add setting of parameters to the ports

- fix ampCmd's param pass

src/image.zig

@@ -1,12 +1,6 @@
 const std = @import("std");
 const lv2 = @import("lv2_helpers.zig");
-
-const c = @cImport({
-    @cInclude("sndfile.h");
-
-    @cInclude("lilv/lilv.h");
-    @cInclude("lv2/core/lv2.h");
-});
+const c = lv2.c;
 
 const plugins = @import("plugin.zig");
 
@@ -14,6 +8,7 @@ pub const ImageError = error{
     OpenFail,
     InvalidPlugin,
     UnknownPlugin,
+    InvalidSymbol,
 };
 
 /// Low level integration function with libsndfile.
@@ -103,13 +98,41 @@ pub const Image = struct {
         pos: plugins.Position,
         params: plugins.ParamList,
     ) !void {
-        var context = try plugins.makeContext(self.allocator, plugin_uri);
-        std.debug.warn("world: {}\n", context.world);
-        std.debug.warn("plugin: {}\n", context.plugin);
+        var ctx = try plugins.makeContext(self.allocator, plugin_uri);
+        std.debug.warn("\tworld: {}\n", ctx.world);
+        std.debug.warn("\tplugin: {}\n", ctx.plugin);
 
-        var ports = try lv2.setupPorts(&context);
-        for (ports) |port| {
-            std.debug.warn("port: {}\n", port.*);
+        var ports = try lv2.setupPorts(&ctx);
+
+        if (ctx.n_audio_in != 1) {
+            std.debug.warn("plugin <{}> does not accept mono input.\n", plugin_uri);
+            return ImageError.InvalidPlugin;
+        }
+
+        // now, for each param for the plugin, we find its port, and set
+        // the value for the port there.
+        var it = params.iterator();
+
+        while (it.next()) |param| {
+            var sym_cstr = try std.cstr.addNullByte(self.allocator, param.sym);
+            defer self.allocator.free(sym_cstr);
+
+            var sym = c.lilv_new_string(ctx.world, sym_cstr.ptr);
+            const port = c.lilv_plugin_get_port_by_symbol(ctx.plugin, sym) orelse blk: {
+                std.debug.warn("assert fail: symbol not found on port");
+                return ImageError.InvalidSymbol;
+            };
+
+            c.lilv_node_free(sym);
+
+            var idx = c.lilv_port_get_index(ctx.plugin, port);
+            std.debug.warn(
+                "sym={}, idx={} to val={}\n",
+                param.sym,
+                idx,
+                param.value,
+            );
+            ports[idx].value = param.value;
         }
     }
 };

src/lv2_helpers.zig

@@ -2,6 +2,7 @@ const std = @import("std");
 const plugin = @import("plugin.zig");
 
 pub const c = @cImport({
+    @cInclude("sndfile.h");
     @cInclude("lilv/lilv.h");
     @cInclude("lv2/core/lv2.h");
 });

src/runner.zig

@@ -143,12 +143,9 @@ pub const Runner = struct {
     /// Run the http://lv2plug.in/plugins/eg-amp plugin over the file.
     fn ampCmd(self: *Runner, split: usize, index: usize, gain: f32) !void {
         var image = try self.getImage();
-        var param = try self.allocator.create(plugin.Param);
-        defer self.allocator.destroy(param);
-
-        param.* = plugin.Param{ .sym = "gain", .value = gain };
 
         var params = plugin.ParamList.init(self.allocator);
+        try params.append(plugin.Param{ .sym = "gain", .value = gain });
         defer params.deinit();
 
         try image.runPlugin(