Separate user and raw stencil settings

src/gpu/GrStencil.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef GrStencil_DEFINED
 #define GrStencil_DEFINED
 
 #include "GrTypes.h"
 #include "SkRegion.h"
 
 class GrProcessorKeyBuilder;
 
 /**
  * Gr uses the stencil buffer to implement complex clipping inside the
  * GrDrawTarget class. The GrDrawTarget makes a subset of the stencil buffer
- * bits available for other uses by external code (clients). Client code can
+ * bits available for other uses by external code (user bits). Client code can
  * modify these bits. GrDrawTarget will ignore ref, mask, and writemask bits
- * provided by clients that overlap the bits used to implement clipping.
+ * provided by clients that fall outside the user range.
  *
  * When code outside the GrDrawTarget class uses the stencil buffer the contract
  * is as follows:
  *
  * > Normal stencil funcs allow the client to pass / fail regardless of the
  *   reserved clip bits.
  * > Additional functions allow a test against the clip along with a limited
- *   set of tests against the client bits.
- * > Client can assume all client bits are zero initially.
+ *   set of tests against the user bits.
+ * > Client can assume all user bits are zero initially.
  * > Client must ensure that after all its passes are finished it has only
  *   written to the color buffer in the region inside the clip. Furthermore, it
- *   must zero all client bits that were modifed (both inside and outside the
+ *   must zero all user bits that were modifed (both inside and outside the
  *   clip).
  */
 
+enum GrStencilFlags {
+    kDisabled_StencilFlag         = 0x1,
+    kNoModifyStencil_StencilFlag  = 0x2,
+    kNoWrapOps_StencilFlag        = 0x4,
+    kSingleSided_StencilFlag      = 0x8,
+
+    kLast_StencilFlag = kSingleSided_StencilFlag,
+    kAll_StencilFlags = kLast_StencilFlag | (kLast_StencilFlag - 1)
+};
+
+template<typename TTest, typename TOp> struct GrTStencilFaceSettings {
+    uint16_t   fRef;        // Reference value for stencil test and ops.
+    TTest      fTest;       // Stencil test function, where fRef is on the left side.
+    uint16_t   fTestMask;   // Bitwise "and" to perform on fRef and stencil values before testing.
+                            // (e.g. (fRef & fTestMask) < (stencil & fTestMask))
+    TOp        fPassOp;     // Op to perform when the test passes.
+    TOp        fFailOp;     // Op to perform when the test fails.
+    uint16_t   fWriteMask;  // Indicates which bits in the stencil buffer should be updated.
+                            // (e.g. stencil = (newValue & fWriteMask) | (stencil & ~fWriteMask))
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+enum class GrUserStencilTest : uint16_t {
+    // Tests that respect the clip bit (if in use).

[bsalomon, 2016/05/10 14:06:21]

Maybe say that these tests "always fail when the clip bit is not set"

[Chris Dalton, 2016/05/10 16:39:30]

How's the reworded comment?

[bsalomon, 2016/05/10 20:10:58]

better, thanks.

