tearing-control-v1: implement

Implement the wp-tearing-control-v1 protocol allowing window to hint
the compositor that they prefer async "tearing" page flips.

Add tearing/no-tearing rules to allow the user to manually
enabled/disable tearing for a window.

Use async "tearing" page flips when a window that should be allowed to
tear is fullscreen.

This still requires several kernel patches to work with the wlroots
atomic DRM backend. For now, either set WLR_DRM_NO_ATOMIC=1 or use a
custom kernel that includes the unmerged patches (such as CachyOS).

Closes: https://codeberg.org/river/river/issues/1094

build.zig

@@ -94,6 +94,7 @@ pub fn build(b: *Build) !void {
     scanner.addSystemProtocol("stable/xdg-shell/xdg-shell.xml");
     scanner.addSystemProtocol("staging/cursor-shape/cursor-shape-v1.xml");
     scanner.addSystemProtocol("staging/ext-session-lock/ext-session-lock-v1.xml");
+    scanner.addSystemProtocol("staging/tearing-control/tearing-control-v1.xml");
     scanner.addSystemProtocol("unstable/pointer-constraints/pointer-constraints-unstable-v1.xml");
     scanner.addSystemProtocol("unstable/pointer-gestures/pointer-gestures-unstable-v1.xml");
     scanner.addSystemProtocol("unstable/tablet/tablet-unstable-v2.xml");
@@ -124,6 +125,7 @@ pub fn build(b: *Build) !void {
     scanner.generate("zxdg_decoration_manager_v1", 1);
     scanner.generate("ext_session_lock_manager_v1", 1);
     scanner.generate("wp_cursor_shape_manager_v1", 1);
+    scanner.generate("wp_tearing_control_manager_v1", 1);
 
     scanner.generate("zriver_control_v1", 1);
     scanner.generate("zriver_status_manager_v1", 4);

build.zig.zon

@@ -12,8 +12,8 @@
             .hash = "1220687c8c47a48ba285d26a05600f8700d37fc637e223ced3aa8324f3650bf52242",
         },
         .@"zig-wlroots" = .{
-            .url = "https://codeberg.org/ifreund/zig-wlroots/archive/ae6151f22ceb4ccd7efb1291dea573785918a7ec.tar.gz",
-            .hash = "12204d99aebfbf88f1ff3ab197362937b3d4bef4f45fde9c4ee0d569e095a2a25889",
+            .url = "https://codeberg.org/ifreund/zig-wlroots/archive/e486223799648d27e8b91c5fe0ea4c088b74b707.tar.gz",
+            .hash = "1220aeb3317e16c38583839961c9d695fa60d23a3d506c8275fb0e8fa9849844f2f7",
         },
         .@"zig-xkbcommon" = .{
             .url = "https://codeberg.org/ifreund/zig-xkbcommon/archive/v0.2.0.tar.gz",

doc/riverctl.1.scd

@@ -307,11 +307,17 @@ matches everything while _\*\*_ and the empty string are invalid.
 	- *fullscreen*: Make the view fullscreen. Applies only to new views.
 	- *no-fullscreen*: Don't make the view fullscreen. Applies only to
 	  new views.
+	- *tearing*: Enable tearing for view when fullscreen regardless of the
+	  supplied tearing hint. Note that tearing additionally requires setting the
+	  *allow-tearing* server option. Applies to new and existing views.
+	- *no-tearing*: Disable tearing for view regardless of the supplied
+	  tearing hint. Applies to new and existing views.
 
 	Both *float* and *no-float* rules are added to the same list,
 	which means that adding a *no-float* rule with the same arguments
 	as a *float* rule will overwrite it. The same holds for *ssd* and
-	*csd*, *fullscreen* and *no-fullscreen* rules.
+	*csd*, *fullscreen* and *no-fullscreen*, *tearing* and
+	*no-tearing* rules.
 
 	If multiple rules in a list match a given view the most specific
 	rule will be applied. For example with the following rules
@@ -364,6 +370,9 @@ matches everything while _\*\*_ and the empty string are invalid.
 	Set the attach mode of the currently focused output, overriding the value of
 	default-attach-mode if any.
 
