showimage: loader, detect, viewer widget, EXIF orientation, tests (gt0)

M1 (task gt0): show one image with zoom/pan.

- src/loader/detect.{c,h}: magic-byte format sniffing (JPEG/PNG/GIF/WebP/
  TIFF/ICO/JXL/AVIF/HEIF) -> GgazeFormat; pure, no I/O, unit-testable.
- src/loader/loader.{c,h}: loader_load() sniffs the header and dispatches to
  the first registered backend; GgazeLoaderBackend struct; pixbuf is the
  fallback (last, accepts UNKNOWN). M1 ships only the pixbuf backend.
- src/loader/backends/pixbuf.c: GdkPixbufLoader decode +
  gdk_pixbuf_apply_embedded_orientation (decision #26) -> GdkTexture via
  gdk_memory_texture_new (avoids the deprecated gdk_texture_new_for_pixbuf).
- src/viewer.{c,h}: GgazeViewer : GtkWidget custom widget (decision #31) —
  fit/100%/in/out zoom, cursor-centered zoom, drag-to-pan with clamping,
  dark background, GtkSnapshot render nodes.
- src/window.c: open -> loader_load -> viewer_set_texture -> stack 'large'.
- tests: unit test_detect (13 cases) + test_loader_pixbuf (plain/rotated-EXIF
  8x4 orient6->4x8/png/rgba/missing/unsupported jxl-avif-heif/corrupt),
  integration test_open_and_show (fixture + rotated + ./sample-images
  skip-if-absent). 6/6 green; detect 97% / loader 91% / pixbuf 87% coverage.
- fixtures: gen.py produces plain.jpg, rot6.jpg, small.png, rgba.png.
- AGENTS.md: documents the ./sample-images optional test corpus convention.

Sub-agent review fixes: use-after-free of c_name in ggaze_window_open
(BLOCKER), gtk_stack_get_pages leak in test_window (BLOCKER), coverage gap,
dead branch, viewer measure, _prefix/_cb naming, include order, extern in
header, pan clamp, stale comments — all addressed.

