Allow GrReducedClip to take non-integer query bounds

Fixes places where AA bloat was being conflated with geometric
boundaries and updates GrReducedClip to work with non-integer query
bounds. This allows for better clip reduction with AA shared edges.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2160093002

Review-Url: https://codereview.chromium.org/2160093002

6 files changed, 162 insertions, 190 deletions

diff --git a/src/gpu/GrClip.cpp b/src/gpu/GrClip.cpp
index dc2208ad43..b0c8db3744 100644
--- a/src/gpu/GrClip.cpp
+++ b/src/gpu/GrClip.cpp
@@ -54,10 +54,10 @@ bool GrFixedClip::apply(GrContext*,
                                     SkIRect::MakeWH(drawContext->width(), drawContext->height()))) {
             return false;
         }
-        if (devBounds && !devBounds->intersects(SkRect::Make(tightScissor))) {
+        if (devBounds && IsOutsideClip(tightScissor, *devBounds)) {
             return false;
         }
-        if (!devBounds || !CanIgnoreScissor(fScissorState.rect(), *devBounds)) {
+        if (!devBounds || !IsInsideClip(fScissorState.rect(), *devBounds)) {
             if (fHasStencilClip) {
                 out->makeScissoredStencil(tightScissor, &fDeviceBounds);
             } else {
diff --git a/src/gpu/GrClipMaskManager.cpp b/src/gpu/GrClipMaskManager.cpp
index 6e2a303844..67c6f6eac3 100644
--- a/src/gpu/GrClipMaskManager.cpp
+++ b/src/gpu/GrClipMaskManager.cpp
@@ -26,6 +26,7 @@
 #include "effects/GrTextureDomain.h"
 
 typedef SkClipStack::Element Element;
+typedef GrReducedClip::InitialState InitialState;
 
 static const int kMaxAnalyticElements = 4;
 
@@ -146,7 +147,7 @@ bool GrClipMaskManager::UseSWOnlyPath(GrContext* context,
 
 static bool get_analytic_clip_processor(const GrReducedClip::ElementList& elements,
                                         bool abortIfAA,
-                                        SkVector& clipToRTOffset,
+                                        const SkVector& clipToRTOffset,
                                         const SkRect& drawBounds,
                                         sk_sp<GrFragmentProcessor>* resultFP) {
     SkRect boundsInClipSpace;
@@ -237,40 +238,32 @@ bool GrClipMaskManager::SetupClipping(GrContext* context,
         return true;
     }
 
+    SkRect devBounds = SkRect::MakeIWH(drawContext->width(), drawContext->height());
+    if (origDevBounds && !devBounds.intersect(*origDevBounds)) {
+        return false;
+    }
+
+    const SkScalar clipX = SkIntToScalar(clip.origin().x()),
+                   clipY = SkIntToScalar(clip.origin().y());
+
     GrReducedClip::ElementList elements;
     int32_t genID = 0;
-    GrReducedClip::InitialState initialState = GrReducedClip::kAllIn_InitialState;
     SkIRect clipSpaceIBounds;
     bool requiresAA = false;
 
