cursor: make xcursor theme configurable

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

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);
+}