+    kAlwaysIfInClip,
+    kEqualIfInClip,
+    kLessIfInClip,
+    kLEqualIfInClip,
+
+    // Tests that ignore the clip bit. The client is responsible to ensure no color writes occur
+    // outside the clip when it is in use.
+    kAlways,
+    kNever,
+    kGreater,
+    kGEqual,
+    kLess,
+    kLEqual,
+    kEqual,
+    kNotEqual
+};
+static constexpr GrUserStencilTest kLastClippedStencilTest = GrUserStencilTest::kLEqualIfInClip;
+static constexpr int kGrUserStencilTestCount = 1 + (int)GrUserStencilTest::kNotEqual;
+
+enum class GrUserStencilOp : uint8_t {
+    kKeep,
+
+    // Ops that only modify user bits. These must not be paired with ops that modify the clip bit.
+    kZero,
+    kReplace, // Replace stencil value with fRef (only the bits enabled in fWriteMask).
+    kInvert,
+    kIncWrap,
+    kDecWrap,
+    // These two should only be used if wrap ops are not supported, or if the math is guaranteed
+    // to not overflow. The user bits may or may not clamp, depending on the state of non-user bits.
+    kIncMaybeClamp,
+    kDecMaybeClamp,
+
+    // Ops that only modify the clip bit. These must not be paired with ops that modify user bits.
+    kZeroClipBit,
+    kSetClipBit,
+    kInvertClipBit,
+
+    // Ops that modify both clip and user bits. These can only be paired with kKeep or each other.
+    kSetClipAndReplaceUserBits,
+    kZeroClipAndUserBits
+};
+static constexpr GrUserStencilOp kLastUserOnlyStencilOp = GrUserStencilOp::kDecMaybeClamp;
+static constexpr GrUserStencilOp kLastClipOnlyStencilOp = GrUserStencilOp::kInvertClipBit;
+static constexpr int kGrUserStencilOpCount = 1 + (int)GrUserStencilOp::kZeroClipAndUserBits;
+
 /**
- * Determines which pixels pass / fail the stencil test.
- * Stencil test passes if (ref & mask) FUNC (stencil & mask) is true
+ * This struct is a compile-time constant representation of user stencil settings. It describes in
+ * abstract terms how a draw will use the stencil buffer. It gets ODR-used at runtime to define a
+ * draw's stencil settings, and is later translated into concrete settings when the pipeline is
+ * finalized.
  */
-enum GrStencilFunc {
-    kAlways_StencilFunc = 0,
-    kNever_StencilFunc,
-    kGreater_StencilFunc,
-    kGEqual_StencilFunc,
-    kLess_StencilFunc,
-    kLEqual_StencilFunc,
-    kEqual_StencilFunc,
-    kNotEqual_StencilFunc,
-
-    // Gr stores the current clip in the
-    // stencil buffer in the high bits that
-    // are not directly accessible modifiable
-    // via the GrDrawTarget interface. The below
-    // stencil funcs test against the current
-    // clip in addition to the GrDrawTarget
-    // client's stencil bits.
-
-    // pass if inside the clip
-    kAlwaysIfInClip_StencilFunc,
-    kEqualIfInClip_StencilFunc,
-    kLessIfInClip_StencilFunc,
-    kLEqualIfInClip_StencilFunc,
-    kNonZeroIfInClip_StencilFunc, // this one forces the ref to be 0
-
-    kLast_StencilFunc = kNonZeroIfInClip_StencilFunc
-};
-
-static const int kStencilFuncCnt = kLast_StencilFunc + 1;
-static const int kClipStencilFuncCnt =
-    kNonZeroIfInClip_StencilFunc - kAlwaysIfInClip_StencilFunc + 1;
-static const int kBasicStencilFuncCnt = kStencilFuncCnt - kClipStencilFuncCnt;
+struct GrUserStencilSettings {
+    typedef GrTStencilFaceSettings<GrUserStencilTest, GrUserStencilOp> Face;
+
+    template<GrUserStencilTest, GrUserStencilOp PassOp, GrUserStencilOp FailOp> struct Attrs;
+
+    // Unfortunately, this is the only way to pass template arguments to a constructor.
