fix: make glass preview visually diagnostic

tools/ferese-effects-probe/src/main.rs

@@ -111,6 +111,9 @@ struct ProbeState {
     layer_surface: Option<ZwlrLayerSurfaceV1>,
     effects: Option<FereseSurfaceEffectsV1>,
     buffer: Option<wl_buffer::WlBuffer>,
+    preview_backdrop_surface: Option<wl_surface::WlSurface>,
+    preview_backdrop_layer: Option<ZwlrLayerSurfaceV1>,
+    preview_backdrop_buffer: Option<wl_buffer::WlBuffer>,
     preview: bool,
     configured: bool,
     closed: bool,
@@ -168,6 +171,29 @@ impl ProbeState {
         effects.set_role(ferese_surface_effects_v1::Role::Panel);
 
         surface.commit();
+
+        if self.preview {
+            let backdrop_surface = compositor.create_surface(qh, ());
+            let backdrop_layer = layer_shell.get_layer_surface(
+                &backdrop_surface,
+                None,
+                zwlr_layer_shell_v1::Layer::Top,
+                "ferese-effects-preview-backdrop".to_owned(),
+                qh,
+                (),
+            );
+            backdrop_layer.set_anchor(
+                zwlr_layer_surface_v1::Anchor::Top | zwlr_layer_surface_v1::Anchor::Right,
+            );
+            backdrop_layer.set_margin(12, 12, 0, 0);
+            backdrop_layer.set_size(520, 260);
+            backdrop_layer.set_exclusive_zone(0);
+            backdrop_surface.commit();
+
+            self.preview_backdrop_surface = Some(backdrop_surface);
+            self.preview_backdrop_layer = Some(backdrop_layer);
+        }
+
         self.surface = Some(surface);
         self.layer_surface = Some(layer_surface);
         self.effects = Some(effects);
@@ -207,6 +233,48 @@ fn create_buffer(
     Ok(buffer)
 }
 
+fn create_preview_backdrop_buffer(
+    shm: &wl_shm::WlShm,
+    qh: &QueueHandle<ProbeState>,
+    width: u32,
+    height: u32,
+) -> Result<wl_buffer::WlBuffer, Box<dyn Error>> {
+    let stride = width * 4;
+    let size = stride * height;
+    let mut file = tempfile::tempfile()?;
+    file.set_len(u64::from(size))?;
+
+    for y in 0..height {
+        for x in 0..width {
+            let checker = (x / 11 + y / 11) % 2 == 0;
+            let stripe = (x / 53) % 3;
+            let pixel = match (checker, stripe) {
+                (true, 0) => [0xf0, 0xf0, 0xf0, 0xff],
+                (false, 0) => [0x08, 0x08, 0x08, 0xff],
+                (true, 1) => [0x30, 0xe8, 0x40, 0xff],
+                (false, 1) => [0x10, 0x18, 0x08, 0xff],
+                (true, _) => [0x30, 0x60, 0xf0, 0xff],
+                (false, _) => [0x18, 0x08, 0x20, 0xff],
+            };
+            file.write_all(&pixel)?;
+        }
+    }
+    file.seek(SeekFrom::Start(0))?;
+
+    let pool = shm.create_pool(file.as_fd(), size as i32, qh, ());
+    let buffer = pool.create_buffer(
+        0,
+        width as i32,
+        height as i32,
+        stride as i32,
+        wl_shm::Format::Argb8888,
+        qh,
+        (),
+    );
+    pool.destroy();
+    Ok(buffer)
+}
+
 impl Dispatch<wl_registry::WlRegistry, ()> for ProbeState {
     fn event(
         state: &mut Self,
@@ -255,6 +323,24 @@ impl Dispatch<ZwlrLayerSurfaceV1, ()> for ProbeState {
                 height,
             } => {
                 layer_surface.ack_configure(serial);
+
+                if state.preview_backdrop_layer.as_ref() == Some(layer_surface) {
+                    let width = if width == 0 { 520 } else { width };
+                    let height = if height == 0 { 260 } else { height };
+                    let surface = state
+                        .preview_backdrop_surface
+                        .clone()
+                        .expect("preview backdrop surface initialized");
+                    let shm = state.shm.as_ref().expect("shm initialized");
+                    let buffer = create_preview_backdrop_buffer(shm, qh, width, height)
+                        .expect("create preview backdrop buffer");
+                    surface.attach(Some(&buffer), 0, 0);
+                    surface.damage_buffer(0, 0, width as i32, height as i32);
+                    surface.commit();
+                    state.preview_backdrop_buffer = Some(buffer);
+                    return;
+                }
+
                 state.configure_count = state.configure_count.saturating_add(1);
                 state.width = if width == 0 { WIDTH } else { width };
                 state.height = if height == 0 { HEIGHT } else { height };