-    SkIRect clipSpaceReduceQueryBounds;
-    SkRect devBounds;
-    if (origDevBounds) {
-        if (!devBounds.intersect(SkRect::MakeIWH(drawContext->width(), drawContext->height()),
-                                 *origDevBounds)) {
-            return false;
-        }
-        devBounds.roundOut(&clipSpaceReduceQueryBounds);
-        clipSpaceReduceQueryBounds.offset(clip.origin());
-    } else {
-        devBounds = SkRect::MakeIWH(drawContext->width(), drawContext->height());
-        clipSpaceReduceQueryBounds.setXYWH(0, 0, drawContext->width(), drawContext->height());
-        clipSpaceReduceQueryBounds.offset(clip.origin());
-    }
-    GrReducedClip::ReduceClipStack(*clip.clipStack(),
-                                    clipSpaceReduceQueryBounds,
-                                    &elements,
-                                    &genID,
-                                    &initialState,
-                                    &clipSpaceIBounds,
-                                    &requiresAA);
+    InitialState initialState = GrReducedClip::ReduceClipStack(*clip.clipStack(),
+                                                               devBounds.makeOffset(clipX, clipY),
+                                                               &elements,
+                                                               &genID,
+                                                               &clipSpaceIBounds,
+                                                               &requiresAA);
     if (elements.isEmpty()) {
         if (GrReducedClip::kAllOut_InitialState == initialState) {
             return false;
         } else {
             SkIRect scissorSpaceIBounds(clipSpaceIBounds);
             scissorSpaceIBounds.offset(-clip.origin());
-            if (!GrClip::CanIgnoreScissor(scissorSpaceIBounds, devBounds)) {
+            if (!GrClip::IsInsideClip(scissorSpaceIBounds, devBounds)) {
                 out->makeScissored(scissorSpaceIBounds);
             }
             return true;
@@ -286,8 +279,6 @@ bool GrClipMaskManager::SetupClipping(GrContext* context,
     // configuration's relative costs of switching RTs to generate a mask vs
     // longer shaders.
     if (elements.count() <= kMaxAnalyticElements) {
-        SkVector clipToRTOffset = { SkIntToScalar(-clip.origin().fX),
-                                    SkIntToScalar(-clip.origin().fY) };
         // When there are multiple samples we want to do per-sample clipping, not compute a
         // fractional pixel coverage.
         bool disallowAnalyticAA = drawContext->isStencilBufferMultisampled();
@@ -299,11 +290,11 @@ bool GrClipMaskManager::SetupClipping(GrContext* context,
         }
         sk_sp<GrFragmentProcessor> clipFP;
         if (requiresAA &&
-            get_analytic_clip_processor(elements, disallowAnalyticAA, clipToRTOffset, devBounds,
+            get_analytic_clip_processor(elements, disallowAnalyticAA, {-clipX, -clipY}, devBounds,
                                         &clipFP)) {
             SkIRect scissorSpaceIBounds(clipSpaceIBounds);
             scissorSpaceIBounds.offset(-clip.origin());
-            if (GrClip::CanIgnoreScissor(scissorSpaceIBounds, devBounds)) {
+            if (GrClip::IsInsideClip(scissorSpaceIBounds, devBounds)) {
                 out->makeFPBased(std::move(clipFP), SkRect::Make(scissorSpaceIBounds));
             } else {
                 out->makeScissoredFPBased(std::move(clipFP), scissorSpaceIBounds);
@@ -370,7 +361,7 @@ bool GrClipMaskManager::SetupClipping(GrContext* context,
     // use both stencil and scissor test to the bounds for the final draw.
     SkIRect scissorSpaceIBounds(clipSpaceIBounds);
     scissorSpaceIBounds.offset(clipSpaceToStencilSpaceOffset);
-    if (GrClip::CanIgnoreScissor(scissorSpaceIBounds, devBounds)) {
+    if (GrClip::IsInsideClip(scissorSpaceIBounds, devBounds)) {
         out->makeStencil(true, devBounds);
     } else {
         out->makeScissoredStencil(scissorSpaceIBounds);
diff --git a/src/gpu/GrReducedClip.cpp b/src/gpu/GrReducedClip.cpp
index 26b8936952..2940f6a682 100644
--- a/src/gpu/GrReducedClip.cpp
+++ b/src/gpu/GrReducedClip.cpp
@@ -7,14 +7,16 @@
 
 #include "GrReducedClip.h"
 
+#include "GrClip.h"
+
 typedef SkClipStack::Element Element;
 
-static void reduced_stack_walker(const SkClipStack& stack,
-                                 const SkRect& queryBounds,
-                                 GrReducedClip::ElementList* result,
-                                 int32_t* resultGenID,
-                                 GrReducedClip::InitialState* initialState,
-                                 bool* requiresAA) {
+static GrReducedClip::InitialState reduced_stack_walker(const SkClipStack& stack,
+                                                        const SkRect& queryBounds,
+                                                        const SkIRect& clipIBounds,
+                                                        GrReducedClip::ElementList* result,
+                                                        int32_t* resultGenID,
+                                                        bool* requiresAA) {
 
     // walk backwards until we get to:
     //  a) the beginning
@@ -23,27 +25,32 @@ static void reduced_stack_walker(const SkClipStack& stack,
 
     static const GrReducedClip::InitialState kUnknown_InitialState =
         static_cast<GrReducedClip::InitialState>(-1);
-    *initialState = kUnknown_InitialState;
+    GrReducedClip::InitialState initialState = kUnknown_InitialState;
 