+    template<uint16_t Ref, GrUserStencilTest Test, uint16_t TestMask,
+             GrUserStencilOp PassOp, GrUserStencilOp FailOp, uint16_t WriteMask> struct Init {};
+
+    template<uint16_t FtRef,            uint16_t BkRef,
+             GrUserStencilTest FtTest,  GrUserStencilTest BkTest,
+             uint16_t FtTestMask,       uint16_t BkTestMask,
+             GrUserStencilOp FtPassOp,  GrUserStencilOp BkPassOp,
+             GrUserStencilOp FtFailOp,  GrUserStencilOp BkFailOp,
+             uint16_t FtWriteMask,      uint16_t BkWriteMask> struct InitSeparate {};
+
+    template<uint16_t Ref, GrUserStencilTest Test, uint16_t TestMask,
+             GrUserStencilOp PassOp, GrUserStencilOp FailOp, uint16_t WriteMask>
+    constexpr static Init<Ref, Test, TestMask, PassOp, FailOp, WriteMask> StaticInit() {
+        return Init<Ref, Test, TestMask, PassOp, FailOp, WriteMask>();
+    }
+
+    template<uint16_t FtRef,            uint16_t BkRef,
+             GrUserStencilTest FtTest,  GrUserStencilTest BkTest,
+             uint16_t FtTestMask,       uint16_t BkTestMask,
+             GrUserStencilOp FtPassOp,  GrUserStencilOp BkPassOp,
+             GrUserStencilOp FtFailOp,  GrUserStencilOp BkFailOp,
+             uint16_t FtWriteMask,      uint16_t BkWriteMask>
+    constexpr static InitSeparate<FtRef, BkRef, FtTest, BkTest, FtTestMask, BkTestMask,
+                                  FtPassOp, BkPassOp, FtFailOp, BkFailOp, FtWriteMask,
+                                  BkWriteMask> StaticInitSeparate() {
+        return InitSeparate<FtRef, BkRef, FtTest, BkTest, FtTestMask, BkTestMask,
+                            FtPassOp, BkPassOp, FtFailOp, BkFailOp, FtWriteMask, BkWriteMask>();
+    }
+
+    // We construct with template arguments in order to enforce that the struct be compile-time
+    // constant and to make use of static asserts.
+    template<uint16_t Ref, GrUserStencilTest Test, uint16_t TestMask,
+             GrUserStencilOp PassOp, GrUserStencilOp FailOp, uint16_t WriteMask,
+             typename Attrs = Attrs<Test, PassOp, FailOp> >
+    constexpr explicit GrUserStencilSettings(
+            const Init<Ref, Test, TestMask, PassOp, FailOp, WriteMask>&)
+        : fFrontFlags{Attrs::Flags(false) | kSingleSided_StencilFlag,
+                      Attrs::Flags(true) | kSingleSided_StencilFlag}
+        , fFront{Ref, Test, Attrs::EffectiveTestMask(TestMask), PassOp, FailOp,
+                 Attrs::EffectiveWriteMask(WriteMask)}
+        , fBackFlags{Attrs::Flags(false) | kSingleSided_StencilFlag,
+                     Attrs::Flags(true) | kSingleSided_StencilFlag}
+        , fBack{Ref, Test, Attrs::EffectiveTestMask(TestMask), PassOp, FailOp,
+                Attrs::EffectiveWriteMask(WriteMask)} {
+    }
+
+    template<uint16_t FtRef,            uint16_t BkRef,
+             GrUserStencilTest FtTest,  GrUserStencilTest BkTest,
+             uint16_t FtTestMask,       uint16_t BkTestMask,
+             GrUserStencilOp FtPassOp,  GrUserStencilOp BkPassOp,
+             GrUserStencilOp FtFailOp,  GrUserStencilOp BkFailOp,
+             uint16_t FtWriteMask,      uint16_t BkWriteMask,
+             typename FtAttrs = Attrs<FtTest, FtPassOp, FtFailOp>,
+             typename BkAttrs = Attrs<BkTest, BkPassOp, BkFailOp> >
+    constexpr explicit GrUserStencilSettings(
+            const InitSeparate<FtRef, BkRef, FtTest, BkTest, FtTestMask, BkTestMask,
+                               FtPassOp, BkPassOp, FtFailOp, BkFailOp, FtWriteMask, BkWriteMask>&)
+        : fFrontFlags{FtAttrs::Flags(false), FtAttrs::Flags(true)}
