[gtk/path-work-rebased: 63/149] path: Implement gsk_path_parse

[Matthias Clasen <matthiasc src gnome org>]

commit 20542de836647da090409d4e60c1760da362f961
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Nov 24 20:01:07 2020 -0500

    path: Implement gsk_path_parse
    
    Implement the SVG path syntax to read back the strings
    that we generate when serializing paths. The tests for
    this code are taken from librsvg.
    
    This includes an elliptical arc implementation according
    to the SVG spec. The code is mostly taken from librsvg,
    but pretty directly follows the SVG spec implementation
    notes. We don't export this, since the parametrization
    is inconvenient. We do want an arc_to API, but
    these are not the arcs we are looking for.

 gsk/gskpath.c | 501 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 gsk/gskpath.h |   4 +
 2 files changed, 505 insertions(+)
---
diff --git a/gsk/gskpath.c b/gsk/gskpath.c
index 7e1840547e..0add21d537 100644
--- a/gsk/gskpath.c
+++ b/gsk/gskpath.c
@@ -1990,3 +1990,504 @@ gsk_path_foreach_with_tolerance (GskPath            *self,
 
   return TRUE;
 }
+
+/* path parser and utilities */
+
+static void
+skip_whitespace (const char **p)
+{
+  while (g_ascii_isspace (**p))
+    (*p)++;
+}
+
+static void
+skip_optional_comma (const char **p)
+{
+  skip_whitespace (p);
+  if (**p == ',')
+    (*p)++;
+}
+
+static gboolean
+parse_number (const char **p,
+              double      *c)
+{
+  char *e;
+  *c = g_ascii_strtod (*p, &e);
+  if (e == *p)
+    return FALSE;
+  *p = e;
+  skip_optional_comma (p);
+  return TRUE;
+}
+
+static gboolean
+parse_coordinate (const char **p,
+                  double      *c)
+{
+  return parse_number (p, c);
+}
+
+static gboolean
+parse_coordinate_pair (const char **p,
+                       double      *x,
+                       double      *y)
+{
+  double xx, yy;
+  const char *o = *p;
+
+  if (!parse_coordinate (p, &xx))
+    {
+      *p = o;
+      return FALSE;
+    }
+  if (!parse_coordinate (p, &yy))
+    {
+      *p = o;
+      return FALSE;
+    }
+
+  *x = xx;
+  *y = yy;
+
+  return TRUE;
+}
+
+static gboolean
+parse_nonnegative_number (const char **p,
+                          double      *x)
+{
+  const char *o = *p;
+  double n;
+
+  if (!parse_number (p, &n))
+    return FALSE;
+
+  if (n < 0)
+    {
+      *p = o;
+      return FALSE;
+    }
+
+  *x = n;
+
+  return TRUE;
+}
+
+static gboolean
+parse_flag (const char **p,
+            gboolean    *f)
+{
+  skip_whitespace (p);
+  if (strchr ("01", **p))
+    {
+      *f = **p == '1';
+      (*p)++;
+      skip_optional_comma (p);
+      return TRUE;
+    }
+
+  return FALSE;
+}
+
+static gboolean
+parse_command (const char **p,
+               char        *cmd)
+{
+  char *s;
+  const char *allowed;
+
+  if (*cmd == 'X')
+    allowed = "mM";
+  else
+    allowed = "mMhHvVzZlLcCsStTqQaA";
+
+  skip_whitespace (p);
+  s = strchr (allowed, **p);
+  if (s)
+    {
+      *cmd = *s;
+      (*p)++;
+      return TRUE;
+    }
+  return FALSE;
+}
+
+/**
+ * gsk_path_parse:
+ * @string: a string
+ *
+ * This is a convenience function that constructs a `GskPath`
+ * from a serialized form.
+ *
+ * The string is expected to be in
+ * [SVG path syntax](https://www.w3.org/TR/SVG11/paths.html#PathData),
+ * as e.g. produced by [method Gsk Path.to_string].
+ *
+ * Returns: (nullable): a new `GskPath`, or %NULL if @string could not be parsed
+ **/
+GskPath *
+gsk_path_parse (const char *string)
+{
+  GskPathBuilder *builder;
+  double x, y;
+  double prev_x1, prev_y1;
+  double path_x, path_y;
+  const char *p;
+  char cmd;
+  char prev_cmd;
+  gboolean after_comma;
+  gboolean repeat;
+
+  builder = gsk_path_builder_new ();
+
+  cmd = 'X';
+  path_x = path_y = 0;
+  x = y = 0;
+  prev_x1 = prev_y1 = 0;
+  after_comma = FALSE;
+
+  p = string;
+  while (*p)
+    {
+      prev_cmd = cmd;
+      repeat = !parse_command (&p, &cmd);
+
+      if (after_comma && !repeat)
+        goto error;
+
+      switch (cmd)
+        {
+        case 'X':
+          goto error;
+
+        case 'Z':
