Shader files compile again on save; an attached GUI runs the session's post chain

shader_build.zig takes the Shadertoy compile out of the GUI's Post: the
process that holds the core compiles each chain file behind the prefix on a
thread, watches its directory (file_watch's new shader slots), and on a
change reads and hashes each file, compiling only one whose bytes moved. A
failed compile keeps the last good SPIR-V and is said once; the same bytes
are never compiled or reported twice. A file is read with std, not fs.zig's
readFile, whose turn hand-off a worker thread does not hold.

A detached session compiles for its frontends and sends them the chain
(wire post: each pass's scene and level or the file's SPIR-V, and
ShaderAnimation) on attach and on every change, so an attached GUI runs the
same passes, levels and animation as a local one while still reading no disk
and running no program. The attached GUI describes its frames to the chain
from the session's chrome and redraws an animating chain on its own.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/file_watch.zig b/src/file_watch.zig
index d028488e..8bd9de8b 100644
--- a/src/file_watch.zig
+++ b/src/file_watch.zig
@@ -70,7 +70,11 @@ pub const Watch = struct {
 /// Sharing the table also shares directory descriptors correctly when a user
 /// happens to open that .zon as an ordinary document.
 pub const theme_slot = pardes.MAX_PANES;
-pub const Table = [pardes.MAX_PANES + 1]?Watch;
+/// After it, one slot a post chain file (shader_build.zig): marked only so
+/// a save there wakes the host, which has the files read again; no
+/// generation of theirs is kept here.
+pub const shader_slot = theme_slot + 1;
+pub const Table = [shader_slot + pardes.config.Runtime.Post.max]?Watch;
 
 /// Whether this OS has a watcher at all. Off it every entry point below
 /// returns the inert answer: `watchPath` installs nothing, so `watches` stays
@@ -423,6 +427,13 @@ pub fn watchPane(
     watchPath(fd, watches, id, path, serial, generation);
 }
 
+/// Mark the post chain files' directories, one slot each, dropping the
+/// marks of files no longer in it.
+pub fn watchShaders(fd: c_int, watches: *Table, paths: []const []const u8) void {
+    for (0..pardes.config.Runtime.Post.max) |i|
+        watchPath(fd, watches, shader_slot + i, if (i < paths.len) paths[i] else null, 0, .{ .text = 0 });
+}
+
 /// Reconcile one marked pane. A true result requests an immediate second pass:
 /// the PDF pathname changed between the stat before MuPDF reopened it and the
 /// stat after, so committing either identity would lose a generation.