[gtk/wip/otte/texture-threads] testsuite: Add a test for downloading textures in a different thread

[Benjamin Otte <otte src gnome org>]

commit ed8aba82b704b3dad52d286bfde0aff4e0f5adca
Author: Benjamin Otte <otte redhat com>
Date:   Mon Sep 13 00:19:35 2021 +0200

    testsuite: Add a test for downloading textures in a different thread
    
    This happens in the real world when using the inspector to look at a
    node recording of a GStreamer video while the video is still playing.
    
    GStreamer will use the GL context in a different thread while we are
    busy trying to download it.

 testsuite/gdk/meson.build       |  1 +
 testsuite/gdk/texture-threads.c | 96 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 97 insertions(+)
---
diff --git a/testsuite/gdk/meson.build b/testsuite/gdk/meson.build
index 5e62e98775..3eff25868d 100644
--- a/testsuite/gdk/meson.build
+++ b/testsuite/gdk/meson.build
@@ -26,6 +26,7 @@ tests = [
   'rgba',
   'seat',
   'texture',
+  'texture-threads',
 ]
 
 foreach t : tests
diff --git a/testsuite/gdk/texture-threads.c b/testsuite/gdk/texture-threads.c
new file mode 100644
index 0000000000..00828e6dbb
--- /dev/null
+++ b/testsuite/gdk/texture-threads.c
@@ -0,0 +1,96 @@
+#include <gtk/gtk.h>
+
+#include "gsk/ngl/gsknglrenderer.h"
+
+/* This function will be called from a thread and/or the main loop.
+ * Textures are threadsafe after all. */
+static void
+ensure_texture_access (GdkTexture *texture)
+{
+  /* Make sure to initialize the pixel to anything but red */
+  guint32 pixel = 0;
+
+  /* Just to be sure */
+  g_assert_cmpint (gdk_texture_get_width (texture), ==, 1);
+  g_assert_cmpint (gdk_texture_get_height (texture), ==, 1);
+
+  /* download the pixel */
+  gdk_texture_download (texture, (guchar *) &pixel, 4);
+
+  /* check the pixel is now red */
+  g_assert_cmphex (pixel, ==, 0xFFFF0000);
+}
+
+static void
+texture_download_done (GObject      *texture,
+                       GAsyncResult *res,
+                       gpointer      loop)
+{
+  ensure_texture_access (GDK_TEXTURE (texture));
+
+  g_main_loop_quit (loop);
+}
+
+static void
+texture_download_thread (GTask        *task,
+                         gpointer      texture,
+                         gpointer      unused,
+                         GCancellable *cancellable)
+{
+  ensure_texture_access (GDK_TEXTURE (texture));
+
+  g_task_return_boolean (task, TRUE);
+}
+
+static void
+texture_threads (void)
+{
+  GdkSurface *surface;
+  GskRenderer *gl_renderer;
+  GskRenderNode *node;
+  GMainLoop *loop;
+  GdkTexture *texture;
+  GTask *task;
+
+  /* 1. Get a GL renderer */
+  surface = gdk_surface_new_toplevel (gdk_display_get_default());
+  gl_renderer = gsk_ngl_renderer_new ();
+  g_assert_true (gsk_renderer_realize (gl_renderer, surface, NULL));
+
+  /* 2. Get a GL texture */
+  node = gsk_color_node_new (&(GdkRGBA) { 1, 0, 0, 1 }, &GRAPHENE_RECT_INIT(0, 0, 1, 1));
+  texture = gsk_renderer_render_texture (gl_renderer, node, &GRAPHENE_RECT_INIT(0, 0, 1, 1));
+  gsk_render_node_unref (node);
+
+  /* 3. This is a bit fishy, but we want to make sure that
+   * the texture's GL context is current in the main thread.
+   *
+   * If we had access to the context, we'd make_current() here.
+   */
+  ensure_texture_access (texture);
+  g_assert_nonnull (gdk_gl_context_get_current ());
+
+  /* 4. Run a thread trying to download the texture */
+  loop = g_main_loop_new (NULL, TRUE);
+  task = g_task_new (texture, NULL, texture_download_done, loop);
+  g_task_run_in_thread (task, texture_download_thread);
+  g_clear_object (&task);
+
+  /* 5. Run the main loop waiting for the thread to return */
+  g_main_loop_run (loop);
+
+  /* 6. All good */
+  g_clear_pointer (&loop, g_main_loop_unref);
+  g_clear_object (&gl_renderer);
+  g_clear_object (&surface);
+}
+
+int
+main (int argc, char *argv[])
+{
+  gtk_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/texture-threads", texture_threads);
+
+  return g_test_run ();
+}