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, 34 insertions, 8 deletions

diff --git a/src/window.c b/src/window.c
index 049be4e..88df578 100644
--- a/src/window.c
+++ b/src/window.c
@@ -2,8 +2,10 @@
  * ggaze — main window
  *
  * Implements GgazeWindow. Builds an AdwHeaderBar + a GtkStack with two named
- * placeholder children ("grid", "large"); the real views arrive in M1 (large)
- * and M7 (grid). Tracks the current GFile for later milestones.
+ * children: "grid" (placeholder until M7) and "large" (the GgazeViewer from
+ * M1). ggaze_window_open() loads the file via the loader and shows it in the
+ * viewer. Real file-vs-folder resolution lands in M2 (navigator); M1 just loads
+ * the one file. See docs/architecture.md "Responsibilities / window".
  *
  * Copyright (c) 2026 ggaze contributors
  * SPDX-License-Identifier: GPL-3.0-or-later
@@ -14,10 +16,14 @@
 #include <adwaita.h>
 #include <glib.h>
 
+#include "viewer.h"
+#include "loader/loader.h"
+
 struct _GgazeWindow {
    GtkApplicationWindow parent_instance;
-   GFile     *p_file;  /* current file/folder, remembered for later use */
-   GtkWidget *p_stack; /* GtkStack: grid/large placeholder children */
+   GFile     *p_file;   /* current file/folder, remembered for later use */
+   GtkWidget *p_stack;  /* GtkStack: grid (placeholder) / large (viewer) */
+   GtkWidget *p_viewer; /* GgazeViewer — the large view */
 };
 
 G_DEFINE_TYPE(GgazeWindow, ggaze_window, GTK_TYPE_APPLICATION_WINDOW)
@@ -26,6 +32,8 @@ static void
 ggaze_window_dispose(GObject *p_obj) {
    GgazeWindow *p_win = GGAZE_WINDOW(p_obj);
    g_clear_object(&p_win->p_file);
+   /* p_stack/p_viewer are GtkWidgets parented to the window; GTK releases them.
+    */
    G_OBJECT_CLASS(ggaze_window_parent_class)->dispose(p_obj);
 }
 
@@ -41,7 +49,8 @@ ggaze_window_init(GgazeWindow *p_win) {
    GtkWidget *p_header = adw_header_bar_new();
    gtk_window_set_titlebar(GTK_WINDOW(p_win), p_header);
 
-   /* Two-view stack. Children are placeholders for M1 (large) and M7 (grid). */
+   /* Two-view stack: "grid" is a placeholder until M7; "large" is the viewer.
+    */
    p_win->p_stack = gtk_stack_new();
    gtk_stack_set_transition_type(GTK_STACK(p_win->p_stack),
                                  GTK_STACK_TRANSITION_TYPE_CROSSFADE);
@@ -49,10 +58,13 @@ ggaze_window_init(GgazeWindow *p_win) {
 
    GtkWidget *p_grid = gtk_label_new("grid");
    gtk_widget_add_css_class(p_grid, "dim-label");
-   GtkWidget *p_large = gtk_label_new("large");
-   gtk_widget_add_css_class(p_large, "dim-label");
    gtk_stack_add_named(GTK_STACK(p_win->p_stack), p_grid, "grid");
-   gtk_stack_add_named(GTK_STACK(p_win->p_stack), p_large, "large");
+
+   p_win->p_viewer = ggaze_viewer_new();
+   gtk_widget_set_hexpand(p_win->p_viewer, TRUE);
+   gtk_widget_set_vexpand(p_win->p_viewer, TRUE);
+   gtk_stack_add_named(GTK_STACK(p_win->p_stack), p_win->p_viewer, "large");
+
    gtk_stack_set_visible_child_name(GTK_STACK(p_win->p_stack), "grid");
 }
 
@@ -68,7 +80,21 @@ ggaze_window_open(GgazeWindow *p_win, GFile *p_file) {
    g_return_if_fail(GGAZE_IS_WINDOW(p_win));
    g_return_if_fail(G_IS_FILE(p_file));
    g_set_object(&p_win->p_file, p_file);
+
    char *c_name = g_file_get_basename(p_file);
    gtk_window_set_title(GTK_WINDOW(p_win), c_name);
+
+   /* Load and display (M1: synchronous; M3 makes this async with cancel). */
+   GError     *p_err = NULL;
+   GdkTexture *p_tex = loader_load(p_file, NULL, &p_err);
+   if (p_tex != NULL) {
+      ggaze_viewer_set_texture(GGAZE_VIEWER(p_win->p_viewer), p_tex);
+      gtk_stack_set_visible_child_name(GTK_STACK(p_win->p_stack), "large");
+      g_object_unref(p_tex); /* viewer holds its own ref */
+   } else {
+      const gchar *c_msg = (p_err != NULL) ? p_err->message : "unknown error";
+      g_warning("ggaze: failed to load %s: %s", c_name, c_msg);
+      g_clear_error(&p_err);
+   }
    g_free(c_name);
 }
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