add invert cmd

doc/README.md

@@ -288,3 +288,7 @@ GVerb algorithm from SWH plugins.
  - drylevel (dB): -70..0, default 0
  - earlylevel (dB): -70..0, default 0
  - taillevel (dB): -70..0, default -17.5
+
+## `invert split index`
+
+> A utility plugin that inverts the signal, also (wrongly) known as a 180 degree phase shift.

examples/invert.scri

@@ -0,0 +1,3 @@
+load :0;
+invert 3 1;
+quicksave;

src/lang.zig

@@ -36,6 +36,7 @@ pub const CommandType = enum {
     ThruZero,
     Foverdrive,
     Gverb,
+    Invert,
 
     Noise,
     WildNoise,
@@ -201,6 +202,7 @@ pub const Lang = struct {
         _ = try self.keywords.put("thruzero", .ThruZero);
         _ = try self.keywords.put("foverdrive", .Foverdrive);
         _ = try self.keywords.put("gverb", .Gverb);
+        _ = try self.keywords.put("invert", .Invert);
 
         // custom implementations (not lv2)
         _ = try self.keywords.put("noise", .Noise);

src/printer.zig

@@ -30,6 +30,7 @@ pub fn printList(list: langs.CommandList, stream: var) !void {
             .ThruZero => "thruzero",
             .Foverdrive => "foverdrive",
             .Gverb => "gverb",
+            .Invert => "invert",
 
             .Noise => "noise",
             .WildNoise => "wildnoise",

src/runner.zig

@@ -344,6 +344,11 @@ pub const Runner = struct {
         try image.runPlugin("http://plugin.org.uk/swh-plugins/gverb", pos, params);
     }
 
+    fn invertCmd(self: *Runner, pos: Position, params: ParamList) !void {
+        var image = try self.getImage();
+        try image.runPlugin("http://plugin.org.uk/swh-plugins/inv", pos, params);
+    }
+
     fn runCommand(self: *Runner, cmd: *lang.Command) !void {
         var params = ParamList.init(self.allocator);
         defer params.deinit();
@@ -629,6 +634,11 @@ pub const Runner = struct {
                 try self.gverbCmd(pos, params);
             },
 
+            .Invert => {
+                const pos = try cmd.consumePosition();
+                try self.gverbCmd(pos, params);
+            },
+
             else => blk: {
                 std.debug.warn("Unsupported command: {}\n", .{cmd.command});
                 break :blk RunError.UnknownCommand;