6 files changed, 53 insertions, 0 deletions

diff --git a/src/platform/cocoa/window.m b/src/platform/cocoa/window.m
index 1efff59..2f9f8e5 100644
--- a/src/platform/cocoa/window.m
+++ b/src/platform/cocoa/window.m
@@ -89,6 +89,8 @@ struct cocoa_surface {
     struct yasl_frame frame;
     struct yasl_damage_list damage;
     bool did_present;
+    /* Extent of the frame in pixels, valid while did_present is set. */
+    struct yasl_vector2i shown_size;
     unsigned idle_frames;
     bool want_draw;
     bool frame_due;
@@ -1073,6 +1075,7 @@ bool cocoa_surface_present(struct cocoa_surface *w, const struct yasl_framebuffe
     }
     yasl_clock_presented(&w->clock, yasl_loop_now_ns(), false);
     w->did_present = true;
+    w->shown_size = w->size;
     return true;
 }
 
@@ -2198,6 +2201,17 @@ static bool impl_surface_place_under_pointer(struct yasl_surface *s, struct yasl
     return cocoa_surface_place_under_pointer((struct cocoa_surface *)s, at);
 }
 
+static bool impl_surface_read_pixels(struct yasl_surface *s, uint32_t *out, size_t cap,
+                                     struct yasl_vector2i *size)
+{
+    struct cocoa_surface *w = (struct cocoa_surface *)s;
+    /* did_present stays set from the last draw until the next one starts, and
+     * pixels are reallocated only when a draw starts. */
+    if (w->closed || w->rendering || !w->did_present || !w->software_queue || !w->pixels)
+        return false;
+    return yasl_copy_frame(w->pixels, w->shown_size, out, cap, size);
+}
+
 static bool impl_surface_bell(struct yasl_surface *s)
 {
     assert([NSThread isMainThread]);
@@ -2266,6 +2280,7 @@ const struct yasl_backend_ops yasl_cocoa_backend = {
     .surface_drag_carry = impl_surface_drag_carry,
     .surface_place_under_pointer = impl_surface_place_under_pointer,
     .surface_bell = impl_surface_bell,
+    .surface_read_pixels = impl_surface_read_pixels,
     .display_get_native_handle = impl_display_get_native_handle,
     .surface_get_native_handle = impl_surface_get_native_handle,
     .surface_get_native_frame = impl_surface_get_native_frame,
diff --git a/src/platform/wayland/api.h b/src/platform/wayland/api.h
index 6c3154c..9f290f5 100644
--- a/src/platform/wayland/api.h
+++ b/src/platform/wayland/api.h
@@ -39,5 +39,7 @@ bool wayland_surface_show_window_menu(struct wayland_surface *s, struct yasl_vec
 bool wayland_surface_drag_carry(struct wayland_surface *s, struct yasl_vector2i offset);
 bool wayland_surface_place_under_pointer(struct wayland_surface *s, struct yasl_vector2i at);
 bool wayland_surface_bell(struct wayland_surface *s);
+bool wayland_surface_read_pixels(struct wayland_surface *s, uint32_t *out, size_t cap,
+                                 struct yasl_vector2i *size);
 
 #endif
diff --git a/src/platform/wayland/backend.c b/src/platform/wayland/backend.c
index ad9ed4c..4585cd6 100644
--- a/src/platform/wayland/backend.c
+++ b/src/platform/wayland/backend.c
@@ -185,6 +185,12 @@ static bool impl_surface_place_under_pointer(struct yasl_surface *s, struct yasl
     return wayland_surface_place_under_pointer((struct wayland_surface *)s, at);
 }
 
