1 files changed, 52 insertions, 0 deletions

diff --git a/tests/common/test_backends.c b/tests/common/test_backends.c
index 74860c8..30f9b67 100644
--- a/tests/common/test_backends.c
+++ b/tests/common/test_backends.c
@@ -112,6 +112,15 @@ static void configure(struct yasl_surface *s, struct yasl_geometry geometry, voi
     if (w->destroy_on_configure) { yasl_surface_destroy(s); w->surface = NULL; }
 }
 
+static void draw_without_present(struct yasl_surface *s, struct yasl_frame *frame, void *ud)
+{
+    (void)s;
+    struct window *w = ud;
+    size_t count = (size_t)frame->target.size.x * (size_t)frame->target.size.y;
+    for (size_t i = 0; i < count; i++) frame->target.pixels[i] = 0xff000000;
+    w->draws++;
+}
+
 static void close_window(struct yasl_surface *s, void *ud)
 {
     struct window *w = ud;
@@ -146,6 +155,48 @@ static struct window create(struct yasl_display *d)
     return (struct window){.surface = s, .display = d};
 }
 
+/* The last presented frame reads back until a later draw replaces it. */
+static void test_read_pixels(struct yasl_loop *loop, struct yasl_display *d, struct window *w)
+{
+    struct yasl_vector2i size = {-1, -1};
+    assert(!yasl_surface_read_pixels(w->surface, NULL, 0, NULL));
+    assert(!yasl_surface_read_pixels(NULL, NULL, 0, &size) && !size.x && !size.y);
+    assert(!yasl_surface_read_pixels(w->surface, NULL, 0, &size));
+    struct yasl_vector2i extent = yasl_surface_geometry(w->surface).size;
+    assert(size.x == extent.x && size.y == extent.y);
+    size_t count = (size_t)size.x * (size_t)size.y;
+    uint32_t *pixels = calloc(count, sizeof(*pixels));
+    assert(pixels);
+    assert(!yasl_surface_read_pixels(w->surface, pixels, count - 1, &size));
+    assert(!pixels[0]);
+    assert(yasl_surface_read_pixels(w->surface, pixels, count, &size));
+    for (size_t i = 0; i < count; i++) assert(pixels[i] == 0xff4080c0);
+
+    /* Draws that never present must not show through. X11 reuses its one
+     * target; Wayland keeps the presented buffer while the compositor holds it. */
+    struct yasl_window_cbs skip = callbacks;
+    skip.draw = draw_without_present;
+    yasl_surface_set_callbacks(w->surface, &skip, w);
+    for (int i = 0; i < 4; i++) {
+        yasl_surface_schedule_redraw(w->surface);
+        pump(loop, d, NULL);
+        if (yasl_surface_read_pixels(w->surface, pixels, count, &size)) {
+            assert(yasl_display_backend(d) != YASL_BACKEND_X11);
+            for (size_t j = 0; j < count; j++) assert(pixels[j] == 0xff4080c0);
+        } else {
+            assert(!size.x && !size.y);
+        }
+    }
+
+    attach(w);
+    yasl_surface_schedule_redraw(w->surface);
+    pump(loop, d, NULL);
+    memset(pixels, 0, count * sizeof(*pixels));
+    assert(yasl_surface_read_pixels(w->surface, pixels, count, &size));
+    assert(pixels[0] == 0xff4080c0 && pixels[count - 1] == 0xff4080c0);
+    free(pixels);
+}
+
 static void test_window_spec(struct yasl_loop *loop, struct yasl_display *d)
 {
     struct window w = {.display = d, .destroy_on_draw = true};
@@ -427,6 +478,7 @@ int main(int argc, char **argv)
         yasl_surface_schedule_redraw(w.surface);
         pump(loop, d, NULL);
         assert(w.draws > 0);
+        test_read_pixels(loop, d, &w);
         if (yasl_display_backend(d) == YASL_BACKEND_X11)
             x11_behavior(loop, d, &w);
         if (w.surface) yasl_surface_destroy(w.surface);