     // During our backwards walk, track whether we've seen ops that either grow or shrink the clip.
     // TODO: track these per saved clip so that we can consider them on the forward pass.
     bool embiggens = false;
     bool emsmallens = false;
 
+    // We use a slightly relaxed set of query bounds for element containment tests. This is to
+    // account for floating point rounding error that may have occurred during coord transforms.
+    SkRect relaxedQueryBounds = queryBounds.makeInset(GrClip::kBoundsTolerance,
+                                                      GrClip::kBoundsTolerance);
+
     SkClipStack::Iter iter(stack, SkClipStack::Iter::kTop_IterStart);
     int numAAElements = 0;
-    while ((kUnknown_InitialState == *initialState)) {
+    while (kUnknown_InitialState == initialState) {
         const Element* element = iter.prev();
         if (nullptr == element) {
-            *initialState = GrReducedClip::kAllIn_InitialState;
+            initialState = GrReducedClip::kAllIn_InitialState;
             break;
         }
         if (SkClipStack::kEmptyGenID == element->getGenID()) {
-            *initialState = GrReducedClip::kAllOut_InitialState;
+            initialState = GrReducedClip::kAllOut_InitialState;
             break;
         }
         if (SkClipStack::kWideOpenGenID == element->getGenID()) {
-            *initialState = GrReducedClip::kAllIn_InitialState;
+            initialState = GrReducedClip::kAllIn_InitialState;
             break;
         }
 
@@ -55,17 +62,17 @@ static void reduced_stack_walker(const SkClipStack& stack,
                 // check if the shape subtracted either contains the entire bounds (and makes
                 // the clip empty) or is outside the bounds and therefore can be skipped.
                 if (element->isInverseFilled()) {
-                    if (element->contains(queryBounds)) {
+                    if (element->contains(relaxedQueryBounds)) {
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
                     }
                 } else {
-                    if (element->contains(queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    if (element->contains(relaxedQueryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
                         skippable = true;
                     }
                 }
@@ -78,17 +85,17 @@ static void reduced_stack_walker(const SkClipStack& stack,
                 // be skipped or it is outside the entire bounds and therefore makes the clip
                 // empty.
                 if (element->isInverseFilled()) {
-                    if (element->contains(queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    if (element->contains(relaxedQueryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
                         skippable = true;
                     }
                 } else {
-                    if (element->contains(queryBounds)) {
+                    if (element->contains(relaxedQueryBounds)) {
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
                     }
                 }
@@ -101,17 +108,17 @@ static void reduced_stack_walker(const SkClipStack& stack,
                 // the bounds is entirely inside the clip. If the union-ed shape is outside the
                 // bounds then this op can be skipped.
                 if (element->isInverseFilled()) {
-                    if (element->contains(queryBounds)) {
+                    if (element->contains(relaxedQueryBounds)) {
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
-                        *initialState = GrReducedClip::kAllIn_InitialState;
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
+                        initialState = GrReducedClip::kAllIn_InitialState;
                         skippable = true;
                     }
                 } else {
-                    if (element->contains(queryBounds)) {
-                        *initialState = GrReducedClip::kAllIn_InitialState;
+                    if (element->contains(relaxedQueryBounds)) {
+                        initialState = GrReducedClip::kAllIn_InitialState;
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
                         skippable = true;
                     }
                 }
@@ -125,15 +132,15 @@ static void reduced_stack_walker(const SkClipStack& stack,
                 // able to take advantage of this in the forward pass. If the xor-ed shape
                 // doesn't intersect the bounds then it can be skipped.
                 if (element->isInverseFilled()) {
-                    if (element->contains(queryBounds)) {
+                    if (element->contains(relaxedQueryBounds)) {
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
                         isFlip = true;
                     }
                 } else {
-                    if (element->contains(queryBounds)) {
+                    if (element->contains(relaxedQueryBounds)) {
                         isFlip = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
                         skippable = true;
                     }
                 }
@@ -147,17 +154,17 @@ static void reduced_stack_walker(const SkClipStack& stack,
                 // the bounds then we know after this element is applied that the bounds will be
                 // all outside the current clip.B
                 if (element->isInverseFilled()) {
-                    if (element->contains(queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    if (element->contains(relaxedQueryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
                         isFlip = true;
                     }
                 } else {
-                    if (element->contains(queryBounds)) {
+                    if (element->contains(relaxedQueryBounds)) {
                         isFlip = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
                     }
                 }
@@ -165,30 +172,31 @@ static void reduced_stack_walker(const SkClipStack& stack,
                     emsmallens = embiggens = true;
                 }
                 break;
+
             case SkRegion::kReplace_Op:
                 // Replace will always terminate our walk. We will either begin the forward walk
                 // at the replace op or detect here than the shape is either completely inside
                 // or completely outside the bounds. In this latter case it can be skipped by
                 // setting the correct value for initialState.
                 if (element->isInverseFilled()) {
-                    if (element->contains(queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    if (element->contains(relaxedQueryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
-                        *initialState = GrReducedClip::kAllIn_InitialState;
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
+                        initialState = GrReducedClip::kAllIn_InitialState;
                         skippable = true;
                     }
                 } else {
-                    if (element->contains(queryBounds)) {
-                        *initialState = GrReducedClip::kAllIn_InitialState;
+                    if (element->contains(relaxedQueryBounds)) {
+                        initialState = GrReducedClip::kAllIn_InitialState;
                         skippable = true;
-                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                    } else if (GrClip::IsOutsideClip(element->getBounds(), queryBounds)) {
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         skippable = true;
                     }
                 }
                 if (!skippable) {
-                    *initialState = GrReducedClip::kAllOut_InitialState;
+                    initialState = GrReducedClip::kAllOut_InitialState;
                     embiggens = emsmallens = true;
                 }
                 break;
@@ -206,7 +214,8 @@ static void reduced_stack_walker(const SkClipStack& stack,
             if (isFlip) {
                 SkASSERT(SkRegion::kXOR_Op == element->getOp() ||
                          SkRegion::kReverseDifference_Op == element->getOp());
-                result->addToHead(queryBounds, SkRegion::kReverseDifference_Op, false);
+                result->addToHead(SkRect::Make(clipIBounds), SkRegion::kReverseDifference_Op,
+                                  false);
             } else {
                 Element* newElement = result->addToHead(*element);
                 if (newElement->isAA()) {
@@ -221,17 +230,18 @@ static void reduced_stack_walker(const SkClipStack& stack,
                     newElement->invertShapeFillType();
                     newElement->setOp(SkRegion::kDifference_Op);
                     if (isReplace) {
-                        SkASSERT(GrReducedClip::kAllOut_InitialState == *initialState);
-                        *initialState = GrReducedClip::kAllIn_InitialState;
+                        SkASSERT(GrReducedClip::kAllOut_InitialState == initialState);
+                        initialState = GrReducedClip::kAllIn_InitialState;
                     }
                 }
             }
         }
     }
 
