Make grid constraint dynamic

Handle dynamic changes:
- adding/removing children
- changing homogeneity
- attaching/detaching from a layout

demos/gtk-demo/constraints4.c

@@ -0,0 +1,178 @@
+/* Constraints/Grid
+ *
+ * GtkConstraintLayout lets you define complex layouts
+ * like grids.
+ */
+
+#include <glib/gi18n.h>
+#include <gtk/gtk.h>
+
+G_DECLARE_FINAL_TYPE (ComplexGrid, complex_grid, COMPLEX, GRID, GtkWidget)
+
+struct _ComplexGrid
+{
+  GtkWidget parent_instance;
+
+  GtkWidget *button1, *button2, *button3;
+  GtkWidget *button4, *button5;
+};
+
+G_DEFINE_TYPE (ComplexGrid, complex_grid, GTK_TYPE_WIDGET)
+
+static void
+complex_grid_destroy (GtkWidget *widget)
+{
+  ComplexGrid *self = COMPLEX_GRID (widget);
+
+  g_clear_pointer (&self->button1, gtk_widget_destroy);
+  g_clear_pointer (&self->button2, gtk_widget_destroy);
+  g_clear_pointer (&self->button3, gtk_widget_destroy);
+  g_clear_pointer (&self->button4, gtk_widget_destroy);
+  g_clear_pointer (&self->button5, gtk_widget_destroy);
+
+  GTK_WIDGET_CLASS (complex_grid_parent_class)->destroy (widget);
+}
+
+static void
+complex_grid_class_init (ComplexGridClass *klass)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
+
+  widget_class->destroy = complex_grid_destroy;
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_CONSTRAINT_LAYOUT);
+}
+
+/* Layout:
+ *
+ *   +--------------------------------------+
+ *   |             +-----------+            |
+ *   |             |  Child 4  |            |
+ *   | +-----------+-----------+----------+ |
+ *   | |  Child 1  |  Child 2  |  Child 3 | |
+ *   | +-----------+-----------+----------+ |
+ *   |             |  Child 5  |            |
+ *   |             +-----------+            |
+ *   +--------------------------------------+
+ *
+ */
+static void
+build_constraints (ComplexGrid         *self,
+                   GtkConstraintLayout *manager)
+{
+  GtkGridConstraint *constraint;
+  GtkConstraint *s;
+
+  s = gtk_constraint_new (NULL, GTK_CONSTRAINT_ATTRIBUTE_LEFT,
+                          GTK_CONSTRAINT_RELATION_EQ,
+                          self->button1, GTK_CONSTRAINT_ATTRIBUTE_LEFT,
+                          1.0, 0.0,
+                          GTK_CONSTRAINT_STRENGTH_REQUIRED);
+  gtk_constraint_layout_add_constraint (manager, s);
+
+  s = gtk_constraint_new (self->button3, GTK_CONSTRAINT_ATTRIBUTE_RIGHT,
+                          GTK_CONSTRAINT_RELATION_EQ,
+                          NULL, GTK_CONSTRAINT_ATTRIBUTE_RIGHT,
+                          1.0, 0.0,
+                          GTK_CONSTRAINT_STRENGTH_REQUIRED);
+  gtk_constraint_layout_add_constraint (manager, s);
+
+  s = gtk_constraint_new (NULL, GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                          GTK_CONSTRAINT_RELATION_EQ,
+                          self->button4, GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                          1.0, 0.0,
+                          GTK_CONSTRAINT_STRENGTH_REQUIRED);
+  gtk_constraint_layout_add_constraint (manager, s);
+
+  s = gtk_constraint_new (NULL, GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                          GTK_CONSTRAINT_RELATION_EQ,
+                          self->button5, GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                          1.0, 0.0,
+                          GTK_CONSTRAINT_STRENGTH_REQUIRED);
+  gtk_constraint_layout_add_constraint (manager, s);
+
+  constraint = gtk_grid_constraint_new ();
+  g_object_set (constraint, "column-homogeneous", TRUE, NULL);
+  gtk_grid_constraint_add (constraint, self->button1, 0, 1, 0, 1);
+  gtk_grid_constraint_add (constraint, self->button2, 1, 2, 0, 1);
+  gtk_grid_constraint_add (constraint, self->button3, 2, 3, 0, 1);
+  gtk_grid_constraint_attach (constraint, manager);
+
+  constraint = gtk_grid_constraint_new ();
+  g_object_set (constraint, "row-homogeneous", TRUE, NULL);
+  gtk_grid_constraint_add (constraint, self->button4, 0, 1, 0, 1);
+  gtk_grid_constraint_add (constraint, self->button2, 0, 1, 1, 2);
+  gtk_grid_constraint_add (constraint, self->button5, 0, 1, 2, 3);
+  gtk_grid_constraint_attach (constraint, manager);
+}
+
+static void
+complex_grid_init (ComplexGrid *self)
+{
+  GtkWidget *widget = GTK_WIDGET (self);
+  GtkLayoutManager *manager = gtk_widget_get_layout_manager (GTK_WIDGET (self));
+
+  self->button1 = gtk_button_new_with_label ("Child 1");
+  gtk_widget_set_parent (self->button1, widget);
+  gtk_widget_set_name (self->button1, "button1");
+
+  self->button2 = gtk_button_new_with_label ("Child 2");
+  gtk_widget_set_parent (self->button2, widget);
+  gtk_widget_set_name (self->button2, "button2");
+
+  self->button3 = gtk_button_new_with_label ("Child 3");
+  gtk_widget_set_parent (self->button3, widget);
+  gtk_widget_set_name (self->button3, "button3");
+
+  self->button4 = gtk_button_new_with_label ("Child 4");
+  gtk_widget_set_parent (self->button4, widget);
+  gtk_widget_set_name (self->button4, "button4");
+
+  self->button5 = gtk_button_new_with_label ("Child 5");
+  gtk_widget_set_parent (self->button5, widget);
+  gtk_widget_set_name (self->button5, "button5");
+
+  build_constraints (self, GTK_CONSTRAINT_LAYOUT (manager));
+}
+
+GtkWidget *
+do_constraints4 (GtkWidget *do_widget)
+{
+ static GtkWidget *window;
+
+ if (!window)
+   {
+     GtkWidget *header, *box, *grid, *button;
+
+     window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+     gtk_window_set_display (GTK_WINDOW (window), gtk_widget_get_display (do_widget));
+
+     header = gtk_header_bar_new ();
+     gtk_header_bar_set_title (GTK_HEADER_BAR (header), "Constraints");
+     gtk_header_bar_set_show_title_buttons (GTK_HEADER_BAR (header), FALSE);
+     gtk_window_set_titlebar (GTK_WINDOW (window), header);
+     g_signal_connect (window, "destroy",
+                       G_CALLBACK (gtk_widget_destroyed), &window);
+
+     box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 12);
+     gtk_container_add (GTK_CONTAINER (window), box);
+
+     grid = g_object_new (complex_grid_get_type (), NULL);
+     gtk_widget_set_hexpand (grid, TRUE);
+     gtk_widget_set_vexpand (grid, TRUE);
+     gtk_container_add (GTK_CONTAINER (box), grid);
+
+     button = gtk_button_new_with_label ("Close");
+     gtk_container_add (GTK_CONTAINER (box), button);
+     gtk_widget_set_hexpand (grid, TRUE);
+     g_signal_connect_swapped (button, "clicked",
+                               G_CALLBACK (gtk_widget_destroy), window);
+   }
+
+ if (!gtk_widget_get_visible (window))
+   gtk_widget_show (window);
+ else
+   gtk_widget_destroy (window);
+
+ return window;
+}

