diff --git a/gm/windowrectangles.cpp b/gm/windowrectangles.cpp
new file mode 100644
index 0000000000..b4ce7c23fb
--- /dev/null
+++ b/gm/windowrectangles.cpp
@@ -0,0 +1,300 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkClipStack.h"
+#include "SkRRect.h"
+
+#if SK_SUPPORT_GPU
+#  include "GrAppliedClip.h"
+#  include "GrDrawContext.h"
+#  include "GrDrawContextPriv.h"
+#  include "GrFixedClip.h"
+#  include "GrReducedClip.h"
+#  include "GrRenderTargetPriv.h"
+#  include "GrResourceProvider.h"
+#  include "effects/GrTextureDomain.h"
+#endif
+
+constexpr static SkIRect kDeviceRect = {0, 0, 600, 600};
+constexpr static SkIRect kLayerRect = {25, 25, 575, 575};
+constexpr static SkIRect kCoverRect = {50, 50, 550, 550};
+constexpr static int kNumWindows = 8;
+
+namespace skiagm {
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+class WindowRectanglesBaseGM : public GM {
+protected:
+    virtual void onCoverClipStack(const SkClipStack&, SkCanvas*) = 0;
+
+private:
+    SkISize onISize() override { return SkISize::Make(kDeviceRect.width(), kDeviceRect.height()); }
+    void onDraw(SkCanvas*) final;
+};
+
+void WindowRectanglesBaseGM::onDraw(SkCanvas* canvas) {
+    sk_tool_utils::draw_checkerboard(canvas, 0xffffffff, 0xffc6c3c6, 25);
+    canvas->saveLayer(SkRect::Make(kLayerRect), nullptr);
+
+    SkClipStack stack;
+    stack.clipDevRect(SkRect::MakeXYWH(370.75, 80.25, 149, 100), SkRegion::kDifference_Op, false);
+    stack.clipDevRect(SkRect::MakeXYWH(80.25, 420.75, 150, 100), SkRegion::kDifference_Op, true);
+    stack.clipDevRRect(SkRRect::MakeRectXY(SkRect::MakeXYWH(200, 200, 200, 200), 60, 45),
+                       SkRegion::kDifference_Op, true);
+
+    SkRRect nine;
+    nine.setNinePatch(SkRect::MakeXYWH(550 - 30.25 - 100, 370.75, 100, 150), 12, 35, 23, 20);
+    stack.clipDevRRect(nine, SkRegion::kDifference_Op, true);
+
+    SkRRect complx;
+    SkVector complxRadii[4] = {{6, 4}, {8, 12}, {16, 24}, {48, 32}};
+    complx.setRectRadii(SkRect::MakeXYWH(80.25, 80.75, 100, 149), complxRadii);
+    stack.clipDevRRect(complx, SkRegion::kDifference_Op, false);
+
+    this->onCoverClipStack(stack, canvas);
+
+    canvas->restore();
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+/**
+ * Draws a clip that will exercise window rectangles if they are supported.
+ */
+class WindowRectanglesGM : public WindowRectanglesBaseGM {
+private:
+    SkString onShortName() final { return SkString("windowrectangles"); }
+    void onCoverClipStack(const SkClipStack&, SkCanvas*) final;
+};
+
+/**
+ * This is a simple helper class for resetting a canvas's clip to our test’s SkClipStack.
+ */
+class ReplayClipStackVisitor final : public SkCanvasClipVisitor {
+public:
+    typedef SkRegion::Op Op;
+    ReplayClipStackVisitor(SkCanvas* canvas) : fCanvas(canvas) {}
+    void clipRect(const SkRect& r, Op op, bool aa) override { fCanvas->clipRect(r, op, aa); }
+    void clipRRect(const SkRRect& rr, Op op, bool aa) override { fCanvas->clipRRect(rr, op, aa); }
+    void clipPath(const SkPath&, Op, bool) override { SkFAIL("Not implemented"); }
+private:
+    SkCanvas* const fCanvas;
+};
+
+void WindowRectanglesGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
+    SkPaint paint;
+    paint.setColor(0xff00aa80);
+
+    // Set up the canvas's clip to match our SkClipStack.
+    ReplayClipStackVisitor visitor(canvas);
+    SkClipStack::Iter iter(stack, SkClipStack::Iter::kBottom_IterStart);
+    for (const SkClipStack::Element* element = iter.next(); element; element = iter.next()) {
+        element->replay(&visitor);
+    }
+
+    canvas->drawRect(SkRect::Make(kCoverRect), paint);
+}
+
+DEF_GM( return new WindowRectanglesGM(); )
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#if SK_SUPPORT_GPU
+
+/**
+ * Visualizes the mask (alpha or stencil) for a clip with several window rectangles. The purpose of
+ * this test is to verify that window rectangles are being used during clip mask generation, and to
+ * visualize where the window rectangles are placed.
+ *
+ * We use window rectangles when generating the clip mask because there is no need to invest time
+ * defining those regions where window rectangles will be in effect during the actual draw anyway.
+ *
+ * This test works by filling the entire clip mask with a small checkerboard pattern before drawing
+ * it, and then covering the mask with a solid color once it has been generated. The regions inside
+ * window rectangles or outside the scissor should still have the initial checkerboard intact.
+ */
+class WindowRectanglesMaskGM : public WindowRectanglesBaseGM {
+private:
+    constexpr static int kMaskCheckerSize = 5;
+    SkString onShortName() final { return SkString("windowrectangles_mask"); }
+    void onCoverClipStack(const SkClipStack&, SkCanvas*) final;
+    void visualizeAlphaMask(GrContext*, GrDrawContext*, const GrReducedClip&, const GrPaint&);
+    void visualizeStencilMask(GrContext*, GrDrawContext*, const GrReducedClip&, const GrPaint&);
+    void stencilCheckerboard(GrDrawContext*, bool flip);
+    void fail(SkCanvas*);
+};
+
+/**
+ * Base class for GrClips that visualize a clip mask.
+ */
+class MaskOnlyClipBase : public GrClip {
+private:
+    bool quickContains(const SkRect&) const final { return false; }
+    bool isRRect(const SkRect& rtBounds, SkRRect* rr, bool* aa) const final { return false; }
+    void getConservativeBounds(int width, int height, SkIRect* rect, bool* iior) const final {
+        rect->set(0, 0, width, height);
+        if (iior) {
+            *iior = false;
+        }
+    }
+};
+
+/**
+ * This class clips a cover by an alpha mask. We use it to visualize the alpha clip mask.
+ */
+class AlphaOnlyClip final : public MaskOnlyClipBase {
+public:
+    AlphaOnlyClip(GrTexture* mask, int x, int y) {
+        int w = mask->width(), h = mask->height();
+        SkMatrix mat = SkMatrix::MakeScale(1.f / SkIntToScalar(w), 1.f / SkIntToScalar(h));
+        mat.preTranslate(SkIntToScalar(-x), SkIntToScalar(-y));
+        fFP = GrTextureDomainEffect::Make(
+                  mask, nullptr, mat,
+                  GrTextureDomain::MakeTexelDomain(mask, SkIRect::MakeWH(w, h)),
+                  GrTextureDomain::kDecal_Mode, GrTextureParams::kNone_FilterMode,
+                  kDevice_GrCoordSet);
+
+    }
+private:
+    bool apply(GrContext*, GrDrawContext*, bool, bool, GrAppliedClip* out) const override {
+        out->addCoverageFP(fFP);
+        return true;
+    }
+    sk_sp<GrFragmentProcessor> fFP;
+};
+
+/**
+ * This class clips a cover by the stencil clip bit. We use it to visualize the stencil mask.
+ */
+class StencilOnlyClip final : public MaskOnlyClipBase {
+private:
+    bool apply(GrContext*, GrDrawContext*, bool, bool, GrAppliedClip* out) const override {
+        out->addStencilClip();
+        return true;
+    }
+};
+
+void WindowRectanglesMaskGM::onCoverClipStack(const SkClipStack& stack, SkCanvas* canvas) {
+    GrContext* ctx = canvas->getGrContext();
+    GrDrawContext* dc = canvas->internal_private_accessTopLayerDrawContext();
+
+    if (!ctx || !dc ||
+        dc->accessRenderTarget()->renderTargetPriv().maxWindowRectangles() < kNumWindows) {
+        this->fail(canvas);
+        return;
+    }
+
+    const GrReducedClip reducedClip(stack, SkRect::Make(kCoverRect), kNumWindows);
+
+    GrPaint paint;
+    paint.setAntiAlias(true);
+    if (!dc->isStencilBufferMultisampled()) {
+        paint.setColor4f(GrColor4f(0, 0.25f, 1, 1));
+        this->visualizeAlphaMask(ctx, dc, reducedClip, paint);
+    } else {
+        paint.setColor4f(GrColor4f(1, 0.25f, 0.25f, 1));
+        this->visualizeStencilMask(ctx, dc, reducedClip, paint);
+    }
+}
+
+void WindowRectanglesMaskGM::visualizeAlphaMask(GrContext* ctx, GrDrawContext* dc,
+                                                const GrReducedClip& reducedClip,
+                                                const GrPaint& paint) {
+    sk_sp<GrDrawContext> maskDC(
+        ctx->makeDrawContextWithFallback(SkBackingFit::kExact, kLayerRect.width(),
+                                         kLayerRect.height(), kAlpha_8_GrPixelConfig, nullptr));
+    if (!maskDC ||
+        !ctx->resourceProvider()->attachStencilAttachment(maskDC->accessRenderTarget())) {
+        return;
+    }
+
+    // Draw a checker pattern into the alpha mask so we can visualize the regions left untouched by
+    // the clip mask generation.
+    this->stencilCheckerboard(maskDC.get(), true);
+    maskDC->clear(nullptr, GrColorPackA4(0xff), true);
+    maskDC->drawContextPriv().drawAndStencilRect(StencilOnlyClip(), &GrUserStencilSettings::kUnused,
+                                                 SkRegion::kDifference_Op, false, false,
+                                                 SkMatrix::I(),
+                                                 SkRect::MakeIWH(maskDC->width(), maskDC->height()));
+    reducedClip.drawAlphaClipMask(maskDC.get());
+    sk_sp<GrTexture> mask(maskDC->asTexture());
+
+    int x = kCoverRect.x() - kLayerRect.x(),
+        y = kCoverRect.y() - kLayerRect.y();
+
+    // Now visualize the alpha mask by drawing a rect over the area where it is defined. The regions
+    // inside window rectangles or outside the scissor should still have the initial checkerboard
+    // intact. (This verifies we didn't spend any time modifying those pixels in the mask.)
+    AlphaOnlyClip clip(mask.get(), x, y);
+    dc->drawRect(clip, paint, SkMatrix::I(),
+                 SkRect::Make(SkIRect::MakeXYWH(x, y, mask->width(), mask->height())));
+}
+
+void WindowRectanglesMaskGM::visualizeStencilMask(GrContext* ctx, GrDrawContext* dc,
+                                                  const GrReducedClip& reducedClip,
+                                                  const GrPaint& paint) {
+    if (!ctx->resourceProvider()->attachStencilAttachment(dc->accessRenderTarget())) {
+        return;
+    }
+
+    // Draw a checker pattern into the stencil buffer so we can visualize the regions left untouched
+    // by the clip mask generation.
+    this->stencilCheckerboard(dc, false);
+    reducedClip.drawStencilClipMask(ctx, dc, {kLayerRect.x(), kLayerRect.y()});
+
+    // Now visualize the stencil mask by covering the entire render target. The regions inside
+    // window rectangless or outside the scissor should still have the initial checkerboard intact.
+    // (This verifies we didn't spend any time modifying those pixels in the mask.)
+    dc->drawPaint(StencilOnlyClip(), paint, SkMatrix::I());
+}
+
+void WindowRectanglesMaskGM::stencilCheckerboard(GrDrawContext* dc, bool flip) {
+    constexpr static GrUserStencilSettings kSetClip(
+        GrUserStencilSettings::StaticInit<
+        0,
+        GrUserStencilTest::kAlways,
+        0,
+        GrUserStencilOp::kSetClipBit,
+        GrUserStencilOp::kKeep,
+        0>()
+    );
+
+    dc->drawContextPriv().clearStencilClip(GrFixedClip::Disabled(), false);
+
+    for (int y = 0; y < kLayerRect.height(); y += kMaskCheckerSize) {
+        for (int x = (y & 1) == flip ? 0 : kMaskCheckerSize;
+             x < kLayerRect.width(); x += 2 * kMaskCheckerSize) {
+            SkIRect checker = SkIRect::MakeXYWH(x, y, kMaskCheckerSize, kMaskCheckerSize);
+            dc->drawContextPriv().stencilRect(GrNoClip(), &kSetClip, false, SkMatrix::I(),
+                                              SkRect::Make(checker));
+        }
+    }
+}
+
+void WindowRectanglesMaskGM::fail(SkCanvas* canvas) {
+    SkPaint paint;
+    paint.setAntiAlias(true);
+    paint.setTextAlign(SkPaint::kCenter_Align);
+    paint.setTextSize(20);
+    sk_tool_utils::set_portable_typeface(&paint);
+
+    SkString errorMsg;
+    errorMsg.printf("Requires GPU with %i window rectangles", kNumWindows);
+
+    canvas->clipRect(SkRect::Make(kCoverRect));
+    canvas->clear(SK_ColorWHITE);
+    canvas->drawText(errorMsg.c_str(), errorMsg.size(), SkIntToScalar(kCoverRect.centerX()),
+                     SkIntToScalar(kCoverRect.centerY() - 10), paint);
+}
+
+DEF_GM( return new WindowRectanglesMaskGM(); )
+
+#endif
+
+}
diff --git a/gyp/gpu.gypi b/gyp/gpu.gypi
index d1a6952f13..33142f2df3 100644
--- a/gyp/gpu.gypi
+++ b/gyp/gpu.gypi
@@ -170,6 +170,7 @@
       '<(skia_src_path)/gpu/GrResourceHandle.h',
       '<(skia_src_path)/gpu/GrResourceProvider.cpp',
       '<(skia_src_path)/gpu/GrResourceProvider.h',
+      '<(skia_src_path)/gpu/GrScissorState.h',
       '<(skia_src_path)/gpu/GrShape.cpp',
       '<(skia_src_path)/gpu/GrShape.h',
       '<(skia_src_path)/gpu/GrStencilAttachment.cpp',
@@ -204,6 +205,7 @@
       '<(skia_src_path)/gpu/GrTRecorder.h',
       '<(skia_src_path)/gpu/GrUserStencilSettings.h',
       '<(skia_src_path)/gpu/GrWindowRectangles.h',
+      '<(skia_src_path)/gpu/GrWindowRectsState.h',
       '<(skia_src_path)/gpu/GrXferProcessor.cpp',
       '<(skia_src_path)/gpu/GrYUVProvider.cpp',
       '<(skia_src_path)/gpu/GrYUVProvider.h',
diff --git a/include/gpu/GrTypesPriv.h b/include/gpu/GrTypesPriv.h
index 8c42d648d0..d60fab1337 100644
--- a/include/gpu/GrTypesPriv.h
+++ b/include/gpu/GrTypesPriv.h
@@ -9,7 +9,6 @@
 #define GrTypesPriv_DEFINED
 
