Stop rendering all the time, render to the texture only when changing.

src/slides_ui.cpp

@@ -215,14 +215,20 @@ void SlidesUI::show_slide() {
   auto& cell = $gui.cell_for("slide");
 
   slide.init(cell, layout);
+
+  $needs_render = true;
 }
 
 void SlidesUI::render(sf::RenderTarget& window) {
   window.clear();
-  $gui.render($view_texture);
   auto& slide = $deck->current_slide();
+
+  if($needs_render) {
+    $gui.render($view_texture);
     slide.render($view_texture);
     $view_texture.display();
+    $needs_render = false;
+  }
 
   if(slide.$shader) {
     slide.$shader->setUniform("u_time", $clock.getElapsedTime().asSeconds());

src/slides_ui.hpp

@@ -50,6 +50,7 @@ struct SlidesUI {
   sf::RenderTexture $view_texture;
   sf::Sprite $view_sprite;
   sf::Clock $clock;
+  bool $needs_render = true;
 
   SlidesUI(std::shared_ptr<SlideDeck> deck, sf::Vector2u size);
   void init();