass))
+
+struct _GskPangoRenderer
+{
+  PangoRenderer parent_instance;
+
+  cairo_t *cr;
+  gboolean do_path;
+  gboolean has_show_text_glyphs;
+  double x_offset, y_offset;
+
+  /* house-keeping options */
+  gboolean is_cached_renderer;
+  gboolean cr_had_current_point;
+};
+
+struct _GskPangoRendererClass
+{
+  PangoRendererClass parent_class;
+};
+
+G_DEFINE_TYPE (GskPangoRenderer, gsk_pango_renderer, PANGO_TYPE_RENDERER)
+
+static void
+set_color (GskPangoRenderer *crenderer,
+           PangoRenderPart     part)
+{
+  PangoColor *color = pango_renderer_get_color ((PangoRenderer *) (crenderer), part);
+  guint16 a = pango_renderer_get_alpha ((PangoRenderer *) (crenderer), part);
+  gdouble red, green, blue, alpha;
+
+  if (!a && !color)
+    return;
+
+  if (color)
+    {
+      red = color->red / 65535.;
+      green = color->green / 65535.;
+      blue = color->blue / 65535.;
+      alpha = 1.;
+    }
+  else
+    {
+      cairo_pattern_t *pattern = cairo_get_source (crenderer->cr);
+
+      if (pattern && cairo_pattern_get_type (pattern) == CAIRO_PATTERN_TYPE_SOLID)
+        cairo_pattern_get_rgba (pattern, &red, &green, &blue, &alpha);
+      else
+        {
+          red = 0.;
+          green = 0.;
+          blue = 0.;
+          alpha = 1.;
+        }
+    }
+
+  if (a)
+    alpha = a / 65535.;
+
+  cairo_set_source_rgba (crenderer->cr, red, green, blue, alpha);
+}
+
+#if 0
+/* note: modifies crenderer->cr without doing cairo_save/restore() */
+static void
+gsk_pango_renderer_draw_frame (GskPangoRenderer *crenderer,
+                               double              x,
+                               double              y,
+                               double              width,
+                               double              height,
+                               double              line_width,
+                               gboolean            invalid)
+{
+  cairo_t *cr = crenderer->cr;
+
+  if (crenderer->do_path)
+    {
+      double d2 = line_width * .5, d = line_width;
+
+      /* we draw an outer box in one winding direction and an inner one in the
+       * opposite direction.  This works for both cairo windings rules.
+       *
+       * what we really want is cairo_stroke_to_path(), but that's not
+       * implemented in cairo yet.
+       */
+
+      /* outer */
+      cairo_rectangle (cr, x-d2, y-d2, width+d, height+d);
+
+      /* inner */
+      if (invalid)
+        {
+          /* delicacies of computing the joint... this is REALLY slow */
+
+          double alpha, tan_alpha2, cos_alpha;
+          double sx, sy;
+
+          alpha = atan2 (height, width);
+
+          tan_alpha2 = tan (alpha * .5);
+          if (tan_alpha2 < 1e-5 || (sx = d2 / tan_alpha2, 2. * sx > width - d))
+            sx = (width - d) * .5;
+
+          cos_alpha = cos (alpha);
+          if (cos_alpha < 1e-5 || (sy = d2 / cos_alpha, 2. * sy > height - d))
+            sy = (height - d) * .5;
+
+          /* top triangle */
+          cairo_new_sub_path (cr);
+          cairo_line_to (cr, x+width-sx, y+d2);
+          cairo_line_to (cr, x+sx, y+d2);
+          cairo_line_to (cr, x+.5*width, y+.5*height-sy);
+          cairo_close_path (cr);
+
+          /* bottom triangle */
+          cairo_new_sub_path (cr);
+          cairo_line_to (cr, x+width-sx, y+height-d2);
+          cairo_line_to (cr, x+.5*width, y+.5*height+sy);
+          cairo_line_to (cr, x+sx, y+height-d2);
+          cairo_close_path (cr);
+
+
+          alpha = G_PI_2 - alpha;