 #include "GrTypes.h"
-#include "SkRect.h"
 #include "SkRefCnt.h"
 
  /**
@@ -420,32 +419,6 @@ enum GrIOType {
     kRW_GrIOType
 };
 
-struct GrScissorState {
-    GrScissorState() : fEnabled(false) {}
-    GrScissorState(const SkIRect& rect) : fEnabled(true), fRect(rect) {}
-    void setDisabled() { fEnabled = false; }
-    void set(const SkIRect& rect) { fRect = rect; fEnabled = true; }
-    bool SK_WARN_UNUSED_RESULT intersect(const SkIRect& rect) {
-        if (!fEnabled) {
-            this->set(rect);
-            return true;
-        }
-        return fRect.intersect(rect);
-    }
-    bool operator==(const GrScissorState& other) const {
-        return fEnabled == other.fEnabled &&
-                (false == fEnabled || fRect == other.fRect);
-    }
-    bool operator!=(const GrScissorState& other) const { return !(*this == other); }
-
-    bool enabled() const { return fEnabled; }
-    const SkIRect& rect() const { return fRect; }
-
-private:
-    bool    fEnabled;
-    SkIRect fRect;
-};
-
 /**
 * Indicates the type of data that a GPU buffer will be used for.
 */
diff --git a/include/private/GrSurfaceProxy.h b/include/private/GrSurfaceProxy.h
index 98979ac819..69656fe4f5 100644
--- a/include/private/GrSurfaceProxy.h
+++ b/include/private/GrSurfaceProxy.h
@@ -9,6 +9,7 @@
 #define GrSurfaceProxy_DEFINED
 
 #include "GrGpuResource.h"
+#include "SkRect.h"
 
 class GrTextureProxy;
 class GrRenderTargetProxy;
diff --git a/src/gpu/GrAppliedClip.h b/src/gpu/GrAppliedClip.h
index c02e9d01c2..3e98c6cb05 100644
--- a/src/gpu/GrAppliedClip.h
+++ b/src/gpu/GrAppliedClip.h
@@ -8,8 +8,8 @@
 #ifndef GrAppliedClip_DEFINED
 #define GrAppliedClip_DEFINED
 
