Initial scene graph (SkSG)

Sketching a thin (as in close-to-skia-semantics) scene graph API, focused on
external animation, inval tracking and minimal repaint.

Only a few concrete classes/features so far:

* Rect/Color/Transform/Group
* basic inval tracking
* a trivial animated sample with inval visualization

Pretty much everything (especially naming) is volatile, so treat accordingly.

The interesting bits to review are likely in Node.{h,cpp} for inval and
SampleSGInval.cpp for usage.

Initial class hierarchy:

  * Node: invalidation/ancestors tracking
  |
   -- * RenderNode: onRender(SkCanvas)
  |   |
  |    -- * Draw (concrete): rendering a [geometry, paint] tuple
  |   |
  |    -- * Group (concrete): grouping multiple RenderNodes
  |   |
  |    -- * EffectNode: single-descendant effect wrapper
  |       |
  |        -- * Transform (concrete): transform effect
  |
   -- * PaintNode: onMakePaint()
  |   |
  |    -- * Color (concrete): SkColor paint wrapper
  |
   -- * GeometryNode: onComputeBounds(), onDraw(SkCanvas, SkPaint)
      |
       -- * Rect (concrete): SkRect wrapper

TBR=

Change-Id: Iacf9b773c181a7582ecd31ee968562f179d1aa1b
Reviewed-on: https://skia-review.googlesource.com/85502
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>

1 files changed, 117 insertions, 0 deletions

diff --git a/experimental/sksg/SkSGNode.cpp b/experimental/sksg/SkSGNode.cpp
new file mode 100644
index 0000000000..3b404edd50
--- /dev/null
+++ b/experimental/sksg/SkSGNode.cpp
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkSGNode.h"
+
+namespace sksg {
+
+class Node::ScopedFlag {
+public:
+    ScopedFlag(Node* node, uint32_t flag)
+        : fNode(node)
+        , fFlag(flag) {
+        SkASSERT(!(fNode->fFlags & fFlag));
+        fNode->fFlags |= fFlag;
+    }
+    ~ScopedFlag() {
+        fNode->fFlags &= ~fFlag;;
+    }
+
+private:
+    Node*    fNode;
+    uint32_t fFlag;
+};
+
+#define TRAVERSAL_GUARD                     \
+    if (this->fFlags & kInTraversal_Flag) { \
+        return;                             \
+    }                                       \
+    ScopedFlag traversal_guard(this, kInTraversal_Flag);
+
+Node::Node()
+    : fInvalReceiver(nullptr)
+    , fFlags(kInvalidated_Flag) {}
+
+Node::~Node() {
+    if (fFlags & kReceiverArray_Flag) {
+        SkASSERT(fInvalReceiverArray->isEmpty());
+        delete fInvalReceiverArray;
+    } else {
+        SkASSERT(!fInvalReceiver);
+    }
+}
+
+void Node::addInvalReceiver(Node* receiver) {
+    if (!(fFlags & kReceiverArray_Flag)) {
+        if (!fInvalReceiver) {
+            fInvalReceiver = receiver;
+            return;
+        }
+
+        auto receivers = new SkTDArray<Node*>();
+        receivers->setReserve(2);
+        receivers->push(fInvalReceiver);
+
+        fInvalReceiverArray = receivers;
+        fFlags |= kReceiverArray_Flag;
+    }
+
+    // No duplicate receivers.
+    SkASSERT(fInvalReceiverArray->find(receiver) < 0);
+
+    fInvalReceiverArray->push(receiver);
+}
+
+void Node::removeInvalReceiver(Node* receiver) {
+    if (!(fFlags & kReceiverArray_Flag)) {
+        SkASSERT(fInvalReceiver == receiver);
+        fInvalReceiver = nullptr;
+        return;
+    }
+
+    const auto idx = fInvalReceiverArray->find(receiver);
+    SkASSERT(idx >= 0);
+    fInvalReceiverArray->remove(idx);
+}
+
+template <typename Func>
+void Node::forEachInvalReceiver(Func&& func) const {
+    if (fFlags & kReceiverArray_Flag) {
+        for (const auto& parent : *fInvalReceiverArray) {
+            func(parent);
+        }
+        return;
+    }
+
+    if (fInvalReceiver) {
+        func(fInvalReceiver);
+    }
+}
+
+void Node::invalidate() {
+    TRAVERSAL_GUARD
+
+    if (this->isInvalidated()) {
+        return;
+    }
+
+    fFlags |= kInvalidated_Flag;
+    forEachInvalReceiver([&](Node* receiver) {
+        receiver->invalidate();
+    });
+}
+
+void Node::revalidate(InvalidationController* ic, const SkMatrix& ctm) {
+    TRAVERSAL_GUARD
+
+    if (this->isInvalidated()) {
+        this->onRevalidate(ic, ctm);
+        fFlags &= ~kInvalidated_Flag;
+    }
+}
+
+} // namespace sksg