From 97766ab3002ba108faf0a98b9eaea3393b14a887 Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <kvarkus@gmail.com>
Date: Mon, 2 Dec 2019 17:23:04 -0500
Subject: [PATCH] Get buffer sub data in wgpu-remote

---
 wgpu-core/src/device.rs   | 35 +++++++++++++++++++++++++++++++++++
 wgpu-remote/src/server.rs | 15 +++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/wgpu-core/src/device.rs b/wgpu-core/src/device.rs
index 017615204a..2169ffe037 100644
--- a/wgpu-core/src/device.rs
+++ b/wgpu-core/src/device.rs
@@ -902,6 +902,41 @@ impl<F: IdentityFilter<BufferId>> Global<F> {
         unmap_buffer(&device.raw, buffer);
     }
 
+    pub fn device_get_buffer_sub_data<B: GfxBackend>(
+        &self,
+        device_id: DeviceId,
+        buffer_id: BufferId,
+        offset: BufferAddress,
+        data: &mut [u8],
+    ) {
+        let hub = B::hub(self);
+        let mut token = Token::root();
+
+        let (device_guard, mut token) = hub.devices.read(&mut token);
+        let (mut buffer_guard, _) = hub.buffers.write(&mut token);
+        let device = &device_guard[device_id];
+        let mut buffer = &mut buffer_guard[buffer_id];
+        assert!(buffer.usage.contains(resource::BufferUsage::MAP_READ));
+        //assert!(buffer isn't used by the GPU);
+
+        match map_buffer(
+            &device.raw,
+            &mut buffer,
+            offset .. offset + data.len() as BufferAddress,
+            HostMap::Read,
+        ) {
+            Ok(ptr) => unsafe {
+                ptr::copy_nonoverlapping(ptr, data.as_mut_ptr(), data.len());
+            },
+            Err(e) => {
+                log::error!("failed to map a buffer: {:?}", e);
+                return;
+            }
+        }
+
+        unmap_buffer(&device.raw, buffer);
+    }
+
     pub fn buffer_destroy<B: GfxBackend>(&self, buffer_id: BufferId) {
         let hub = B::hub(self);
         let mut token = Token::root();
diff --git a/wgpu-remote/src/server.rs b/wgpu-remote/src/server.rs
index 572b3e9352..f8b7e8c545 100644
--- a/wgpu-remote/src/server.rs
+++ b/wgpu-remote/src/server.rs
@@ -79,3 +79,18 @@ pub extern "C" fn wgpu_server_device_set_buffer_sub_data(
     };
     gfx_select!(self_id => global.device_set_buffer_sub_data(self_id, buffer_id, offset, slice));
 }
+
+#[no_mangle]
+pub extern "C" fn wgpu_server_device_get_buffer_sub_data(
+    global: &Global<()>,
+    self_id: id::DeviceId,
+    buffer_id: id::BufferId,
+    offset: core::BufferAddress,
+    data: *mut u8,
+    size: core::BufferAddress,
+) {
+    let slice = unsafe {
+        slice::from_raw_parts_mut(data, size as usize)
+    };
+    gfx_select!(self_id => global.device_get_buffer_sub_data(self_id, buffer_id, offset, slice));
+}