Implement KRNodeProperty to reduce boilerplate needed for adding new node attributes

CMakeLists.txt

@@ -1,6 +1,6 @@
 cmake_minimum_required (VERSION 3.16)
 
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 

kraken/nodes/KRNode.h

@@ -37,6 +37,7 @@
 #include "KROctreeNode.h"
 #include "KRBehavior.h"
 #include "KRShaderReflection.h"
+#include <type_traits>
 
 using namespace kraken;
 
@@ -65,6 +66,59 @@ class XMLNode;
 class XMLAttribute;
 }
 
+template <typename T, class config>
+class KRNodeProperty
+{
+public:
+  static constexpr T defaultVal = config::defaultVal;
+  static constexpr const char* name = config::name;
+  KRNodeProperty()
+    : val(config::defaultVal)
+  {
+  }
+
+  KRNodeProperty(T& val)
+    : val(val)
+  {
+  }
+
+  KRNodeProperty& operator=(const T& v)
+  {
+    val = v;
+    return *this;
+  }
+
+  operator const T& () const
+  {
+    return val;
+  }
+
+  void save(tinyxml2::XMLElement* element) const
+  {
+    element->SetAttribute(config::name, val);
+  }
+
+  void load(tinyxml2::XMLElement* element)
+  {
+    if constexpr (std::is_same<T, float>::value) {
+      if (element->QueryFloatAttribute(config::name, &val) != tinyxml2::XML_SUCCESS) {
+        val = config::defaultVal;
+      }
+    } else {
+      static_assert(false, "Typename not implemented.");
+    }
+  }
+
+  T val;
+};
+
+#define KRNODE_PROPERTY(PROP_TYPE, VAR, PROP_DEFAULT, PROP_NAME) \
+   struct VAR ## _config { \
+    static constexpr float defaultVal = PROP_DEFAULT; \
+    static constexpr const char* name = PROP_NAME; \
+  }; \
+  KRNodeProperty<PROP_TYPE, VAR ## _config> VAR;
+
 class KRNode
   : public KRContextObject
   , public KRReflectedObject

kraken/nodes/KRSprite.cpp

@@ -50,7 +50,7 @@ using namespace hydra;
 void KRSprite::InitNodeInfo(KrNodeInfo* nodeInfo)
 {
   KRNode::InitNodeInfo(nodeInfo);
-  nodeInfo->sprite.alpha = 1.0f;
+  nodeInfo->sprite.alpha = decltype(m_spriteAlpha)::defaultVal;
   nodeInfo->sprite.texture = -1;
 }
 
@@ -58,7 +58,6 @@ KRSprite::KRSprite(KRScene& scene, std::string name)
   : KRNode(scene, name)
   , m_spriteTexture(KRTextureBinding(KRTexture::TEXTURE_USAGE_SPRITE))
 {
-  m_spriteAlpha = 1.0f;
 }
 
 KRSprite::~KRSprite()
@@ -73,7 +72,7 @@ tinyxml2::XMLElement* KRSprite::saveXML(tinyxml2::XMLNode* parent)
 {
   tinyxml2::XMLElement* e = KRNode::saveXML(parent);
   e->SetAttribute("sprite_texture", m_spriteTexture.getName().c_str());
-  e->SetAttribute("sprite_alpha", m_spriteAlpha);
+  m_spriteAlpha.save(e);
   return e;
 }
 
@@ -81,9 +80,7 @@ void KRSprite::loadXML(tinyxml2::XMLElement* e)
 {
   KRNode::loadXML(e);
 
-  if (e->QueryFloatAttribute("sprite_alpha", &m_spriteAlpha) != tinyxml2::XML_SUCCESS) {
+  m_spriteAlpha.load(e);
-    m_spriteAlpha = 1.0f;
-  }
 
   const char* szSpriteTexture = e->Attribute("sprite_texture");
   if (szSpriteTexture) {

kraken/nodes/KRSprite.h

@@ -62,5 +62,6 @@ protected:
   bool getShaderValue(ShaderValue value, float* output) const override;
 
   KRTextureBinding m_spriteTexture;
-  float m_spriteAlpha;
+
+  KRNODE_PROPERTY(float, m_spriteAlpha, 1.f, "sprite_alpha");
 };