demos/gtk-demo/constraints5.c

@@ -0,0 +1,354 @@
+/* Constraints/Words
+ *
+ * GtkConstraintLayout lets you define big grids.
+ */
+
+#include <glib/gi18n.h>
+#include <gtk/gtk.h>
+
+#define WORDS_TYPE_BASE (words_base_get_type ())
+#define WORDS_TYPE_GRID (words_grid_get_type ())
+#define WORDS_TYPE_CONSTRAINT (words_constraint_get_type ())
+
+typedef struct
+{
+  GtkWidget parent_instance;
+} WordsBase;
+
+typedef WordsBase WordsGrid;
+typedef WordsBase WordsConstraint;
+
+typedef GtkWidgetClass WordsBaseClass;
+typedef GtkWidgetClass WordsGridClass;
+typedef GtkWidgetClass WordsConstraintClass;
+
+G_DEFINE_TYPE (WordsBase, words_base, GTK_TYPE_WIDGET)
+G_DEFINE_TYPE (WordsGrid, words_grid, WORDS_TYPE_BASE)
+G_DEFINE_TYPE (WordsConstraint, words_constraint, WORDS_TYPE_BASE)
+
+static void
+words_grid_init (WordsGrid *words)
+{
+}
+
+static void
+words_grid_class_init (WordsGridClass *class)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_GRID_LAYOUT);
+}
+
+static void
+words_constraint_init (WordsGrid *words)
+{
+}
+
+static void
+words_constraint_class_init (WordsConstraintClass *class)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_CONSTRAINT_LAYOUT);
+}
+
+static void
+word_base_dispose (GObject *object)
+{
+  GtkWidget *self = GTK_WIDGET (object);
+  GtkWidget *child;
+
+  while ((child = gtk_widget_get_first_child (self)) != NULL)
+    gtk_widget_unparent (child);
+
+  G_OBJECT_CLASS (words_base_parent_class)->dispose (object);
+}
+
+static void
+words_base_class_init (WordsBaseClass *klass)
+{
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->dispose = word_base_dispose;
+}
+
+static int num_words = 100;
+static gboolean use_constraints = FALSE;
+
+static void
+read_words (WordsBase *self)
+{
+  GBytes *data;
+  const char *words;
+  int left, top;
+  GtkWidget *child = NULL;
+  GtkLayoutManager *layout = gtk_widget_get_layout_manager (GTK_WIDGET (self));
+  GtkGridConstraint *grid;
+  GtkConstraint *constraint;
+  int count;
+  int rightmost;
+  GtkWidget *right_child = NULL;
+  gboolean use_constraint = GTK_IS_CONSTRAINT_LAYOUT (layout);
+
+  if (use_constraint)
+    {
+      grid = gtk_grid_constraint_new ();
+      g_object_set (grid,
+                    "row-homogeneous", TRUE,
+                    "column-homogeneous", FALSE,
+                    NULL);
+    }
+  else
+    {
+      gtk_grid_layout_set_row_homogeneous (GTK_GRID_LAYOUT (layout), TRUE);
+      gtk_grid_layout_set_column_homogeneous (GTK_GRID_LAYOUT (layout), FALSE);
+    }
+
+  data = g_resources_lookup_data ("/constraints5/words", 0, NULL);
+  words = g_bytes_get_data (data, NULL);
+  count = 0;
+
+  rightmost = 0;
+  left = 0;
+  top = 0;
+  while (words && words[0])
+    {
+      char *p = strchr (words, '\n');
+      char *word;
+      int len;
+
+      if (p)
+        {
+          word = strndup (words, p - words);
+          words = p + 1;
+        }
+      else
+        {
+          word = strdup (words);
+          words = NULL;
+        }
+
+      len = strlen (word);
+      child = gtk_button_new_with_label (word);
+
+      if (left + len > 50)
+        {
+          top++;
+          left = 0;
+        }
+
+      gtk_widget_set_parent (child, GTK_WIDGET (self));
+
+      if (left + len > rightmost)
+        {
+          rightmost = left + len;
+          right_child = child;
+        }
+
+      if (use_constraint)
+        {
+          gtk_grid_constraint_add (grid, child,
+                                   left, left + len,
+                                   top, top + 1);
+          if (left == 0 && top == 0)
+            {
+              constraint = gtk_constraint_new (NULL,
+                                               GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                                               GTK_CONSTRAINT_RELATION_EQ,
+                                               child,
+                                               GTK_CONSTRAINT_ATTRIBUTE_TOP,
+                                               1.0,
+                                               0.0,
+                                               GTK_CONSTRAINT_STRENGTH_REQUIRED);
+              gtk_constraint_layout_add_constraint (GTK_CONSTRAINT_LAYOUT (layout),
+                                                    constraint);
+              constraint = gtk_constraint_new (NULL,
+                                               GTK_CONSTRAINT_ATTRIBUTE_LEFT,
+                                               GTK_CONSTRAINT_RELATION_EQ,
+                                               child,
+                                               GTK_CONSTRAINT_ATTRIBUTE_LEFT,
+                                               1.0,
+                                               0.0,
+                                               GTK_CONSTRAINT_STRENGTH_REQUIRED);
+               gtk_constraint_layout_add_constraint (GTK_CONSTRAINT_LAYOUT (layout),
+                                                     constraint);
+            }
+        }
+      else
+        {
+          GtkGridLayoutChild *grid_child = GTK_GRID_LAYOUT_CHILD (gtk_layout_manager_get_layout_child (layout, child));
+
+          g_object_set (grid_child,
+                        "left-attach", left,
+                        "top-attach", top,
+                        "column-span", len,
+                        "row-span", 1,
+                        NULL);
+        }
+
+      left = left + len;
+      count++;
+
+      if (count >= num_words)
+        break;
+    }
+
+  if (use_constraint)
+    {
+      constraint = gtk_constraint_new (NULL,
+                                       GTK_CONSTRAINT_ATTRIBUTE_RIGHT,
+                                       GTK_CONSTRAINT_RELATION_EQ,
+                                       right_child,
