kmscon: implement dynamic font-resizing via shortcuts

This implements two new keyboard shortcuts zoom-in and zoom-out that
increase/decrease font size of the current terminal.

This is similar to how wlterm does it and allows runtime modification of
fonts.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

4 files changed, 54 insertions, 0 deletions

diff --git a/docs/man/kmscon.xml b/docs/man/kmscon.xml
index dbe0dcf..7777ede 100644
--- a/docs/man/kmscon.xml
+++ b/docs/man/kmscon.xml
@@ -372,6 +372,22 @@
       </varlistentry>
 
       <varlistentry>
+        <term><option>--grab-zoom-in {grab}</option></term>
+        <listitem>
+          <para>Increase font size of the current terminal.
+                (default: &lt;Ctrl&gt;Plus)</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><option>--grab-zoom-out {grab}</option></term>
+        <listitem>
+          <para>Decrease font size of the current terminal.
+                (default: &lt;Ctrl&gt;Minus)</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
         <term><option>--grab-session-next {grab}</option></term>
         <listitem>
           <para>Switch to next session.
diff --git a/src/kmscon_conf.c b/src/kmscon_conf.c
index 8edd5ee..d960c42 100644
--- a/src/kmscon_conf.c
+++ b/src/kmscon_conf.c
@@ -119,6 +119,10 @@ static void print_help()
 		"\t                                  Shortcut to scroll page up\n"
 		"\t    --grab-page-down <grab>     [<Shift>Next]\n"
 		"\t                                  Shortcut to scroll page down\n"
+		"\t    --grab-zoom-in <grab>       [<Ctrl>Plus]\n"
+		"\t                                  Shortcut to increase font size\n"
+		"\t    --grab-zoom-out <grab>      [<Ctrl>Minus]\n"
+		"\t                                  Shortcut to decrease font size\n"
 		"\t    --grab-session-next <grab>  [<Ctrl><Logo>Right]\n"
 		"\t                                  Switch to next session\n"
 		"\t    --grab-session-prev <grab>  [<Ctrl><Logo>Left]\n"
@@ -510,6 +514,12 @@ static struct conf_grab def_grab_page_up =
 static struct conf_grab def_grab_page_down =
 		CONF_SINGLE_GRAB(SHL_SHIFT_MASK, XKB_KEY_Next);
 
+static struct conf_grab def_grab_zoom_in =
+		CONF_SINGLE_GRAB(SHL_CONTROL_MASK, XKB_KEY_plus);
+
+static struct conf_grab def_grab_zoom_out =
+		CONF_SINGLE_GRAB(SHL_CONTROL_MASK, XKB_KEY_minus);
+
 static struct conf_grab def_grab_session_next =
 		CONF_SINGLE_GRAB(SHL_CONTROL_MASK | SHL_LOGO_MASK, XKB_KEY_Right);
 
@@ -579,6 +589,8 @@ int kmscon_conf_new(struct conf_ctx **out)
 		CONF_OPTION_GRAB(0, "grab-scroll-down", &conf->grab_scroll_down, &def_grab_scroll_down),
 		CONF_OPTION_GRAB(0, "grab-page-up", &conf->grab_page_up, &def_grab_page_up),
 		CONF_OPTION_GRAB(0, "grab-page-down", &conf->grab_page_down, &def_grab_page_down),
+		CONF_OPTION_GRAB(0, "grab-zoom-in", &conf->grab_zoom_in, &def_grab_zoom_in),
+		CONF_OPTION_GRAB(0, "grab-zoom-out", &conf->grab_zoom_out, &def_grab_zoom_out),
 		CONF_OPTION_GRAB(0, "grab-session-next", &conf->grab_session_next, &def_grab_session_next),
 		CONF_OPTION_GRAB(0, "grab-session-prev", &conf->grab_session_prev, &def_grab_session_prev),
 		CONF_OPTION_GRAB(0, "grab-session-dummy", &conf->grab_session_dummy, &def_grab_session_dummy),
diff --git a/src/kmscon_conf.h b/src/kmscon_conf.h
index b18cc80..4cb4789 100644
--- a/src/kmscon_conf.h
+++ b/src/kmscon_conf.h
@@ -118,6 +118,10 @@ struct kmscon_conf_t {
 	struct conf_grab *grab_page_up;
 	/* page-down grab */
 	struct conf_grab *grab_page_down;
+	/* zoom-in grab */
+	struct conf_grab *grab_zoom_in;
+	/* zoom-out grab */
+	struct conf_grab *grab_zoom_out;
 	/* session-next grab */
 	struct conf_grab *grab_session_next;
 	/* session-prev grab */
diff --git a/src/kmscon_terminal.c b/src/kmscon_terminal.c
index d917fc7..740a27c 100644
--- a/src/kmscon_terminal.c
+++ b/src/kmscon_terminal.c
@@ -426,6 +426,28 @@ static void input_event(struct uterm_input *input,
 		ev->handled = true;
 		return;
 	}
+	if (conf_grab_matches(term->conf->grab_zoom_in,
+			      ev->mods, ev->num_syms, ev->keysyms)) {
+		ev->handled = true;
+		if (term->font_attr.points + 1 < term->font_attr.points)
+			return;
+
+		++term->font_attr.points;
+		if (font_set(term))
+			--term->font_attr.points;
+		return;
+	}
+	if (conf_grab_matches(term->conf->grab_zoom_out,
+			      ev->mods, ev->num_syms, ev->keysyms)) {
+		ev->handled = true;
+		if (term->font_attr.points <= 1)
+			return;
+
+		--term->font_attr.points;
+		if (font_set(term))
+			++term->font_attr.points;
+		return;
+	}
 
 	/* TODO: xkbcommon supports multiple keysyms, but it is currently
 	 * unclear how this feature will be used. There is no keymap, which