+          tan_alpha2 = tan (alpha * .5);
+          if (tan_alpha2 < 1e-5 || (sy = d2 / tan_alpha2, 2. * sy > height - d))
+            sy = (height - d) * .5;
+
+          cos_alpha = cos (alpha);
+          if (cos_alpha < 1e-5 || (sx = d2 / cos_alpha, 2. * sx > width - d))
+            sx = (width - d) * .5;
+
+          /* left triangle */
+          cairo_new_sub_path (cr);
+          cairo_line_to (cr, x+d2, y+sy);
+          cairo_line_to (cr, x+d2, y+height-sy);
+          cairo_line_to (cr, x+.5*width-sx, y+.5*height);
+          cairo_close_path (cr);
+
+          /* right triangle */
+          cairo_new_sub_path (cr);
+          cairo_line_to (cr, x+width-d2, y+sy);
+          cairo_line_to (cr, x+.5*width+sx, y+.5*height);
+          cairo_line_to (cr, x+width-d2, y+height-sy);
+          cairo_close_path (cr);
+        }
+      else
+        cairo_rectangle (cr, x+width-d2, y+d2, - (width-d), height-d);
+    }
+  else
+    {
+      cairo_rectangle (cr, x, y, width, height);
+
+      if (invalid)
+        {
+          /* draw an X */
+
+          cairo_new_sub_path (cr);
+          cairo_move_to (cr, x, y);
+          cairo_rel_line_to (cr, width, height);
+
+          cairo_new_sub_path (cr);
+          cairo_move_to (cr, x + width, y);
+          cairo_rel_line_to (cr, -width, height);
+
+          cairo_set_line_cap (cr, CAIRO_LINE_CAP_BUTT);
+        }
+
+      cairo_set_line_width (cr, line_width);
+      cairo_set_line_join (cr, CAIRO_LINE_JOIN_MITER);
+      cairo_set_miter_limit (cr, 2.);
+      cairo_stroke (cr);
+    }
+}
+
+static void
+gsk_pango_renderer_draw_box_glyph (GskPangoRenderer *crenderer,
+                                   PangoGlyphInfo     *gi,
+                                   double              cx,
+                                   double              cy,
+                                   gboolean            invalid)
+{
+  cairo_save (crenderer->cr);
+
+  gsk_pango_renderer_draw_frame (crenderer,
+                                    cx + 1.5,
+                                    cy + 1.5 - PANGO_UNKNOWN_GLYPH_HEIGHT,
+                                    (double)gi->geometry.width / PANGO_SCALE - 3.0,
+                                    PANGO_UNKNOWN_GLYPH_HEIGHT - 3.0,
+                                    1.0,
+                                    invalid);
+
+  cairo_restore (crenderer->cr);
+}
+#endif
+
+static gboolean
+_pango_cairo_font_install (PangoFont *font,
+                           cairo_t   *cr)
+{
+  cairo_scaled_font_t *scaled_font = pango_cairo_font_get_scaled_font ((PangoCairoFont *)font);
+
+  if (G_UNLIKELY (scaled_font == NULL || cairo_scaled_font_status (scaled_font) != CAIRO_STATUS_SUCCESS))
+    return FALSE;
+
+  cairo_set_scaled_font (cr, scaled_font);
+
+  return TRUE;
+}
+
+static void
+gsk_pango_renderer_draw_unknown_glyph (GskPangoRenderer *crenderer,
+                                       PangoFont          *font,
+                                       PangoGlyphInfo     *gi,
+                                       double              cx,
+                                       double              cy)
+{
+#if 0
+  char buf[7];
+  double x0, y0;
+  int row, col;
+  int rows, cols;
+  double width, lsb;
+  char hexbox_string[2] = {0, 0};
+  PangoCairoFontHexBoxInfo *hbi;
+  gunichar ch;
+  gboolean invalid_input;
+
+  cairo_save (crenderer->cr);
+
+  ch = gi->glyph & ~PANGO_GLYPH_UNKNOWN_FLAG;
+  invalid_input = G_UNLIKELY (gi->glyph == PANGO_GLYPH_INVALID_INPUT || ch > 0x10FFFF);