+                                       GTK_CONSTRAINT_ATTRIBUTE_RIGHT,
+                                       1.0,
+                                       0.0,
+                                       GTK_CONSTRAINT_STRENGTH_REQUIRED);
+      gtk_constraint_layout_add_constraint (GTK_CONSTRAINT_LAYOUT (layout),
+                                            constraint);
+      constraint = gtk_constraint_new (NULL,
+                                       GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                                       GTK_CONSTRAINT_RELATION_EQ,
+                                       child,
+                                       GTK_CONSTRAINT_ATTRIBUTE_BOTTOM,
+                                       1.0,
+                                       0.0,
+                                       GTK_CONSTRAINT_STRENGTH_REQUIRED);
+      gtk_constraint_layout_add_constraint (GTK_CONSTRAINT_LAYOUT (layout),
+                                            constraint);
+
+      gtk_grid_constraint_attach (grid, GTK_CONSTRAINT_LAYOUT (layout));
+    }
+
+  g_bytes_unref (data);
+}
+
+static void
+words_base_init (WordsBase *self)
+{
+  read_words (self);
+}
+
+static void
+show_words (GtkWidget *parent)
+{
+  GtkWidget *window;
+  GtkWidget *header, *box, *grid, *button;
+  GtkWidget *swin;
+
+  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+  gtk_window_set_transient_for (GTK_WINDOW (window),
+                                GTK_WINDOW (gtk_widget_get_root (parent)));
+  gtk_window_set_modal (GTK_WINDOW (window), TRUE);
+
+  header = gtk_header_bar_new ();
+  gtk_header_bar_set_title (GTK_HEADER_BAR (header), use_constraints ? "Constraints" : "Grid");
+  gtk_header_bar_set_show_title_buttons (GTK_HEADER_BAR (header), FALSE);
+  gtk_window_set_titlebar (GTK_WINDOW (window), header);
+  gtk_window_set_resizable (GTK_WINDOW (window), TRUE);
+  gtk_window_set_default_size (GTK_WINDOW (window), 600, 400);
+
+  box = gtk_box_new (GTK_ORIENTATION_VERTICAL, 0);
+  gtk_container_add (GTK_CONTAINER (window), box);
+
+  swin = gtk_scrolled_window_new (NULL, NULL);
+  gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW (swin),
+                                  GTK_POLICY_AUTOMATIC,
+                                  GTK_POLICY_AUTOMATIC);
+  gtk_scrolled_window_set_propagate_natural_width (GTK_SCROLLED_WINDOW (swin), TRUE);
+  gtk_scrolled_window_set_propagate_natural_height (GTK_SCROLLED_WINDOW (swin), TRUE);
+  gtk_widget_set_hexpand (swin, TRUE);
+  gtk_widget_set_vexpand (swin, TRUE);
+  gtk_widget_set_halign (swin, GTK_ALIGN_FILL);
+  gtk_widget_set_valign (swin, GTK_ALIGN_FILL);
+  gtk_container_add (GTK_CONTAINER (box), swin);
+
+  if (use_constraints)
+    grid = g_object_new (WORDS_TYPE_CONSTRAINT, NULL);
+  else
+    grid = g_object_new (WORDS_TYPE_GRID, NULL);
+
+  gtk_widget_set_halign (swin, GTK_ALIGN_START);
+  gtk_widget_set_valign (swin, GTK_ALIGN_START);
+
+  gtk_container_add (GTK_CONTAINER (swin), grid);
+
+  button = gtk_button_new_with_label ("Close");
+  gtk_container_add (GTK_CONTAINER (box), button);
+  g_signal_connect_swapped (button, "clicked",
+                            G_CALLBACK (gtk_widget_destroy), window);
+
+  gtk_widget_show (window);
+}
+
+static void
+use_constraints_cb (GtkButton *button)
+{
+  use_constraints = gtk_toggle_button_get_active (GTK_TOGGLE_BUTTON (button));
+}
+
+static void
+word_count_cb (GtkSpinButton *button)
+{
+  num_words = gtk_spin_button_get_value_as_int (button);
+}
+
+GtkWidget *
+do_constraints5 (GtkWidget *do_widget)
+{
+ static GtkWidget *window;
+
+ if (!window)
+   {
+     GtkWidget *header, *grid, *button, *label;
+
+     window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+
+     header = gtk_header_bar_new ();
+     gtk_header_bar_set_title (GTK_HEADER_BAR (header), "Words");
+     gtk_header_bar_set_show_title_buttons (GTK_HEADER_BAR (header), TRUE);
+     gtk_window_set_titlebar (GTK_WINDOW (window), header);
+     gtk_window_set_resizable (GTK_WINDOW (window), FALSE);
+     g_signal_connect (window, "destroy",
+                       G_CALLBACK (gtk_widget_destroyed), &window);
+
+     grid = gtk_grid_new ();
+     g_object_set (grid,
+                   "margin", 12,
+                   "row-spacing", 12,
+                   "column-spacing", 6,
+                   "halign", GTK_ALIGN_FILL,
+                   "valign", GTK_ALIGN_FILL,
+                   "hexpand", TRUE,
+                   "vexpand", TRUE,
+                   NULL);
+     gtk_container_add (GTK_CONTAINER (window), grid);
+
+     label = gtk_label_new ("Constraints:");
+     gtk_label_set_xalign (GTK_LABEL (label), 1.0);
+     gtk_grid_attach (GTK_GRID (grid), label, 0, 0, 1, 1);
+     button = gtk_check_button_new ();
+     g_signal_connect (button, "clicked", G_CALLBACK (use_constraints_cb), NULL);
+     gtk_grid_attach (GTK_GRID (grid), button, 1, 0, 1, 1);
+     label = gtk_label_new ("Words:");
+     gtk_label_set_xalign (GTK_LABEL (label), 1.0);
+     gtk_grid_attach (GTK_GRID (grid), label, 0, 1, 1, 1);
+     button = gtk_spin_button_new_with_range (0, 1300, 1);
+     g_signal_connect (button, "value-changed", G_CALLBACK (word_count_cb), NULL);
+     gtk_spin_button_set_value (GTK_SPIN_BUTTON (button), 10);
+     gtk_grid_attach (GTK_GRID (grid), button, 1, 1, 1, 1);
+
+     button = gtk_button_new_with_label ("Show");
+     gtk_widget_set_halign (button, GTK_ALIGN_END);
+     gtk_widget_set_valign (button, GTK_ALIGN_END);
+     g_signal_connect_swapped (button, "clicked",
+                               G_CALLBACK (show_words), window);
+     gtk_grid_attach (GTK_GRID (grid), button, 0, 2, 2, 1);
+   }
+
+ if (!gtk_widget_get_visible (window))
+   gtk_widget_show (window);
+ else
+   gtk_widget_destroy (window);
+
+ return window;
+}

