Finish companion controls and retain panel textures during manipulation

src/texture_refresh.hpp

@@ -0,0 +1,14 @@
+#pragma once
+#include <utility>
+
+namespace frameyap {
+// Follow docs/rendering-performance.md: retain initialized images throughout
+// manipulation, leaving content invalidation pending until the next refresh.
+template<class Render, class Upload>
+bool refresh_texture(bool manipulating, bool initialized, Render&& render, Upload&& upload) {
+    if (manipulating && initialized) return false;
+    if (!std::forward<Render>(render)()) return false;
+    std::forward<Upload>(upload)();
+    return true;
+}
+}