-    if ((GrReducedClip::kAllOut_InitialState == *initialState && !embiggens) ||
-        (GrReducedClip::kAllIn_InitialState == *initialState && !emsmallens)) {
+    if ((GrReducedClip::kAllOut_InitialState == initialState && !embiggens) ||
+        (GrReducedClip::kAllIn_InitialState == initialState && !emsmallens)) {
         result->reset();
+        numAAElements = 0;
     } else {
         Element* element = result->headIter().get();
         while (element) {
@@ -239,20 +249,20 @@ static void reduced_stack_walker(const SkClipStack& stack,
             switch (element->getOp()) {
                 case SkRegion::kDifference_Op:
                     // subtracting from the empty set yields the empty set.
-                    skippable = GrReducedClip::kAllOut_InitialState == *initialState;
+                    skippable = GrReducedClip::kAllOut_InitialState == initialState;
                     break;
                 case SkRegion::kIntersect_Op:
                     // intersecting with the empty set yields the empty set
-                    if (GrReducedClip::kAllOut_InitialState == *initialState) {
+                    if (GrReducedClip::kAllOut_InitialState == initialState) {
                         skippable = true;
                     } else {
                         // We can clear to zero and then simply draw the clip element.
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                        initialState = GrReducedClip::kAllOut_InitialState;
                         element->setOp(SkRegion::kReplace_Op);
                     }
                     break;
                 case SkRegion::kUnion_Op:
-                    if (GrReducedClip::kAllIn_InitialState == *initialState) {
+                    if (GrReducedClip::kAllIn_InitialState == initialState) {
                         // unioning the infinite plane with anything is a no-op.
                         skippable = true;
                     } else {
@@ -261,23 +271,23 @@ static void reduced_stack_walker(const SkClipStack& stack,
                     }
                     break;
                 case SkRegion::kXOR_Op:
-                    if (GrReducedClip::kAllOut_InitialState == *initialState) {
+                    if (GrReducedClip::kAllOut_InitialState == initialState) {
                         // xor could be changed to diff in the kAllIn case, not sure it's a win.
                         element->setOp(SkRegion::kReplace_Op);
                     }
                     break;
                 case SkRegion::kReverseDifference_Op:
-                    if (GrReducedClip::kAllIn_InitialState == *initialState) {
+                    if (GrReducedClip::kAllIn_InitialState == initialState) {
                         // subtracting the whole plane will yield the empty set.
                         skippable = true;
-                        *initialState = GrReducedClip::kAllOut_InitialState;
+                        initialState = GrReducedClip::kAllOut_InitialState;
                     } else {
                         // this picks up flips inserted in the backwards pass.
                         skippable = element->isInverseFilled() ?
-                            !SkRect::Intersects(element->getBounds(), queryBounds) :
-                            element->contains(queryBounds);
+                            GrClip::IsOutsideClip(element->getBounds(), queryBounds) :
+                            element->contains(relaxedQueryBounds);
                         if (skippable) {
-                            *initialState = GrReducedClip::kAllIn_InitialState;
+                            initialState = GrReducedClip::kAllIn_InitialState;
                         } else {
                             element->setOp(SkRegion::kReplace_Op);
                         }
@@ -305,12 +315,15 @@ static void reduced_stack_walker(const SkClipStack& stack,
     *requiresAA = numAAElements > 0;
 