demos/gtk-demo/demo.gresource.xml

@@ -59,6 +59,9 @@
     <file>cssview.css</file>
     <file>reset.css</file>
   </gresource>
+  <gresource prefix="/constraints5">
+    <file>words</file>
+  </gresource>
   <gresource prefix="/cursors">
     <file>cursors.ui</file>
     <file>alias_cursor.png</file>
@@ -153,6 +156,8 @@
     <file>constraints.c</file>
     <file>constraints2.c</file>
     <file>constraints3.c</file>
+    <file>constraints4.c</file>
+    <file>constraints5.c</file>
     <file>css_accordion.c</file>
     <file>css_basics.c</file>
     <file>css_blendmodes.c</file>

demos/gtk-demo/meson.build

@@ -11,6 +11,8 @@ demos = files([
   'constraints.c',
   'constraints2.c',
   'constraints3.c',
+  'constraints4.c',
+  'constraints5.c',
   'css_accordion.c',
   'css_basics.c',
   'css_blendmodes.c',

gtk/gtk.h

@@ -132,6 +132,7 @@
 #include <gtk/gtkgesturezoom.h>
 #include <gtk/gtkglarea.h>
 #include <gtk/gtkgrid.h>
+#include <gtk/gtkgridconstraint.h>
 #include <gtk/gtkgridlayout.h>
 #include <gtk/gtkheaderbar.h>
 #include <gtk/gtkicontheme.h>