+
+  hbi = pango_cairo_font_get_hex_box_info ((PangoCairoFont *)font);
+  if (!hbi || !_pango_cairo_font_install ((PangoFont *)(hbi->font), crenderer->cr))
+    {
+      gsk_pango_renderer_draw_box_glyph (crenderer, gi, cx, cy, invalid_input);
+      goto done;
+    }
+
+  rows = hbi->rows;
+  if (G_UNLIKELY (invalid_input))
+    {
+      cols = 1;
+    }
+  else
+    {
+      cols = (ch > 0xffff ? 6 : 4) / rows;
+      g_snprintf (buf, sizeof(buf), (ch > 0xffff) ? "%06X" : "%04X", ch);
+    }
+
+  width = (3 * hbi->pad_x + cols * (hbi->digit_width + hbi->pad_x));
+  lsb = ((double)gi->geometry.width / PANGO_SCALE - width) * .5;
+  lsb = floor (lsb / hbi->pad_x) * hbi->pad_x;
+
+  gsk_pango_renderer_draw_frame (crenderer,
+                                 cx + lsb + .5 * hbi->pad_x,
+                                 cy + hbi->box_descent - hbi->box_height + hbi->pad_y * 0.5,
+                                 width - hbi->pad_x,
+                                 (hbi->box_height - hbi->pad_y),
+                                 hbi->line_width,
+                                 invalid_input);
+
+  if (invalid_input)
+    goto done;
+
+  x0 = cx + lsb + hbi->pad_x * 2;
+  y0 = cy + hbi->box_descent - hbi->pad_y * 2;
+
+  for (row = 0; row < rows; row++)
+    {
+      double y = y0 - (rows - 1 - row) * (hbi->digit_height + hbi->pad_y);
+      for (col = 0; col < cols; col++)
+        {
+          double x = x0 + col * (hbi->digit_width + hbi->pad_x);
+
+          cairo_move_to (crenderer->cr, x, y);
+
+          hexbox_string[0] = buf[row * cols + col];
+
+          if (crenderer->do_path)
+              cairo_text_path (crenderer->cr, hexbox_string);
+          else
+              cairo_show_text (crenderer->cr, hexbox_string);
+        }
+    }
+
+done:
+  cairo_restore (crenderer->cr);
+#endif
+}
+
+#ifndef STACK_BUFFER_SIZE
+#define STACK_BUFFER_SIZE (512 * sizeof (int))
+#endif
+
+#define STACK_ARRAY_LENGTH(T) (STACK_BUFFER_SIZE / sizeof(T))
+
+static void
+gsk_pango_renderer_show_text_glyphs (PangoRenderer        *renderer,
+                                     const char           *text,
+                                     int                   text_len,
+                                     PangoGlyphString     *glyphs,
+                                     cairo_text_cluster_t *clusters,
+                                     int                   num_clusters,
+                                     gboolean              backward,
+                                     PangoFont            *font,
+                                     int                   x,
+                                     int                   y)
+{
+  GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
+
+  int i, count;
+  int x_position = 0;
+  cairo_glyph_t *cairo_glyphs;
+  cairo_glyph_t stack_glyphs[STACK_ARRAY_LENGTH (cairo_glyph_t)];
+  double base_x = crenderer->x_offset + (double)x / PANGO_SCALE;
+  double base_y = crenderer->y_offset + (double)y / PANGO_SCALE;
+
+  cairo_save (crenderer->cr);
+  if (!crenderer->do_path)
+    set_color (crenderer, PANGO_RENDER_PART_FOREGROUND);
+
+  if (!_pango_cairo_font_install (font, crenderer->cr))
+    {
+      for (i = 0; i < glyphs->num_glyphs; i++)
+        {
+          PangoGlyphInfo *gi = &glyphs->glyphs[i];
+
+          if (gi->glyph != PANGO_GLYPH_EMPTY)
+            {
+              double cx = base_x + (double)(x_position + gi->geometry.x_offset) / PANGO_SCALE;
+              double cy = gi->geometry.y_offset == 0 ?
