wayland: Add support for compositor protocol version < 4.

The current implementation of DamageBuffer uses wl_surface_damage_buffer, which
relies on the assumption that the compositor protocol version is at least 4. This CL adds a fallback to wl_surface_damage when the protocol version is less than 4.

Bug: 1039481
Change-Id: I20ba46e49fd08925e0f7df1af491c8e800f210e2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1999081
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Reviewed-by: Maksim Sisov <msisov@igalia.com>
Auto-Submit: Erik Chen <erikchen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731653}

ui/ozone/platform/wayland/host/wayland_buffer_manager_host.cc

@@ -283,14 +283,40 @@ class WaylandBufferManagerHost::Surface {
       pending_damage_region.set_size(buffer->size);
     DCHECK(!pending_damage_region.size().IsEmpty());
 
-    wl_surface_damage_buffer(window_->surface(), pending_damage_region.x(),
-                             pending_damage_region.y(),
-                             pending_damage_region.width(),
-                             pending_damage_region.height());
+    if (connection_->compositor_version() >=
+        WL_SURFACE_DAMAGE_BUFFER_SINCE_VERSION) {
+      // wl_surface_damage_buffer relies on compositor API version 4. See
+      // https://bit.ly/2u00lv6 for details.
+      // We don't need to apply any scaling because pending_damage_region is
+      // already in buffer coordinates.
+      wl_surface_damage_buffer(window_->surface(), pending_damage_region.x(),
+                               pending_damage_region.y(),
+                               pending_damage_region.width(),
+                               pending_damage_region.height());
+    } else {
+      // The calculation for damage region relies on two assumptions:
+      // 1) The buffer is always attached at surface location (0, 0)
+      // 2) The API wl_surface::set_buffer_transform is not used.
+      // It's possible to write logic that accounts for both cases above, but
+      // it's currently unnecessary.
+      //
+      // Note: The damage region may not be an integer multiple of scale. To
+      // keep the implementation simple, the x() and y() coordinates round down,
+      // and the width() and height() calculations always add an extra pixel.
+      int scale = window_->buffer_scale();
+      wl_surface_damage(window_->surface(), pending_damage_region.x() / scale,
+                        pending_damage_region.y() / scale,
+                        pending_damage_region.width() / scale + 1,
+                        pending_damage_region.height() / scale + 1);
+    }
   }
 
   void AttachBuffer(WaylandBuffer* buffer) {
     DCHECK(window_);
+
+    // The logic in DamageBuffer currently relies on attachment coordinates of
+    // (0, 0). If this changes, then the calculation in DamageBuffer will also
+    // need to be updated.
     wl_surface_attach(window_->surface(), buffer->wl_buffer.get(), 0, 0);
   }
 

ui/ozone/platform/wayland/host/wayland_connection.cc

@@ -281,6 +281,7 @@ void WaylandConnection::Global(void* data,
   if (!connection->compositor_ && strcmp(interface, "wl_compositor") == 0) {
     connection->compositor_ = wl::Bind<wl_compositor>(
         registry, name, std::min(version, kMaxCompositorVersion));
+    connection->compositor_version_ = version;
     if (!connection->compositor_)
       LOG(ERROR) << "Failed to bind to wl_compositor global";
   } else if (!connection->subcompositor_ &&

ui/ozone/platform/wayland/host/wayland_connection.h

@@ -52,6 +52,7 @@ class WaylandConnection : public PlatformEventSource,
 
   wl_display* display() const { return display_.get(); }
   wl_compositor* compositor() const { return compositor_.get(); }
+  uint32_t compositor_version() const { return compositor_version_; }
   wl_subcompositor* subcompositor() const { return subcompositor_.get(); }
   xdg_wm_base* shell() const { return shell_.get(); }
   zxdg_shell_v6* shell_v6() const { return shell_v6_.get(); }
@@ -177,6 +178,7 @@ class WaylandConnection : public PlatformEventSource,
   wl::Object<wl_display> display_;
   wl::Object<wl_registry> registry_;
   wl::Object<wl_compositor> compositor_;
+  uint32_t compositor_version_ = 0;
   wl::Object<wl_subcompositor> subcompositor_;
   wl::Object<wl_seat> seat_;
   wl::Object<xdg_wm_base> shell_;