feat: add type-safe native platform headers and portable drag support

- Add include/yasl/native/{wayland,cocoa,x11}.h with type-safe handle accessors.
- Unify drag-and-drop and window carry support across Wayland, X11, and Cocoa.
- Preserve full ABI compatibility for capability flags.
- Install native headers conditionally based on enabled backend.
- Include missing tablet example and backend test suites.

1 files changed, 71 insertions, 1 deletions

diff --git a/src/x11/window.c b/src/x11/window.c
index 85f1d22..5e3dba9 100644
--- a/src/x11/window.c
+++ b/src/x11/window.c
@@ -89,6 +89,14 @@ struct x11_display {
     bool xi2;
     Atom abs_pressure, abs_tilt_x, abs_tilt_y, tool_type, eraser;
     struct x11_pointer *pointers;
+    struct {
+        bool active;
+        struct x11_surface *origin;
+        struct x11_surface *carried;
+        struct yasl_vector2i carry_offset;
+        struct yasl_drag_listener listener;
+        void *ud;
+    } drag;
 };
 
 static struct x11_display *display_of(const struct yasl_surface *s)
@@ -96,6 +104,10 @@ static struct x11_display *display_of(const struct yasl_surface *s)
     return (struct x11_display *)s->display;
 }
 
+static bool place(struct yasl_surface *base, struct yasl_vector2i at);
+static void drag_end(struct x11_display *d, enum yasl_drag_end how);
+static void drag_cancel(struct yasl_display *base);
+
 static void leave(struct x11_display *d)
 {
     if (--d->depth) return;
@@ -284,6 +296,10 @@ static void xi_event(struct x11_display *d, XGenericEventCookie *cookie)
         cookie->evtype != XI_ButtonRelease) return;
     Window window = crossing ? ((XIEnterEvent *)cookie->data)->event :
                                ((XIDeviceEvent *)cookie->data)->event;
+    if (cookie->evtype == XI_Motion && d->drag.active && d->drag.carried)
+        place(&d->drag.carried->base, d->drag.carry_offset);
+    else if (cookie->evtype == XI_ButtonRelease && d->drag.active)
+        drag_end(d, YASL_DRAG_DROPPED);
     struct x11_surface *s = d->surfaces;
     while (s && s->window != window) s = s->next;
     if (!s) return;
@@ -357,6 +373,8 @@ static void surface_destroy(struct yasl_surface *base)
     struct x11_surface *s = (struct x11_surface *)base;
     if (s->destroyed) return;
     struct x11_display *d = display_of(base);
+    if (d->drag.active && (d->drag.origin == s || d->drag.carried == s))
+        drag_end(d, YASL_DRAG_CANCELLED);
     s->destroyed = true;
     for (struct x11_surface **p = &d->surfaces; *p; p = &(*p)->next) {
         if (*p == s) { *p = s->next; break; }
@@ -648,6 +666,8 @@ static void dispatch(struct yasl_display *base)
                 mouse.pos = (struct yasl_vector2i){event.xmotion.x, event.xmotion.y};
                 mouse.kind = YASL_PTR_MOTION;
                 state = event.xmotion.state;
+                if (d->drag.active && d->drag.carried)
+                    place(&d->drag.carried->base, d->drag.carry_offset);
             } else if (event.type == LeaveNotify) {
                 mouse.pos = (struct yasl_vector2i){event.xcrossing.x, event.xcrossing.y};
                 mouse.kind = YASL_PTR_LEAVE;
@@ -663,6 +683,8 @@ static void dispatch(struct yasl_display *base)
                 } else {
                     mouse.kind = event.type == ButtonPress ? YASL_PTR_PRESS : YASL_PTR_RELEASE;
                     mouse.button = pointer_button(button);
+                    if (event.type == ButtonRelease && d->drag.active)
+                        drag_end(d, YASL_DRAG_DROPPED);
                 }
             }
             d->mods = mouse.mods = modifiers(state);
@@ -849,6 +871,7 @@ static void display_close(struct yasl_display *base)
 {
     struct x11_display *d = (struct x11_display *)base;
     assert(!d->surfaces && "destroy every surface before its display");
+    drag_cancel(base);
     cancel_pastes(d, NULL);
     if (d->loop && d->watch > 0) yasl_loop_del_fd(d->loop, d->watch);
     if (d->owns_loop && d->loop) {
@@ -868,7 +891,8 @@ static void display_close(struct yasl_display *base)
 
 static uint32_t caps(const struct yasl_display *d)
 {
-    return YASL_CAP_PLACE_WINDOW | YASL_CAP_PRIMARY_SELECTION |
+    return YASL_CAP_DRAG | YASL_CAP_DRAG_CARRY | YASL_CAP_PLACE_WINDOW |
+        YASL_CAP_PRIMARY_SELECTION |
         (((const struct x11_display *)d)->xi2 ? YASL_CAP_TABLET : 0);
 }
 
@@ -984,6 +1008,49 @@ static bool place(struct yasl_surface *base, struct yasl_vector2i at)
     return true;
 }
 
+static void drag_end(struct x11_display *d, enum yasl_drag_end how)
+{
+    if (!d || !d->drag.active) return;
+    struct yasl_drag_listener l = d->drag.listener;
+    void *ud = d->drag.ud;
+    d->drag.active = false;
+    d->drag.origin = NULL;
+    d->drag.carried = NULL;
+    if (l.end)
+        l.end(ud, how);
+}
+
+static bool drag_start(struct yasl_display *base, struct yasl_surface *origin,
+                       const struct yasl_drag_image *image,
+                       const struct yasl_drag_listener *l, void *ud)
+{
+    (void)image;
+    struct x11_display *d = (struct x11_display *)base;
+    if (!d || !origin || d->drag.active || !l)
+        return false;
+    d->drag.active = true;
+    d->drag.origin = (struct x11_surface *)origin;
+    d->drag.carried = NULL;
+    d->drag.listener = *l;
+    d->drag.ud = ud;
+    return true;
+}
+
+static void drag_cancel(struct yasl_display *base)
+{
+    drag_end((struct x11_display *)base, YASL_DRAG_CANCELLED);
+}
+
+static bool drag_carry(struct yasl_surface *base, struct yasl_vector2i offset)
+{
+    struct x11_display *d = display_of(base);
+    if (!d || !d->drag.active)
+        return false;
+    d->drag.carried = (struct x11_surface *)base;
+    d->drag.carry_offset = offset;
+    return place(base, offset);
+}
+
 static bool interactive_move(struct yasl_surface *base)
 {
     struct x11_surface *s = (struct x11_surface *)base;
@@ -1008,6 +1075,8 @@ const struct yasl_backend_ops yasl_x11_backend = {
     .display_modifiers = mods,
     .display_copy = copy,
     .display_paste = paste,
+    .display_drag_start = drag_start,
+    .display_drag_cancel = drag_cancel,
     .surface_create_toplevel = create_toplevel,
     .surface_destroy = surface_destroy,
     .surface_display = surface_display,
@@ -1021,6 +1090,7 @@ const struct yasl_backend_ops yasl_x11_backend = {
     .surface_timing = timing,
     .surface_frame_time_ns = frame_time,
     .surface_set_cursor = cursor,
+    .surface_drag_carry = drag_carry,
     .surface_place_under_pointer = place,
     .surface_start_interactive_move = interactive_move,
     .display_get_native_handle = native_display,