-#include "GrTypesPriv.h"
-#include "GrWindowRectangles.h"
+#include "GrScissorState.h"
+#include "GrWindowRectsState.h"
 
 class GrFragmentProcessor;
 
@@ -25,7 +25,7 @@ public:
     }
 
     const GrScissorState& scissorState() const { return fScissorState; }
-    const GrWindowRectangles& windowRects() const { return fWindowRects; }
+    const GrWindowRectsState& windowRectsState() const { return fWindowRectsState; }
     GrFragmentProcessor* clipCoverageFragmentProcessor() const { return fClipCoverageFP.get(); }
     bool hasStencilClip() const { return fHasStencilClip; }
 
@@ -36,12 +36,15 @@ public:
         return fScissorState.intersect(irect) && fClippedDrawBounds.intersect(SkRect::Make(irect));
     }
 
-    /**
-     * Adds an exclusive window rectangle to the clip. It is not currently supported to switch the
-     * windows to inclusive mode.
-     */
-    void addWindowRectangle(const SkIRect& window) {
-        fWindowRects.addWindow(window);
+    void addWindowRectangles(const GrWindowRectsState& windowState) {
+        SkASSERT(!fWindowRectsState.enabled());
+        fWindowRectsState = windowState;
+    }
+
+    void addWindowRectangles(const GrWindowRectangles& windows, const SkIPoint& origin,
+                             GrWindowRectsState::Mode mode) {
+        SkASSERT(!fWindowRectsState.enabled());
+        fWindowRectsState.set(windows, origin, mode);
     }
 
     void addCoverageFP(sk_sp<GrFragmentProcessor> fp) {
@@ -62,7 +65,7 @@ public:
 
 private:
     GrScissorState             fScissorState;
-    GrWindowRectangles         fWindowRects;
+    GrWindowRectsState         fWindowRectsState;
     sk_sp<GrFragmentProcessor> fClipCoverageFP;
     bool                       fHasStencilClip;
     SkRect                     fClippedDrawBounds;
diff --git a/src/gpu/GrClipStackClip.cpp b/src/gpu/GrClipStackClip.cpp
index 4572db5f32..d6ad1d90f8 100644
--- a/src/gpu/GrClipStackClip.cpp
+++ b/src/gpu/GrClipStackClip.cpp
@@ -287,11 +287,14 @@ bool GrClipStackClip::apply(GrContext* context, GrDrawContext* drawContext, bool
         return false;
     }
 
+    GrRenderTarget* rt = drawContext->accessRenderTarget();
+
     const SkScalar clipX = SkIntToScalar(fOrigin.x()),
                    clipY = SkIntToScalar(fOrigin.y());
 
     SkRect clipSpaceDevBounds = devBounds.makeOffset(clipX, clipY);
-    const GrReducedClip reducedClip(*fStack, clipSpaceDevBounds);
+    const GrReducedClip reducedClip(*fStack, clipSpaceDevBounds,
+                                    rt->renderTargetPriv().maxWindowRectangles());
 
     if (reducedClip.hasIBounds() &&
         !GrClip::IsInsideClip(reducedClip.ibounds(), clipSpaceDevBounds)) {
@@ -300,29 +303,17 @@ bool GrClipStackClip::apply(GrContext* context, GrDrawContext* drawContext, bool
         out->addScissor(scissorSpaceIBounds);
     }
 
+    if (!reducedClip.windowRectangles().empty()) {
+        out->addWindowRectangles(reducedClip.windowRectangles(), fOrigin,
+                                 GrWindowRectsState::Mode::kExclusive);
+    }
+
     if (reducedClip.elements().isEmpty()) {
         return InitialState::kAllIn == reducedClip.initialState();
     }
 
     SkASSERT(reducedClip.hasIBounds());
 
-    // Attempt to implement difference clip rects with window rectangles. This will eventually
-    // become more comprehensive.
-    if (drawContext->accessRenderTarget()->renderTargetPriv().supportsWindowRectangles() &&
-        1 == reducedClip.elements().count() && !reducedClip.requiresAA() &&
-        InitialState::kAllIn == reducedClip.initialState()) {
-        const Element* element = reducedClip.elements().head();
-        SkRegion::Op op = element->getOp();
-        if (Element::kRect_Type == element->getType() &&
-            (SkRegion::kDifference_Op == op || SkRegion::kXOR_Op == op)) {
-            SkIRect window;
-            element->getRect().round(&window);
-            window.offset(-fOrigin);
-            out->addWindowRectangle(window);
-            return true;
-        }
-    }
-
     // An element count of 4 was chosen because of the common pattern in Blink of:
     //   isect RR
     //   diff  RR
@@ -377,12 +368,15 @@ bool GrClipStackClip::apply(GrContext* context, GrDrawContext* drawContext, bool
     // use the stencil clip if we can't represent the clip as a rectangle.
     // TODO: these need to be swapped over to using a StencilAttachmentProxy
     GrStencilAttachment* stencilAttachment =
-        context->resourceProvider()->attachStencilAttachment(drawContext->accessRenderTarget());
+        context->resourceProvider()->attachStencilAttachment(rt);
     if (nullptr == stencilAttachment) {
         SkDebugf("WARNING: failed to attach stencil buffer for clip mask. Clip will be ignored.\n");
         return true;
     }
 
+    // This relies on the property that a reduced sub-rect of the last clip will contain all the
+    // relevant window rectangles that were in the last clip. This subtle requirement will go away
+    // after clipping is overhauled.
     if (stencilAttachment->mustRenderClip(reducedClip.elementsGenID(), reducedClip.ibounds(),
                                           fOrigin)) {
         reducedClip.drawStencilClipMask(context, drawContext, fOrigin);
diff --git a/src/gpu/GrDrawContext.cpp b/src/gpu/GrDrawContext.cpp
index 1fd113dce3..87252f3979 100644
--- a/src/gpu/GrDrawContext.cpp
+++ b/src/gpu/GrDrawContext.cpp
@@ -215,9 +215,12 @@ void GrDrawContextPriv::clear(const GrFixedClip& clip,
 void GrDrawContext::internalClear(const GrFixedClip& clip,
                                   const GrColor color,
                                   bool canIgnoreClip) {
-    bool isFull = !clip.scissorEnabled() ||
-                  (canIgnoreClip && fContext->caps()->fullClearIsFree()) ||
-                  clip.scissorRect().contains(SkIRect::MakeWH(this->width(), this->height()));
+    bool isFull = false;
+    if (!clip.hasWindowRectangles()) {
+        isFull = !clip.scissorEnabled() ||
+                 (canIgnoreClip && fContext->caps()->fullClearIsFree()) ||
+                 clip.scissorRect().contains(SkIRect::MakeWH(this->width(), this->height()));
+    }
 
     if (fContext->caps()->useDrawInsteadOfClear()) {
         // This works around a driver bug with clear by drawing a rect instead.
diff --git a/src/gpu/GrDrawTarget.cpp b/src/gpu/GrDrawTarget.cpp
index 3b9f1ec1a6..0117d0e1a1 100644
--- a/src/gpu/GrDrawTarget.cpp
+++ b/src/gpu/GrDrawTarget.cpp
@@ -381,7 +381,7 @@ void GrDrawTarget::drawBatch(const GrPipelineBuilder& pipelineBuilder,
         sk_sp_address_as_pointer_address(pipelineBuilder.fCoverageFragmentProcessors.begin()),
         pipelineBuilder.numCoverageFragmentProcessors());
     args.fScissor = &appliedClip.scissorState();
-    args.fWindowRects = &appliedClip.windowRects();
+    args.fWindowRectsState = &appliedClip.windowRectsState();
     args.fHasStencilClip = appliedClip.hasStencilClip();
     if (!this->setupDstReadIfNecessary(pipelineBuilder, drawContext->accessRenderTarget(),
                                        clip, args.fOpts,
diff --git a/src/gpu/GrFixedClip.cpp b/src/gpu/GrFixedClip.cpp
index ebdd49bbf8..7385028baf 100644
--- a/src/gpu/GrFixedClip.cpp
+++ b/src/gpu/GrFixedClip.cpp
@@ -10,25 +10,45 @@
 #include "GrAppliedClip.h"
 #include "GrDrawContext.h"
 