+        , fFront{FtRef, FtTest, FtAttrs::EffectiveTestMask(FtTestMask), FtPassOp, FtFailOp,
+                 FtAttrs::EffectiveWriteMask(FtWriteMask)}
+        , fBackFlags{BkAttrs::Flags(false), BkAttrs::Flags(true)}
+        , fBack{BkRef, BkTest, BkAttrs::EffectiveTestMask(BkTestMask), BkPassOp, BkFailOp,
+                BkAttrs::EffectiveWriteMask(BkWriteMask)} {}
+
+    // This struct can only be constructed with static initializers.
+    GrUserStencilSettings() = delete;
+    GrUserStencilSettings(const GrUserStencilSettings&) = delete;
+
+    const uint16_t   fFrontFlags[2]; // frontFlagsForDraw = fFrontFlags[hasStencilClip].
+    const Face       fFront;
+    const uint16_t   fBackFlags[2]; // backFlagsForDraw = fBackFlags[hasStencilClip].
+    const Face       fBack;
+
+    static const GrUserStencilSettings& kUnused;
+};
+
+template<GrUserStencilTest Test, GrUserStencilOp PassOp, GrUserStencilOp FailOp>
+struct GrUserStencilSettings::Attrs {
+    // Ensure an op that only modifies user bits isn't paired with one that modifies clip bits.
+    GR_STATIC_ASSERT(GrUserStencilOp::kKeep == PassOp || GrUserStencilOp::kKeep == FailOp ||
+                     (PassOp <= kLastUserOnlyStencilOp) == (FailOp <= kLastUserOnlyStencilOp));
+    // Ensure an op that only modifies clip bits isn't paired with one that modifies clip and user.
+    GR_STATIC_ASSERT(GrUserStencilOp::kKeep == PassOp || GrUserStencilOp::kKeep == FailOp ||
+                     (PassOp <= kLastClipOnlyStencilOp) == (FailOp <= kLastClipOnlyStencilOp));
+
+    static constexpr bool TestAlwaysPasses(bool hasStencilClip) {
+        return (!hasStencilClip && GrUserStencilTest::kAlwaysIfInClip == Test) ||
+                GrUserStencilTest::kAlways == Test;
+    }
+    static constexpr bool DoesNotModifyStencil(bool hasStencilClip) {
+        return (GrUserStencilTest::kNever == Test || GrUserStencilOp::kKeep == PassOp) &&
+                (TestAlwaysPasses(hasStencilClip) || GrUserStencilOp::kKeep == FailOp);
+    }
+    static constexpr bool IsDisabled(bool hasStencilClip) {
+        return TestAlwaysPasses(hasStencilClip) && DoesNotModifyStencil(hasStencilClip);
+    }
+    static constexpr bool UsesWrapOps() {
+        return GrUserStencilOp::kIncWrap == PassOp || GrUserStencilOp::kDecWrap == PassOp ||
+               GrUserStencilOp::kIncWrap == FailOp || GrUserStencilOp::kDecWrap == FailOp;
+    }
+    static constexpr bool TestIgnoresRef() {
+        return (GrUserStencilTest::kAlwaysIfInClip == Test || GrUserStencilTest::kAlways == Test ||
+                GrUserStencilTest::kNever == Test);
+    }
+    static constexpr uint16_t Flags(bool hasStencilClip) {
+        return (IsDisabled(hasStencilClip) ? kDisabled_StencilFlag : 0) |
+               (DoesNotModifyStencil(hasStencilClip) ? kNoModifyStencil_StencilFlag : 0) |
+               (UsesWrapOps() ? 0 : kNoWrapOps_StencilFlag);
+    }
+    static constexpr uint16_t EffectiveTestMask(uint16_t testMask) {
+        return TestIgnoresRef() ? 0 : testMask;
+    }
+    static constexpr uint16_t EffectiveWriteMask(uint16_t writeMask) {
+        // We don't modify the mask differently when hasStencilClip=false because either the entire
+        // face gets disabled in that case (e.g. Test=kAlwaysIfInClip, PassOp=kKeep), or the
+        // effective mask stays the same either way.
+        return DoesNotModifyStencil(true) ? 0 : writeMask;
+    }
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+
+enum class GrStencilTest : uint16_t {

