cursor: make xcursor theme configurable

- add a new command to set the theme
- export the theme of the default seat through environment variables

doc/riverctl.1.scd

@@ -124,6 +124,12 @@ that tag 1 through 9 are visible.
 	- *outer_padding* _non-negative_integer_
 	- *view_padding* _non-negative_integer_
 
+*xcursor-theme* _theme_name_ [_size_]
+	Set the xcursor theme to _theme_name_ and optionally set the
+	_size_. The theme of the default seat determines the default
+	for XWayland and made available through the _XCURSOR_THEME_ and
+	_XCURSOR_SIZE_ environment variables.
+
 # EXAMPLES
 
 Bind bemenu-run to Super+P:

river/Cursor.zig

@@ -39,6 +39,8 @@ const CursorMode = enum {
     Resize,
 };
 
+const default_size = 24;
+
 seat: *Seat,
 wlr_cursor: *c.wlr_cursor,
 wlr_xcursor_manager: *c.wlr_xcursor_manager,
@@ -71,35 +73,14 @@ pub fn init(self: *Self, seat: *Seat) !void {
 
     // Creates a wlroots utility for tracking the cursor image shown on screen.
     self.wlr_cursor = c.wlr_cursor_create() orelse return error.OutOfMemory;
-
-    // Creates an xcursor manager, another wlroots utility which loads up
-    // Xcursor themes to source cursor images from and makes sure that cursor
-    // images are available at all scale factors on the screen (necessary for
-    // HiDPI support). We add a cursor theme at scale factor 1 to begin with.
-    self.wlr_xcursor_manager = c.wlr_xcursor_manager_create(null, 24) orelse return error.OutOfMemory;
     c.wlr_cursor_attach_output_layout(self.wlr_cursor, seat.input_manager.server.root.wlr_output_layout);
-    if (c.wlr_xcursor_manager_load(self.wlr_xcursor_manager, 1) == 0) {
-        if (build_options.xwayland) {
-            if (c.wlr_xcursor_manager_get_xcursor(
-                self.wlr_xcursor_manager,
-                "left_ptr",
-                1,
-            )) |wlr_xcursor| {
-                const image: *c.wlr_xcursor_image = wlr_xcursor.*.images[0];
-                c.wlr_xwayland_set_cursor(
-                    seat.input_manager.server.wlr_xwayland,
-                    image.buffer,
-                    image.width * 4,
-                    image.width,
-                    image.height,
-                    @intCast(i32, image.hotspot_x),
-                    @intCast(i32, image.hotspot_y),
-                );
-            }
-        }
-    } else {
-        log.err(.cursor, "failed to load an xcursor theme", .{});
-    }
+
+    // This is here so that self.wlr_xcursor_manager doesn't need to be an
+    // optional pointer. This isn't optimal as it does a needless allocation,
+    // but this is not a hot path.
+    self.wlr_xcursor_manager = c.wlr_xcursor_manager_create(null, default_size) orelse
+        return error.OutOfMemory;
+    try self.setTheme(null, null);
 
     self.mode = CursorMode.Passthrough;
     self.grabbed_view = undefined;
@@ -136,6 +117,49 @@ pub fn deinit(self: *Self) void {
     c.wlr_cursor_destroy(self.wlr_cursor);
 }
 
