zig api: (WIP) add a Zig API/bindings for libremidi, also add the possibility to build using the Zig Build System

This commit adds Zig bindings for libremidi and implements a subset
of the build logic in Zig's build system.

At this point, I'm satisfied with the API I landed on for the bindings,
now awaiting feedback!

Work still needed on build logic.

Author: lelahx

.gitignore

@@ -93,3 +93,6 @@ build
 
 .vscode
 
+# Zig related
+.zig-cache
+zig-out

bindings/zig/examples/zig_api.zig

@@ -0,0 +1,108 @@
+const std = @import("std");
+const lm = @import("libremidi");
+
+
+const EnumeratedPorts = extern struct {
+    in_ports: [256]lm.midi.in.port.Handle = .{ lm.midi.in.port.Handle{} } ** 256,
+    out_ports: [256]lm.midi.out.port.Handle = .{ lm.midi.out.port.Handle{} } ** 256,
+    in_port_count: usize = 0,
+    out_port_count: usize = 0,
+};
+
+pub fn main() !void {
+
+    std.debug.print("Hello from midi Zig(ified) API example!\n", .{});
+    std.debug.print("libremidi version: {s}\n\n", .{ lm.getVersion() });
+
+    var e: EnumeratedPorts = .{};
+
+    const observer: lm.observer.Handle = try .init(&.{
+        .track_hardware = true,
+        .track_virtual = true,
+        .track_any = true,
+        .input_added = .{
+            .context = &e,
+            .callback = on_input_port_found,
+        },
+        .output_added = .{
+            .context = &e,
+            .callback = on_output_port_found,
+        },
+    }, &.{
+        .conf_type = .observer,
+        .api = .alsa_seq,
+    });
+    defer free_observer(observer, &e);
+
+    try enumerate_ports(observer, &e);
+
+    const midi_in: lm.midi.in.Handle = try .init(&.{
+        .version = .midi1,
+        .port = .{ .input = e.in_ports[0] },
+        .msg_callback = .{ .on_midi1_message = .{ .callback = on_midi1_message } },
+    }, &.{
+        .conf_type = .input,
+        .api = .alsa_seq,
+    });
+    defer midi_in.free();
+
+    const midi_out: lm.midi.out.Handle = try .init(&.{
+        .version = .midi1,
+        .virtual_port = true,
+        .port_name = "my-app",
+    }, &.{
+        .conf_type = .output,
+        .api = .alsa_seq,
+    });
+    defer midi_out.free();
+
+
+    for (0..99) |_| std.time.sleep(1e9); // sleep 1s, 100 times
+}
+
+fn free_observer(observer: lm.observer.Handle, e: *EnumeratedPorts) void {
+
+    for (e.in_ports) |port| port.free();
+    for (e.out_ports) |port| port.free();
+
+    observer.free();
+}
+
+export fn on_input_port_found(ctx: ?*anyopaque, port: lm.midi.in.port.Handle) callconv(.C) void {
+
+    std.debug.print("input: {s}\n", .{ port.getName() catch "" });
+
+    var e: *EnumeratedPorts = @ptrCast(@alignCast(ctx));
+    e.in_ports[e.in_port_count] = port.clone() catch lm.midi.in.port.Handle{};
+    e.in_port_count += 1;
+}
+
+export fn on_output_port_found(ctx: ?*anyopaque, port: lm.midi.out.port.Handle) callconv(.C) void {
+
+    std.debug.print("output: {s}\n", .{ port.getName() catch "" });
+
+    var e: *EnumeratedPorts = @ptrCast(@alignCast(ctx));
+    e.out_ports[e.out_port_count] = port.clone() catch lm.midi.out.port.Handle{};
+    e.out_port_count += 1;
+}
+
+fn on_midi1_message(ctx: ?*anyopaque, ts: lm.Timestamp, msg: [*]const lm.midi.v1.Symbol, len: usize) callconv(.C) void {
+    _ = ctx;
+    _ = ts;
+    _ = len;
+
+    std.debug.print("0x{x:02} 0x{x:02} 0x{x:02}\n", .{ msg[0], msg[1], msg[2] });
+}
+
+fn on_midi2_message(ctx: ?*anyopaque, ts: lm.Timestamp, msg: [*]const lm.midi.v2.Symbol, len: usize) callconv(.C) void {
+    _ = ctx;
+    _ = ts;
+    _ = len;
+
+    std.debug.print("0x{x:02} 0x{x:02} 0x{x:02}\n", .{ msg[0], msg[1], msg[2] });
+}
+
+fn enumerate_ports(observer: lm.observer.Handle, e: *EnumeratedPorts) !void {
+    try observer.enumerateInputPorts(e, on_input_port_found);
+    try observer.enumerateOutputPorts(e, on_output_port_found);
+}