+*allow-tearing* *enabled*|*disabled*
+	Allow windows to tear if requested by either the program or the user.
+
 *background-color* _0xRRGGBB_|_0xRRGGBBAA_
 	Set the background color.
 

river/Config.zig

@@ -31,6 +31,11 @@ const Mode = @import("Mode.zig");
 const RuleList = @import("rule_list.zig").RuleList;
 const View = @import("View.zig");
 
+pub const AllowTearing = enum {
+    disabled,
+    enabled,
+};
+
 pub const AttachMode = union(enum) {
     top,
     bottom,
@@ -68,6 +73,9 @@ pub const Dimensions = struct {
     height: u31,
 };
 
+/// Whether to allow tearing page flips if a view requests it.
+allow_tearing: AllowTearing = .disabled,
+
 /// Color of background in RGBA with premultiplied alpha (alpha should only affect nested sessions)
 background_color: [4]f32 = [_]f32{ 0.0, 0.16862745, 0.21176471, 1.0 }, // Solarized base03
 
@@ -98,6 +106,7 @@ rules: struct {
     position: RuleList(Position) = .{},
     dimensions: RuleList(Dimensions) = .{},
     fullscreen: RuleList(bool) = .{},
+    tearing: RuleList(bool) = .{},
 } = .{},
 
 /// The selected focus_follows_cursor mode

river/Output.zig

@@ -538,10 +538,12 @@ fn handleFrame(listener: *wl.Listener(*wlr.Output), _: *wlr.Output) void {
 }
 
 fn renderAndCommit(output: *Output, scene_output: *wlr.SceneOutput) !void {
-    if (output.gamma_dirty) {
     var state = wlr.Output.State.init();
     defer state.finish();
 
+    if (!scene_output.buildState(&state, null)) return error.CommitFailed;
+
+    if (output.gamma_dirty) {
         const control = server.root.gamma_control_manager.getControl(output.wlr_output);
         if (!wlr.GammaControlV1.apply(control, &state)) return error.OutOfMemory;
 
@@ -553,15 +555,20 @@ fn renderAndCommit(output: *Output, scene_output: *wlr.SceneOutput) !void {
             // has a null LUT. The wayland backend for example has this behavior.
             state.committed.gamma_lut = false;
         }
+    }
 
-        if (!scene_output.buildState(&state, null)) return error.CommitFailed;
+    if (output.allowTearing() and server.config.allow_tearing == .enabled) {
+        state.tearing_page_flip = true;
+
+        if (!output.wlr_output.testState(&state)) {
+            log.debug("tearing page flip test failed for {s}, retrying without tearing", .{output.wlr_output.name});
+            state.tearing_page_flip = false;
+        }
+    }
 
     if (!output.wlr_output.commitState(&state)) return error.CommitFailed;
 
-        output.gamma_dirty = false;
-    } else {
-        if (!scene_output.commit(null)) return error.CommitFailed;
-    }
+    if (output.gamma_dirty) output.gamma_dirty = false;
 
     if (server.lock_manager.state == .locked or
         (server.lock_manager.state == .waiting_for_lock_surfaces and output.locked_content.node.enabled) or
@@ -635,6 +642,14 @@ fn setTitle(output: Output) void {
     }
 }
 
+fn allowTearing(output: *Output) bool {
+    if (output.current.fullscreen) |fullscreen_view| {
+        return fullscreen_view.allowTearing();
+    }
+
+    return false;
+}
+
 pub fn handleLayoutNamespaceChange(output: *Output) void {
     // The user changed the layout namespace of this output. Try to find a
     // matching layout.

river/Server.zig

@@ -84,6 +84,8 @@ screencopy_manager: *wlr.ScreencopyManagerV1,
 
 foreign_toplevel_manager: *wlr.ForeignToplevelManagerV1,
 
+tearing_control_manager: *wlr.TearingControlManagerV1,
+
 input_manager: InputManager,
 root: Root,
 config: Config,
@@ -159,6 +161,8 @@ pub fn init(server: *Server, runtime_xwayland: bool) !void {
 