     if (0 == result->count()) {
-        if (*initialState == GrReducedClip::kAllIn_InitialState) {
+        if (initialState == GrReducedClip::kAllIn_InitialState) {
             *resultGenID = SkClipStack::kWideOpenGenID;
         } else {
             *resultGenID = SkClipStack::kEmptyGenID;
         }
     }
+
+    SkASSERT(SkClipStack::kInvalidGenID != *resultGenID);
+    return initialState;
 }
 
 /*
@@ -320,15 +333,13 @@ for the case where the bounds are kInsideOut_BoundsType. We could restrict earli
 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.
 */
-void GrReducedClip::ReduceClipStack(const SkClipStack& stack,
-                                    const SkIRect& queryBounds,
-                                    ElementList* result,
-                                    int32_t* resultGenID,
-                                    InitialState* initialState,
-                                    SkIRect* tighterBounds,
-                                    bool* requiresAA) {
-    SkASSERT(tighterBounds);
-    SkASSERT(requiresAA);
+GrReducedClip::InitialState GrReducedClip::ReduceClipStack(const SkClipStack& stack,
+                                                           const SkRect& queryBounds,
+                                                           ElementList* result,
+                                                           int32_t* resultGenID,
+                                                           SkIRect* clipIBounds,
+                                                           bool* requiresAA) {
+    SkASSERT(!queryBounds.isEmpty());
     result->reset();
 
     // The clip established by the element list might be cached based on the last
@@ -336,85 +347,55 @@ void GrReducedClip::ReduceClipStack(const SkClipStack& stack,
     // id that lead to the state. Make a conservative guess.
     *resultGenID = stack.getTopmostGenID();
 
+    // TODO: instead devise a way of telling the caller to disregard some or all of the clip bounds.
+    *clipIBounds = GrClip::GetPixelIBounds(queryBounds);
+
     if (stack.isWideOpen()) {
-        *initialState = kAllIn_InitialState;
-        return;
+        return kAllIn_InitialState;
     }
 
-
-    // We initially look at whether the bounds alone is sufficient. We also use the stack bounds to
-    // attempt to compute the tighterBounds.
-
     SkClipStack::BoundsType stackBoundsType;
     SkRect stackBounds;
     bool iior;
     stack.getBounds(&stackBounds, &stackBoundsType, &iior);
 
