widgets(terminal): send a redraw event

examples/vt.zig

@@ -56,17 +56,21 @@ pub fn main() !void {
     defer vt.deinit();
     try vt.spawn();
 
+    var redraw: bool = false;
     while (true) {
         std.time.sleep(8 * std.time.ns_per_ms);
         // try vt events first
         while (vt.tryEvent()) |event| {
+            redraw = true;
             switch (event) {
                 .bell => {},
                 .title_change => {},
                 .exited => return,
+                .redraw => {},
             }
         }
         while (loop.tryEvent()) |event| {
+            redraw = true;
             switch (event) {
                 .key_press => |key| {
                     if (key.matches('c', .{ .ctrl = true })) return;
@@ -77,6 +81,8 @@ pub fn main() !void {
                 },
             }
         }
+        if (!redraw) continue;
+        redraw = false;
 
         const win = vx.window();
         win.hideCursor();

src/widgets/terminal/Terminal.zig

@@ -18,6 +18,7 @@ const key = @import("key.zig");
 
 pub const Event = union(enum) {
     exited,
+    redraw,
     bell,
     title_change,
 };
@@ -66,6 +67,8 @@ back_screen_alt: Screen,
 // only applies to primary screen
 scroll_offset: usize = 0,
 back_mutex: std.Thread.Mutex = .{},
+// dirty is protected by back_mutex. Only access this field when you hold that mutex
+dirty: bool = false,
 
 unicode: *const vaxis.Unicode,
 should_quit: bool = false,
@@ -192,8 +195,10 @@ pub fn draw(self: *Terminal, win: vaxis.Window) !void {
         defer self.back_mutex.unlock();
         // We keep this as a separate condition so we don't deadlock by obtaining the lock but not
         // having sync
-        if (!self.mode.sync)
+        if (!self.mode.sync) {
             try self.back_screen.copyTo(&self.front_screen);
+            self.dirty = false;
+        }
     }
 
     var row: usize = 0;
@@ -261,6 +266,10 @@ fn run(self: *Terminal) !void {
         self.back_mutex.lock();
         defer self.back_mutex.unlock();
 
+        defer if (!self.dirty and self.event_queue.tryPush(.redraw)) {
+            self.dirty = true;
+        };
+
         switch (event) {
             .print => |str| {
                 var iter = grapheme.Iterator.init(str, &self.unicode.grapheme_data);