+                          base_y :
+                          base_y + (double)(gi->geometry.y_offset) / PANGO_SCALE;
+
+              gsk_pango_renderer_draw_unknown_glyph (crenderer, font, gi, cx, cy);
+            }
+          x_position += gi->geometry.width;
+        }
+
+      goto done;
+    }
+
+  if (glyphs->num_glyphs > (int) G_N_ELEMENTS (stack_glyphs))
+    cairo_glyphs = g_new (cairo_glyph_t, glyphs->num_glyphs);
+  else
+    cairo_glyphs = stack_glyphs;
+
+  count = 0;
+  for (i = 0; i < glyphs->num_glyphs; i++)
+    {
+      PangoGlyphInfo *gi = &glyphs->glyphs[i];
+
+      if (gi->glyph != PANGO_GLYPH_EMPTY)
+        {
+          double cx = base_x + (double)(x_position + gi->geometry.x_offset) / PANGO_SCALE;
+          double cy = gi->geometry.y_offset == 0 ?
+                      base_y :
+                      base_y + (double)(gi->geometry.y_offset) / PANGO_SCALE;
+
+          if (gi->glyph & PANGO_GLYPH_UNKNOWN_FLAG)
+            gsk_pango_renderer_draw_unknown_glyph (crenderer, font, gi, cx, cy);
+          else
+            {
+              cairo_glyphs[count].index = gi->glyph;
+              cairo_glyphs[count].x = cx;
+              cairo_glyphs[count].y = cy;
+              count++;
+            }
+        }
+      x_position += gi->geometry.width;
+    }
+
+  if (G_UNLIKELY (crenderer->do_path))
+    cairo_glyph_path (crenderer->cr, cairo_glyphs, count);
+  else
+    if (G_UNLIKELY (clusters))
+      cairo_show_text_glyphs (crenderer->cr,
+                              text, text_len,
+                              cairo_glyphs, count,
+                              clusters, num_clusters,
+                              backward ? CAIRO_TEXT_CLUSTER_FLAG_BACKWARD : 0);
+    else
+      cairo_show_glyphs (crenderer->cr, cairo_glyphs, count);
+
+  if (cairo_glyphs != stack_glyphs)
+    g_free (cairo_glyphs);
+
+done:
+  cairo_restore (crenderer->cr);
+}
+
+static void
+gsk_pango_renderer_draw_glyphs (PangoRenderer     *renderer,
+                                PangoFont         *font,
+                                PangoGlyphString  *glyphs,
+                                int                x,
+                                int                y)
+{
+  gsk_pango_renderer_show_text_glyphs (renderer,
+                                       NULL, 0,
+                                       glyphs,
+                                       NULL, 0,
+                                       FALSE,
+                                       font,
+                                       x, y);
+}
+
+static void
+gsk_pango_renderer_draw_glyph_item (PangoRenderer  *renderer,
+                                    const char     *text,
+                                    PangoGlyphItem *glyph_item,
+                                    int             x,
+                                    int             y)
+{
+  GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
+  PangoFont          *font      = glyph_item->item->analysis.font;
+  PangoGlyphString   *glyphs    = glyph_item->glyphs;
+  PangoItem          *item      = glyph_item->item;
+  gboolean            backward  = (item->analysis.level & 1) != 0;
+
+  PangoGlyphItemIter   iter;
+  cairo_text_cluster_t *cairo_clusters;
+  cairo_text_cluster_t stack_clusters[STACK_ARRAY_LENGTH (cairo_text_cluster_t)];
+  int num_clusters;
+