gtk/gtkgridconstraint.c

@@ -0,0 +1,635 @@
+/* gtkgridconstraint.c: Make a grid with constraints
+ * Copyright 2019  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 2.1 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/>.
+ *
+ * Author: Matthias Clasen
+ */
+
+#include "config.h"
+
+#include "gtkgridconstraint.h"
+
+#include "gtkintl.h"
+#include "gtktypebuiltins.h"
+
+enum {
+  POS_LEFT,
+  POS_RIGHT,
+  POS_TOP,
+  POS_BOTTOM,
+  LAST_POS,
+  SIZE_WIDTH = LAST_POS,
+  SIZE_HEIGHT,
+  LAST_CONSTRAINT
+};
+
+/* We maintain constraints of the form:
+ *
+ * child.top = row_x
+ * child.bottom = row_y
+ *
+ * (and similar for columns). We avoid introducing
+ * extra variables for rows and columns by keeping
+ * track of the first child we encounter that ends
+ * at a given position, and using that instead:
+ *
+ * child.top = first.bottom
+ *
+ * (assuming that @first is the first child we saw
+ * that ends at row x (and has its bottom edge there).
+ *
+ * For homogeneous grids, we additionally maintain
+ * constraints of the form:
+ *
+ * a.width / a.colspan = b.width / b.colspan
+ *
+ * (and similar for heights). We only maintain
+ * these relations between a child and its
+ * predecessor in the list of children.
+ */
+
+typedef struct {
+  GtkConstraintTarget *child;
+  int left;
+  int right;
+  int top;
+  int bottom;
+
+  /* We hold a ref on these */
+  GtkConstraint *constraints[LAST_CONSTRAINT];
+} GtkGridConstraintChild;
+
+typedef struct {
+  GtkConstraintTarget *target;
+  GtkConstraintAttribute attr;
+} Attach;
+
+struct _GtkGridConstraint {
+  GObject parent;
+
+  GtkConstraintLayout *layout;
+
+  gboolean row_homogeneous;
+  gboolean column_homogeneous;
+
+  /* List<GtkGridConstraintChild>, owned */
+  GPtrArray *children;
+
+  /* List<GtkConstaint>, not owned */
+  GPtrArray *constraints;
+
+  /* Array<Attach>, not owning Attach.target */
+  GArray *rows;
+  GArray *cols;
+};
+
+enum {
+  PROP_ROW_HOMOGENEOUS = 1,
+  PROP_COLUMN_HOMOGENEOUS,
+  N_PROPERTIES
+};
+
+static GParamSpec *obj_props[N_PROPERTIES];
+
+G_DEFINE_TYPE (GtkGridConstraint, gtk_grid_constraint, G_TYPE_OBJECT)
+
+static void set_row_homogeneous    (GtkGridConstraint *self,
+                                    gboolean           homogeneous);
+static void set_column_homogeneous (GtkGridConstraint *self,
+                                    gboolean           homogeneous);
+
+static void
+gtk_constraint_set_property (GObject      *gobject,
+                             guint         prop_id,
+                             const GValue *value,
+                             GParamSpec   *pspec)
+{
+  GtkGridConstraint *self = GTK_GRID_CONSTRAINT (gobject);
+
+  switch (prop_id)
+    {
+    case PROP_ROW_HOMOGENEOUS:
+      set_row_homogeneous (self, g_value_get_boolean (value));
+      break;
+
+    case PROP_COLUMN_HOMOGENEOUS:
+      set_column_homogeneous (self, g_value_get_boolean (value));
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_constraint_get_property (GObject    *gobject,
+                             guint       prop_id,
+                             GValue     *value,
+                             GParamSpec *pspec)
+{
+  GtkGridConstraint *self = GTK_GRID_CONSTRAINT (gobject);
+
+  switch (prop_id)
+    {
+    case PROP_ROW_HOMOGENEOUS:
+      g_value_set_boolean (value, self->row_homogeneous);
+      break;
+
+    case PROP_COLUMN_HOMOGENEOUS:
+      g_value_set_boolean (value, self->column_homogeneous);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (gobject, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_grid_constraint_init (GtkGridConstraint *self)
+{
+  self->children = g_ptr_array_new_with_free_func (g_free);
+
+  self->constraints = g_ptr_array_new ();
+
+  self->rows = g_array_new (FALSE, TRUE, sizeof (Attach));
+  self->cols = g_array_new (FALSE, TRUE, sizeof (Attach));
+}
+
+static void
+gtk_constraint_finalize (GObject *gobject)
+{
+  GtkGridConstraint *self = GTK_GRID_CONSTRAINT (gobject);
+
+  g_array_free (self->rows, TRUE);
+  g_array_free (self->cols, TRUE);
+
+  if (self->layout)
+    gtk_grid_constraint_detach (self);
+  g_assert (self->constraints->len == 0);
+  g_ptr_array_free (self->constraints, TRUE);
+
+  g_ptr_array_free (self->children, TRUE);
+
+  G_OBJECT_CLASS (gtk_grid_constraint_parent_class)->finalize (gobject);
+}
+
+static void
+gtk_grid_constraint_class_init (GtkGridConstraintClass *klass)
+{
+  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
+
+  gobject_class->set_property = gtk_constraint_set_property;
+  gobject_class->get_property = gtk_constraint_get_property;
+  gobject_class->finalize = gtk_constraint_finalize;
+
+  /**
+   * GtkGridConstraint:row-homogeneous:
+   *
+   * Whether to make all rows the same height.
+   */
+  obj_props[PROP_ROW_HOMOGENEOUS] =
+    g_param_spec_boolean ("row-homogeneous",
+                          P_("Row homogeneous"),
+                          P_("Row homogeneous"),
+                          FALSE,
+                          G_PARAM_READWRITE |
+                          G_PARAM_STATIC_STRINGS);
+
+  /**
+   * GtkGridConstraint:column-homogeneous:
+   *
+   * Whether to make all columns the same width.
+   */
+  obj_props[PROP_COLUMN_HOMOGENEOUS] =
+    g_param_spec_boolean ("column-homogeneous",
+                          P_("Column homogeneous"),
+                          P_("Column homogeneous"),
+                          FALSE,
+                          G_PARAM_READWRITE |
+                          G_PARAM_STATIC_STRINGS);
+
+  g_object_class_install_properties (gobject_class, N_PROPERTIES, obj_props);
+}
+
+static void
+remove_child_constraint (GtkGridConstraint      *self,
+                         GtkGridConstraintChild *child,
+                         int                     pos)
+{
+  if (child->constraints[pos] == NULL)
+    return;
+
+  if (self->layout)
+    gtk_constraint_layout_remove_constraint (self->layout,
