Calculate paint invalidation rect for scrollbars

third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp

Index: third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..5d704386d590aa0dfba4eb61ce7cf6277beb6638
--- /dev/null
+++ b/third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp
@@ -0,0 +1,84 @@
+// Copyright 2015 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.
+
+#include "config.h"
+#include "core/paint/PaintInvalidationCapableScrollableArea.h"
+
+#include "core/frame/Settings.h"
+#include "core/html/HTMLFrameOwnerElement.h"
+#include "core/layout/LayoutBox.h"
+#include "core/layout/LayoutScrollbar.h"
+#include "core/layout/LayoutScrollbarPart.h"
+#include "core/layout/PaintInvalidationState.h"
+#include "core/paint/PaintLayer.h"
+
+namespace blink {
+
+void PaintInvalidationCapableScrollableArea::willRemoveScrollbar(LayoutBox& box, Scrollbar* scrollbar, ScrollbarOrientation orientation)
+{
+    if (!scrollbar->isCustomScrollbar()
+        && !(orientation == HorizontalScrollbar ? layerForHorizontalScrollbar() : layerForVerticalScrollbar()))
+        box.invalidateDisplayItemClient(*scrollbar);
+
+    ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
+}
+
+// Returns true if the scroll control is invalidated.
+static bool invalidatePaintOfScrollControlIfNeeded(const IntRect& scrollControlRect, LayoutRect& previousPaintInvalidationRect, bool needsPaintInvalidation, LayoutBox& ownerBox, const PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer)
+{
+    LayoutRect paintInvalidationRect(scrollControlRect);
+    if (!paintInvalidationRect.isEmpty())
+        PaintLayer::mapRectToPaintInvalidationBacking(&ownerBox, &paintInvalidationContainer, paintInvalidationRect, &paintInvalidationState);
+
+    if (paintInvalidationRect != previousPaintInvalidationRect) {
+        ownerBox.invalidatePaintUsingContainer(paintInvalidationContainer, previousPaintInvalidationRect, PaintInvalidationScroll);
+        previousPaintInvalidationRect = paintInvalidationRect;
+        needsPaintInvalidation = true;
+    }
+
+    if (needsPaintInvalidation) {
+        ownerBox.invalidatePaintUsingContainer(paintInvalidationContainer, paintInvalidationRect, PaintInvalidationScroll);
+        return true;
+    }
+
+    return false;
+}
+
+static void invalidatePaintOfScrollbarIfNeeded(Scrollbar* scrollbar, GraphicsLayer* scrollbarGraphicsLayer, LayoutRect& previousPaintInvalidationRect, bool needsPaintInvalidation, LayoutBox& ownerBox, const PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer)
+{
+    IntRect scrollbarRect = scrollbar && !scrollbarGraphicsLayer ? scrollbar->frameRect() : IntRect();
+    if (!invalidatePaintOfScrollControlIfNeeded(scrollbarRect, previousPaintInvalidationRect, needsPaintInvalidation, ownerBox, paintInvalidationState, paintInvalidationContainer))
+        return;
+    if (!scrollbar)
+        return;
+
+    paintInvalidationContainer.invalidateDisplayItemClientOnBacking(*scrollbar, PaintInvalidationScroll, &previousPaintInvalidationRect);
+    if (scrollbar->isCustomScrollbar())
+        toLayoutScrollbar(scrollbar)->invalidateDisplayItemClientsOfScrollbarParts(paintInvalidationContainer, previousPaintInvalidationRect);
+}
+
+void PaintInvalidationCapableScrollableArea::invalidatePaintOfScrollControlsIfNeeded(LayoutBox& ownerBox, const PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer, LayoutScrollbarPart* scrollCorner, LayoutScrollbarPart* resizer)
+{
+    LayoutRect oldRect = m_horizontalScrollbarPreviousPaintInvalidationRect;
+    invalidatePaintOfScrollbarIfNeeded(horizontalScrollbar(), layerForHorizontalScrollbar(), m_horizontalScrollbarPreviousPaintInvalidationRect, horizontalScrollbarNeedsPaintInvalidation(), ownerBox, paintInvalidationState, paintInvalidationContainer);
+    bool scrollbarGeometryChanged = oldRect != m_horizontalScrollbarPreviousPaintInvalidationRect;
+
+    oldRect = m_verticalScrollbarPreviousPaintInvalidationRect;
+    invalidatePaintOfScrollbarIfNeeded(verticalScrollbar(), layerForVerticalScrollbar(), m_verticalScrollbarPreviousPaintInvalidationRect, verticalScrollbarNeedsPaintInvalidation(), ownerBox, paintInvalidationState, paintInvalidationContainer);
+    scrollbarGeometryChanged |= oldRect != m_verticalScrollbarPreviousPaintInvalidationRect;
+
+    if (scrollbarGeometryChanged)
+        paintInvalidationContainer.invalidateDisplayItemClientOnBacking(ownerBox, PaintInvalidationScroll, nullptr);
+
+    if (invalidatePaintOfScrollControlIfNeeded(scrollCornerRect(), m_scrollCornerPreviousPaintInvalidationRect, scrollCornerNeedsPaintInvalidation(), ownerBox, paintInvalidationState, paintInvalidationContainer)) {
+        if (scrollCorner)

[chrishtr, 2015/11/17 01:34:20]

Roll lines 75-78 into invalidatePaintOfScrollControlIfNeeded?

[Xianzhu, 2015/11/17 18:31:37]

It seems not feasible for invalidatePaintOfScrollControlIfNeeded to handle the
specialties of customized scrollbars and scroll corners/resizers.

+            scrollCorner->invalidateDisplayItemClientsIncludingNonCompositingDescendants(&paintInvalidationContainer, PaintInvalidationScroll, &m_scrollCornerPreviousPaintInvalidationRect);
+        if (resizer)
+            resizer->invalidateDisplayItemClientsIncludingNonCompositingDescendants(&paintInvalidationContainer, PaintInvalidationScroll, &m_scrollCornerPreviousPaintInvalidationRect);
+    }
+
+    clearNeedsPaintInvalidationForScrollControls();
+}
+
+} // namespace blink