tests: Add resizing drag icon test

The test can verify that dynamic drag icon resizing and hotspot
adjustment work as intended.

tests/meson.build

@@ -31,6 +31,7 @@ gtk_tests = [
   ['testdialog'],
   ['testdnd'],
   ['testdnd2'],
+  ['testdndresize'],
   ['testellipsise'],
   ['testentrycompletion'],
   ['testentryicons'],

tests/testdndresize.c

@@ -0,0 +1,123 @@
+#include "gtkcssprovider.h"
+#include <gtk/gtk.h>
+
+static GtkRequisition size;
+static gint64 start_time;
+static gboolean stop_update_size;
+
+static gboolean
+update_size (GtkWidget *widget, GdkFrameClock *clock, gpointer data)
+{
+  GdkDrag *drag = data;
+  gint64 now = g_get_monotonic_time ();
+  float t;
+  int width, height;
+
+  if (stop_update_size)
+    return G_SOURCE_REMOVE;
+
+  t = fmodf ((now - start_time) / (float) G_TIME_SPAN_SECOND, 1);
+  if (t >= 0.5)
+    t = 1 - t;
+
+  width = size.width + t * 300;
+  height = size.height + t * 150;
+
+  gtk_widget_set_size_request (widget, width, height);
+  gdk_drag_set_hotspot (drag, width / 2, height / 2);
+
+  return G_SOURCE_CONTINUE;
+}
+
+static void
+drag_begin (GtkDragSource *source,
+            GdkDrag       *drag)
+{
+  GtkWidget *widget;
+  GtkWidget *icon;
+
+  icon = gtk_drag_icon_get_for_drag (drag);
+
+  widget = gtk_label_new ("This Should Resize\n\nAnd Stay Centered");
+  gtk_widget_add_css_class (widget, "dnd");
+  gtk_widget_get_preferred_size (widget, NULL, &size);
+
+  gtk_drag_icon_set_child (GTK_DRAG_ICON (icon), widget);
+  gtk_widget_set_size_request (widget, size.width, size.height);
+  gdk_drag_set_hotspot (drag, size.width / 2, size.height / 2);
+
+  start_time = g_get_monotonic_time ();
+  stop_update_size = FALSE;
+  gtk_widget_add_tick_callback (widget, update_size, drag, NULL);
+}
+
+static void
+drag_end (GtkDragSource *source,
+          GdkDrag       *drag,
+          gboolean       delete_data,
+          gboolean       data)
+{
+  stop_update_size = TRUE;
+}
+
+static void
+quit_cb (GtkWidget *widget,
+         gpointer   data)
+{
+  gboolean *done = data;
+
+  *done = TRUE;
+
+  g_main_context_wakeup (NULL);
+}
+
+int
+main (int argc, char *argv[])
+{
+  GtkCssProvider *provider;
+  GtkWidget *window;
+  GtkWidget *label;
+  GtkDragSource *source;
+  GdkContentProvider *content;
+  gboolean done = FALSE;
+
+  gtk_init ();
+
+  provider = gtk_css_provider_new ();
+  gtk_css_provider_load_from_data (provider,
+                                   ".dnd {"
+                                   "background-color: red;"
+                                   "border-top: 10px solid rebeccapurple;"
+                                   "}",
+                                   -1);
+  gtk_style_context_add_provider_for_display (gdk_display_get_default (),
+                                              GTK_STYLE_PROVIDER(provider),
+                                              GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+
+  window = gtk_window_new ();
+  g_signal_connect (window, "destroy", G_CALLBACK (quit_cb), &done);
+
+  label = gtk_label_new ("Drag Me");
+  g_object_set (label,
+                "margin-start", 64,
+                "margin-end", 64,
+                "margin-top", 64,
+                "margin-bottom", 64,
+                NULL);
+
+  source = gtk_drag_source_new ();
+  content = gdk_content_provider_new_typed (G_TYPE_STRING, "I'm data!");
+  gtk_drag_source_set_content (source, content);
+  g_signal_connect (source, "drag-begin", G_CALLBACK (drag_begin), NULL);
+  g_signal_connect (source, "drag-end", G_CALLBACK (drag_end), NULL);
+  gtk_widget_add_controller (label, GTK_EVENT_CONTROLLER (source));
+
+  gtk_window_set_child (GTK_WINDOW (window), label);
+
+  gtk_window_present (GTK_WINDOW (window));
+
+  while (!done)
+    g_main_context_iteration (NULL, TRUE);
+
+  return 0;
+}