+  if (!crenderer->has_show_text_glyphs || crenderer->do_path)
+    {
+      gsk_pango_renderer_show_text_glyphs (renderer,
+                                           NULL, 0,
+                                           glyphs,
+                                           NULL, 0,
+                                           FALSE,
+                                           font,
+                                           x, y);
+      return;
+    }
+
+  if (glyphs->num_glyphs > (int) G_N_ELEMENTS (stack_clusters))
+    cairo_clusters = g_new (cairo_text_cluster_t, glyphs->num_glyphs);
+  else
+    cairo_clusters = stack_clusters;
+
+  num_clusters = 0;
+  if (pango_glyph_item_iter_init_start (&iter, glyph_item, text))
+    {
+      do {
+        int num_bytes, num_glyphs, i;
+
+        num_bytes  = iter.end_index - iter.start_index;
+        num_glyphs = backward ? iter.start_glyph - iter.end_glyph : iter.end_glyph - iter.start_glyph;
+
+        if (num_bytes < 1)
+          g_warning ("gsk_pango_renderer_draw_glyph_item: bad cluster has num_bytes %d", num_bytes);
+        if (num_glyphs < 1)
+          g_warning ("gsk_pango_renderer_draw_glyph_item: bad cluster has num_glyphs %d", num_glyphs);
+
+        /* Discount empty and unknown glyphs */
+        for (i = MIN (iter.start_glyph, iter.end_glyph+1);
+             i < MAX (iter.start_glyph+1, iter.end_glyph);
+             i++)
+          {
+            PangoGlyphInfo *gi = &glyphs->glyphs[i];
+
+            if (gi->glyph == PANGO_GLYPH_EMPTY ||
+                gi->glyph & PANGO_GLYPH_UNKNOWN_FLAG)
+              num_glyphs--;
+          }
+
+        cairo_clusters[num_clusters].num_bytes  = num_bytes;
+        cairo_clusters[num_clusters].num_glyphs = num_glyphs;
+        num_clusters++;
+      } while (pango_glyph_item_iter_next_cluster (&iter));
+    }
+
+  gsk_pango_renderer_show_text_glyphs (renderer,
+                                         text + item->offset, item->length,
+                                         glyphs,
+                                         cairo_clusters, num_clusters,
+                                         backward,
+                                         font,
+                                         x, y);
+
+  if (cairo_clusters != stack_clusters)
+    g_free (cairo_clusters);
+}
+
+static void
+gsk_pango_renderer_draw_rectangle (PangoRenderer     *renderer,
+                                     PangoRenderPart    part,
+                                     int                x,
+                                     int                y,
+                                     int                width,
+                                     int                height)
+{
+  GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
+
+  if (!crenderer->do_path)
+    {
+      cairo_save (crenderer->cr);
+
+      set_color (crenderer, part);
+    }
+
+  cairo_rectangle (crenderer->cr,
+                   crenderer->x_offset + (double)x / PANGO_SCALE,
+                   crenderer->y_offset + (double)y / PANGO_SCALE,
+                   (double)width / PANGO_SCALE, (double)height / PANGO_SCALE);
+
+  if (!crenderer->do_path)
+    {
+      cairo_fill (crenderer->cr);
+
+      cairo_restore (crenderer->cr);
+    }
+}
+
+static void
+gsk_pango_renderer_draw_trapezoid (PangoRenderer     *renderer,
+                                     PangoRenderPart    part,