-    const SkIRect* bounds = &queryBounds;
-
-    SkRect scalarQueryBounds = SkRect::Make(queryBounds);
+    if (stackBounds.isEmpty() || GrClip::IsOutsideClip(stackBounds, queryBounds)) {
+        bool insideOut = SkClipStack::kInsideOut_BoundsType == stackBoundsType;
+        return insideOut ? kAllIn_InitialState : kAllOut_InitialState;
+    }
 
     if (iior) {
+        // "Is intersection of rects" means the clip is a single rect indicated by the stack bounds.
+        // This should only be true if aa/non-aa status matches among all elements.
         SkASSERT(SkClipStack::kNormal_BoundsType == stackBoundsType);
-        SkRect isectRect;
-        if (stackBounds.contains(scalarQueryBounds)) {
-            *initialState = GrReducedClip::kAllIn_InitialState;
-            *tighterBounds = queryBounds;
-            *requiresAA = false;
-        } else if (isectRect.intersect(stackBounds, scalarQueryBounds)) {
-            // If the caller asked for tighter integer bounds we may be able to
-            // return kAllIn and give the bounds with no elements
-            isectRect.roundOut(tighterBounds);
-            SkRect scalarTighterBounds = SkRect::Make(*tighterBounds);
-            if (scalarTighterBounds == isectRect) {
-                // the round-out didn't add any area outside the clip rect.
-                *requiresAA = false;
-                *initialState = GrReducedClip::kAllIn_InitialState;
-                return;
-            }
-            *initialState = kAllOut_InitialState;
-            // iior should only be true if aa/non-aa status matches among all elements.
-            SkClipStack::Iter iter(stack, SkClipStack::Iter::kTop_IterStart);
-            bool doAA = iter.prev()->isAA();
-            result->addToHead(isectRect, SkRegion::kReplace_Op, doAA);
-            *requiresAA = doAA;
-        } else {
-            *initialState = kAllOut_InitialState;
-            *requiresAA = false;
+        SkClipStack::Iter iter(stack, SkClipStack::Iter::kTop_IterStart);
+        if (!iter.prev()->isAA() || GrClip::IsPixelAligned(stackBounds)) {
+            // The clip is a non-aa rect. This is the one spot where we can actually implement the
+            // clip (using clipIBounds) rather than just telling the caller what it should be.
+            stackBounds.round(clipIBounds);
+            return kAllIn_InitialState;
         }
-        return;
-    } else {
-        if (SkClipStack::kNormal_BoundsType == stackBoundsType) {
-            if (!SkRect::Intersects(stackBounds, scalarQueryBounds)) {
-                *initialState = kAllOut_InitialState;
-               *requiresAA = false;
-                return;
-            }
-            SkIRect stackIBounds;
-            stackBounds.roundOut(&stackIBounds);
-            if (!tighterBounds->intersect(queryBounds, stackIBounds)) {
-                SkASSERT(0);
-                tighterBounds->setEmpty();
-            }
-            bounds = tighterBounds;
-        } else {
-            if (stackBounds.contains(scalarQueryBounds)) {
-                *initialState = kAllOut_InitialState;
-                // We know that the bounding box contains all the pixels that are outside the clip,
-                // but we don't know that *all* the pixels in the box are outside the clip. So
-                // proceed to walking the stack.
-            }
-            *tighterBounds = queryBounds;
+        if (GrClip::IsInsideClip(stackBounds, queryBounds)) {
+            return kAllIn_InitialState;
         }
+
+        // Implement the clip with an AA rect element.
+        result->addToHead(stackBounds, SkRegion::kReplace_Op, true/*doAA*/);
+        *requiresAA = true;
+
+        SkAssertResult(clipIBounds->intersect(GrClip::GetPixelIBounds(stackBounds)));
+        return kAllOut_InitialState;
     }
 
-    SkRect scalarBounds = SkRect::Make(*bounds);
+    SkRect tighterQuery = queryBounds;
+    if (SkClipStack::kNormal_BoundsType == stackBoundsType) {
+        // Tighten the query by introducing a new clip at the stack's pixel boundaries. (This new
+        // clip will be enforced by the scissor through clipIBounds.)
+        SkAssertResult(tighterQuery.intersect(GrClip::GetPixelBounds(stackBounds)));
+        *clipIBounds = GrClip::GetPixelIBounds(tighterQuery);
+    }
 
