tests: add tests to ensure GL dma-buf screenshot correctness

This tests our dma-buf buffer support for GL screenshots. We use two
backends that have outputs with different y origin in order to exercise
the implementation.

Signed-off-by: Leandro Ribeiro <leandro.ribeiro@collabora.com>

tests/dmabuf-screenshot-test.c

@@ -0,0 +1,164 @@
+/*
+ * Copyright (C) 2026 Amazon.com, Inc. or its affiliates
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "config.h"
+
+#include "weston-test-client-helper.h"
+
+struct setup_args {
+	struct fixture_metadata meta;
+	enum weston_compositor_backend backend;
+};
+
+/**
+ * It is important to use different backends because they have outputs with
+ * different Y origin (bottom-left in the case of DRM-backend, top-left in the
+ * case of headless), and GL-renderer needs to make the screenshot work for both
+ * cases.
+ */
+static const struct setup_args my_setup_args[] = {
+	{
+		.meta.name = "headless",
+		.backend = WESTON_BACKEND_HEADLESS,
+	},
+	{
+		.meta.name = "DRM",
+		.backend = WESTON_BACKEND_DRM,
+	},
+};
+
+static enum test_result_code
+fixture_setup(struct weston_test_harness *harness, const struct setup_args *arg)
+{
+	struct compositor_setup setup;
+
+	compositor_setup_defaults(&setup);
+        setup.backend = arg->backend;
+	setup.renderer = WESTON_RENDERER_GL;
+	setup.width = 200;
+	setup.height = 200;
+	setup.shell = SHELL_TEST_DESKTOP;
+        setup.refresh = HIGHEST_OUTPUT_REFRESH;
+
+	return weston_test_harness_execute_as_client(harness, &setup);
+}
+DECLARE_FIXTURE_SETUP_WITH_ARG(fixture_setup, my_setup_args, meta);
+
+static struct buffer *
+surface_commit_color(struct client *client, struct wl_surface *surface,
+		     pixman_color_t *color, int width, int height)
+{
+	struct buffer *buf;
+
+	buf = create_shm_buffer_a8r8g8b8(client, width, height);
+	fill_image_with_color(buf->image, color);
+	wl_surface_attach(surface, buf->proxy, 0, 0);
+	wl_surface_damage_buffer(surface, 0, 0, width, height);
+	wl_surface_commit(surface);
+
+	return buf;
+}
+
+TEST(screenshot)
+{
+        struct client *client;
+        struct wl_subcompositor *subco;
+	struct wl_surface *surf;
+	struct wl_subsurface *subsurf;
+        struct buffer *buf_main, *buf_sub;
+        struct buffer *buf_screenshot;
+        struct rectangle clip;
+        char *fname;
+        bool match;
+        pixman_image_t *reference;
+        pixman_image_t *diffimg;
+        pixman_color_t red, green;
+
+	if (!client_buffer_util_is_dmabuf_supported()) {
+		testlog("%s: Skipped: udmabuf not supported\n", get_test_name());
+		return RESULT_SKIP;
+	}
+
+	color_rgb888(&red, 255, 0, 0);
+	color_rgb888(&green, 0, 255, 0);
+
+        client = create_client_and_test_surface(0, 0, 100, 100);
+        subco = client_get_subcompositor(client);
+
+	/* move the pointer clearly away from our screenshooting area */
+	weston_test_move_pointer(client->test->weston_test, 0, 1, 0, 2, 30);
+
+        surf = wl_compositor_create_surface(client->wl_compositor);
+	subsurf = wl_subcompositor_get_subsurface(subco, surf,
+						  client->surface->wl_surface);
+
+        buf_main = surface_commit_color(client, client->surface->wl_surface,
+                                        &red, 100, 100);
+
+        wl_subsurface_set_position(subsurf, 100, 100);
+        buf_sub = surface_commit_color(client, surf,
+                                       &green, 100, 100);
+
+        wl_surface_commit(client->surface->wl_surface);
+
+        buf_screenshot = client_capture_output(client, client->output,
+                                               WESTON_CAPTURE_V1_SOURCE_FRAMEBUFFER,
+                                               CLIENT_BUFFER_TYPE_DMABUF);
+
+        /* load reference image */
+        fname = screenshot_reference_filename("dmabuf-screenshot", 0);
+        reference = load_image_from_png(fname);
+        free(fname);
+
+        /* only the colored squares area matters */
+	clip.x = 0;
+	clip.y = 0;
+	clip.width = 200;
+	clip.height = 200;
+
+	client_buffer_util_maybe_sync_dmabuf_start(buf_screenshot->buf);
+        match = check_images_match(buf_screenshot->image, reference, &clip, NULL);
+	client_buffer_util_maybe_sync_dmabuf_end(buf_screenshot->buf);
+
+	testlog("Screenshot %s reference image\n", match? "equal to" : "different from");
+	if (!match) {
+		diffimg = visualize_image_difference(buf_screenshot->image, reference, &clip, NULL);
+		fname = output_filename_for_test_case("error", 0, "png");
+		write_image_as_png(diffimg, fname);
+		pixman_image_unref(diffimg);
+		free(fname);
+	}
+
+        pixman_image_unref(reference);
+	buffer_destroy(buf_sub);
+	buffer_destroy(buf_main);
+	buffer_destroy(buf_screenshot);
+	wl_subcompositor_destroy(subco);
+	wl_subsurface_destroy(subsurf);
+	wl_surface_destroy(surf);
+        client_destroy(client);
+
+        return match ? RESULT_OK : RESULT_FAIL;
+}

tests/meson.build

@@ -59,6 +59,7 @@ tests = [
 	},
         {       'name': 'custom-env', },
 	{	'name': 'devices', },
+	{	'name': 'dmabuf-screenshot', },
 	{
 		'name': 'drm-formats',
 		'dep_objs': dep_libdrm_headers,