Fix intermittent blanking/flickering

Clearing and printing were done in two separate write syscalls. This fix
consists in grouping them in the same write syscall by scheduling a
clear in advance. This prevents UI glitches due to the delay between
both writes.

3 files changed, 28 insertions, 11 deletions

diff --git a/libtui/layout/layout.ha b/libtui/layout/layout.ha
index 8391c2f..b9d5672 100644
--- a/libtui/layout/layout.ha
+++ b/libtui/layout/layout.ha
@@ -19,7 +19,8 @@ export fn newlayout(widgets: *widget::widget...) layout = {
 
 // Display all the widgets contained in the given layout.
 export fn print(layout: layout) (void | widget::error) = {
-	libtui::clear(layout.widgets[0].ui);
+	//libtui::clear(layout.widgets[0].ui);
+	libtui::doclear(&layout.widgets[0].ui);
 	for (let i = 0z; i < len(layout.widgets); i += 1) {
 		match (layout.widgets[i].print) {
 		case null =>
diff --git a/libtui/libtui.ha b/libtui/libtui.ha
index 3d33680..5f862b0 100644
--- a/libtui/libtui.ha
+++ b/libtui/libtui.ha
@@ -19,8 +19,11 @@ export type ttyui = struct {
 	term: tty::termios,
 	f: io::file,
 	listeners: []listener,
+	doclear: bool,
 };
 
+const CLEARESC: str = "\x1B[2J\x1B[1;1H\r";
+
 // Initializes the UI and returns a ttyui.
 export fn init() ttyui = {
 	let f = match (tty::open()) {
@@ -45,16 +48,17 @@ export fn init() ttyui = {
 		term = term,
 		f = f,
 		listeners = [],
+		doclear = false,
 	};
-	hidecursor(ui);
+	hidecursor(&ui);
 	return ui;
 };
 
-export fn hidecursor(ui: ttyui) void = {
+export fn hidecursor(ui: *ttyui) void = {
 	print(ui, "\x1B[?25l");
 };
 
-export fn showcursor(ui: ttyui) void = {
+export fn showcursor(ui: *ttyui) void = {
 	print(ui, "\x1B[?25h");
 };
 
@@ -65,7 +69,7 @@ export fn getwinsize(ui: ttyui) (tty::ttysize | tty::error) = {
 
 // Suspend the UI. To restore it, use [[resume]].
 export fn suspend(ui: *ttyui) void = {
-	showcursor(*ui);
+	showcursor(ui);
 	tty::termios_restore(&ui.term);
 };
 
@@ -73,13 +77,13 @@ export fn suspend(ui: *ttyui) void = {
 export fn resume(ui: *ttyui) void = {
 	tty::makeraw(&ui.term)!;
 	tty::noecho(&ui.term)!;
-	hidecursor(*ui);
+	hidecursor(ui);
 };
 
 // Restores the UI state and closes and frees the resources associated with the
 // given ttyui.
 export fn finish(ui: *ttyui) void = {
-	showcursor(*ui);
+	showcursor(ui);
 	tty::termios_restore(&ui.term);
 	io::close(ui.f)!;
 	free(ui.listeners);
@@ -134,12 +138,24 @@ export fn addlistener(ui: *ttyui, l: listener) void = {
 };
 
 // Print a string or rune to the ttyui.
-export fn print(ui: ttyui, arg: (str | rune)) void = {
-	fmt::fprint(ui.f, arg)!;
+export fn print(ui: *ttyui, arg: str) void = {
+	if (ui.doclear) {
+		fmt::fprint(ui.f, strings::concat(CLEARESC, arg))!;
+		ui.doclear = false;
+	} else {
+		fmt::fprint(ui.f, arg)!;
+	};
 	//fmt::fprintf(ui.f, "{}\r", arg)!;
 };
 
 // Clear the ttyui.
 export fn clear(ui: ttyui) void = {
-	fmt::fprintf(ui.f, "\x1B[2J\x1B[1;1H\r")!;
+	fmt::fprintf(ui.f, CLEARESC)!;
+};
+
+// Schedule a clear on the next print to the ttyui. Used to optimize printing
+// and avoid intermittent blanking/flickering by grouping the clear and print in
+// the same write syscall.
+export fn doclear(ui: *ttyui) void = {
+	ui.doclear = true;
 };
diff --git a/libtui/widget/list/list.ha b/libtui/widget/list/list.ha
index d6eebda..3bfd499 100644
--- a/libtui/widget/list/list.ha
+++ b/libtui/widget/list/list.ha
@@ -149,7 +149,7 @@ export fn print(list: *widget::widget) (void | widget::error) = {
 	// unsupported?
 	//io::copy(list.ui.f, &st)?;
 	let s = strio::string(&st);
-	libtui::print(list.widget.ui, s);
+	libtui::print(&list.widget.ui, s);
 	io::close(&st)?;
 };