     // Now that we have determined the bounds to use and filtered out the trivial cases, call the
     // helper that actually walks the stack.
-    reduced_stack_walker(stack, scalarBounds, result, resultGenID, initialState, requiresAA);
-
-    // The list that was computed in this function may be cached based on the gen id of the last
-    // element.
-    SkASSERT(SkClipStack::kInvalidGenID != *resultGenID);
+    return reduced_stack_walker(stack, tighterQuery, *clipIBounds, result, resultGenID, requiresAA);
 }
diff --git a/src/gpu/GrReducedClip.h b/src/gpu/GrReducedClip.h
index da0bae6bfc..780f6f1ff5 100644
--- a/src/gpu/GrReducedClip.h
+++ b/src/gpu/GrReducedClip.h
@@ -21,24 +21,27 @@ public:
     };
 
     /**
-     * This function takes a clip stack and a query rectangle and it produces a
-     * reduced set of SkClipStack::Elements that are equivalent to applying the
-     * full stack to the rectangle. The clip stack generation id that represents
-     * the list of elements is returned in resultGenID. The initial state of the
-     * query rectangle before the first clip element is applied is returned via
-     * initialState. The reducer output tighterBounds is a tighter bounds on the
-     * clip. tighterBounds will always be contained by queryBounds after return.
-     * It is assumed that the caller will not draw outside of tighterBounds.
-     * The requiresAA output will indicate whether anti-aliasing is required to
-     * process any of the elements in the element list result.
+     * This function produces a reduced set of SkClipStack::Elements that are equivalent to applying
+     * a full clip stack within a specified query rectangle.
+     *
+     * @param stack          the clip stack to reduce.
+     * @param queryBounds    bounding box of geometry the stack will clip.
+     * @param result         populated with a minimal list of elements that implement the clip
+     *                       within the provided query bounds.
+     * @param resultGenID    uniquely identifies the resulting reduced clip.
+     * @param clipIBounds    bounding box within which the reduced clip is valid. The caller must
+     *                       not draw any pixels outside this box. NOTE: this box may be undefined
+     *                       if no pixels are valid (e.g. empty result, "all out" initial state.)
+     * @param requiresAA     indicates whether anti-aliasing is required to process any of the
+     *                       elements in the element list result. Undefined if the result is empty.
+     * @return the initial clip state within clipIBounds ("all in" or "all out").
      */
-    static void ReduceClipStack(const SkClipStack& stack,
-                                const SkIRect& queryBounds,
-                                ElementList* result,
-                                int32_t* resultGenID,
-                                InitialState* initialState,
-                                SkIRect* tighterBounds,
-                                bool* requiresAA);
+    static InitialState ReduceClipStack(const SkClipStack& stack,
+                                        const SkRect& queryBounds,
+                                        ElementList* result,
+                                        int32_t* resultGenID,
+                                        SkIRect* clipIBounds,
+                                        bool* requiresAA);
 };
 
 #endif
diff --git a/src/gpu/gl/GrGLIRect.h b/src/gpu/gl/GrGLIRect.h
index 44f5280fd6..41ac13b753 100644
--- a/src/gpu/gl/GrGLIRect.h
+++ b/src/gpu/gl/GrGLIRect.h
@@ -54,9 +54,7 @@ struct GrGLIRect {
         }
         fHeight = height;
 
-        SkASSERT(fLeft >= 0);
         SkASSERT(fWidth >= 0);
-        SkASSERT(fBottom >= 0);
         SkASSERT(fHeight >= 0);
     }
 
diff --git a/src/utils/SkLua.cpp b/src/utils/SkLua.cpp
index d2ff5551af..a3a1685eae 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -638,12 +638,12 @@ static int lcanvas_getClipStack(lua_State* L) {
 int SkLua::lcanvas_getReducedClipStack(lua_State* L) {
 #if SK_SUPPORT_GPU
     const SkCanvas* canvas = get_ref<SkCanvas>(L, 1);
-    SkIRect queryBounds = canvas->getTopLayerBounds();
+    SkRect queryBounds = SkRect::Make(canvas->getTopLayerBounds());
 
     GrReducedClip::ElementList elements;
-    GrReducedClip::InitialState initialState;
     int32_t genID;
     SkIRect resultBounds;
+    bool requiresAA;
 
     const SkClipStack& stack = *canvas->getClipStack();
 
@@ -651,9 +651,8 @@ int SkLua::lcanvas_getReducedClipStack(lua_State* L) {
                                    queryBounds,
                                    &elements,
                                    &genID,
-                                   &initialState,
                                    &resultBounds,
-                                   nullptr);
+                                   &requiresAA);
 
     GrReducedClip::ElementList::Iter iter(elements);
     int i = 0;