-void GrFixedClip::getConservativeBounds(int width, int height, SkIRect* devResult,
-                                        bool* isIntersectionOfRects) const {
-    devResult->setXYWH(0, 0, width, height);
+bool GrFixedClip::quickContains(const SkRect& rect) const {
+    if (fWindowRectsState.enabled()) {
+        return false;
+    }
+    return !fScissorState.enabled() || GrClip::IsInsideClip(fScissorState.rect(), rect);
+}
+
+void GrFixedClip::getConservativeBounds(int w, int h, SkIRect* devResult, bool* iior) const {
+    devResult->setXYWH(0, 0, w, h);
     if (fScissorState.enabled()) {
         if (!devResult->intersect(fScissorState.rect())) {
             devResult->setEmpty();
         }
     }
-    if (isIntersectionOfRects) {
-        *isIntersectionOfRects = true;
+    if (iior) {
+        *iior = true;
     }
 }
 
-bool GrFixedClip::apply(GrContext*, GrDrawContext* drawContext, bool isHWAntiAlias,
-                        bool hasUserStencilSettings, GrAppliedClip* out) const {
+bool GrFixedClip::isRRect(const SkRect& rtBounds, SkRRect* rr, bool* aa) const {
+    if (fWindowRectsState.enabled()) {
+        return false;
+    }
     if (fScissorState.enabled()) {
-        SkIRect tightScissor;
-        if (!tightScissor.intersect(fScissorState.rect(),
-                                    SkIRect::MakeWH(drawContext->width(), drawContext->height()))) {
+        SkRect rect = SkRect::Make(fScissorState.rect());
+        if (!rect.intersects(rtBounds)) {
+            return false;
+        }
+        rr->setRect(rect);
+        *aa = false;
+        return true;
+    }
+    return false;
+};
+
+bool GrFixedClip::apply(GrContext*, GrDrawContext* dc, bool, bool, GrAppliedClip* out) const {
+    if (fScissorState.enabled()) {
+        SkIRect tightScissor = SkIRect::MakeWH(dc->width(), dc->height());
+        if (!tightScissor.intersect(fScissorState.rect())) {
             return false;
         }
         if (IsOutsideClip(tightScissor, out->clippedDrawBounds())) {
@@ -39,6 +59,10 @@ bool GrFixedClip::apply(GrContext*, GrDrawContext* drawContext, bool isHWAntiAli
         }
     }
 
+    if (fWindowRectsState.enabled()) {
+        out->addWindowRectangles(fWindowRectsState);
+    }
+
     return true;
 }
 
diff --git a/src/gpu/GrFixedClip.h b/src/gpu/GrFixedClip.h
index 8b3a9c1c9e..6fb7d23ed1 100644
--- a/src/gpu/GrFixedClip.h
+++ b/src/gpu/GrFixedClip.h
@@ -9,7 +9,8 @@
 #define GrFixedClip_DEFINED
 
 #include "GrClip.h"
-#include "GrTypesPriv.h"
+#include "GrScissorState.h"
+#include "GrWindowRectsState.h"
 
 /**
  * GrFixedClip is a clip that gets implemented by fixed-function hardware.
@@ -29,32 +30,26 @@ public:
         return fScissorState.intersect(irect);
     }
 
-    bool quickContains(const SkRect& rect) const final {
-        return !fScissorState.enabled() || GrClip::IsInsideClip(fScissorState.rect(), rect);
+    const GrWindowRectsState& windowRectsState() const { return fWindowRectsState; }
+    bool hasWindowRectangles() const { return fWindowRectsState.enabled(); }
+
+    void disableWindowRectangles() { fWindowRectsState.setDisabled(); }
+
+    void setWindowRectangles(const GrWindowRectangles& windows, const SkIPoint& origin,
+                             GrWindowRectsState::Mode mode) {
+        fWindowRectsState.set(windows, origin, mode);
     }
-    void getConservativeBounds(int width, int height, SkIRect* devResult,
-                               bool* isIntersectionOfRects) const final;
 
-    bool isRRect(const SkRect& rtBounds, SkRRect* rr, bool* aa) const override {
-        if (fScissorState.enabled()) {
-            SkRect rect = SkRect::Make(fScissorState.rect());
-            if (!rect.intersects(rtBounds)) {
-                return false;
-            }
-            rr->setRect(rect);
-            *aa = false;
-            return true;
-        }
-        return false;
-    };
-
-    bool apply(GrContext*, GrDrawContext*, bool useHWAA, bool hasUserStencilSettings,
-               GrAppliedClip* out) const final;
+    bool quickContains(const SkRect&) const override;
+    void getConservativeBounds(int w, int h, SkIRect* devResult, bool* iior) const override;
+    bool isRRect(const SkRect& rtBounds, SkRRect* rr, bool* aa) const override;
+    bool apply(GrContext*, GrDrawContext*, bool, bool, GrAppliedClip* out) const override;
 
     static const GrFixedClip& Disabled();
 
 private:
-    GrScissorState   fScissorState;
+    GrScissorState       fScissorState;
+    GrWindowRectsState   fWindowRectsState;
 };
 
 #endif
diff --git a/src/gpu/GrPipeline.cpp b/src/gpu/GrPipeline.cpp
index 8fe321d667..892bccd319 100644
--- a/src/gpu/GrPipeline.cpp
+++ b/src/gpu/GrPipeline.cpp
@@ -27,7 +27,7 @@ GrPipeline* GrPipeline::CreateAt(void* memory, const CreateArgs& args,
     pipeline->fRenderTarget.reset(rt);
     SkASSERT(pipeline->fRenderTarget);
     pipeline->fScissorState = *args.fScissor;
-    pipeline->fWindowRects = *args.fWindowRects;
+    pipeline->fWindowRectsState = *args.fWindowRectsState;
     if (builder.hasUserStencilSettings() || args.fHasStencilClip) {
         const GrRenderTargetPriv& rtPriv = rt->renderTargetPriv();
         pipeline->fStencilSettings.reset(*builder.getUserStencil(), args.fHasStencilClip,
@@ -230,7 +230,7 @@ bool GrPipeline::AreEqual(const GrPipeline& a, const GrPipeline& b,
         a.fFragmentProcessors.count() != b.fFragmentProcessors.count() ||
         a.fNumColorProcessors != b.fNumColorProcessors ||
         a.fScissorState != b.fScissorState ||
-        a.fWindowRects != b.fWindowRects ||
+        !a.fWindowRectsState.cheapEqualTo(b.fWindowRectsState) ||
         a.fFlags != b.fFlags ||
         a.fStencilSettings != b.fStencilSettings ||
         a.fDrawFace != b.fDrawFace ||
diff --git a/src/gpu/GrPipeline.h b/src/gpu/GrPipeline.h
index 18f1a2a266..8c2f538e27 100644
--- a/src/gpu/GrPipeline.h
+++ b/src/gpu/GrPipeline.h
@@ -16,9 +16,9 @@
 #include "GrPrimitiveProcessor.h"
 #include "GrProcOptInfo.h"
 #include "GrProgramDesc.h"
+#include "GrScissorState.h"
 #include "GrStencilSettings.h"
-#include "GrTypesPriv.h"
-#include "GrWindowRectangles.h"
+#include "GrWindowRectsState.h"
 #include "SkMatrix.h"
 #include "SkRefCnt.h"
 
@@ -60,7 +60,7 @@ public:
         const GrCaps*               fCaps;
         GrPipelineOptimizations     fOpts;
         const GrScissorState*       fScissor;
-        const GrWindowRectangles*   fWindowRects;
+        const GrWindowRectsState*   fWindowRectsState;
         bool                        fHasStencilClip;
         GrXferProcessor::DstTexture fDstTexture;
     };
@@ -154,7 +154,7 @@ public:
 
     const GrScissorState& getScissorState() const { return fScissorState; }
 
-    const GrWindowRectangles& getWindowRectangles() const { return fWindowRects; }
+    const GrWindowRectsState& getWindowRectsState() const { return fWindowRectsState; }
 
     bool isHWAntialiasState() const { return SkToBool(fFlags & kHWAA_Flag); }
     bool snapVerticesToPixelCenters() const { return SkToBool(fFlags & kSnapVertices_Flag); }
@@ -223,7 +223,7 @@ private:
     typedef GrPendingProgramElement<const GrXferProcessor> ProgramXferProcessor;
     RenderTarget                        fRenderTarget;
     GrScissorState                      fScissorState;
-    GrWindowRectangles                  fWindowRects;
+    GrWindowRectsState                  fWindowRectsState;
     GrStencilSettings                   fStencilSettings;
     GrDrawFace                          fDrawFace;
     uint32_t                            fFlags;
diff --git a/src/gpu/GrReducedClip.cpp b/src/gpu/GrReducedClip.cpp
index dfc0a2651b..89690d3663 100644
--- a/src/gpu/GrReducedClip.cpp
+++ b/src/gpu/GrReducedClip.cpp
@@ -28,7 +28,8 @@ typedef SkClipStack::Element Element;
  * based on later intersect operations, and perhaps remove intersect-rects. We could optionally
  * take a rect in case the caller knows a bound on what is to be drawn through this clip.
  */
-GrReducedClip::GrReducedClip(const SkClipStack& stack, const SkRect& queryBounds) {
+GrReducedClip::GrReducedClip(const SkClipStack& stack, const SkRect& queryBounds,
+                             int maxWindowRectangles) {
     SkASSERT(!queryBounds.isEmpty());
     fHasIBounds = false;
 
