Keep world sharp behind linking books

src/main/java/net/dnorberg/rivencraft/client/screen/LinkingBookScreen.java

@@ -74,6 +74,12 @@ public final class LinkingBookScreen extends Screen {
         }
     }
 
+    @Override
+    public void renderBackground(GuiGraphics graphics, int mouseX, int mouseY, float partialTick) {
+        // The open book is the complete GUI background. Avoid Minecraft's
+        // default full-screen world blur behind it.
+    }
+
     @Override
     public void render(GuiGraphics graphics, int mouseX, int mouseY, float partialTick) {
         int left = (width - BOOK_WIDTH) / 2;