Helpers for caching object transformations.

src/Object.cpp

@@ -41,6 +41,8 @@ void Object::setParent(Object* parent) {
         _parent->_children.erase(this);
 
     _parent = parent;
+
+    setDirty();
 }
 
 Matrix4 Object::transformation(bool absolute) {
@@ -87,4 +89,25 @@ Scene* Object::scene() const {
     return 0;
 }
 
+void Object::setDirty() {
+    /* The object (and all its children) are already dirty, nothing to do */
+    if(dirty) return;
+
+    dirty = true;
+
+    /* Make all children dirty */
+    for(set<Object*>::iterator it = _children.begin(); it != _children.end(); ++it)
+        (*it)->setDirty();
+}
+
+void Object::setClean() {
+    /* The object (and all its parents) is already clean, nothing to do */
+    if(!dirty) return;
+
+    dirty = false;
+
+    /* Make all parents clean */
+    if(_parent != 0 && _parent != this) _parent->setClean();
+}
+
 }

src/Object.h

@@ -45,7 +45,7 @@ class Object {
          *
          * Sets all transformations to their default values.
          */
-        inline Object(Object* parent = 0): _parent(0) {
+        inline Object(Object* parent = 0): _parent(0), dirty(true) {
             setParent(parent);
         }
 
@@ -85,7 +85,10 @@ class Object {
         virtual Matrix4 transformation(bool absolute = false);
 
         /** @brief Set transformation matrix */
-        inline void setTransformation(const Matrix4& transformation) { _transformation = transformation; }
+        inline void setTransformation(const Matrix4& transformation) {
+            _transformation = transformation;
+            setDirty();
+        }
 
         /**
          * @brief Multiply transformation matrix
@@ -98,6 +101,7 @@ class Object {
          */
         inline void multiplyTransformation(const Matrix4& transformation, bool global = true) {
             _transformation = global ? transformation*_transformation : _transformation*transformation;
+            setDirty();
         }
 
         /**
@@ -153,6 +157,54 @@ class Object {
             rotate(angle, Vector3(x, y, z), global);
         }
 
+        /** @{ @name Caching helpers
+         *
+         * If the object transformation is used many times when drawing (such
+         * as e.g. position of light object), it's good to cache these values,
+         * so they don't have to be computed again on every request.
+         *
+         * If the object or any parent is transformed, the transformed object
+         * and all its children are marked as dirty. If currently active camera
+         * is transformed, the scene goes through all children and calls
+         * setDirty() recursively on every clean object (if the object is
+         * already dirty, it and all its children are skipped, because they are
+         * dirty too).
+         *
+         * These functions are used to manage dirty status of the object. If
+         * the object doesn't cache anything, it's no need to bother about them,
+         * but if does, setClean() should be reimplemented and used to
+         * regenerate the cache. Thus the dirty status is managed only for
+         * these objects, which are calling setClean().
+         */
+
+        /**
+         * @brief Whether the object is dirty
+         * @return  True, if transformation of the object, any parent or camera
+         *      has changed since last asking, false otherwise.
+         */
+        inline bool isDirty() const { return dirty; }
+
+        /**
+         * @brief Set object and all its children as dirty
+         *
+         * Recursively calls setDirty() on every child. If the object is already
+         * marked as dirty, the function does nothing.
+         * @attention Reimplementations must also call this function!
+         */
+        virtual void setDirty();
+
+        /**
+         * @brief Set object and all its parents as clean
+         *
+         * Recursively calls setClean() on every parent. Default implementation
+         * only marks the object as clean, but if the object does any caching,
+         * this function should be reimplemented to regenerate the cache.
+         * @attention Reimplementations must also call this function!
+         */
+        virtual void setClean();
+
+        /*@}*/
+
         /**
          * @brief Draw object
          *
@@ -164,6 +216,7 @@ class Object {
         Object* _parent;
         std::set<Object*> _children;
         Matrix4 _transformation;
+        bool dirty;
 };
 
 }

src/Test/ObjectTest.cpp

@@ -62,4 +62,27 @@ void ObjectTest::scene() {
     QVERIFY(childOfOrphan->scene() == 0);
 }
 
+void ObjectTest::dirty() {
+    Scene scene;
+
+    Object* childOne = new Object(&scene);
+    Object* childTwo = new Object(childOne);
+    Object* childThree = new Object(childTwo);
+
+    /* Object is dirty at the beginning */
+    QVERIFY(childOne->isDirty());
+
+    /* Clean the object and all its parents */
+    childThree->setClean();
+    QVERIFY(!childThree->isDirty());
+    QVERIFY(!childTwo->isDirty());
+    QVERIFY(!childOne->isDirty());
+    QVERIFY(!scene.isDirty());
+
+    /* Mark object and all its children as dirty */
+    childTwo->setDirty();
+    QVERIFY(childTwo->isDirty());
+    QVERIFY(childThree->isDirty());
+}
+
 }}

src/Test/ObjectTest.h

@@ -27,6 +27,7 @@ class ObjectTest: public QObject {
     private slots:
         void parenting();
         void scene();
+        void dirty();
 };
 
 }}