From a3d3f39fbd110c81bf833a08b0808eb067cf8ab3 Mon Sep 17 00:00:00 2001
From: Raph Levien <raph.levien@gmail.com>
Date: Mon, 18 Oct 2021 12:23:06 -0700
Subject: [PATCH] Wait on query results

This shouldn't be necessary, but was causing NOT_READY errors.
---
 piet-gpu-hal/src/vulkan.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/piet-gpu-hal/src/vulkan.rs b/piet-gpu-hal/src/vulkan.rs
index 5b0dfd6..e1d78f2 100644
--- a/piet-gpu-hal/src/vulkan.rs
+++ b/piet-gpu-hal/src/vulkan.rs
@@ -708,12 +708,16 @@ impl crate::backend::Device for VkDevice {
     unsafe fn fetch_query_pool(&self, pool: &Self::QueryPool) -> Result<Vec<f64>, Error> {
         let device = &self.device.device;
         let mut buf = vec![0u64; pool.n_queries as usize];
+        // It's unclear to me why WAIT is needed here, as the wait on the command buffer's
+        // fence should make the query available, but otherwise we get sporadic NOT_READY
+        // results (Windows 10, AMD 5700 XT).
+        let flags = vk::QueryResultFlags::TYPE_64 | vk::QueryResultFlags::WAIT;
         device.get_query_pool_results(
             pool.pool,
             0,
             pool.n_queries,
             &mut buf,
-            vk::QueryResultFlags::TYPE_64,
+            flags,
         )?;
         let ts0 = buf[0];
         let tsp = self.timestamp_period as f64 * 1e-9;