         .foreign_toplevel_manager = try wlr.ForeignToplevelManagerV1.create(wl_server),
 
+        .tearing_control_manager = try wlr.TearingControlManagerV1.create(wl_server, 1),
+
         .config = try Config.init(),
 
         .root = undefined,

river/View.zig

@@ -23,6 +23,7 @@ const math = std.math;
 const posix = std.posix;
 const wlr = @import("wlroots");
 const wl = @import("wayland").server.wl;
+const wp = @import("wayland").server.wp;
 
 const server = &@import("main.zig").server;
 const util = @import("util.zig");
@@ -59,6 +60,12 @@ const AttachRelativeMode = enum {
     below,
 };
 
+const TearingMode = enum {
+    override_false,
+    override_true,
+    window_hint,
+};
+
 pub const State = struct {
     /// The output the view is currently assigned to.
     /// May be null if there are no outputs or for newly created views.
@@ -177,6 +184,9 @@ foreign_toplevel_handle: ForeignToplevelHandle = .{},
 /// Connector name of the output this view occupied before an evacuation.
 output_before_evac: ?[]const u8 = null,
 
+// Current tearing mode of the view. Defaults to using the window tearing hint.
+tearing_mode: TearingMode = .window_hint,
+
 pub fn create(impl: Impl) error{OutOfMemory}!*View {
     assert(impl != .none);
 
@@ -572,6 +582,17 @@ pub fn getAppId(view: View) ?[*:0]const u8 {
     };
 }
 
+/// Return true if the view can currently tear.
+pub fn allowTearing(view: *View) bool {
+    switch (view.tearing_mode) {
+        TearingMode.override_false => return false,
+        TearingMode.override_true => return true,
+        TearingMode.window_hint => if (view.rootSurface()) |root_surface| {
+            return server.tearing_control_manager.hintFromSurface(root_surface) == .@"async";
+        } else return false,
+    }
+}
+
 /// Clamp the width/height of the box to the constraints of the view
 pub fn applyConstraints(view: *View, box: *wlr.Box) void {
     box.width = math.clamp(box.width, view.constraints.min_width, view.constraints.max_width);
@@ -640,6 +661,10 @@ pub fn map(view: *View) !void {
         view.pending.ssd = ssd;
     }
 
+    if (server.config.rules.tearing.match(view)) |tearing| {
+        view.tearing_mode = if (tearing) .override_true else .override_false;
+    }
+
     if (server.config.rules.dimensions.match(view)) |dimensions| {
         view.pending.box.width = dimensions.width;
         view.pending.box.height = dimensions.height;

river/command.zig

@@ -41,6 +41,7 @@ const command_impls = std.StaticStringMap(
 ).initComptime(
     .{
         // zig fmt: off
+        .{ "allow-tearing",             @import("command/config.zig").allowTearing },
         .{ "attach-mode",               @import("command/attach_mode.zig").defaultAttachMode },
         .{ "background-color",          @import("command/config.zig").backgroundColor },
         .{ "border-color-focused",      @import("command/config.zig").borderColorFocused },

river/command/config.zig

@@ -24,6 +24,17 @@ const Error = @import("../command.zig").Error;
 const Seat = @import("../Seat.zig");
 const Config = @import("../Config.zig");
 
+pub fn allowTearing(
+    _: *Seat,
+    args: []const [:0]const u8,
+    _: *?[]const u8,
+) Error!void {
+    if (args.len < 2) return Error.NotEnoughArguments;
+    if (args.len > 2) return Error.TooManyArguments;
+    server.config.allow_tearing = std.meta.stringToEnum(Config.AllowTearing, args[1]) orelse
+        return Error.UnknownOption;
+}
+
 pub fn borderWidth(
     _: *Seat,
     args: []const [:0]const u8,

river/command/rule.zig

@@ -38,6 +38,8 @@ const Action = enum {
     dimensions,
     fullscreen,
     @"no-fullscreen",
+    tearing,
+    @"no-tearing",
 };
 