+                                             child->constraints[pos]);
+  g_object_unref (child->constraints[pos]);
+  child->constraints[pos] = NULL;
+}
+
+/* Ensure that the child variable @var is placed
+ * at the grid edge @pos. If we already have a variable
+ * that needs to end up there, we use it to assert
+ * var = vars[top], otherwise we put @var in the
+ * the list of variables.
+ *
+ * @attr may be one of LEFT/RIGHT/TOP/BOTTOM here.
+ */
+static void
+add_child_constraint (GtkGridConstraint      *self,
+                      GtkGridConstraintChild *child,
+                      GtkConstraintAttribute  attr,
+                      int                     pos)
+{
+  Attach *attach;
+  GArray *vars;
+  int cpos;
+
+  switch ((int)attr)
+    {
+    case GTK_CONSTRAINT_ATTRIBUTE_LEFT:
+      vars = self->cols;
+      cpos = POS_LEFT;
+      break;
+    case GTK_CONSTRAINT_ATTRIBUTE_RIGHT:
+      vars = self->cols;
+      cpos = POS_RIGHT;
+      break;
+    case GTK_CONSTRAINT_ATTRIBUTE_TOP:
+      vars = self->rows;
+      cpos = POS_TOP;
+      break;
+    case GTK_CONSTRAINT_ATTRIBUTE_BOTTOM:
+      vars = self->rows;
+      cpos = POS_BOTTOM;
+      break;
+    default:
+      g_assert_not_reached ();
+    }
+
+  if (vars->len <= pos)
+    g_array_set_size (vars, pos + 1);
+
+  attach = &g_array_index (vars, Attach, pos);
+  if (attach->target == NULL)
+    {
+      attach->target = child->child;
+      attach->attr = attr;
+    }
+  else
+    {
+      g_assert (child->constraints[cpos] == NULL);
+
+      child->constraints[cpos] = gtk_constraint_new (child->child, attr,
+                                       GTK_CONSTRAINT_RELATION_EQ,
+                                       attach->target, attach->attr,
+                                       1.0, 0.0,
+                                       GTK_CONSTRAINT_STRENGTH_REQUIRED);
+      if (self->layout)
+        gtk_constraint_layout_add_constraint (self->layout,
+                                              child->constraints[cpos]);
+    }
+}
+
+/* Create the contraint:
+ *
+ * child1.width/child1.colspan = child2.width/child2.colspan
+ *
+ * @attr can be WIDTH or HEIGHT here.
+ */
+static void
+add_homogeneous_constraint (GtkGridConstraint      *self,
+                            GtkGridConstraintChild *child1,
+                            GtkGridConstraintChild *child2,
+                            GtkConstraintAttribute  attr)
+{
+  int span1, span2;
+  int pos;
+
+  if (attr == GTK_CONSTRAINT_ATTRIBUTE_WIDTH)
+    {
+      pos = SIZE_WIDTH;
+      span1 = child1->right - child1->left;
+      span2 = child2->right - child2->left;
+    }
+  else
+    {
+      pos = SIZE_HEIGHT;
+      span1 = child1->bottom - child1->top;
+      span2 = child2->bottom - child2->top;
+    }
+
+  g_assert (child1->constraints[pos] == NULL);
+ 
+  child1->constraints[pos] = gtk_constraint_new (child1->child, attr,
+                                   GTK_CONSTRAINT_RELATION_EQ,
+                                   child2->child, attr,
+                                   (double) span1 / (double) span2,
+                                   0.0,
+                                   GTK_CONSTRAINT_STRENGTH_REQUIRED);
+
+  if (self->layout)
+    gtk_constraint_layout_add_constraint (self->layout,
+                                          child1->constraints[pos]);
+}
+
+static void
+set_row_homogeneous (GtkGridConstraint *self,
+                     gboolean           homogeneous)
+{
+  GtkGridConstraintChild *child1;
+  GtkGridConstraintChild *child2;
+  int i;
+
+  if (self->row_homogeneous == homogeneous)
+    return;
+
+  self->row_homogeneous = homogeneous;
+
+  for (i = 1; i < self->children->len; i++)
+    {
+      child1 = g_ptr_array_index (self->children, i);
+      child2 = g_ptr_array_index (self->children, i - 1);
+      if (homogeneous)
+        add_homogeneous_constraint (self, child1, child2, GTK_CONSTRAINT_ATTRIBUTE_HEIGHT);
+      else
+        remove_child_constraint (self, child1, SIZE_HEIGHT);
+    }
+
+  g_object_notify (G_OBJECT (self), "row-homogeneous");
+}
+
+static void
+set_column_homogeneous (GtkGridConstraint *self,
+                        gboolean           homogeneous)
+{
+  GtkGridConstraintChild *child1;
+  GtkGridConstraintChild *child2;
+  int i;
+
+  if (self->column_homogeneous == homogeneous)
+    return;
+
+  self->column_homogeneous = homogeneous;
+
+  for (i = 1; i < self->children->len; i++)
+    {
+      child1 = g_ptr_array_index (self->children, i);
+      child2 = g_ptr_array_index (self->children, i - 1);
+      if (homogeneous)
+        add_homogeneous_constraint (self, child1, child2, GTK_CONSTRAINT_ATTRIBUTE_WIDTH);
+      else
+        remove_child_constraint (self, child1, SIZE_WIDTH);
+    }
+
+  g_object_notify (G_OBJECT (self), "column-homogeneous");
+}
+
+/* Fix up attachment constraints for the removal of @target.
+ * We are fixing up the attachment at row/col @rows and
+ * position @pos. If @target was not the representative
+ * for this position, there is nothing to do (all of @targets
+ * constraints are already removed). Otherwise, look over
+ * all children that are attached to @target for this position,
+ * pick a new representative, and fix up the constraints
+ * for all others to attach to the new representative.
+ */
+static void
+fix_up_attach (GtkGridConstraint   *self,
+               GtkConstraintTarget *target,
+               gboolean             rows,
+               int                  pos)
+{
+  int i;
+  Attach *attach;
+
+  if (rows)
+    attach = &g_array_index (self->rows, Attach, pos);
+  else
+    attach = &g_array_index (self->cols, Attach, pos);
+
+  if (attach->target != target)
+    return;
+
+  attach->target = NULL;
+
+  for (i = 0; i < self->children->len; i++)
+    {
+      int cpos;
+      GtkGridConstraintChild *child;
+      GtkConstraintAttribute attr;
+
+      child = g_ptr_array_index (self->children, i);