@@ -94,10 +95,15 @@ GrReducedClip::GrReducedClip(const SkClipStack& stack, const SkRect& queryBounds
 
     // Now that we have determined the bounds to use and filtered out the trivial cases, call the
     // helper that actually walks the stack.
-    this->walkStack(stack, tighterQuery);
+    this->walkStack(stack, tighterQuery, maxWindowRectangles);
+
+    if (fWindowRects.count() < maxWindowRectangles) {
+        this->addInteriorWindowRectangles(maxWindowRectangles);
+    }
 }
 
-void GrReducedClip::walkStack(const SkClipStack& stack, const SkRect& queryBounds) {
+void GrReducedClip::walkStack(const SkClipStack& stack, const SkRect& queryBounds,
+                              int maxWindowRectangles) {
     // walk backwards until we get to:
     //  a) the beginning
     //  b) an operation that is known to make the bounds all inside/outside
@@ -156,6 +162,10 @@ void GrReducedClip::walkStack(const SkClipStack& stack, const SkRect& queryBound
                         skippable = true;
                     } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
                         skippable = true;
+                    } else if (fWindowRects.count() < maxWindowRectangles && !embiggens &&
+                               !element->isAA() && Element::kRect_Type == element->getType()) {
+                        this->addWindowRectangle(element->getRect(), false);
+                        skippable = true;
                     }
                 }
                 if (!skippable) {
@@ -420,10 +430,88 @@ void GrReducedClip::walkStack(const SkClipStack& stack, const SkRect& queryBound
     fInitialState = static_cast<GrReducedClip::InitialState>(initialTriState);
 }
 
+static bool element_is_pure_subtract(SkRegion::Op op) {
+    SkASSERT(op >= 0);
+    return op <= SkRegion::kIntersect_Op;
+
+    GR_STATIC_ASSERT(0 == SkRegion::kDifference_Op);
+    GR_STATIC_ASSERT(1 == SkRegion::kIntersect_Op);
+}
+
+void GrReducedClip::addInteriorWindowRectangles(int maxWindowRectangles) {
+    SkASSERT(fWindowRects.count() < maxWindowRectangles);
+    // Walk backwards through the element list and add window rectangles to the interiors of
+    // "difference" elements. Quit if we encounter an element that may grow the clip.
+    ElementList::Iter iter(fElements, ElementList::Iter::kTail_IterStart);
+    for (; iter.get() && element_is_pure_subtract(iter.get()->getOp()); iter.prev()) {
+        const Element* element = iter.get();
+        if (SkRegion::kDifference_Op != element->getOp()) {
+            continue;
+        }
+
+        if (Element::kRect_Type == element->getType()) {
+            SkASSERT(element->isAA());
+            this->addWindowRectangle(element->getRect(), true);
+            if (fWindowRects.count() >= maxWindowRectangles) {
+                return;
+            }
+            continue;
+        }
+
+        if (Element::kRRect_Type == element->getType()) {
+            // For round rects we add two overlapping windows in the shape of a plus.
+            const SkRRect& clipRRect = element->getRRect();
+            SkVector insetTL = clipRRect.radii(SkRRect::kUpperLeft_Corner);
+            SkVector insetBR = clipRRect.radii(SkRRect::kLowerRight_Corner);
+            if (SkRRect::kComplex_Type == clipRRect.getType()) {
+                const SkVector& insetTR = clipRRect.radii(SkRRect::kUpperRight_Corner);
+                const SkVector& insetBL = clipRRect.radii(SkRRect::kLowerLeft_Corner);
+                insetTL.fX = SkTMax(insetTL.x(), insetBL.x());
+                insetTL.fY = SkTMax(insetTL.y(), insetTR.y());
+                insetBR.fX = SkTMax(insetBR.x(), insetTR.x());
+                insetBR.fY = SkTMax(insetBR.y(), insetBL.y());
+            }
+            const SkRect& bounds = clipRRect.getBounds();
+            if (insetTL.x() + insetBR.x() >= bounds.width() ||
+                insetTL.y() + insetBR.y() >= bounds.height()) {
+                continue; // The interior "plus" is empty.
+            }
+
+            SkRect horzRect = SkRect::MakeLTRB(bounds.left(), bounds.top() + insetTL.y(),
+                                               bounds.right(), bounds.bottom() - insetBR.y());
+            this->addWindowRectangle(horzRect, element->isAA());
+            if (fWindowRects.count() >= maxWindowRectangles) {
+                return;
+            }
+
+            SkRect vertRect = SkRect::MakeLTRB(bounds.left() + insetTL.x(), bounds.top(),
+                                               bounds.right() - insetBR.x(), bounds.bottom());
+            this->addWindowRectangle(vertRect, element->isAA());
+            if (fWindowRects.count() >= maxWindowRectangles) {
+                return;
+            }
+            continue;
+        }
+    }
+}
+
+inline void GrReducedClip::addWindowRectangle(const SkRect& elementInteriorRect, bool elementIsAA) {
+    SkIRect window;
+    if (!elementIsAA) {
+        elementInteriorRect.round(&window);
+    } else {
+        elementInteriorRect.roundIn(&window);
+    }
+    if (!window.isEmpty()) { // Skip very thin windows that round to zero or negative dimensions.
+        fWindowRects.addWindow(window);
+    }
+}
+
 inline bool GrReducedClip::intersectIBounds(const SkIRect& irect) {
     SkASSERT(fHasIBounds);
     if (!fIBounds.intersect(irect)) {
         fHasIBounds = false;
+        fWindowRects.reset();
         fElements.reset();
         fRequiresAA = false;
         fInitialState = InitialState::kAllOut;
@@ -503,6 +591,11 @@ bool GrReducedClip::drawAlphaClipMask(GrDrawContext* dc) const {
     // we populate with a rasterization of the clip.
     GrFixedClip clip(SkIRect::MakeWH(fIBounds.width(), fIBounds.height()));
 
+    if (!fWindowRects.empty()) {
+        clip.setWindowRectangles(fWindowRects, {fIBounds.left(), fIBounds.top()},
+                                 GrWindowRectsState::Mode::kExclusive);
+    }
+
     // The scratch texture that we are drawing into can be substantially larger than the mask. Only
     // clear the part that we care about.
     GrColor initialCoverage = InitialState::kAllIn == this->initialState() ? -1 : 0;
@@ -570,18 +663,23 @@ public:
     StencilClip(const SkIRect& scissorRect) : fFixedClip(scissorRect) {}
     const GrFixedClip& fixedClip() const { return fFixedClip; }
 
+    void setWindowRectangles(const GrWindowRectangles& windows, const SkIPoint& origin,
+                             GrWindowRectsState::Mode mode) {
+        fFixedClip.setWindowRectangles(windows, origin, mode);
+    }
+
 private:
-    bool quickContains(const SkRect&) const final {
+    bool quickContains(const SkRect&) const override {
         return false;
     }
-    void getConservativeBounds(int width, int height, SkIRect* devResult, bool* iior) const final {
-        fFixedClip.getConservativeBounds(width, height, devResult, iior);
+    void getConservativeBounds(int width, int height, SkIRect* bounds, bool* iior) const override {
+        fFixedClip.getConservativeBounds(width, height, bounds, iior);
     }
-    bool isRRect(const SkRect& rtBounds, SkRRect* rr, bool* aa) const final {
+    bool isRRect(const SkRect& rtBounds, SkRRect* rr, bool* aa) const override {
         return false;
     }
     bool apply(GrContext* context, GrDrawContext* drawContext, bool useHWAA,
-               bool hasUserStencilSettings, GrAppliedClip* out) const final {
+               bool hasUserStencilSettings, GrAppliedClip* out) const override {
         if (!fFixedClip.apply(context, drawContext, useHWAA, hasUserStencilSettings, out)) {
             return false;
         }
@@ -600,6 +698,11 @@ bool GrReducedClip::drawStencilClipMask(GrContext* context,
     // We set the current clip to the bounds so that our recursive draws are scissored to them.
     StencilClip stencilClip(fIBounds.makeOffset(-clipOrigin.x(), -clipOrigin.y()));
 