[bsalomon, 2016/05/10 14:06:21]

I'm wondering if this could be in another file that is only included in a
handful of places (pipeline, gpu)

[Chris Dalton, 2016/05/10 16:39:30]

Done. Good idea.

+    kAlways,
+    kNever,
+    kGreater,
+    kGEqual,
+    kLess,
+    kLEqual,
+    kEqual,
+    kNotEqual
+};
+static constexpr int kGrStencilTestCount = 1 + (int)GrStencilTest::kNotEqual;
+
+enum class GrStencilOp : uint8_t {
+    kKeep,
+    kZero,
+    kReplace, // Replace stencil value with fRef (only the bits enabled in fWriteMask).
+    kInvert,
+    kIncWrap,
+    kDecWrap,
+    // NOTE: clamping occurs before the write mask. So if the MSB is zero and masked out, stencil
+    // values will still wrap when using clamping ops.
+    kIncClamp,
+    kDecClamp
+};
+static constexpr int kGrStencilOpCount = 1 + (int)GrStencilOp::kDecClamp;
 
 /**
- * Operations to perform based on whether stencil test passed failed.
- */
-enum GrStencilOp {
-    kKeep_StencilOp = 0,    // preserve existing stencil value
-    kReplace_StencilOp,     // replace with reference value from stencl test
-    kIncWrap_StencilOp,     // increment and wrap at max
-    kIncClamp_StencilOp,    // increment and clamp at max
-    kDecWrap_StencilOp,     // decrement and wrap at 0
-    kDecClamp_StencilOp,    // decrement and clamp at 0
-    kZero_StencilOp,        // zero stencil bits
-    kInvert_StencilOp,      // invert stencil bits
-    kLast_StencilOp = kInvert_StencilOp
-};
-static const int kStencilOpCnt = kLast_StencilOp + 1;
-
-/**
- * Class representing stencil state.
+ * This class defines concrete stencil settings that map directly to the underlying hardware. It
+ * is deduced from user stencil settings, stencil clip status, and the number of bits in the
+ * target stencil buffer.
  */
 class GrStencilSettings {
 public:
-    enum Face {
-        kFront_Face = 0,
-        kBack_Face  = 1,
+    GrStencilSettings() { this->setDisabled(); }
+    GrStencilSettings(const GrUserStencilSettings& user, bool hasStencilClip, int numStencilBits) {
+        this->reset(user, hasStencilClip, numStencilBits);
+    }
+    GrStencilSettings(const GrStencilSettings& that) { this->reset(that); }
+    GrStencilSettings& operator=(const GrStencilSettings& that) { this->reset(that); return *this; }
+
+    void invalidate() { fFlags |= kInvalid_PrivateFlag; }
+    void setDisabled() { fFlags = kAll_StencilFlags; }
+    void reset(const GrUserStencilSettings&, bool hasStencilClip, int numStencilBits);
+    void reset(const GrStencilSettings&);
+
+    bool isValid() const { return !(fFlags & kInvalid_PrivateFlag); }
+    bool isDisabled() const { SkASSERT(this->isValid()); return fFlags & kDisabled_StencilFlag; }
+    bool doesWrite() const { SkASSERT(this->isValid());
+                             return !(fFlags & kNoModifyStencil_StencilFlag); }
+    bool isTwoSided() const { SkASSERT(this->isValid());
+                              return !(fFlags & kSingleSided_StencilFlag); }
+    bool usesWrapOp() const { SkASSERT(this->isValid());
+                              return !(fFlags & kNoWrapOps_StencilFlag); }
+
+    void genKey(GrProcessorKeyBuilder* b) const;
+
+    bool operator!=(const GrStencilSettings& that) const { return !(*this == that); }
+    bool operator==(const GrStencilSettings&) const;
+
+    struct Face : public GrTStencilFaceSettings<GrStencilTest, GrStencilOp> {
+        void reset(const GrUserStencilSettings::Face&, bool useStencilClip, int numStencilBits);
+        void setDisabled();
     };
 