+        case 'z':
+          if (repeat)
+            goto error;
+          else
+            {
+              gsk_path_builder_close (builder);
+              x = path_x;
+              y = path_y;
+            }
+          break;
+
+        case 'M':
+        case 'm':
+          {
+            double x1, y1;
+
+            if (parse_coordinate_pair (&p, &x1, &y1))
+              {
+                if (cmd == 'm')
+                  {
+                    x1 += x;
+                    y1 += y;
+                  }
+                if (repeat)
+                  gsk_path_builder_line_to (builder, x1, y1);
+                else
+                  {
+                    gsk_path_builder_move_to (builder, x1, y1);
+                    if (strchr ("zZX", prev_cmd))
+                      {
+                        path_x = x1;
+                        path_y = y1;
+                      }
+                  }
+                x = x1;
+                y = y1;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'L':
+        case 'l':
+          {
+            double x1, y1;
+
+            if (parse_coordinate_pair (&p, &x1, &y1))
+              {
+                if (cmd == 'l')
+                  {
+                    x1 += x;
+                    y1 += y;
+                  }
+
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_line_to (builder, x1, y1);
+                x = x1;
+                y = y1;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'H':
+        case 'h':
+          {
+            double x1;
+
+            if (parse_coordinate (&p, &x1))
+              {
+                if (cmd == 'h')
+                  x1 += x;
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_line_to (builder, x1, y);
+                x = x1;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'V':
+        case 'v':
+          {
+            double y1;
+
+            if (parse_coordinate (&p, &y1))
+              {
+                if (cmd == 'v')
+                  y1 += y;
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_line_to (builder, x, y1);
+                y = y1;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'C':
+        case 'c':
+          {
+            double x0, y0, x1, y1, x2, y2;
+
+            if (parse_coordinate_pair (&p, &x0, &y0) &&
+                parse_coordinate_pair (&p, &x1, &y1) &&
+                parse_coordinate_pair (&p, &x2, &y2))
+              {
+                if (cmd == 'c')
+                  {
+                    x0 += x;
+                    y0 += y;
+                    x1 += x;
+                    y1 += y;
+                    x2 += x;
+                    y2 += y;
+                  }
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_curve_to (builder, x0, y0, x1, y1, x2, y2);
+                prev_x1 = x1;
+                prev_y1 = y1;
+                x = x2;
+                y = y2;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'S':
+        case 's':
+          {
+            double x0, y0, x1, y1, x2, y2;
+
+            if (parse_coordinate_pair (&p, &x1, &y1) &&
+                parse_coordinate_pair (&p, &x2, &y2))
+              {
+                if (cmd == 's')
+                  {
+                    x1 += x;
+                    y1 += y;
+                    x2 += x;
+                    y2 += y;
+                  }
+                if (strchr ("CcSs", prev_cmd))
+                  {
+                    x0 = 2 * x - prev_x1;
+                    y0 = 2 * y - prev_y1;
+                  }
+                else
+                  {
+                    x0 = x;
+                    y0 = y;
+                  }
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_curve_to (builder, x0, y0, x1, y1, x2, y2);
+                prev_x1 = x1;
+                prev_y1 = y1;
+                x = x2;
+                y = y2;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'Q':
+        case 'q':
+          {
+            double x1, y1, x2, y2, xx1, yy1, xx2, yy2;
+
+            if (parse_coordinate_pair (&p, &x1, &y1) &&
+                parse_coordinate_pair (&p, &x2, &y2))
