Introducing on-dirty handler (aka YGNodeSetDirtiedFunc)

Summary:
@public
Currently, we can dirty leaf nodes with `measure` function, we also can get `dirty` status for any node, but we cannot handle a moment when this change happen. This diff introduces a new call-back-manner handler for it.
We need this to plug Yoga inside and outside other layout systems without maintaining own dirty propagation infrastructure.
Consider using Yoga for flex-box layout in React Native where we can have deeply nested layout like `<View><Text><View><Text/></View></Text></View>` where all content of all <Text> nodes are laid out using native text/inline (not flex-box!) layout system. In this case, when some change dirties some deeply nested Yoga node, we have to propagate the dirty state down to outer one. Having this handler makes possible to wire up `on-dirty` handler on the root node and `setDirtied` for the leaf node.
Removing custom dirting mechanism from React Native should drastically simplify rendering layer and bring a huge performance win.

Reviewed By: emilsjolander

Differential Revision: D6597856

fbshipit-source-id: 6588cd712f9c1dede4af32f3d326f90103e48ff0

yoga/YGNode.cpp

@@ -35,6 +35,10 @@ YGBaselineFunc YGNode::getBaseline() const {
   return baseline_;
 }
 
+YGDirtiedFunc YGNode::getDirtied() const {
+  return dirtied_;
+}
+
 YGStyle& YGNode::getStyle() {
   return style_;
 }
@@ -128,6 +132,10 @@ void YGNode::setBaseLineFunc(YGBaselineFunc baseLineFunc) {
   baseline_ = baseLineFunc;
 }
 
+void YGNode::setDirtiedFunc(YGDirtiedFunc dirtiedFunc) {
+  dirtied_ = dirtiedFunc;
+}
+
 void YGNode::setStyle(YGStyle style) {
   style_ = style;
 }
@@ -169,7 +177,13 @@ void YGNode::setConfig(YGConfigRef config) {
 }
 
 void YGNode::setDirty(bool isDirty) {
+  if (isDirty == isDirty_) {
+    return;
+  }
   isDirty_ = isDirty;
+  if (isDirty && dirtied_) {
+    dirtied_(this);
+  }
 }
 
 bool YGNode::removeChild(YGNodeRef child) {
@@ -238,6 +252,7 @@ YGNode::YGNode()
       nodeType_(YGNodeTypeDefault),
       measure_(nullptr),
       baseline_(nullptr),
+      dirtied_(nullptr),
       style_(gYGNodeStyleDefaults),
       layout_(gYGNodeLayoutDefaults),
       lineIndex_(0),
@@ -255,6 +270,7 @@ YGNode::YGNode(const YGNode& node)
       nodeType_(node.nodeType_),
       measure_(node.measure_),
       baseline_(node.baseline_),
+      dirtied_(node.dirtied_),
       style_(node.style_),
       layout_(node.layout_),
       lineIndex_(node.lineIndex_),
@@ -276,6 +292,7 @@ YGNode::YGNode(
     YGNodeType nodeType,
     YGMeasureFunc measure,
     YGBaselineFunc baseline,
+    YGDirtiedFunc dirtied,
     YGStyle style,
     YGLayout layout,
     uint32_t lineIndex,
@@ -291,6 +308,7 @@ YGNode::YGNode(
       nodeType_(nodeType),
       measure_(measure),
       baseline_(baseline),
+      dirtied_(dirtied),
       style_(style),
       layout_(layout),
       lineIndex_(lineIndex),
@@ -316,6 +334,7 @@ YGNode& YGNode::operator=(const YGNode& node) {
   nodeType_ = node.getNodeType();
   measure_ = node.getMeasure();
   baseline_ = node.getBaseline();
+  dirtied_ = node.getDirtied();
   style_ = node.style_;
   layout_ = node.layout_;
   lineIndex_ = node.getLineIndex();
@@ -415,7 +434,7 @@ void YGNode::cloneChildrenIfNeeded() {
 
 void YGNode::markDirtyAndPropogate() {
   if (!isDirty_) {
-    isDirty_ = true;
+    setDirty(true);
     setLayoutComputedFlexBasis(YGUndefined);
     if (parent_) {
       parent_->markDirtyAndPropogate();