+                                     double             y1_,
+                                     double             x11,
+                                     double             x21,
+                                     double             y2,
+                                     double             x12,
+                                     double             x22)
+{
+  GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
+  cairo_t *cr;
+  double x, y;
+
+  cr = crenderer->cr;
+
+  cairo_save (cr);
+
+  if (!crenderer->do_path)
+    set_color (crenderer, part);
+
+  x = crenderer->x_offset,
+  y = crenderer->y_offset;
+  cairo_user_to_device_distance (cr, &x, &y);
+  cairo_identity_matrix (cr);
+  cairo_translate (cr, x, y);
+
+  cairo_move_to (cr, x11, y1_);
+  cairo_line_to (cr, x21, y1_);
+  cairo_line_to (cr, x22, y2);
+  cairo_line_to (cr, x12, y2);
+  cairo_close_path (cr);
+
+  if (!crenderer->do_path)
+    cairo_fill (cr);
+
+  cairo_restore (cr);
+}
+
+/* Draws an error underline that looks like one of:
+ *              H       E                H
+ *     /\      /\      /\        /\      /\               -
+ *   A/  \    /  \    /  \     A/  \    /  \              |
+ *    \   \  /    \  /   /D     \   \  /    \             |
+ *     \   \/  C   \/   /        \   \/   C  \            | height = HEIGHT_SQUARES * square
+ *      \      /\  F   /          \  F   /\   \           |
+ *       \    /  \    /            \    /  \   \G         |
+ *        \  /    \  /              \  /    \  /          |
+ *         \/      \/                \/      \/           -
+ *         B                         B
+ *         |---|
+ *       unit_width = (HEIGHT_SQUARES - 1) * square
+ *
+ * The x, y, width, height passed in give the desired bounding box;
+ * x/width are adjusted to make the underline a integer number of units
+ * wide.
+ */
+#define HEIGHT_SQUARES 2.5
+
+static void
+draw_error_underline (cairo_t *cr,
+                      double   x,
+                      double   y,
+                      double   width,
+                      double   height)
+{
+  double square = height / HEIGHT_SQUARES;
+  double unit_width = (HEIGHT_SQUARES - 1) * square;
+  double double_width = 2 * unit_width;
+  int width_units = (width + unit_width / 2) / unit_width;
+  double y_top, y_bottom;
+  double x_left, x_middle, x_right;
+  int i;
+
+  x += (width - width_units * unit_width) / 2;
+
+  y_top = y;
+  y_bottom = y + height;
+
+  /* Bottom of squiggle */
+  x_middle = x + unit_width;
+  x_right  = x + double_width;
+  cairo_move_to (cr, x - square / 2, y_top + square / 2); /* A */
+  for (i = 0; i < width_units-2; i += 2)
+    {
+      cairo_line_to (cr, x_middle, y_bottom); /* B */
+      cairo_line_to (cr, x_right, y_top + square); /* C */
+
+      x_middle += double_width;
+      x_right  += double_width;
+    }
+  cairo_line_to (cr, x_middle, y_bottom); /* B */
+
+  if (i + 1 == width_units)
+    cairo_line_to (cr, x_middle + square / 2, y_bottom - square / 2); /* G */
+  else if (i + 2 == width_units) {
+    cairo_line_to (cr, x_right + square / 2, y_top + square / 2); /* D */
+    cairo_line_to (cr, x_right, y_top); /* E */
+  }
+
+  /* Top of squiggle */
+  x_left = x_middle - unit_width;
+  for (; i >= 0; i -= 2)
+    {
+      cairo_line_to (cr, x_middle, y_bottom - square); /* F */
