Merge pull request #2200 from mucamaca/fix_transparency

Fix #1857 -> transparency in swaylock

swaylock/render.c

@@ -30,6 +30,8 @@ void render_frame(struct swaylock_surface *surface) {
 	cairo_t *cairo = surface->current_buffer->cairo;
 	cairo_identity_matrix(cairo);
 
+	cairo_save(cairo);
+	cairo_set_operator(cairo, CAIRO_OPERATOR_SOURCE);
 	if (state->args.mode == BACKGROUND_MODE_SOLID_COLOR || !surface->image) {
 		cairo_set_source_u32(cairo, state->args.color);
 		cairo_paint(cairo);
@@ -37,6 +39,7 @@ void render_frame(struct swaylock_surface *surface) {
 		render_background_image(cairo, surface->image,
 				state->args.mode, buffer_width, buffer_height);
 	}
+	cairo_restore(cairo);
 	cairo_identity_matrix(cairo);
 
 	int arc_radius = ARC_RADIUS * surface->scale;