add main plugin run loop

src/image.zig

@@ -41,6 +41,24 @@ fn sopen(
     return file.?;
 }
 
+///Read a single frame from a file into an interleaved buffer.
+///If more channels are required than are available in the file, the remaining
+///channels are distributed in a round-robin fashion (LRLRL).
+fn sread(file_opt: ?*c.SNDFILE, file_chans: c_int, buf: []f32) bool {
+    var file = file_opt.?;
+
+    const n_read: c.sf_count_t = c.sf_readf_float(file, buf.ptr, 1);
+    const buf_chans = @intCast(c_int, buf.len);
+
+    var i = file_chans - 1;
+    while (i < buf_chans) : (i += 1) {
+        //buf[@intCast(usize, i)] = buf[i % file_chans];
+        buf[@intCast(usize, i)] = buf[@intCast(usize, @mod(i, file_chans))];
+    }
+
+    return n_read == 1;
+}
+
 fn getEndPos(path: []const u8) !usize {
     var file = try std.fs.File.openRead(path);
     defer file.close();
@@ -204,5 +222,35 @@ pub const Image = struct {
         std.debug.warn("file end: {}\n", end_pos);
         const seek_pos = position.seekPos(end_pos);
         std.debug.warn("start {} end {}\n", seek_pos.start, seek_pos.end);
+
+        var i: usize = 0;
+
+        while (i < end_pos) : (i += 1) {
+            // if we're still on the bmp header phase, copy bytes
+            // if we aren't in the range from seek_pos, copy bytes
+            // if we are in the range, run lilv plugin
+
+            // TODO speed this up by not reading byte-by-byte.
+            // TODO check value of this
+            _ = c.sf_readf_float(self.sndfile, rctx.in_buf.ptr, 1);
+
+            if (i < BMPHeaderSize or !seek_pos.contains(i)) {
+                _ = c.sf_writef_float(out_file, rctx.in_buf.ptr, 1);
+            } else {
+                lv2.lilv_instance_run(rctx.instance, 1);
+
+                var count = c.sf_writef_float(out_file, rctx.out_buf.ptr, 1);
+                if (count != 1) {
+                    std.debug.warn(
+                        "Failed to write to output file at idx {}.\n",
+                        i,
+                    );
+
+                    // maybe we return an error?
+                }
+            }
+        }
+
+        _ = c.sf_close(out_file);
     }
 };

src/plugin.zig

@@ -21,6 +21,10 @@ pub const ParamList = std.ArrayList(Param);
 pub const SeekPos = struct {
     start: usize,
     end: usize,
+
+    pub fn contains(self: SeekPos, idx: usize) bool {
+        return (self.start <= idx) and (idx <= self.end);
+    }
 };
 
 /// Represents a relative position in the image