+      cairo_line_to (cr, x_left, y_top);   /* H */
+
+      x_left   -= double_width;
+      x_middle -= double_width;
+    }
+}
+
+static void
+gsk_pango_renderer_draw_error_underline (PangoRenderer *renderer,
+                                           int            x,
+                                           int            y,
+                                           int            width,
+                                           int            height)
+{
+  GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
+  cairo_t *cr = crenderer->cr;
+
+  if (!crenderer->do_path)
+    {
+      cairo_save (cr);
+
+      set_color (crenderer, PANGO_RENDER_PART_UNDERLINE);
+
+      cairo_new_path (cr);
+    }
+
+  draw_error_underline (cr,
+                        crenderer->x_offset + (double)x / PANGO_SCALE,
+                        crenderer->y_offset + (double)y / PANGO_SCALE,
+                        (double)width / PANGO_SCALE, (double)height / PANGO_SCALE);
+
+  if (!crenderer->do_path)
+    {
+      cairo_fill (cr);
+
+      cairo_restore (cr);
+    }
+}
+
+static void
+gsk_pango_renderer_draw_shape (PangoRenderer  *renderer,
+                                 PangoAttrShape *attr,
+                                 int             x,
+                                 int             y)
+{
+#if 0
+  GskPangoRenderer *crenderer = (GskPangoRenderer *) (renderer);
+  cairo_t *cr = crenderer->cr;
+  PangoLayout *layout;
+  GskPangoShapeRendererFunc shape_renderer;
+  gpointer                    shape_renderer_data;
+  double base_x, base_y;
+
+  layout = pango_renderer_get_layout (renderer);
+
+  if (!layout)
+        return;
+
+  shape_renderer = gsk_pango_context_get_shape_renderer (pango_layout_get_context (layout),
+                                                           &shape_renderer_data);
+
+  if (!shape_renderer)
+    return;
+
+  base_x = crenderer->x_offset + (double)x / PANGO_SCALE;
+  base_y = crenderer->y_offset + (double)y / PANGO_SCALE;
+
+  cairo_save (cr);
+  if (!crenderer->do_path)
+    set_color (crenderer, PANGO_RENDER_PART_FOREGROUND);
+
+  cairo_move_to (cr, base_x, base_y);
+
+  shape_renderer (cr, attr, crenderer->do_path, shape_renderer_data);
+
+  cairo_restore (cr);
+#endif
+}
+
+static void
+gsk_pango_renderer_init (GskPangoRenderer *renderer G_GNUC_UNUSED)
+{
+}
+
+static void
+gsk_pango_renderer_class_init (GskPangoRendererClass *klass)
+{
+  PangoRendererClass *renderer_class = PANGO_RENDERER_CLASS (klass);
+
+  renderer_class->draw_glyphs = gsk_pango_renderer_draw_glyphs;
+  renderer_class->draw_glyph_item = gsk_pango_renderer_draw_glyph_item;
+  renderer_class->draw_rectangle = gsk_pango_renderer_draw_rectangle;
+  renderer_class->draw_trapezoid = gsk_pango_renderer_draw_trapezoid;
+  renderer_class->draw_error_underline = gsk_pango_renderer_draw_error_underline;
+  renderer_class->draw_shape = gsk_pango_renderer_draw_shape;
+}
+
+static GskPangoRenderer *cached_renderer = NULL; /* MT-safe */
+G_LOCK_DEFINE_STATIC (cached_renderer);
+
+static GskPangoRenderer *
+acquire_renderer (void)
+{
+  GskPangoRenderer *renderer;
+
+  if (G_LIKELY (G_TRYLOCK (cached_renderer)))
+    {
+      if (G_UNLIKELY (!cached_renderer))
+        {
+          cached_renderer = g_object_new (GSK_TYPE_PANGO_RENDERER, NULL);
+          cached_renderer->is_cached_renderer = TRUE;
+        }
+
+      renderer = cached_renderer;