-    constexpr GrStencilSettings(GrStencilOp passOp,
-                                GrStencilOp failOp,
-                                GrStencilFunc func,
-                                unsigned short funcMask,
-                                unsigned short funcRef,
-                                unsigned short writeMask)
-        : fPassOps{(uint8_t)passOp, (uint8_t)passOp}
-        , fFailOps{(uint8_t)failOp, (uint8_t)failOp}
-        , fFuncs{(uint8_t)func, (uint8_t)func}
-        , fPad0(0)
-        , fPad1(0)
-        , fFuncMasks{funcMask, funcMask}
-        , fFuncRefs{funcRef, funcRef}
-        , fWriteMasks{writeMask, writeMask}
-        , fFlags(ComputeFlags(passOp,    passOp,
-                              failOp,    failOp,
-                              func,      func,
-                              writeMask, writeMask)) {
-    }
-
-    constexpr GrStencilSettings(GrStencilOp frontPassOp,  GrStencilOp backPassOp,
-                                GrStencilOp frontFailOp,  GrStencilOp backFailOp,
-                                GrStencilFunc frontFunc,  GrStencilFunc backFunc,
-                                uint16_t frontFuncMask,   uint16_t backFuncMask,
-                                uint16_t frontFuncRef,    uint16_t backFuncRef,
-                                uint16_t frontWriteMask,  uint16_t backWriteMask)
-        : fPassOps{(uint8_t)frontPassOp, (uint8_t)backPassOp}
-        , fFailOps{(uint8_t)frontFailOp, (uint8_t)backFailOp}
-        , fFuncs{(uint8_t)frontFunc, (uint8_t)backFunc}
-        , fPad0(0)
-        , fPad1(0)
-        , fFuncMasks{frontFuncMask, backFuncMask}
-        , fFuncRefs{frontFuncRef, backFuncRef}
-        , fWriteMasks{frontWriteMask, backWriteMask}
-        , fFlags(ComputeFlags(frontPassOp,    backPassOp,
-                              frontFailOp,    backFailOp,
-                              frontFunc,      backFunc,
-                              frontWriteMask, backWriteMask)) {
-    }
-
-    GrStencilSettings() {
-        fPad0 = fPad1 = 0;
-        this->setDisabled();
-    }
-
-    GrStencilOp passOp(Face f) const { return static_cast<GrStencilOp>(fPassOps[f]); }
-    GrStencilOp failOp(Face f) const { return static_cast<GrStencilOp>(fFailOps[f]); }
-    GrStencilFunc func(Face f) const { return static_cast<GrStencilFunc>(fFuncs[f]); }
-    uint16_t funcMask(Face f) const  { return fFuncMasks[f]; }
-    uint16_t funcRef(Face f) const   { return fFuncRefs[f]; }
-    uint16_t writeMask(Face f) const { return fWriteMasks[f]; }
-
-    void setPassOp(Face f, GrStencilOp op) { fPassOps[f] = op; fFlags = 0;}
-    void setFailOp(Face f, GrStencilOp op) { fFailOps[f] = op; fFlags = 0;}
-    void setFunc(Face f, GrStencilFunc func) { fFuncs[f] = func; fFlags = 0;}
-    void setFuncMask(Face f, unsigned short mask) { fFuncMasks[f] = mask; }
-    void setFuncRef(Face f, unsigned short ref) { fFuncRefs[f] = ref; }
-    void setWriteMask(Face f, unsigned short writeMask) { fWriteMasks[f] = writeMask; }
-
-    void copyFrontSettingsToBack() {
-        fPassOps[kBack_Face]    = fPassOps[kFront_Face];
-        fFailOps[kBack_Face]    = fFailOps[kFront_Face];
-        fFuncs[kBack_Face]      = fFuncs[kFront_Face];
-        fFuncMasks[kBack_Face]  = fFuncMasks[kFront_Face];
-        fFuncRefs[kBack_Face]   = fFuncRefs[kFront_Face];
-        fWriteMasks[kBack_Face] = fWriteMasks[kFront_Face];
-        fFlags = 0;
-    }
-
-    void setDisabled() {
-        memset(this, 0, sizeof(*this));
-        GR_STATIC_ASSERT(0 == kKeep_StencilOp);
-        GR_STATIC_ASSERT(0 == kAlways_StencilFunc);
-        fFlags = kIsDisabled_StencilFlag | kDoesNotWrite_StencilFlag;
-    }
-
-    bool isTwoSided() const {
-        return fPassOps[kFront_Face]    != fPassOps[kBack_Face]   ||
-               fFailOps[kFront_Face]    != fFailOps[kBack_Face]   ||
-               fFuncs[kFront_Face]      != fFuncs[kBack_Face]     ||
-               fFuncMasks[kFront_Face]  != fFuncMasks[kBack_Face] ||
-               fFuncRefs[kFront_Face]   != fFuncRefs[kBack_Face]  ||
-               fWriteMasks[kFront_Face] != fWriteMasks[kBack_Face];
-    }
-
-    bool usesWrapOp() const {
-        return kIncWrap_StencilOp == fPassOps[kFront_Face] ||
-               kDecWrap_StencilOp == fPassOps[kFront_Face] ||
-               kIncWrap_StencilOp == fPassOps[kBack_Face]  ||
-               kDecWrap_StencilOp == fPassOps[kBack_Face]  ||
-               kIncWrap_StencilOp == fFailOps[kFront_Face] ||
-               kDecWrap_StencilOp == fFailOps[kFront_Face] ||
-               kIncWrap_StencilOp == fFailOps[kBack_Face]  ||
-               kDecWrap_StencilOp == fFailOps[kBack_Face];
-    }
-
-    bool isDisabled() const {
-        if (fFlags & kIsDisabled_StencilFlag) {
-            return true;
-        }
-        if (fFlags & kNotDisabled_StencilFlag) {
-            return false;
-        }
-        bool disabled = this->computeIsDisabled();
-        fFlags |= disabled ? kIsDisabled_StencilFlag : kNotDisabled_StencilFlag;
-        return disabled;
-    }
-
-    bool doesWrite() const {
-        if (fFlags & kDoesWrite_StencilFlag) {
-            return true;
-        }
-        if (fFlags & kDoesNotWrite_StencilFlag) {
-            return false;
-        }
-        bool writes = this->computeDoesWrite();
-        fFlags |= writes ? kDoesWrite_StencilFlag : kDoesNotWrite_StencilFlag;
-        return writes;
-    }
-
-    void invalidate()  {
-        // write an illegal value to the first member
-        fPassOps[0] = kStencilOpCnt;
-        fFlags = 0;
-    }
-
-    bool isValid() const { return fPassOps[0] < kStencilOpCnt; }
-
-    void genKey(GrProcessorKeyBuilder* b) const;
-
-    bool operator==(const GrStencilSettings& s) const {
-        static const size_t gCompareSize = sizeof(GrStencilSettings) -
-                                           sizeof(fFlags);
-        SkASSERT((const char*)&fFlags + sizeof(fFlags) ==
-                 (const char*)this + sizeof(GrStencilSettings));
-        if (this->isDisabled() & s.isDisabled()) { // using & not &&
-            return true;
-        }
-        return 0 == memcmp(this, &s, gCompareSize);
-    }
-
-    bool operator!=(const GrStencilSettings& s) const {
-        return !(*this == s);
-    }
-
-    GrStencilSettings& operator=(const GrStencilSettings& s) {
-        memcpy(this, &s, sizeof(GrStencilSettings));
-        return *this;
-    }
-
-private:
-    friend class GrClipMaskManager;
-
-    enum {
-        kMaxStencilClipPasses = 2  // maximum number of passes to add a clip
-                                   // element to the stencil buffer.
-    };
+    const Face& front() const { SkASSERT(!this->isDisabled()); return fFront; }
+    const Face& back() const { SkASSERT(this->isTwoSided()); return fBack; }
 