1 files changed, 138 insertions, 0 deletions

diff --git a/tests/test_open_and_show.c b/tests/test_open_and_show.c
new file mode 100644
index 0000000..e707555
--- /dev/null
+++ b/tests/test_open_and_show.c
@@ -0,0 +1,138 @@
+/*:*
+ * ggaze — open-and-show integration test
+ *
+ * Exercises the window wiring: ggaze_window_open() loads a fixture via the
+ * loader, sets the viewer texture, and switches the stack to "large". Asserts
+ * the stack is on "large" and the viewer holds a texture of the right size.
+ *
+ * An optional second test opens an image from ./sample-images (the realistic
+ * local corpus, not git-tracked) and is skipped if $GGAZE_SAMPLE_DIR is unset
+ * or the directory is absent — so CI (which only has tests/fixtures/) stays
+ * green. Needs a display (integration suite; CI runs under xvfb).
+ *
+ * Copyright (c) 2026 ggaze contributors
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ *:*/
+
+#include "window.h"
+#include "viewer.h"
+
+#include <gdk/gdk.h>
+#include <gio/gio.h>
+#include <glib.h>
+#include <gtk/gtk.h>
+
+static GFile *
+fixture_file(const gchar *c_name) {
+   const gchar *c_dir = g_getenv("GGAZE_FIXTURES_DIR");
+   g_assert_nonnull(c_dir);
+   gchar *c_path = g_build_filename(c_dir, c_name, NULL);
+   GFile *p_file = g_file_new_for_path(c_path);
+   g_free(c_path);
+   return (p_file);
+}
+
+static GgazeWindow *
+new_window(void) {
+   return (GGAZE_WINDOW(g_object_new(GGAZE_TYPE_WINDOW, NULL)));
+}
+
+static void
+assert_shown_large_with_dims(GgazeWindow *p_win, int i_w, int i_h) {
+   GtkWidget *p_child = gtk_window_get_child(GTK_WINDOW(p_win));
+   g_assert_true(GTK_IS_STACK(p_child));
+   g_assert_cmpstr(gtk_stack_get_visible_child_name(GTK_STACK(p_child)), ==,
+                   "large");
+
+   GtkWidget *p_large =
+      gtk_stack_get_child_by_name(GTK_STACK(p_child), "large");
+   g_assert_true(GGAZE_IS_VIEWER(p_large));
+   GdkTexture *p_tex = ggaze_viewer_get_texture(GGAZE_VIEWER(p_large));
+   g_assert_nonnull(p_tex);
+   g_assert_cmpint(gdk_texture_get_width(p_tex), ==, i_w);
+   g_assert_cmpint(gdk_texture_get_height(p_tex), ==, i_h);
+}
+
+static void
+test_open_fixture_shows_large(void) {
+   GgazeWindow *p_win  = new_window();
+   GFile       *p_file = fixture_file("plain.jpg");
+   ggaze_window_open(p_win, p_file);
+   assert_shown_large_with_dims(p_win, 6, 3);
+   g_object_unref(p_file);
+   g_object_unref(p_win);
+}
+
+static void
+test_open_rotated_fixture(void) {
+   GgazeWindow *p_win  = new_window();
+   GFile       *p_file = fixture_file("rot6.jpg");
+   ggaze_window_open(p_win, p_file);
+   assert_shown_large_with_dims(p_win, 4, 8);
+   g_object_unref(p_file);
+   g_object_unref(p_win);
+}
+
+static void
+test_open_sample_image(void) {
+   const gchar *c_dir = g_getenv("GGAZE_SAMPLE_DIR");
+   if (c_dir == NULL || *c_dir == '\0') {
+      g_test_skip("GGAZE_SAMPLE_DIR unset (./sample-images not available)");
+      return;
+   }
+   if (!g_file_test(c_dir, G_FILE_TEST_IS_DIR)) {
+      g_test_skip("GGAZE_SAMPLE_DIR is not a directory");
+      return;
+   }
+   /* Pick the first JPEG in the corpus. */
+   GError *p_err = NULL;
+   GDir   *p_dir = g_dir_open(c_dir, 0, &p_err);
+   g_assert_no_error(p_err);
+   const gchar *c_name = NULL;
+   while ((c_name = g_dir_read_name(p_dir)) != NULL) {
+      if (g_str_has_suffix(c_name, ".jpg") ||
+          g_str_has_suffix(c_name, ".JPG") ||
+          g_str_has_suffix(c_name, ".png")) {
+         break;
+      }
+   }
+   if (c_name == NULL) {
+      g_test_skip("no sample image found in corpus");
+      g_dir_close(p_dir);
+      return;
+   }
+   gchar *c_path = g_build_filename(c_dir, c_name, NULL);
+   g_dir_close(p_dir);
+
+   GgazeWindow *p_win  = new_window();
+   GFile       *p_file = g_file_new_for_path(c_path);
+   ggaze_window_open(p_win, p_file);
+   GtkWidget *p_child = gtk_window_get_child(GTK_WINDOW(p_win));
+   g_assert_cmpstr(gtk_stack_get_visible_child_name(GTK_STACK(p_child)), ==,
+                   "large");
+   GtkWidget *p_large =
+      gtk_stack_get_child_by_name(GTK_STACK(p_child), "large");
+   GdkTexture *p_tex = ggaze_viewer_get_texture(GGAZE_VIEWER(p_large));
+   g_assert_nonnull(p_tex); /* loaded, whatever its dims */
+
+   g_object_unref(p_file);
+   g_object_unref(p_win);
+   g_free(c_path);
+}
+
+int
+main(int i_argc, char **c_argv) {
+   g_test_init(&i_argc, &c_argv, NULL);
+   /* Tolerate host GTK WARNINGs; keep CRITICALs fatal. */
+   g_log_set_always_fatal(G_LOG_LEVEL_ERROR | G_LOG_LEVEL_CRITICAL);
+
+   if (!gtk_init_check()) {
+      g_test_skip("no display available (run under xvfb)");
+      return (g_test_run());
+   }
+
+   g_test_add_func("/open/fixture_shows_large", test_open_fixture_shows_large);
+   g_test_add_func("/open/rotated_fixture", test_open_rotated_fixture);
+   g_test_add_func("/open/sample_image", test_open_sample_image);
+   return (g_test_run());
+}
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