+              {
+                if (cmd == 'q')
+                  {
+                    x1 += x;
+                    y1 += y;
+                    x2 += x;
+                    y2 += y;
+                  }
+                xx1 = (x + 2.0 * x1) / 3.0;
+                yy1 = (y + 2.0 * y1) / 3.0;
+                xx2 = (x2 + 2.0 * x1) / 3.0;
+                yy2 = (y2 + 2.0 * y1) / 3.0;
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_curve_to (builder, xx1, yy1, xx2, yy2, x2, y2);
+                prev_x1 = x1;
+                prev_y1 = y1;
+                x = x2;
+                y = y2;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'T':
+        case 't':
+          {
+            double x1, y1, x2, y2, xx1, yy1, xx2, yy2;
+
+            if (parse_coordinate_pair (&p, &x2, &y2))
+              {
+                if (cmd == 't')
+                  {
+                    x2 += x;
+                    y2 += y;
+                  }
+                if (strchr ("QqTt", prev_cmd))
+                  {
+                    x1 = 2 * x - prev_x1;
+                    y1 = 2 * y - prev_y1;
+                  }
+                else
+                  {
+                    x1 = x;
+                    y1 = y;
+                  }
+                xx1 = (x + 2.0 * x1) / 3.0;
+                yy1 = (y + 2.0 * y1) / 3.0;
+                xx2 = (x2 + 2.0 * x1) / 3.0;
+                yy2 = (y2 + 2.0 * y1) / 3.0;
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_curve_to (builder, xx1, yy1, xx2, yy2, x2, y2);
+                prev_x1 = x1;
+                prev_y1 = y1;
+                x = x2;
+                y = y2;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        case 'A':
+        case 'a':
+          {
+            double rx, ry;
+            double x_axis_rotation;
+            int large_arc, sweep;
+            double x1, y1;
+
+            if (parse_nonnegative_number (&p, &rx) &&
+                parse_nonnegative_number (&p, &ry) &&
+                parse_number (&p, &x_axis_rotation) &&
+                parse_flag (&p, &large_arc) &&
+                parse_flag (&p, &sweep) &&
+                parse_coordinate_pair (&p, &x1, &y1))
+              {
+                if (cmd == 'a')
+                  {
+                    x1 += x;
+                    y1 += y;
+                  }
+
+                if (strchr ("zZ", prev_cmd))
+                  {
+                    gsk_path_builder_move_to (builder, x, y);
+                    path_x = x;
+                    path_y = y;
+                  }
+                gsk_path_builder_svg_arc_to (builder,
+                                             rx, ry, x_axis_rotation,
+                                             large_arc, sweep,
+                                             x1, y1);
+                x = x1;
+                y = y1;
+              }
+            else
+              goto error;
+          }
+          break;
+
+        default:
+          goto error;
+        }
+
+      after_comma = (p > string) && p[-1] == ',';
+    }
+
+  if (after_comma)
+    goto error;
+
+  return gsk_path_builder_free_to_path (builder);
+
+error:
+  //g_warning ("Can't parse string '%s' as GskPath, error at %ld", string, p - string);
+  gsk_path_builder_unref (builder);
+
+  return NULL;
+}
diff --git a/gsk/gskpath.h b/gsk/gskpath.h
index 9fb24f14d7..73068126e6 100644
--- a/gsk/gskpath.h
+++ b/gsk/gskpath.h
@@ -64,6 +64,10 @@ void                    gsk_path_print                          (GskPath
                                                                  GString                *string);
 GDK_AVAILABLE_IN_ALL
 char *                  gsk_path_to_string                      (GskPath                *self);
+
+GDK_AVAILABLE_IN_ALL
+GskPath *               gsk_path_parse                          (const char             *string);
+
 GDK_AVAILABLE_IN_ALL
 void                    gsk_path_to_cairo                       (GskPath                *self,
                                                                  cairo_t                *cr);