1 files changed, 96 insertions, 0 deletions
diff --git a/rust/crates/compositor/tests/offscreen_render.rs b/rust/crates/compositor/tests/offscreen_render.rs
new file mode 100755
index 00000000..a3c6df10
--- /dev/null
+++ b/rust/crates/compositor/tests/offscreen_render.rs
@@ -0,0 +1,96 @@
+#![cfg(not(target_arch = "wasm32"))]
+
+use compositor::{
+    CanvasClearDescriptor, Compositor, FrameDescriptor, FrameItemDescriptor, LayerDescriptor,
+    QuadTransformDescriptor,
+};
+use gpu::GpuContext;
+
+fn block_on<F: Future>(future: F) -> F::Output {
+    use std::sync::Arc;
+    use std::task::{Context, Poll, Wake, Waker};
+
+    struct ThreadWaker(std::thread::Thread);
+
+    impl Wake for ThreadWaker {
+        fn wake(self: Arc<Self>) {
+            self.0.unpark();
+        }
+    }
+
+    let waker = Waker::from(Arc::new(ThreadWaker(std::thread::current())));
+    let mut context = Context::from_waker(&waker);
+    let mut future = Box::pin(future);
+    loop {
+        match future.as_mut().poll(&mut context) {
+            Poll::Ready(output) => return output,
+            Poll::Pending => std::thread::park(),
+        }
+    }
+}
+
+#[test]
+fn renders_solid_layer_offscreen() {
+    let Some(context) = block_on(GpuContext::new()).ok() else {
+        eprintln!("skipping: no GPU adapter available");
+        return;
+    };
+    let mut compositor = Compositor::new(&context);
+
+    let width = 64;
+    let height = 64;
+    let red = [255u8, 0, 0, 255];
+    let pixels: Vec<u8> = red.repeat((width * height) as usize);
+    let texture = context.create_render_texture(width, height, "test-source");
+    context.queue().write_texture(
+        texture.as_image_copy(),
+        &pixels,
+        gpu::wgpu::TexelCopyBufferLayout {
+            offset: 0,
+            bytes_per_row: Some(width * 4),
+            rows_per_image: Some(height),
+        },
+        texture.size(),
+    );
+    compositor.upsert_texture("source".to_string(), texture);
+
+    let frame = FrameDescriptor {
+        width,
+        height,
+        clear: CanvasClearDescriptor {
+            color: [0.0, 0.0, 0.0, 1.0],
+        },
+        items: vec![FrameItemDescriptor::Layer(LayerDescriptor {
+            texture_id: "source".to_string(),
+            transform: QuadTransformDescriptor {
+                center_x: 32.0,
+                center_y: 32.0,
+                width: width as f32,
+                height: height as f32,
+                rotation_degrees: 0.0,
+                flip_x: false,
+                flip_y: false,
+            },
+            opacity: 1.0,
+            blend_mode: compositor::BlendMode::Normal,
+            effect_pass_groups: Vec::new(),
+            mask: None,
+        })],
+    };
+
+    let output = compositor
+        .render_frame_to_texture(&context, &frame)
+        .expect("render");
+    let rendered = block_on(context.read_texture(&output)).expect("readback");
+    assert_eq!(rendered.len(), (width * height * 4) as usize);
+
+    let red_count = rendered
+        .chunks_exact(4)
+        .filter(|px| px[0] > 200 && px[1] < 60 && px[2] < 60)
+        .count();
+    let total = (width * height) as usize;
+    assert!(
+        red_count * 100 / total > 90,
+        "expected mostly red frame, got {red_count}/{total} red pixels"
+    );
+}