main: add --render-engine option

This option allows changing the console renderer during runtime. This is
only useful for debugging. The default choice should be best for all
situations.

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

src/main.c

@@ -433,6 +433,7 @@ static void print_help()
 		"\t    --dumb                  [off]   Use dumb DRM instead of hardware-\n"
 		"\t                                    accelerated DRM devices\n"
 		"\t    --fps                   [50]    Limit frame-rate\n"
+		"\t    --render-engine <eng>   [-]     Console renderer\n"
 		"\n"
 		"Input Device Options:\n"
 		"\t    --xkb-layout <layout>   [us]    Set XkbLayout for input devices\n"
@@ -525,6 +526,7 @@ struct conf_option options[] = {
 	CONF_OPTION_BOOL(0, "fbdev", NULL, &kmscon_conf.use_fbdev, false),
 	CONF_OPTION_BOOL(0, "dumb", NULL, &kmscon_conf.dumb, false),
 	CONF_OPTION_UINT(0, "fps", NULL, &kmscon_conf.fps, 50),
+	CONF_OPTION_STRING(0, "render-engine", NULL, &kmscon_conf.render_engine, NULL),
 	CONF_OPTION_BOOL('s', "switchvt", NULL, &kmscon_conf.switchvt, false),
 	CONF_OPTION_BOOL('l', "login", aftercheck_login, &kmscon_conf.login, false),
 	CONF_OPTION_STRING('t', "term", NULL, &kmscon_conf.term, "vt220"),

src/main.h

@@ -51,6 +51,8 @@ struct kmscon_conf_t {
 	bool use_fbdev;
 	/* use dumb DRM devices */
 	bool dumb;
+	/* render engine */
+	char *render_engine;
 
 	/* input KBD layout */
 	char *xkb_layout;

src/terminal.c

@@ -212,7 +212,9 @@ static int add_display(struct kmscon_terminal *term, struct uterm_display *disp)
 	}
 
 	ret = uterm_screen_use(scr->screen);
-	if (!ret)
+	if (kmscon_conf.render_engine)
+		be = kmscon_conf.render_engine;
+	else if (!ret)
 		be = "gltex";
 	else
 		be = NULL;