+/// Set the cursor theme for the given seat, as well as the xwayland theme if
+/// this is the default seat.
+pub fn setTheme(self: *Self, theme: ?[*:0]const u8, size: ?u32) !void {
+    const server = self.seat.input_manager.server;
+
+    c.wlr_xcursor_manager_destroy(self.wlr_xcursor_manager);
+    self.wlr_xcursor_manager = c.wlr_xcursor_manager_create(theme, size orelse default_size) orelse
+        return error.OutOfMemory;
+
+    // For each output, ensure a theme of the proper scale is loaded
+    var it = server.root.outputs.first;
+    while (it) |node| : (it = node.next) {
+        const wlr_output = node.data.wlr_output;
+        if (c.wlr_xcursor_manager_load(self.wlr_xcursor_manager, wlr_output.scale) != 0)
+            log.err(.cursor, "failed to load xcursor theme '{}' at scale {}", .{ theme, wlr_output.scale });
+    }
+
+    // If this cursor belongs to the default seat, set the xcursor environment
+    // variables and the xwayland cursor theme.
+    if (self.seat == self.seat.input_manager.default_seat) {
+        const size_str = try std.fmt.allocPrint0(util.gpa, "{}", .{size});
+        defer util.gpa.free(size_str);
+        if (c.setenv("XCURSOR_SIZE", size_str, 1) < 0) return error.OutOfMemory;
+        if (theme) |t| if (c.setenv("XCURSOR_THEME", t, 1) < 0) return error.OutOfMemory;
+
+        if (build_options.xwayland) {
+            if (c.wlr_xcursor_manager_load(self.wlr_xcursor_manager, 1) == 0) {
+                const wlr_xcursor = c.wlr_xcursor_manager_get_xcursor(self.wlr_xcursor_manager, "left_ptr", 1).?;
+                const image: *c.wlr_xcursor_image = wlr_xcursor.*.images[0];
+                c.wlr_xwayland_set_cursor(
+                    server.wlr_xwayland,
+                    image.buffer,
+                    image.width * 4,
+                    image.width,
+                    image.height,
+                    @intCast(i32, image.hotspot_x),
+                    @intCast(i32, image.hotspot_y),
+                );
+            } else log.err(.cursor, "failed to load xcursor theme '{}' at scale 1", .{theme});
+        }
+    }
+}
+
 fn handleAxis(listener: ?*c.wl_listener, data: ?*c_void) callconv(.C) void {
     // This event is forwarded by the cursor when a pointer emits an axis event,
     // for example when you move the scroll wheel.

river/command.zig

@@ -39,6 +39,7 @@ const impl = struct {
     const toggleFocusedTags = @import("command/tags.zig").toggleFocusedTags;
     const toggleFullscreen = @import("command/toggle_fullscreen.zig").toggleFullscreen;
     const toggleViewTags = @import("command/tags.zig").toggleViewTags;
+    const xcursorTheme = @import("command/xcursor_theme.zig").xcursorTheme;
     const zoom = @import("command/zoom.zig").zoom;
 };
 
@@ -79,9 +80,10 @@ const str_to_impl_fn = [_]struct {
     .{ .name = "spawn",               .impl = impl.spawn },
     .{ .name = "toggle-float",        .impl = impl.toggleFloat },
     .{ .name = "toggle-focused-tags", .impl = impl.toggleFocusedTags },
-    .{ .name = "toggle-view-tags",    .impl = impl.toggleViewTags },
-    .{ .name = "zoom",                .impl = impl.zoom },
     .{ .name = "toggle-fullscreen",   .impl = impl.toggleFullscreen },
+    .{ .name = "toggle-view-tags",    .impl = impl.toggleViewTags },
+    .{ .name = "xcursor-theme",       .impl = impl.xcursorTheme },
+    .{ .name = "zoom",                .impl = impl.zoom },
 };
 // zig fmt: on
 

river/command/xcursor_theme.zig

@@ -0,0 +1,38 @@
+// This file is part of river, a dynamic tiling wayland compositor.
+//
+// Copyright 2020 Isaac Freund
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+
+const Error = @import("../command.zig").Error;
+const Seat = @import("../Seat.zig");
+
+pub fn xcursorTheme(
+    allocator: *std.mem.Allocator,
+    seat: *Seat,
+    args: []const []const u8,
+    out: *?[]const u8,
+) Error!void {
+    if (args.len < 2) return Error.NotEnoughArguments;
+    if (args.len > 3) return Error.TooManyArguments;
+
+    // TODO: get rid of this allocation
+    const name = try std.cstr.addNullByte(allocator, args[1]);
+    defer allocator.free(name);
+    const size = if (args.len == 3) try std.fmt.parseInt(u32, args[2], 10) else null;
+
+    try seat.cursor.setTheme(name, size);
+}