Add Lua function to Win for directly editing cell styling by position

ui-terminal.c

@@ -69,6 +69,9 @@ struct UiTermWin {
 #include "ui-terminal-vt100.c"
 #endif
 
+/* helper macro for handling UiTerm.cells */
+#define CELL_AT_POS(UI, X, Y) (((UI)->cells) + (X) + ((Y) * (UI)->width));
+
 __attribute__((noreturn)) static void ui_die(Ui *ui, const char *msg, va_list ap) {
 	UiTerm *tui = (UiTerm*)ui;
 	ui_term_backend_free(tui);
@@ -305,6 +308,17 @@ static void ui_window_style_set(UiWin *w, Cell *cell, enum UiStyle id) {
 	memcpy(&cell->style, &set, sizeof(CellStyle));
 }
 
+static bool ui_window_style_set_pos(UiWin *w, int x, int y, enum UiStyle id) {
+	UiTermWin *win = (UiTermWin*)w;
+	UiTerm *tui = win->ui;
+	if (x < 0 || y < 0 || y >= win->height || x >= win->width) {
+		return false;
+	}
+	Cell *cell = CELL_AT_POS(tui, win->x + x, win->y + y)
+	ui_window_style_set(w, cell, id);
+	return true;
+}
+
 static void ui_window_status(UiWin *w, const char *status) {
 	UiTermWin *win = (UiTermWin*)w;
 	if (!(win->options & UI_OPTION_STATUSBAR))
@@ -534,6 +548,7 @@ static UiWin *ui_window_new(Ui *ui, Win *w, enum UiOption options) {
 
 	win->uiwin = (UiWin) {
 		.style_set = ui_window_style_set,
+		.style_set_pos = ui_window_style_set_pos,
 		.status = ui_window_status,
 		.options_set = ui_window_options_set,
 		.options_get = ui_window_options_get,

ui.h

@@ -97,6 +97,7 @@ struct Ui {
 
 struct UiWin {
 	void (*style_set)(UiWin*, Cell*, enum UiStyle);
+	bool (*style_set_pos)(UiWin*, int x, int y, enum UiStyle);
 	void (*status)(UiWin*, const char *txt);
 	void (*options_set)(UiWin*, enum UiOption);
 	enum UiOption (*options_get)(UiWin*);

vis-lua.c

@@ -2106,6 +2106,32 @@ static int window_style(lua_State *L) {
 	return 0;
 }
 
+/***
+ * Style the single terminal cell at the given coordinates, relative to this window.
+ *
+ * Completely independent of the file buffer, and can be used to style UI elements,
+ * such as the status bar.
+ * The style will be cleared after every window redraw.
+ * @function style_pos
+ * @tparam int id display style registered with @{style_define}
+ * @tparam int x 0-based x coordinate within Win, where (0,0) is the top left corner
+ * @tparam int y See above
+ * @treturn bool false if the coordinates would be outside the window's dimensions
+ * @see style_define
+ * @usage
+ * win:style_pos(win.STYLE_COLOR_COLUMN, 0, win.height - 1)
+ * -- Styles the first character of the status bar (or the last line, if disabled)
+ */
+static int window_style_pos(lua_State *L) {
+	Win *win = obj_ref_check(L, 1, VIS_LUA_TYPE_WINDOW);
+	enum UiStyle style = luaL_checkunsigned(L, 2);
+	size_t x = checkpos(L, 3);
+	size_t y = checkpos(L, 4);
+	bool ret = win->ui->style_set_pos(win->ui, (int)x, (int)y, style);
+	lua_pushboolean(L, ret);
+	return 1;
+}
+
 /***
  * Set window status line.
  *
@@ -2175,6 +2201,7 @@ static const struct luaL_Reg window_funcs[] = {
 	{ "unmap", window_unmap },
 	{ "style_define", window_style_define },
 	{ "style", window_style },
+	{ "style_pos", window_style_pos },
 	{ "status", window_status },
 	{ "draw", window_draw },
 	{ "close", window_close },