add basic lilv instantiation support

src/image.zig

@@ -9,6 +9,7 @@ pub const ImageError = error{
     InvalidPlugin,
     UnknownPlugin,
     InvalidSymbol,
+    InstantiateFail,
 };
 
 /// Low level integration function with libsndfile.
@@ -68,14 +69,8 @@ fn temporaryName(allocator: *std.mem.Allocator) ![]u8 {
     return error.TempGenFail;
 }
 
-pub const Image = struct {
+fn mkSfInfo() c.SF_INFO {
-    allocator: *std.mem.Allocator,
+    return c.SF_INFO{
-    sndfile: *c.SNDFILE,
-    path: []const u8,
-
-    /// Open a BMP file.
-    pub fn open(allocator: *std.mem.Allocator, path: []const u8) !*Image {
-        var in_fmt = c.SF_INFO{
         .frames = c_int(0),
         .samplerate = c_int(44100),
         .channels = c_int(1),
@@ -83,6 +78,16 @@ pub const Image = struct {
         .sections = c_int(0),
         .seekable = c_int(0),
     };
+}
+
+pub const Image = struct {
+    allocator: *std.mem.Allocator,
+    sndfile: *c.SNDFILE,
+    path: []const u8,
+
+    /// Open a BMP file.
+    pub fn open(allocator: *std.mem.Allocator, path: []const u8) !*Image {
+        var in_fmt = mkSfInfo();
 
         var sndfile = try sopen(allocator, path, c.SFM_READ, &in_fmt);
         var image = try allocator.create(Image);
@@ -174,5 +179,12 @@ pub const Image = struct {
         // running the plugin on that file
         var tmpnam = try temporaryName(self.allocator);
         std.debug.warn("temporary name: {}\n", tmpnam);
+
+        var out_fmt = mkSfInfo();
+        var out_file = try sopen(self.allocator, tmpnam, c.SFM_WRITE, &out_fmt);
+
+        var rctx = try plugins.RunContext.init(self.allocator, ctx.plugin);
+        rctx.connectPorts(ports);
+        lv2.lilv_instance_activate(rctx.instance);
     }
 };

src/plugin.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 
-const c = @import("lv2_helpers.zig").c;
+const lv2 = @import("lv2_helpers.zig");
+const c = lv2.c;
 
 const ImageError = @import("image.zig").ImageError;
 
@@ -26,13 +27,59 @@ pub const Position = struct {
 pub const Context = struct {
     allocator: *std.mem.Allocator,
     world: *c.LilvWorld,
-    plugin: ?*const c.LilvPlugin,
+    plugin: *const c.LilvPlugin,
 
     // they should both be 1.
     n_audio_in: usize = 0,
     n_audio_out: usize = 0,
 };
 
+/// Represents the specific run context of plugin instantation.
+pub const RunContext = struct {
+    in_buf: []f32,
+    out_buf: []f32,
+    instance: *c.LilvInstance,
+
+    pub fn init(
+        allocator: *std.mem.Allocator,
+        plugin: *const c.LilvPlugin,
+    ) !RunContext {
+        var instance = c.lilv_plugin_instantiate(plugin, f64(44100), null);
+        if (instance == null) {
+            return ImageError.InstantiateFail;
+        }
+
+        return RunContext{
+            .in_buf = try allocator.alloc(f32, 1),
+            .out_buf = try allocator.alloc(f32, 1),
+            .instance = instance.?,
+        };
+    }
+
+    pub fn connectPorts(self: *RunContext, ports: []*lv2.Port) void {
+        var i: usize = 0;
+        var o: usize = 0;
+
+        for (ports) |port, p_idx| {
+            var p = @intCast(u32, p_idx);
+
+            switch (port.ptype) {
+                .Control => lv2.lilv_instance_connect_port(self.instance, p, &port.value),
+                .Audio => blk: {
+                    if (port.is_input) {
+                        lv2.lilv_instance_connect_port(self.instance, p, &self.in_buf[i]);
+                        i += 1;
+                    } else {
+                        lv2.lilv_instance_connect_port(self.instance, p, &self.out_buf[o]);
+                        o += 1;
+                    }
+                },
+                else => lv2.lilv_instance_connect_port(self.instance, p, null),
+            }
+        }
+    }
+};
+
 pub fn makeContext(allocator: *std.mem.Allocator, plugin_uri: []const u8) !Context {
     const cstr_plugin_uri = try std.cstr.addNullByte(allocator, plugin_uri);
     var world = c.lilv_world_new().?;

src/runner.zig

@@ -148,6 +148,9 @@ pub const Runner = struct {
         try params.append(plugin.Param{ .sym = "gain", .value = gain });
         defer params.deinit();
 
+        // TODO if we could detect that the next command is a quicksave then
+        // we don't need the temporary file in runPlugin and instead we
+        // dump it all on the output image for it.
         try image.runPlugin(
             "http://lv2plug.in/plugins/eg-amp",
             plugin.Position{ .split = split, .index = index },