2 files changed, 25 insertions, 0 deletions
diff --git a/src/common/backend.c b/src/common/backend.c
index b15233f..bb5ae33 100644
--- a/src/common/backend.c
+++ b/src/common/backend.c
@@ -322,6 +322,15 @@ bool yasl_surface_poll_event(struct yasl_surface *s, struct yasl_event *ev)
     return input_queue_pop(&s->input, ev);
 }
 
+bool yasl_surface_read_pixels(struct yasl_surface *s, uint32_t *out, size_t cap,
+                              struct yasl_vector2i *size)
+{
+    if (!size) return false;
+    *size = (struct yasl_vector2i){0};
+    if (!s || (!out && cap) || !s->display->ops->surface_read_pixels) return false;
+    return s->display->ops->surface_read_pixels(s, out, cap, size);
+}
+
 bool yasl_surface_set_pointer_mode(struct yasl_surface *s, enum yasl_pointer_mode mode)
 {
     if (!s || (mode != YASL_POINTER_NORMAL && mode != YASL_POINTER_RELATIVE))
diff --git a/src/common/backend.h b/src/common/backend.h
index 96ce9e7..13ce9b5 100644
--- a/src/common/backend.h
+++ b/src/common/backend.h
@@ -7,6 +7,8 @@
 #include "common/input.h"
 #include "common/timing.h"
 
+#include <string.h>
+
 struct yasl_backend_ops;
 
 struct yasl_display {
@@ -43,6 +45,17 @@ void yasl_surface_clear_timers(struct yasl_surface *s);
 struct yasl_surface *yasl_create_toplevel(struct yasl_display *d,
         const struct yasl_window_spec *spec, void *graphics_device);
 
+/* Report a presented CPU frame's extent, and copy it when out can hold it. */
+static inline bool yasl_copy_frame(const uint32_t *pixels, struct yasl_vector2i extent,
+        uint32_t *out, size_t cap, struct yasl_vector2i *size)
+{
+    *size = extent;
+    size_t count = (size_t)extent.x * (size_t)extent.y;
+    if (!count || count > cap) return false;
+    memcpy(out, pixels, count * sizeof(*pixels));
+    return true;
+}
+
 static inline uint64_t yasl_frame_begin(struct yasl_surface *s)
 {
     if (++s->frame_generation == 0) ++s->frame_generation;
@@ -95,6 +108,9 @@ struct yasl_backend_ops {
     bool (*surface_place_under_pointer)(struct yasl_surface *s, struct yasl_vector2i at);
     /* Optional; NULL means the bell is unsupported. */
     bool (*surface_bell)(struct yasl_surface *s);
+    /* Optional; NULL means no readback. Fills size only for an available frame. */
+    bool (*surface_read_pixels)(struct yasl_surface *s, uint32_t *out, size_t cap,
+            struct yasl_vector2i *size);
     void *(*display_get_native_handle)(struct yasl_display *d);
     void *(*surface_get_native_handle)(struct yasl_surface *s);
     bool (*surface_get_native_frame)(struct yasl_surface *s,