+      if (rows && child->top == pos)
+        {
+          cpos = POS_TOP;
+          attr = GTK_CONSTRAINT_ATTRIBUTE_TOP;
+        }
+      else if (rows && child->bottom == pos)
+        {
+          cpos = POS_BOTTOM;
+          attr = GTK_CONSTRAINT_ATTRIBUTE_BOTTOM;
+        }
+      else if (!rows && child->left == pos)
+        {
+          cpos = POS_LEFT;
+          attr = GTK_CONSTRAINT_ATTRIBUTE_LEFT;
+        }
+      else if (!rows && child->right == pos)
+        {
+          cpos = POS_LEFT;
+          attr = GTK_CONSTRAINT_ATTRIBUTE_LEFT;
+        }
+      else
+        continue;
+
+      remove_child_constraint (self, child, cpos);
+
+      if (attach->target == NULL)
+        {
+          attach->target = child->child;
+          attach->attr = attr;
+        }
+      else
+        {
+          child->constraints[cpos] =
+            gtk_constraint_new (child->child, attr,
+                                GTK_CONSTRAINT_RELATION_EQ,
+                                attach->target, attach->attr,
+                                1.0, 0.0,
+                                GTK_CONSTRAINT_STRENGTH_REQUIRED);
+          if (self->layout)
+            gtk_constraint_layout_add_constraint (self->layout,
+                                                  g_object_ref (child->constraints[cpos]));
+
+        }
+    }
+}
+
+GtkGridConstraint *
+gtk_grid_constraint_new (void)
+{
+  return g_object_new (GTK_TYPE_GRID_CONSTRAINT, NULL);
+}
+
+void
+gtk_grid_constraint_add (GtkGridConstraint *self,
+                         GtkWidget         *child,
+                         int                left,
+                         int                right,
+                         int                top,
+                         int                bottom)
+{
+  GtkGridConstraintChild *child1;
+  GtkGridConstraintChild *child2;
+
+  g_return_if_fail (GTK_IS_GRID_CONSTRAINT (self));
+  g_return_if_fail (GTK_IS_WIDGET (child));
+  g_return_if_fail (left < right);
+  g_return_if_fail (top < bottom);
+  g_return_if_fail (self->layout == NULL);
+
+  child1 = g_new0 (GtkGridConstraintChild, 1);
+
+  child1->child = GTK_CONSTRAINT_TARGET (child);
+  child1->left = left;
+  child1->right = right;
+  child1->top = top;
+  child1->bottom = bottom;
+
+  if (self->children->len > 0)
+    child2 = g_ptr_array_index (self->children, self->children->len - 1);
+  else
+    child2 = NULL;
+
+  add_child_constraint (self, child1, GTK_CONSTRAINT_ATTRIBUTE_TOP, top);
+  add_child_constraint (self, child1, GTK_CONSTRAINT_ATTRIBUTE_BOTTOM, bottom);
+  add_child_constraint (self, child1, GTK_CONSTRAINT_ATTRIBUTE_LEFT, left);
+  add_child_constraint (self, child1, GTK_CONSTRAINT_ATTRIBUTE_RIGHT, right);
+
+  if (self->row_homogeneous && child2)
+    add_homogeneous_constraint (self, child1, child2, GTK_CONSTRAINT_ATTRIBUTE_HEIGHT);
+  if (self->column_homogeneous && child2)
+    add_homogeneous_constraint (self, child1, child2, GTK_CONSTRAINT_ATTRIBUTE_WIDTH);
+
+  g_ptr_array_add (self->children, child1);
+}
+
+void
+gtk_grid_constraint_remove (GtkGridConstraint *self,
+                            GtkWidget         *child)
+{
+  GtkGridConstraintChild *child1 = NULL;
+  GtkGridConstraintChild *next = NULL;
+  GtkGridConstraintChild *prev = NULL;
+  GtkConstraintTarget *target = (GtkConstraintTarget *)child;
+  int i;
+  int left, right, top, bottom;
+
+  for (i = 0; i < self->children->len; i++)
+    {
+      child1 = g_ptr_array_index (self->children, i);
+      if (child1->child == target)
+        break;
+      child1 = NULL;
+    }
+
+  if (child1 == NULL)
+    return;
+
+  if (i > 0)
+    prev = g_ptr_array_index (self->children, i - 1);
+  if (i + 1 < self->children->len)
+    next = g_ptr_array_index (self->children, i + 1);
+
+  for (i = 0; i < LAST_CONSTRAINT; i++)
+    remove_child_constraint (self, child1, i);
+
+  top = child1->top;
+  bottom = child1->bottom;
+  left = child1->left;
+  right = child1->right;
+
+  g_ptr_array_remove (self->children, child1);
+
+  fix_up_attach (self, target, TRUE, top);
+  fix_up_attach (self, target, TRUE, bottom);
+  fix_up_attach (self, target, FALSE, right);
+  fix_up_attach (self, target, FALSE, left);
+
+  if (self->column_homogeneous && next)
+    {
+      remove_child_constraint (self, next, SIZE_WIDTH);
+      if (prev)
+        add_homogeneous_constraint (self, next, prev, GTK_CONSTRAINT_ATTRIBUTE_WIDTH);
+    }
+  if (self->row_homogeneous && next)
+    {
+      remove_child_constraint (self, next, SIZE_HEIGHT);
+      if (prev)
+        add_homogeneous_constraint (self, next, prev, GTK_CONSTRAINT_ATTRIBUTE_HEIGHT);
+    }
+}
+
+gboolean
+gtk_grid_constraint_is_attached (GtkGridConstraint *self)
+{
+  return self->layout != NULL;
+}
+
+void
+gtk_grid_constraint_attach (GtkGridConstraint   *self,
+                            GtkConstraintLayout *layout)
+{
+  int i, j;
+
+  g_return_if_fail (self->layout == NULL);
+
+  self->layout = layout;
+
+  for (i = 0; i < self->children->len; i++)
+    {
+      GtkGridConstraintChild *child = g_ptr_array_index (self->children, i);
+      for (j = 0; j < LAST_CONSTRAINT; j++)
+        {
+          if (child->constraints[j] != NULL)
+            gtk_constraint_layout_add_constraint (self->layout,
+                                     g_object_ref (child->constraints[j]));
+        }
+    }
+}
+
+void
+gtk_grid_constraint_detach (GtkGridConstraint *self)
+{
+  int i, j;
+
+  if (self->layout == NULL)
+    return;
+
+  for (i = 0; i < self->children->len; i++)
+    {
+      GtkGridConstraintChild *child = g_ptr_array_index (self->children, i);
+      for (j = 0; j < LAST_CONSTRAINT; j++)
+        {
+          if (child->constraints[j] != NULL)
+            gtk_constraint_layout_remove_constraint (self->layout,
+                                                     child->constraints[j]);
+        }
+    }
+
+  self->layout = NULL;
+}