+    if (!fWindowRects.empty()) {
+        stencilClip.setWindowRectangles(fWindowRects, clipOrigin,
+                                        GrWindowRectsState::Mode::kExclusive);
+    }
+
     bool initialState = InitialState::kAllIn == this->initialState();
     drawContext->drawContextPriv().clearStencilClip(stencilClip.fixedClip(), initialState);
 
diff --git a/src/gpu/GrReducedClip.h b/src/gpu/GrReducedClip.h
index 731d58f61c..b8413e6df4 100644
--- a/src/gpu/GrReducedClip.h
+++ b/src/gpu/GrReducedClip.h
@@ -8,6 +8,7 @@
 #ifndef GrReducedClip_DEFINED
 #define GrReducedClip_DEFINED
 
+#include "GrWindowRectangles.h"
 #include "SkClipStack.h"
 #include "SkTLList.h"
 
@@ -20,11 +21,11 @@ class GrDrawContext;
  */
 class SK_API GrReducedClip {
 public:
-    GrReducedClip(const SkClipStack& stack, const SkRect& queryBounds);
+    GrReducedClip(const SkClipStack&, const SkRect& queryBounds, int maxWindowRectangles = 0);
 
     /**
-     * If hasIBounds() is true, this is the bounding box within which the reduced clip is valid, and
-     * the caller must not modify any pixels outside this box. Undefined if hasIBounds() is false.
+     * If hasIBounds() is true, this is the bounding box within which the clip elements are valid.
+     * The caller must not modify any pixels outside this box. Undefined if hasIBounds() is false.
      */
     const SkIRect& ibounds() const { SkASSERT(fHasIBounds); return fIBounds; }
     int left() const { return this->ibounds().left(); }
@@ -38,10 +39,16 @@ public:
      */
     bool hasIBounds() const { return fHasIBounds; }
 
+    /**
+     * If nonempty, this is a set of "exclusive" windows within which the clip elements are NOT
+     * valid. The caller must not modify any pixels inside these windows.
+     */
+    const GrWindowRectangles& windowRectangles() const { return fWindowRects; }
+
     typedef SkTLList<SkClipStack::Element, 16> ElementList;
 
     /**
-     * Populated with a minimal list of elements that implement the clip.
+     * Populated with a minimal list of elements required to fully implement the clip.
      */
     const ElementList& elements() const { return fElements; }
 
@@ -67,15 +74,18 @@ public:
     bool drawStencilClipMask(GrContext*, GrDrawContext*, const SkIPoint& clipOrigin) const;
 
 private:
-    void walkStack(const SkClipStack&, const SkRect& queryBounds);
+    void walkStack(const SkClipStack&, const SkRect& queryBounds, int maxWindowRectangles);
+    void addInteriorWindowRectangles(int maxWindowRectangles);
+    void addWindowRectangle(const SkRect& elementInteriorRect, bool elementIsAA);
     bool intersectIBounds(const SkIRect&);
 
-    SkIRect        fIBounds;
-    bool           fHasIBounds;
-    ElementList    fElements;
-    int32_t        fElementsGenID;
-    bool           fRequiresAA;
-    InitialState   fInitialState;
+    SkIRect              fIBounds;
+    bool                 fHasIBounds;
+    GrWindowRectangles   fWindowRects;
+    ElementList          fElements;
+    int32_t              fElementsGenID;
+    bool                 fRequiresAA;
+    InitialState         fInitialState;
 };
 
 #endif
diff --git a/src/gpu/GrRenderTarget.cpp b/src/gpu/GrRenderTarget.cpp
index 90f94b324b..2053a166e5 100644
--- a/src/gpu/GrRenderTarget.cpp
+++ b/src/gpu/GrRenderTarget.cpp
@@ -127,3 +127,8 @@ const GrGpu::MultisampleSpecs&
 GrRenderTargetPriv::getMultisampleSpecs(const GrStencilSettings& stencil) const {
     return fRenderTarget->getGpu()->getMultisampleSpecs(fRenderTarget, stencil);
 }
+
+int GrRenderTargetPriv::maxWindowRectangles() const {
+    return (this->flags() & Flags::kWindowRectsSupport) ?
+           fRenderTarget->getGpu()->caps()->maxWindowRectangles() : 0;
+}
diff --git a/src/gpu/GrRenderTargetPriv.h b/src/gpu/GrRenderTargetPriv.h
index 2c828ec59a..698288e1cd 100644
--- a/src/gpu/GrRenderTargetPriv.h
+++ b/src/gpu/GrRenderTargetPriv.h
@@ -38,7 +38,7 @@ public:
     typedef GrRenderTarget::Flags Flags;
 
     Flags flags() const { return fRenderTarget->fFlags; }
-    bool supportsWindowRectangles() const { return this->flags() & Flags::kWindowRectsSupport; }
+    int maxWindowRectangles() const;
 
 private:
     explicit GrRenderTargetPriv(GrRenderTarget* renderTarget) : fRenderTarget(renderTarget) {}
diff --git a/src/gpu/GrScissorState.h b/src/gpu/GrScissorState.h
new file mode 100644
index 0000000000..59ea088078
--- /dev/null
+++ b/src/gpu/GrScissorState.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrScissorState_DEFINED
+#define GrScissorState_DEFINED
+
+#include "SkRect.h"
+
+class GrScissorState {
+public:
+    GrScissorState() : fEnabled(false) {}
+    GrScissorState(const SkIRect& rect) : fEnabled(true), fRect(rect) {}
+    void setDisabled() { fEnabled = false; }
+    void set(const SkIRect& rect) { fRect = rect; fEnabled = true; }
+    bool SK_WARN_UNUSED_RESULT intersect(const SkIRect& rect) {
+        if (!fEnabled) {
+            this->set(rect);
+            return true;
+        }
+        return fRect.intersect(rect);
+    }
+    bool operator==(const GrScissorState& other) const {
+        return fEnabled == other.fEnabled &&
+                (false == fEnabled || fRect == other.fRect);
+    }
+    bool operator!=(const GrScissorState& other) const { return !(*this == other); }
+
+    bool enabled() const { return fEnabled; }
+    const SkIRect& rect() const { return fRect; }
+
+private:
+    bool    fEnabled;
+    SkIRect fRect;
+};
+
+#endif
diff --git a/src/gpu/GrWindowRectangles.h b/src/gpu/GrWindowRectangles.h
index b2f6e1ab4a..076c40d7a4 100644
--- a/src/gpu/GrWindowRectangles.h
+++ b/src/gpu/GrWindowRectangles.h
@@ -15,21 +15,15 @@ class GrWindowRectangles {
 public:
     constexpr static int kMaxWindows = 8;
 
-    enum class Mode : bool {
-        kExclusive,
-        kInclusive
-    };
-
-    GrWindowRectangles(Mode mode = Mode::kExclusive) : fMode(mode), fCount(0) {}
+    GrWindowRectangles() : fCount(0) {}
     GrWindowRectangles(const GrWindowRectangles& that) : fCount(0) { *this = that; }
     ~GrWindowRectangles() { SkSafeUnref(this->rec()); }
 
-    Mode mode() const { return fMode; }
+    bool empty() const { return !fCount; }
     int count() const { return fCount; }
-    bool disabled() const { return Mode::kExclusive == fMode && !fCount; }
     const SkIRect* data() const;
 
-    void reset(Mode = Mode::kExclusive);
+    void reset();
     GrWindowRectangles& operator=(const GrWindowRectangles&);
 
     SkIRect& addWindow(const SkIRect& window) { return this->addWindow() = window; }
@@ -44,8 +38,7 @@ private:
 
     const Rec* rec() const { return fCount <= kNumLocalWindows ? nullptr : fRec; }
 
-    Mode      fMode;
-    uint8_t   fCount;
+    int fCount;
     union {
         SkIRect   fLocalWindows[kNumLocalWindows]; // If fCount <= kNumLocalWindows.
         Rec*      fRec;                            // If fCount > kNumLocalWindows.
@@ -65,15 +58,13 @@ inline const SkIRect* GrWindowRectangles::data() const {
     return fCount <= kNumLocalWindows ? fLocalWindows : fRec->fData;
 }
 