+static bool impl_surface_read_pixels(struct yasl_surface *s, uint32_t *out, size_t cap,
+                                     struct yasl_vector2i *size)
+{
+    return wayland_surface_read_pixels((struct wayland_surface *)s, out, cap, size);
+}
+
 static bool impl_surface_bell(struct yasl_surface *s)
 {
     return wayland_surface_bell((struct wayland_surface *)s);
@@ -240,6 +246,7 @@ const struct yasl_backend_ops yasl_wayland_backend = {
     .surface_drag_carry = impl_surface_drag_carry,
     .surface_place_under_pointer = impl_surface_place_under_pointer,
     .surface_bell = impl_surface_bell,
+    .surface_read_pixels = impl_surface_read_pixels,
     .display_get_native_handle = impl_display_get_native_handle,
     .surface_get_native_handle = impl_surface_get_native_handle,
 };
diff --git a/src/platform/wayland/buffer.c b/src/platform/wayland/buffer.c
index f5a2c0f..b906f4f 100644
--- a/src/platform/wayland/buffer.c
+++ b/src/platform/wayland/buffer.c
@@ -472,9 +472,20 @@ bool wayland_surface_present(struct wayland_surface *w, const struct yasl_frameb
         return false;
     commit_buffer(w, w->cur);
     w->frame_presented = true;
+    w->shown = w->cur;
+    w->has_shown = true;
     return true;
 }
 
+bool wayland_surface_read_pixels(struct wayland_surface *w, uint32_t *out, size_t cap,
+                                 struct yasl_vector2i *size)
+{
+    if (!w || w->closed || w->frame_active || !w->has_shown) return false;
+    const struct buffer *b = &w->buffers[w->shown];
+    if (!b->pixels) return false;
+    return yasl_copy_frame(b->pixels, (struct yasl_vector2i){b->width, b->height}, out, cap, size);
+}
+
 void surface_draw_frame(struct wayland_surface *w)
 {
     if (w->closed || !w->configured)
@@ -491,6 +502,9 @@ void surface_draw_frame(struct wayland_surface *w)
         w->frames_skipped++;
         return;
     }
+    /* Drawing reuses the presented buffer only after the compositor released it. */
+    if (w->has_shown && idx == w->shown)
+        w->has_shown = false;
     if (buffer_prepare(w, &w->buffers[idx], w->width, w->height, &buffer_listener) < 0) {
         w->frames_skipped++;
         return;
diff --git a/src/platform/wayland/internal.h b/src/platform/wayland/internal.h
index 84a603d..34d4133 100644
--- a/src/platform/wayland/internal.h
+++ b/src/platform/wayland/internal.h
@@ -307,6 +307,8 @@ struct wayland_surface {
     int ime_shown_begin, ime_shown_end;
     int floating_width, floating_height;
     int cur;
+    /* Buffer holding the last presented frame, valid while has_shown is set. */
+    int shown;
     int width, height;
     int logical_width, logical_height;
     int req_width, req_height;
@@ -318,6 +320,7 @@ struct wayland_surface {
     /* 1-byte booleans packed tightly */
     bool frame_active;
     bool frame_presented;
+    bool has_shown;
     bool size_pending;
     bool sample_refresh;
     bool has_pending_serial;
diff --git a/src/platform/x11/window.c b/src/platform/x11/window.c
index 724987f..765d83c 100644
--- a/src/platform/x11/window.c
+++ b/src/platform/x11/window.c
@@ -473,6 +473,8 @@ static bool resize(struct x11_surface *s, struct yasl_vector2i size)
         return true;
     }
     uint64_t start = yasl_loop_now_ns();
+    /* The presented frame goes with the old pixels. */
+    s->presented = false;
 
     if (s->shm_active) {
         XShmDetach(d->native, &s->shm_info);
@@ -1883,6 +1885,15 @@ static int double_click_ms(const struct yasl_display *base)
     return portal_double_click_ms();
 }
 
+static bool read_pixels(struct yasl_surface *base, uint32_t *out, size_t cap,
+                        struct yasl_vector2i *size)
+{
+    struct x11_surface *s = (struct x11_surface *)base;
+    /* presented stays set from the last draw until the next one starts. */
+    if (s->destroyed || s->drawing || !s->presented || !s->pixels) return false;
+    return yasl_copy_frame(s->pixels, s->size, out, cap, size);
+}
+
 static bool bell(struct yasl_surface *base)
 {
     struct x11_surface *s = (struct x11_surface *)base;
@@ -2138,6 +2149,7 @@ const struct yasl_backend_ops yasl_x11_backend = {
     .surface_drag_carry = drag_carry,
     .surface_place_under_pointer = place,
     .surface_bell = bell,
+    .surface_read_pixels = read_pixels,
     .display_double_click_ms = double_click_ms,
     .surface_start_interactive_move = interactive_move,
     .surface_start_interactive_resize = interactive_resize,