gtk/gtkgridconstraint.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2019 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 2.1 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 __GTK_GRID_CONSTRAINT_H__
+#define __GTK_GRID_CONSTRAINT_H__
+
+#include <gtk/gtkwidget.h>
+#include <gtk/gtkconstraintlayout.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_GRID_CONSTRAINT (gtk_grid_constraint_get_type ())
+
+/**
+ * GtkGridConstraint:
+ *
+ * An object used for managing constraints for children in
+ * a constraints layout that are to be arranged in a grid.
+ */
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_FINAL_TYPE (GtkGridConstraint, gtk_grid_constraint, GTK, GRID_CONSTRAINT, GObject)
+
+GDK_AVAILABLE_IN_ALL
+GtkGridConstraint * gtk_grid_constraint_new     (void);
+
+GDK_AVAILABLE_IN_ALL
+void                gtk_grid_constraint_add     (GtkGridConstraint   *self,
+                                                 GtkWidget           *child,
+                                                 int                  left,
+                                                 int                  right,
+                                                 int                  top,
+                                                 int                  bottom);
+
+GDK_AVAILABLE_IN_ALL
+void                gtk_grid_constraint_remove (GtkGridConstraint   *self,
+                                                 GtkWidget           *child);
+GDK_AVAILABLE_IN_ALL
+void     gtk_grid_constraint_attach      (GtkGridConstraint   *self,
+                                          GtkConstraintLayout *layout);
+GDK_AVAILABLE_IN_ALL
+void     gtk_grid_constraint_detach      (GtkGridConstraint   *self);
+GDK_AVAILABLE_IN_ALL
+gboolean gtk_grid_constraint_is_attached (GtkGridConstraint   *self);
+
+
+G_END_DECLS
+
+#endif  /* __GTK_GRID_CONSTRAINT_H__ */

gtk/meson.build

@@ -254,6 +254,7 @@ gtk_public_sources = files([
   'gtkgesturezoom.c',
   'gtkglarea.c',
   'gtkgrid.c',
+  'gtkgridconstraint.c',
   'gtkgridlayout.c',
   'gtkheaderbar.c',
   'gtkicontheme.c',