-inline void GrWindowRectangles::reset(Mode mode) {
+inline void GrWindowRectangles::reset() {
     SkSafeUnref(this->rec());
-    fMode = mode;
     fCount = 0;
 }
 
 inline GrWindowRectangles& GrWindowRectangles::operator=(const GrWindowRectangles& that) {
     SkSafeUnref(this->rec());
-    fMode = that.fMode;
     fCount = that.fCount;
     if (fCount <= kNumLocalWindows) {
         memcpy(fLocalWindows, that.fLocalWindows, fCount * sizeof(SkIRect));
@@ -98,7 +89,7 @@ inline SkIRect& GrWindowRectangles::addWindow() {
 }
 
 inline bool GrWindowRectangles::operator==(const GrWindowRectangles& that) const {
-    if (fMode != that.fMode || fCount != that.fCount) {
+    if (fCount != that.fCount) {
         return false;
     }
     if (fCount > kNumLocalWindows && fRec == that.fRec) {
diff --git a/src/gpu/GrWindowRectsState.h b/src/gpu/GrWindowRectsState.h
new file mode 100644
index 0000000000..9d3b61b9cb
--- /dev/null
+++ b/src/gpu/GrWindowRectsState.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrWindowRectsState_DEFINED
+#define GrWindowRectsState_DEFINED
+
+#include "GrWindowRectangles.h"
+
+class GrWindowRectsState {
+public:
+    enum class Mode : bool {
+        kExclusive,
+        kInclusive
+    };
+
+    GrWindowRectsState() : fMode(Mode::kExclusive) {}
+    GrWindowRectsState(const GrWindowRectangles& windows, const SkIPoint& origin, Mode mode)
+        : fMode(mode)
+        , fOrigin(origin)
+        , fWindows(windows) {
+    }
+
+    bool enabled() const { return Mode::kInclusive == fMode || !fWindows.empty(); }
+    Mode mode() const { return fMode; }
+    const SkIPoint& origin() const { return fOrigin; }
+    const GrWindowRectangles& windows() const { return fWindows; }
+    int numWindows() const { return fWindows.count(); }
+
+    void setDisabled() {
+        fMode = Mode::kExclusive;
+        fWindows.reset();
+    }
+
+    void set(const GrWindowRectangles& windows, const SkIPoint& origin, Mode mode) {
+        fMode = mode;
+        fOrigin = origin;
+        fWindows = windows;
+    }
+
+    bool cheapEqualTo(const GrWindowRectsState& that) const {
+        if (fMode != that.fMode) {
+            return false;
+        }
+        if (!fWindows.empty() && fOrigin != that.fOrigin) {
+            return false;
+        }
+        return fWindows == that.fWindows;
+    }
+
+private:
+    Mode                 fMode;
+    SkIPoint             fOrigin;
+    GrWindowRectangles   fWindows;
+};
+
+#endif
diff --git a/src/gpu/batches/GrClearBatch.h b/src/gpu/batches/GrClearBatch.h
index 27e19fab6e..16f1ddd7f4 100644
--- a/src/gpu/batches/GrClearBatch.h
+++ b/src/gpu/batches/GrClearBatch.h
@@ -71,6 +71,9 @@ private:
         // same color.
         GrClearBatch* cb = t->cast<GrClearBatch>();
         SkASSERT(cb->fRenderTarget == fRenderTarget);
+        if (!fClip.windowRectsState().cheapEqualTo(cb->fClip.windowRectsState())) {
+            return false;
+        }
         if (cb->contains(this)) {
             fClip = cb->fClip;
             this->replaceBounds(*t);
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index 466af6c6ab..e002d5101b 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -564,7 +564,7 @@ void GrGLGpu::onResetContext(uint32_t resetBits) {
 
     if (resetBits & kView_GrGLBackendState) {
         fHWScissorSettings.invalidate();
-        fHWWindowRects.invalidate();
+        fHWWindowRectsState.invalidate();
         fHWViewport.invalidate();
     }
 
@@ -1997,39 +1997,42 @@ void GrGLGpu::flushScissor(const GrScissorState& scissorState,
     this->disableScissor();
 }
 
-void GrGLGpu::flushWindowRectangles(const GrWindowRectangles& windows, const GrGLRenderTarget* rt) {
-    typedef GrWindowRectangles::Mode Mode;
-    SkASSERT(windows.count() <= this->caps()->maxWindowRectangles());
-    SkASSERT(windows.disabled() || rt->renderFBOID()); // Window rectangles can't be used on-screen.
+void GrGLGpu::flushWindowRectangles(const GrWindowRectsState& windowState,
+                                    const GrGLRenderTarget* rt) {
+    typedef GrWindowRectsState::Mode Mode;
+    SkASSERT(!windowState.enabled() || rt->renderFBOID()); // Window rects can't be used on-screen.
+    SkASSERT(windowState.numWindows() <= this->caps()->maxWindowRectangles());
 
     if (!this->caps()->maxWindowRectangles() ||
-        fHWWindowRects.equal(rt->origin(), rt->getViewport(), windows)) {
+        fHWWindowRectsState.knownEqualTo(rt->origin(), rt->getViewport(), windowState)) {
         return;
     }
 
     // This is purely a workaround for a spurious warning generated by gcc. Otherwise the above
     // assert would be sufficient. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=5912
-    int numWindows = SkTMin(windows.count(), int(GrWindowRectangles::kMaxWindows));
-    SkASSERT(windows.count() == numWindows);
+    int numWindows = SkTMin(windowState.numWindows(), int(GrWindowRectangles::kMaxWindows));
+    SkASSERT(windowState.numWindows() == numWindows);
 
     GrGLIRect glwindows[GrWindowRectangles::kMaxWindows];
-    const SkIRect* skwindows = windows.data();
+    const SkIRect* skwindows = windowState.windows().data();
+    int dx = -windowState.origin().x(), dy = -windowState.origin().y();
     for (int i = 0; i < numWindows; ++i) {
-        glwindows[i].setRelativeTo(rt->getViewport(), skwindows[i], rt->origin());
+        const SkIRect& skwindow = skwindows[i].makeOffset(dx, dy);
+        glwindows[i].setRelativeTo(rt->getViewport(), skwindow, rt->origin());
     }
 
-    GrGLenum glmode = (Mode::kExclusive == windows.mode()) ? GR_GL_EXCLUSIVE : GR_GL_INCLUSIVE;
+    GrGLenum glmode = (Mode::kExclusive == windowState.mode()) ? GR_GL_EXCLUSIVE : GR_GL_INCLUSIVE;
     GL_CALL(WindowRectangles(glmode, numWindows, glwindows->asInts()));
 
-    fHWWindowRects.set(rt->origin(), rt->getViewport(), windows);
+    fHWWindowRectsState.set(rt->origin(), rt->getViewport(), windowState);
 }
 
 void GrGLGpu::disableWindowRectangles() {
-    if (!this->caps()->maxWindowRectangles() || fHWWindowRects.disabled()) {
+    if (!this->caps()->maxWindowRectangles() || fHWWindowRectsState.knownDisabled()) {
         return;
     }
     GL_CALL(WindowRectangles(GR_GL_EXCLUSIVE, 0, nullptr));
-    fHWWindowRects.setDisabled();
+    fHWWindowRectsState.setDisabled();
 }
 
 void GrGLGpu::flushMinSampleShading(float minSampleShading) {
@@ -2079,7 +2082,7 @@ bool GrGLGpu::flushGLState(const GrPipeline& pipeline, const GrPrimitiveProcesso
     GrGLRenderTarget* glRT = static_cast<GrGLRenderTarget*>(pipeline.getRenderTarget());
     this->flushStencil(pipeline.getStencil());
     this->flushScissor(pipeline.getScissorState(), glRT->getViewport(), glRT->origin());
-    this->flushWindowRectangles(pipeline.getWindowRectangles(), glRT);
+    this->flushWindowRectangles(pipeline.getWindowRectsState(), glRT);
     this->flushHWAAState(glRT, pipeline.isHWAntialiasState(), !pipeline.getStencil().isDisabled());
 
     // This must come after textures are flushed because a texture may need
@@ -2207,7 +2210,7 @@ void GrGLGpu::clear(const GrFixedClip& clip, GrColor color, GrRenderTarget* targ
 
     this->flushRenderTarget(glRT, clip.scissorEnabled() ? &clip.scissorRect() : nullptr);
     this->flushScissor(clip.scissorState(), glRT->getViewport(), glRT->origin());
-    this->disableWindowRectangles();
+    this->flushWindowRectangles(clip.windowRectsState(), glRT);
 
     GrGLfloat r, g, b, a;
     static const GrGLfloat scale255 = 1.f / 255.f;
@@ -2271,7 +2274,7 @@ void GrGLGpu::clearStencilClip(const GrFixedClip& clip,
     this->flushRenderTarget(glRT, &SkIRect::EmptyIRect());
 
     this->flushScissor(clip.scissorState(), glRT->getViewport(), glRT->origin());
-    this->disableWindowRectangles();
+    this->flushWindowRectangles(clip.windowRectsState(), glRT);
 