+    }
+  else
+    {
+      renderer = g_object_new (GSK_TYPE_PANGO_RENDERER, NULL);
+    }
+
+  return renderer;
+}
+
+static void
+release_renderer (GskPangoRenderer *renderer)
+{
+  if (G_LIKELY (renderer->is_cached_renderer))
+    {
+      renderer->cr = NULL;
+      renderer->do_path = FALSE;
+      renderer->has_show_text_glyphs = FALSE;
+      renderer->x_offset = 0.;
+      renderer->y_offset = 0.;
+
+      G_UNLOCK (cached_renderer);
+    }
+  else
+    g_object_unref (renderer);
+}
+
+static void
+save_current_point (GskPangoRenderer *renderer)
+{
+  renderer->cr_had_current_point = cairo_has_current_point (renderer->cr);
+  cairo_get_current_point (renderer->cr, &renderer->x_offset, &renderer->y_offset);
+
+  /* abuse save_current_point() to cache cairo_has_show_text_glyphs() result */
+  renderer->has_show_text_glyphs = cairo_surface_has_show_text_glyphs (cairo_get_target (renderer->cr));
+}
+
+static void
+restore_current_point (GskPangoRenderer *renderer)
+{
+  if (renderer->cr_had_current_point)
+    /* XXX should do cairo_set_current_point() when we have that function */
+    cairo_move_to (renderer->cr, renderer->x_offset, renderer->y_offset);
+  else
+    cairo_new_sub_path (renderer->cr);
+}
+
+
+/* convenience wrappers using the default renderer */
+
+static void
+gsk_pango_do_layout (cairo_t     *cr,
+                     PangoLayout *layout,
+                     gboolean     do_path)
+{
+  GskPangoRenderer *crenderer = acquire_renderer ();
+  PangoRenderer *renderer = (PangoRenderer *) crenderer;
+
+  crenderer->cr = cr;
+  crenderer->do_path = do_path;
+  save_current_point (crenderer);
+
+  pango_renderer_draw_layout (renderer, layout, 0, 0);
+
+  restore_current_point (crenderer);
+
+  release_renderer (crenderer);
+}
+
+void
+gsk_pango_show_layout (cairo_t     *cr,
+                       PangoLayout *layout)
+{
+  g_return_if_fail (cr != NULL);
+  g_return_if_fail (PANGO_IS_LAYOUT (layout));
+
+  gsk_pango_do_layout (cr, layout, FALSE);
+}
diff --git a/gtk/gskpango.h b/gtk/gskpango.h
new file mode 100644
index 0000000..75a54d8
--- /dev/null
+++ b/gtk/gskpango.h
@@ -0,0 +1,43 @@
+/* GSK - The GTK Scene Kit
+ *
+ * Copyright 2017 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __GSK_PANGO_H__
+#define __GSK_PANGO_H__
+
+#include <gsk/gsk.h>
+
+G_BEGIN_DECLS
+
+#define GSK_TYPE_PANGO_RENDERER (gsk_pango_renderer_get_type ())
+
+#define GSK_PANGO_RENDERER(obj)               (G_TYPE_CHECK_INSTANCE_CAST ((obj), GSK_TYPE_PANGO_RENDERER, 
GskPangoRenderer))
+#define GSK_IS_PANGO_RENDERER(obj)            (G_TYPE_CHECK_INSTANCE_TYPE ((obj), GSK_TYPE_PANGO_RENDERER))
+
+typedef struct _GskPangoRenderer        GskPangoRenderer;
+typedef struct _GskPangoRendererClass   GskPangoRendererClass;
+
+GDK_AVAILABLE_IN_3_92
+GType gsk_pango_renderer_get_type (void) G_GNUC_CONST;
+
+GDK_AVAILABLE_IN_3_92
+void gsk_pango_show_layout (cairo_t     *cr,
+                            PangoLayout *layout);
+
+G_END_DECLS
+
+#endif /* __GSK_PANGO_H__ */
diff --git a/gtk/meson.build b/gtk/meson.build
index a5985a3..5fed5b7 100644
--- a/gtk/meson.build
+++ b/gtk/meson.build
@@ -231,6 +231,7 @@ gtk_public_sources = files([
   'gtkpagesetup.c',
   'gtkpaned.c',
   'gtkpango.c',
+  'gskpango.c',
   'gtkpapersize.c',
   'gtkpathbar.c',
   'gtkplacessidebar.c',


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