Make it possible to set a slide background image and test that a slide with only an image works.

sample/01-a-good-first-program.md

@@ -1,7 +1,6 @@
 {
   "title": "Test",
-  "description": "Test",
+  "description": "Test"
-  "bg_image": "assets/sample_bg.jpg"
 }
 ===
 # 1: A Good First Program
@@ -20,6 +19,9 @@
 
 !(assets/sample_bg.jpg)
 ---
+{
+"bg_image": "assets/sample_bg.jpg"
+}
 # Common Student Questions
 
 * This again.
@@ -33,3 +35,7 @@
 
 - See You Soon!
 ---
+{
+"bg_image": "assets/sample_bg.jpg"
+}
+---

src/slides_ui.cpp

@@ -27,7 +27,10 @@ void Slide::init(lel::Cell& cell) {
     $gui.layout(
         "[=*%(300,200)title|_|_]"
         "[_|_|_]"
-        "[=*%(300,400)content|_|_]"
+        "[=*%(300,600)content|_|_]"
+        "[_|_|_]"
+        "[_|_|_]"
+        "[_|_|_]"
         "[_|_|_]"
         "[_|_|_]");
 
@@ -62,7 +65,7 @@ SlidesUI::SlidesUI(shared_ptr<SlideDeck> deck) {
   $gui.position(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
   $gui.layout(
       "[t_left|t_center|t_right]"
-      "[*%(300,400)slide|_|_|m_right|_]"
+      "[*%(300,400)slide|_|_|_|_]"
       "[_|_|_|_|_]"
       "[_|_|_|_|_]"
       "[_|_|_|_|_]"
@@ -106,9 +109,16 @@ void SlidesUI::show_slide() {
   auto& bg = $gui.get<guecs::Background>($gui.MAIN);
   sf::Color color = guecs::THEME.FILL_COLOR;
 
-  if($deck->config.contains("bg_image")) {
+  if(slide.$config.contains("bg_image")) {
+    bg.set_sprite(slide.$config["bg_image"], true);
+  } else if($deck->config.contains("bg_image")) {
     bg.set_sprite($deck->config["bg_image"], true);
-  } else if(slide.$config.contains("bg_color")) {
+  } else {
+    bg.sprite = nullptr;
+    bg.texture = nullptr;
+  }
+
+  if(slide.$config.contains("bg_color")) {
     auto color_conf = slide.$config["bg_color"];
     color = {color_conf[0], color_conf[1], color_conf[2], color_conf[3]};
   }