1 files changed, 43 insertions, 28 deletions

diff --git a/src/common/backend.c b/src/common/backend.c
index 939ec71..ad9e218 100644
--- a/src/common/backend.c
+++ b/src/common/backend.c
@@ -133,16 +133,21 @@ int yasl_private_display_double_click_ms(const struct yasl_private_display *d)
 
 bool yasl_private_display_drag_start(struct yasl_private_display *d, struct yasl_surface *origin, const struct yasl_private_drag_image *image, const struct yasl_private_drag_listener *l, void *ud)
 {
-    if (!d || !d->ops->display_drag_start)
-        return 0;
-    if (!origin || origin->display != d)
-        return false;
+    if (!d || !origin || origin->display != d) { errno = EINVAL; return false; }
+    if (!d->ops->display_drag_start) { errno = ENOTSUP; return false; }
     if (image && (!image->pixels || image->size.x <= 0 || image->size.y <= 0 ||
         image->size.x > 32767 || image->size.y > 32767 ||
-        (int64_t)image->size.x * image->size.y * 4 > INT32_MAX))
+        (int64_t)image->size.x * image->size.y * 4 > INT32_MAX ||
+        image->hotspot.x < 0 || image->hotspot.y < 0 ||
+        image->hotspot.x >= image->size.x || image->hotspot.y >= image->size.y)) {
+        errno = EINVAL;
         return false;
+    }
     const struct yasl_private_drag_listener empty = {0};
-    return d->ops->display_drag_start(d, origin, image, l ? l : &empty, ud);
+    errno = 0;
+    bool ok = d->ops->display_drag_start(d, origin, image, l ? l : &empty, ud);
+    if (!ok && !errno) errno = EIO;
+    return ok;
 }
 
 void yasl_private_display_drag_cancel(struct yasl_private_display *d)
@@ -326,13 +331,18 @@ bool yasl_private_surface_read_pixels(struct yasl_surface *s, uint32_t *out, siz
 
 bool yasl_private_surface_set_pointer_mode(struct yasl_surface *s, enum yasl_private_pointer_mode mode)
 {
-    if (!s || (mode != YASL_PRIVATE_POINTER_NORMAL && mode != YASL_PRIVATE_POINTER_RELATIVE))
+    if (!s || (mode != YASL_PRIVATE_POINTER_NORMAL && mode != YASL_PRIVATE_POINTER_RELATIVE)) {
+        errno = EINVAL;
         return false;
+    }
     if (mode == s->pointer_mode)
         return true;
     const struct yasl_private_backend_ops *ops = s->display ? s->display->ops : NULL;
-    if (!ops || !ops->surface_set_pointer_mode)
-        return mode == YASL_PRIVATE_POINTER_NORMAL;
+    if (!ops || !ops->surface_set_pointer_mode) {
+        if (mode == YASL_PRIVATE_POINTER_NORMAL) return true;
+        errno = ENOTSUP;
+        return false;
+    }
     if (!ops->surface_set_pointer_mode(s, mode))
         return false;
     s->pointer_mode = mode;
@@ -416,43 +426,48 @@ void yasl_private_surface_set_ime_caret(struct yasl_surface *s, struct yasl_priv
     s->display->ops->surface_set_ime_caret(s, caret);
 }
 
+/* Backend operations that may be missing: ENOTSUP when absent, EIO when a backend
+ * fails without saying why. */
+#define OPTIONAL_OP(s, op, ...)                                                          \
+    do {                                                                                 \
+        if (!(s)) { errno = EINVAL; return false; }                                      \
+        if (!(s)->display->ops->op) { errno = ENOTSUP; return false; }                   \
+        errno = 0;                                                                       \
+        bool ok_ = (s)->display->ops->op(__VA_ARGS__);                                   \
+        if (!ok_ && !errno) errno = EIO;                                                 \
+        return ok_;                                                                      \
+    } while (0)
+
 bool yasl_private_surface_start_interactive_move(struct yasl_surface *s)
 {
-    if (!s || !s->display->ops->surface_start_interactive_move)
-        return 0;
-    return s->display->ops->surface_start_interactive_move(s);
+    OPTIONAL_OP(s, surface_start_interactive_move, s);
 }
 
 bool yasl_private_surface_start_interactive_resize(struct yasl_surface *s, enum yasl_private_resize_edge edge)
 {
-    if (!s || !s->display->ops->surface_start_interactive_resize ||
-        (edge != YASL_PRIVATE_EDGE_TOP && edge != YASL_PRIVATE_EDGE_BOTTOM &&
-         edge != YASL_PRIVATE_EDGE_LEFT && edge != YASL_PRIVATE_EDGE_RIGHT &&
-         edge != YASL_PRIVATE_EDGE_TOP_LEFT && edge != YASL_PRIVATE_EDGE_TOP_RIGHT &&
-         edge != YASL_PRIVATE_EDGE_BOTTOM_LEFT && edge != YASL_PRIVATE_EDGE_BOTTOM_RIGHT))
-        return 0;
-    return s->display->ops->surface_start_interactive_resize(s, edge);
+    if (edge != YASL_PRIVATE_EDGE_TOP && edge != YASL_PRIVATE_EDGE_BOTTOM &&
+        edge != YASL_PRIVATE_EDGE_LEFT && edge != YASL_PRIVATE_EDGE_RIGHT &&
+        edge != YASL_PRIVATE_EDGE_TOP_LEFT && edge != YASL_PRIVATE_EDGE_TOP_RIGHT &&
+        edge != YASL_PRIVATE_EDGE_BOTTOM_LEFT && edge != YASL_PRIVATE_EDGE_BOTTOM_RIGHT) {
+        errno = EINVAL;
+        return false;
+    }
+    OPTIONAL_OP(s, surface_start_interactive_resize, s, edge);
 }
 
 bool yasl_private_surface_show_window_menu(struct yasl_surface *s, struct yasl_private_vector2i pos)
 {
-    if (!s || !s->display->ops->surface_show_window_menu)
-        return 0;
-    return s->display->ops->surface_show_window_menu(s, pos);
+    OPTIONAL_OP(s, surface_show_window_menu, s, pos);
 }
 
 bool yasl_private_surface_drag_carry(struct yasl_surface *s, struct yasl_private_vector2i offset)
 {
-    if (!s || !s->display->ops->surface_drag_carry)
-        return 0;
-    return s->display->ops->surface_drag_carry(s, offset);
+    OPTIONAL_OP(s, surface_drag_carry, s, offset);
 }
 
 bool yasl_private_surface_place_under_pointer(struct yasl_surface *s, struct yasl_private_vector2i at)
 {
-    if (!s || !s->display->ops->surface_place_under_pointer)
-        return 0;
-    return s->display->ops->surface_place_under_pointer(s, at);
+    OPTIONAL_OP(s, surface_place_under_pointer, s, at);
 }
 
 void yasl_private_surface_clear_timers(struct yasl_surface *s)