     /**
      * Given a thing to draw into the stencil clip, a fill type, and a set op
      * this function determines:
      *      1. Whether the thing can be draw directly to the stencil clip or
      *      needs to be drawn to the client portion of the stencil first.
      *      2. How many passes are needed.
      *      3. What those passes are.
-     *      4. The fill rule that should actually be used to render (will
-     *         always be non-inverted).
      *
-     * @param op                the set op to combine this element with the
-     *                          existing clip
-     * @param stencilClipMask   mask with just the stencil bit used for clipping
-     *                          enabled.
+     * @param op                the set op to combine this element with the existing clip
+     * @param canBeDirect       can the caller draw this element directly (without using stencil)?
      * @param invertedFill      is this path inverted
-     * @param numPasses         out: the number of passes needed to add the
-     *                               element to the clip.
-     * @param settings          out: the stencil settings to use for each pass
+     * @param drawDirectToClip  out: true if caller should draw the element directly, false if it
+     *                          should draw it into the user stencil bits first.
      *
-     * @return true if the clip element's geometry can be drawn directly to the
-     *         stencil clip bit. Will only be true if canBeDirect is true.
-     *         numPasses will be 1 if return value is true.
+     * @return a null-terminated array of settings for stencil passes.
+     *
+     *         If drawDirectToClip is false, the caller must first draw the element into the user
+     *         stencil bits, and then cover the clip area with multiple passes using the returned
+     *         stencil settings.
+     *
+     *         If drawDirectToClip is true, the returned array will only have one pass and the
+     *         caller should use those stencil settings while drawing the element directly.
      */
-    static bool GetClipPasses(SkRegion::Op op,
-                              bool canBeDirect,
-                              unsigned int stencilClipMask,
-                              bool invertedFill,
-                              int* numPasses,
-                              GrStencilSettings settings[kMaxStencilClipPasses]);
+    static GrUserStencilSettings const* const* GetClipPasses(SkRegion::Op op,
+                                                             bool canBeDirect,
+                                                             bool invertedFill,
+                                                             bool* drawDirectToClip);
 
