First step of PaintInvalidator implementation

third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ObjectPaintInvalidator_h
+#define ObjectPaintInvalidator_h
+
+#include "platform/graphics/PaintInvalidationReason.h"
+#include "wtf/Allocator.h"
+
+namespace blink {
+
+class LayoutObject;
+class LayoutRect;
+struct PaintInvalidatorContext;
+
+class ObjectPaintInvalidator {
+    STACK_ALLOCATED();
+public:
+    ObjectPaintInvalidator(const LayoutObject& object, const PaintInvalidatorContext& context)
+        : m_object(object), m_context(context) { }
+
+    static void objectWillBeDestroyed(const LayoutObject&);
+
+    PaintInvalidationReason invalidatePaintIfNeeded() { return invalidatePaintIfNeededWithComputedReason(computePaintInvalidationReason()); }
+
+    PaintInvalidationReason computePaintInvalidationReason();
+    PaintInvalidationReason invalidatePaintIfNeededWithComputedReason(PaintInvalidationReason);
+
+private:
+    void invalidateSelectionIfNeeded(PaintInvalidationReason);
+
+    // This function tries to minimize the amount of invalidation generated by invalidating the "difference" between
+    // |m_context.oldBounds| and |m_context.newBounds|. This means invalidating the union of the previous rectangles
+    // but not their intersection. The use case is when an element only requires a paint invalidation (which means
+    // that its content didn't change) and its bounds changed but its location didn't.
+    // If we don't meet the criteria for an incremental paint, the alternative is a full paint invalidation.
+    void incrementallyInvalidatePaint();
+
+    // This function generates a full invalidation, which means invalidating both |oldBounds| and |newBounds|.
+    // This is the default choice when generating an invalidation, as it is always correct, albeit it may force some extra painting.
+    void fullyInvalidatePaint(PaintInvalidationReason, const LayoutRect& oldBounds, const LayoutRect& newBounds);
+
+    const LayoutObject& m_object;
+    const PaintInvalidatorContext& m_context;
+};
+
+} // namespace blink
+
+#endif