     GL_CALL(StencilMask((uint32_t) clipStencilMask));
     GL_CALL(ClearStencil(value));
diff --git a/src/gpu/gl/GrGLGpu.h b/src/gpu/gl/GrGLGpu.h
index 3fe4204807..62803ee84c 100644
--- a/src/gpu/gl/GrGLGpu.h
+++ b/src/gpu/gl/GrGLGpu.h
@@ -18,6 +18,7 @@
 #include "GrGLVertexArray.h"
 #include "GrGpu.h"
 #include "GrTypes.h"
+#include "GrWindowRectsState.h"
 #include "GrXferProcessor.h"
 #include "SkTArray.h"
 #include "SkTypes.h"
@@ -314,7 +315,7 @@ private:
     // disables the scissor
     void disableScissor();
 
-    void flushWindowRectangles(const GrWindowRectangles&, const GrGLRenderTarget*);
+    void flushWindowRectangles(const GrWindowRectsState&, const GrGLRenderTarget*);
     void disableWindowRectangles();
 
     void initFSAASupport();
@@ -424,39 +425,36 @@ private:
 
     class {
     public:
-        bool valid() const { return kInvalidOrigin != fOrigin; }
-        void invalidate() { fOrigin = kInvalidOrigin; }
+        bool valid() const { return kInvalidSurfaceOrigin != fRTOrigin; }
+        void invalidate() { fRTOrigin = kInvalidSurfaceOrigin; }
+        bool knownDisabled() const { return this->valid() && !fWindowState.enabled(); }
+        void setDisabled() { fRTOrigin = kDefault_GrSurfaceOrigin, fWindowState.setDisabled(); }
 
-        bool disabled() const {
-            return this->valid() && Mode::kExclusive == fWindows.mode() && !fWindows.count();
+        void set(GrSurfaceOrigin rtOrigin, const GrGLIRect& viewport,
+                 const GrWindowRectsState& windowState) {
+            fRTOrigin = rtOrigin;
+            fViewport = viewport;
+            fWindowState = windowState;
         }
-        void setDisabled() { fOrigin = kDefault_GrSurfaceOrigin, fWindows.reset(); }
 
-        bool equal(GrSurfaceOrigin org, const GrGLIRect& viewp,
-                   const GrWindowRectangles& windows) const {
+        bool knownEqualTo(GrSurfaceOrigin rtOrigin, const GrGLIRect& viewport,
+                          const GrWindowRectsState& windowState) const {
             if (!this->valid()) {
                 return false;
             }
-            if (fWindows.count() && (fOrigin != org || fViewport != viewp)) {
+            if (fWindowState.numWindows() && (fRTOrigin != rtOrigin || fViewport != viewport)) {
                 return false;
             }
-            return fWindows == windows;
-        }
-
-        void set(GrSurfaceOrigin org, const GrGLIRect& viewp, const GrWindowRectangles& windows) {
-            fOrigin = org;
-            fViewport = viewp;
-            fWindows = windows;
+            return fWindowState.cheapEqualTo(windowState);
         }
 
     private:
-        typedef GrWindowRectangles::Mode Mode;
-        enum { kInvalidOrigin = -1 };
+        enum { kInvalidSurfaceOrigin = -1 };
 
-        int                  fOrigin;
+        int                  fRTOrigin;
         GrGLIRect            fViewport;
-        GrWindowRectangles   fWindows;
-    } fHWWindowRects;
+        GrWindowRectsState   fWindowState;
+    } fHWWindowRectsState;
 
     GrGLIRect                   fHWViewport;
 
diff --git a/src/gpu/vk/GrVkGpuCommandBuffer.cpp b/src/gpu/vk/GrVkGpuCommandBuffer.cpp
index 6144cf9f8e..e3c7cb77cc 100644
--- a/src/gpu/vk/GrVkGpuCommandBuffer.cpp
+++ b/src/gpu/vk/GrVkGpuCommandBuffer.cpp
@@ -162,6 +162,7 @@ void GrVkGpuCommandBuffer::onClearStencilClip(GrRenderTarget* target,
                                               const GrFixedClip& clip,
                                               bool insideStencilMask) {
     SkASSERT(target);
+    SkASSERT(!clip.hasWindowRectangles());
 
     GrVkRenderTarget* vkRT = static_cast<GrVkRenderTarget*>(target);
     GrStencilAttachment* sb = target->renderTargetPriv().getStencilAttachment();
@@ -215,6 +216,7 @@ void GrVkGpuCommandBuffer::onClearStencilClip(GrRenderTarget* target,
 void GrVkGpuCommandBuffer::onClear(GrRenderTarget* target, const GrFixedClip& clip, GrColor color) {
     // parent class should never let us get here with no RT
     SkASSERT(target);
+    SkASSERT(!clip.hasWindowRectangles());
 
     VkClearColorValue vkColor;
     GrColorToRGBAFloat(color, vkColor.float32);
diff --git a/tests/ProxyTest.cpp b/tests/ProxyTest.cpp
index 016ce5e763..367dee426a 100644
--- a/tests/ProxyTest.cpp
+++ b/tests/ProxyTest.cpp
@@ -162,7 +162,8 @@ DEF_GPUTEST_FOR_RENDERING_CONTEXTS(WrappedProxyTest, reporter, ctxInfo) {
                         GrGpu* gpu = ctxInfo.grContext()->getGpu();
                         sk_sp<GrRenderTarget> defaultFBO(
                             gpu->wrapBackendRenderTarget(backendDesc, kBorrow_GrWrapOwnership));
-                        SkASSERT(!defaultFBO->renderTargetPriv().supportsWindowRectangles());
+                        REPORTER_ASSERT(reporter,
+                                        !defaultFBO->renderTargetPriv().maxWindowRectangles());
 
                         sk_sp<GrRenderTargetProxy> rtProxy(
                             GrRenderTargetProxy::Make(caps, defaultFBO));
@@ -178,8 +179,9 @@ DEF_GPUTEST_FOR_RENDERING_CONTEXTS(WrappedProxyTest, reporter, ctxInfo) {
                         desc.fFlags = kRenderTarget_GrSurfaceFlag;
                         tex.reset(provider->createTexture(desc, budgeted));
                         sk_sp<GrRenderTarget> rt(sk_ref_sp(tex->asRenderTarget()));
-                        SkASSERT(caps.maxWindowRectangles() <= 0 ||
-                                rt->renderTargetPriv().supportsWindowRectangles());
+                        REPORTER_ASSERT(reporter,
+                                        caps.maxWindowRectangles() ==
+                                        rt->renderTargetPriv().maxWindowRectangles());
 
                         sk_sp<GrRenderTargetProxy> rtProxy(GrRenderTargetProxy::Make(caps, rt));
                         check_surface(reporter, rtProxy.get(), origin,
diff --git a/tests/WindowRectanglesTest.cpp b/tests/WindowRectanglesTest.cpp
index d569f1d7aa..e9545651af 100644
--- a/tests/WindowRectanglesTest.cpp
+++ b/tests/WindowRectanglesTest.cpp
@@ -31,7 +31,6 @@ DEF_TEST(WindowRectangles, reporter) {
 
         GrWindowRectangles wr2(wr);
         REPORTER_ASSERT(reporter, wr2 == wr);
-        REPORTER_ASSERT(reporter, wr2.mode() == wr.mode());
         REPORTER_ASSERT(reporter, wr2.count() == wr.count());
         REPORTER_ASSERT(reporter, !memcmp(wr2.data(), wr.data(), i * sizeof(SkIRect)));
 
@@ -72,21 +71,6 @@ DEF_TEST(WindowRectangles, reporter) {
         REPORTER_ASSERT(reporter, !memcmp(A.data(), windowData,
                                           GrWindowRectangles::kMaxWindows * sizeof(SkIRect)));
     }
-
-    GrWindowRectangles wrI(GrWindowRectangles::Mode::kInclusive);
-    for (int i = 0; i < wr.count(); ++i) {
-        wrI.addWindow(windowData[i]);
-    }
-    REPORTER_ASSERT(reporter, wrI != wr);
-    REPORTER_ASSERT(reporter, wrI.mode() != wr.mode());
-    REPORTER_ASSERT(reporter, wrI.count() == wr.count());
-    REPORTER_ASSERT(reporter, !memcmp(wrI.data(), wr.data(), wr.count() * sizeof(SkIRect)));
-
-    wr.reset(GrWindowRectangles::Mode::kInclusive);
-    for (int i = 0; i < wrI.count(); ++i) {
-        wr.addWindow(windowData[i]);
-    }
-    REPORTER_ASSERT(reporter, wrI == wr);
 }
 
 #endif