transactions: handle preemption take 2

This implementation is far simpler than c0d7e71 as it takes advantage of
wlroots's tracking of pending state.

Additionally, we now send frame done events if a view that we are
configuring commits with the wrong dimensions. This is necessary in
order to trigger a redraw for some clients as well as being a more
correct implementation of the protocol.

river/Root.zig

@@ -139,9 +139,9 @@ fn startTransaction(self: *Self) void {
                 view.configure();
                 self.pending_configures += 1;
 
-                // We save the current buffer, so we can send an early
-                // frame done event to give the client a head start on
-                // redrawing.
+                // Send a frame done that the client will commit a new frame
+                // with the dimensions we sent in the configure. Normally this
+                // event would be sent in the render function.
                 view.sendFrameDone();
             }
 
@@ -165,6 +165,10 @@ fn startTransaction(self: *Self) void {
             self.commitTransaction();
         }
     } else {
+        // No views need configures, clear the current timer in case we are
+        // interrupting another transaction and commit.
+        if (c.wl_event_source_timer_update(self.transaction_timer, 0) < 0)
+            Log.Error.log("error disarming timer", .{});
         self.commitTransaction();
     }
 }

river/View.zig

@@ -112,12 +112,10 @@ pub fn deinit(self: Self) void {
 }
 
 pub fn needsConfigure(self: Self) bool {
-    if (self.pending_box) |pending_box| {
-        return pending_box.width != self.current_box.width or
-            pending_box.height != self.current_box.height;
-    } else {
-        return false;
-    }
+    return switch (self.impl) {
+        .xdg_toplevel => |xdg_toplevel| xdg_toplevel.needsConfigure(),
+        .xwayland_view => |xwayland_view| xwayland_view.needsConfigure(),
+    };
 }
 
 pub fn configure(self: Self) void {
@@ -238,6 +236,8 @@ pub fn getTitle(self: Self) [*:0]const u8 {
 pub fn map(self: *Self) void {
     const root = self.output.root;
 
+    Log.Debug.log("View '{}' mapped", .{self.getTitle()});
+
     // Add the view to the stack of its output
     const node = @fieldParentPtr(ViewStack(Self).Node, "view", self);
     self.output.views.push(node);
@@ -260,6 +260,8 @@ pub fn map(self: *Self) void {
 pub fn unmap(self: *Self) void {
     const root = self.output.root;
 
+    Log.Debug.log("View '{}' unmapped", .{self.getTitle()});
+
     self.wlr_surface = null;
 
     // Inform all seats that the view has been unmapped so they can handle focus

river/VoidView.zig

@@ -23,6 +23,10 @@ const c = @import("c.zig");
 
 const Box = @import("Box.zig");
 
+pub fn needsConfigure(self: Self) bool {
+    unreachable;
+}
+
 pub fn configure(self: Self, pending_box: Box) void {
     unreachable;
 }

river/XdgToplevel.zig

@@ -63,6 +63,25 @@ pub fn init(self: *Self, view: *View, wlr_xdg_surface: *c.wlr_xdg_surface) void
     c.wl_signal_add(&self.wlr_xdg_surface.events.unmap, &self.listen_unmap);
 }
 
+/// Returns true if a configure must be sent to ensure the dimensions of the
+/// pending_box are applied.
+pub fn needsConfigure(self: Self) bool {
+    const pending_box = self.view.pending_box orelse return false;
+
+    const wlr_xdg_toplevel: *c.wlr_xdg_toplevel = @field(
+        self.wlr_xdg_surface,
+        c.wlr_xdg_surface_union,
+    ).toplevel;
+
+    // Checking server_pending is sufficient here since it will be either in
+    // sync with the current dimensions or be the dimensions sent with the
+    // most recent configure. In both cases server_pending has the values we
+    // want to check against.
+    return pending_box.width != wlr_xdg_toplevel.server_pending.width or
+        pending_box.height != wlr_xdg_toplevel.server_pending.height;
+}
+
+/// Send a configure event, applying the width/height of the pending box.
 pub fn configure(self: Self, pending_box: Box) void {
     self.view.pending_serial = c.wlr_xdg_toplevel_set_size(
         self.wlr_xdg_surface,
@@ -106,7 +125,7 @@ pub fn getTitle(self: Self) [*:0]const u8 {
         self.wlr_xdg_surface,
         c.wlr_xdg_surface_union,
     ).toplevel;
-    return wlr_xdg_toplevel.title;
+    return wlr_xdg_toplevel.title orelse "NULL";
 }
 
 /// Called when the xdg surface is destroyed
@@ -153,8 +172,6 @@ fn handleMap(listener: ?*c.wl_listener, data: ?*c_void) callconv(.C) void {
     const state = &wlr_xdg_toplevel.current;
     const app_id: [*:0]const u8 = if (wlr_xdg_toplevel.app_id) |id| id else "NULL";
 
-    Log.Debug.log("View with app_id '{}' mapped", .{app_id});
-
     for (root.server.config.float_filter.items) |filter_app_id| {
         // Make views with app_ids listed in the float filter float
         if (std.mem.eql(u8, std.mem.span(app_id), std.mem.span(filter_app_id))) {
@@ -194,6 +211,12 @@ fn handleCommit(listener: ?*c.wl_listener, data: ?*c_void) callconv(.C) void {
         if (s == self.wlr_xdg_surface.configure_serial) {
             view.output.root.notifyConfigured();
             view.pending_serial = null;
+        } else {
+            // If the view has not yet acked our configure, we need to send a
+            // frame done event so that they commit another buffer. These
+            // buffers won't be rendered since we are still rendering our
+            // stashed buffer from when the transaction started.
+            view.sendFrameDone();
         }
     }
 }

river/XwaylandView.zig

@@ -57,6 +57,12 @@ pub fn init(self: *Self, view: *View, wlr_xwayland_surface: *c.wlr_xwayland_surf
     c.wl_signal_add(&self.wlr_xwayland_surface.events.unmap, &self.listen_unmap);
 }
 
+/// Don't really care about efficiency with xwayland, we don't wait for them
+/// to ack anyways since they don't use serials.
+pub fn needsConfigure(self: Self) bool {
+    return true;
+}
+
 /// Tell the client to take a new size
 pub fn configure(self: Self, pending_box: Box) void {
     c.wlr_xwayland_surface_configure(