 pub fn ruleAdd(_: *Seat, args: []const [:0]const u8, _: *?[]const u8) Error!void {
@@ -53,7 +55,7 @@ pub fn ruleAdd(_: *Seat, args: []const [:0]const u8, _: *?[]const u8) Error!void
     const action = std.meta.stringToEnum(Action, result.args[0]) orelse return Error.UnknownOption;
 
     const positional_arguments_count: u8 = switch (action) {
-        .float, .@"no-float", .ssd, .csd, .fullscreen, .@"no-fullscreen" => 1,
+        .float, .@"no-float", .ssd, .csd, .fullscreen, .@"no-fullscreen", .tearing, .@"no-tearing" => 1,
         .tags, .output => 2,
         .position, .dimensions => 3,
     };
@@ -83,6 +85,14 @@ pub fn ruleAdd(_: *Seat, args: []const [:0]const u8, _: *?[]const u8) Error!void
             apply_ssd_rules();
             server.root.applyPending();
         },
+        .tearing, .@"no-tearing" => {
+            try server.config.rules.tearing.add(.{
+                .app_id_glob = app_id_glob,
+                .title_glob = title_glob,
+                .value = (action == .tearing),
+            });
+            apply_tearing_rules();
+        },
         .tags => {
             const tags = try fmt.parseInt(u32, result.args[1], 10);
             try server.config.rules.tags.add(.{
@@ -177,6 +187,10 @@ pub fn ruleDel(_: *Seat, args: []const [:0]const u8, _: *?[]const u8) Error!void
         .fullscreen, .@"no-fullscreen" => {
             _ = server.config.rules.fullscreen.del(rule);
         },
+        .tearing, .@"no-tearing" => {
+            _ = server.config.rules.tearing.del(rule);
+            apply_tearing_rules();
+        },
     }
 }
 
@@ -191,6 +205,17 @@ fn apply_ssd_rules() void {
     }
 }
 
+fn apply_tearing_rules() void {
+    var it = server.root.views.iterator(.forward);
+    while (it.next()) |view| {
+        if (view.destroying) continue;
+
+        if (server.config.rules.tearing.match(view)) |tearing| {
+            view.tearing_mode = if (tearing) .override_true else .override_false;
+        }
+    }
+}
+
 pub fn listRules(_: *Seat, args: []const [:0]const u8, out: *?[]const u8) Error!void {
     if (args.len < 2) return error.NotEnoughArguments;
     if (args.len > 2) return error.TooManyArguments;
@@ -203,6 +228,7 @@ pub fn listRules(_: *Seat, args: []const [:0]const u8, out: *?[]const u8) Error!
         position,
         dimensions,
         fullscreen,
+        tearing,
     }, args[1]) orelse return Error.UnknownOption;
     const max_glob_len = switch (rule_list) {
         inline else => |list| @field(server.config.rules, @tagName(list)).getMaxGlobLen(),
@@ -218,12 +244,13 @@ pub fn listRules(_: *Seat, args: []const [:0]const u8, out: *?[]const u8) Error!
     try writer.writeAll("action\n");
 
     switch (rule_list) {
-        inline .float, .ssd, .output, .fullscreen => |list| {
+        inline .float, .ssd, .output, .fullscreen, .tearing => |list| {
             const rules = switch (list) {
                 .float => server.config.rules.float.rules.items,
                 .ssd => server.config.rules.ssd.rules.items,
                 .output => server.config.rules.output.rules.items,
                 .fullscreen => server.config.rules.fullscreen.rules.items,
+                .tearing => server.config.rules.tearing.rules.items,
                 else => unreachable,
             };
             for (rules) |rule| {
@@ -234,6 +261,7 @@ pub fn listRules(_: *Seat, args: []const [:0]const u8, out: *?[]const u8) Error!
                     .ssd => if (rule.value) "ssd" else "csd",
                     .output => rule.value,
                     .fullscreen => if (rule.value) "fullscreen" else "no-fullscreen",
+                    .tearing => if (rule.value) "tearing" else "no-tearing",
                     else => unreachable,
                 }});
             }