-    constexpr static bool IsDisabled(GrStencilOp frontPassOp,  GrStencilOp backPassOp,
-                                     GrStencilOp frontFailOp,  GrStencilOp backFailOp,
-                                     GrStencilFunc frontFunc,  GrStencilFunc backFunc) {
-        return (((frontPassOp == kKeep_StencilOp && frontFailOp == kKeep_StencilOp)) &&
-                ((backPassOp  == kKeep_StencilOp &&  backFailOp == kKeep_StencilOp))  &&
-                frontFunc   == kAlways_StencilFunc &&
-                backFunc   == kAlways_StencilFunc);
-    }
+private:
+    // Internal flag for backends to optionally mark their tracked stencil state as invalid.
+    enum { kInvalid_PrivateFlag = (kLast_StencilFlag << 1) };
 
-    constexpr static bool DoesWrite(GrStencilOp frontPassOp,  GrStencilOp backPassOp,
-                                    GrStencilOp frontFailOp,  GrStencilOp backFailOp,
-                                    GrStencilFunc frontFunc,  GrStencilFunc backFunc,
-                                    uint16_t frontWriteMask,  uint16_t backWriteMask) {
-        return (0 != (frontWriteMask | backWriteMask)) &&
-                // Can we write due to a front face passing the stencil test?
-               ((frontFunc != kNever_StencilFunc  && frontPassOp != kKeep_StencilOp) ||
-                // Can we write due to a back face passing the stencil test?
-                (backFunc  != kNever_StencilFunc  && backPassOp  != kKeep_StencilOp) ||
-                // Can we write due to a front face failing the stencil test?
-                (frontFunc != kAlways_StencilFunc && frontFailOp != kKeep_StencilOp) ||
-                // Can we write due to a back face failing the stencil test?
-                (backFunc  != kAlways_StencilFunc && backFailOp  != kKeep_StencilOp));
-    }
-
-    constexpr static uint32_t ComputeFlags(GrStencilOp frontPassOp,  GrStencilOp backPassOp,
-                                           GrStencilOp frontFailOp,  GrStencilOp backFailOp,
-                                           GrStencilFunc frontFunc,  GrStencilFunc backFunc,
-                                           uint16_t frontWriteMask,  uint16_t backWriteMask) {
-        return (IsDisabled(frontPassOp, backPassOp, frontFailOp, backFailOp,
-                           frontFunc, backFunc)
-                    ? kIsDisabled_StencilFlag
-                    : kNotDisabled_StencilFlag) |
-               (DoesWrite(frontPassOp, backPassOp, frontFailOp, backFailOp,
-                          frontFunc, backFunc, frontWriteMask, backWriteMask)
-                    ? kDoesWrite_StencilFlag
-                    : kDoesNotWrite_StencilFlag);
-    }
-
-    bool computeIsDisabled() const {
-        return IsDisabled((GrStencilOp) fPassOps[kFront_Face], (GrStencilOp) fPassOps[kBack_Face],
-                          (GrStencilOp) fFailOps[kFront_Face], (GrStencilOp) fFailOps[kBack_Face],
-                          (GrStencilFunc) fFuncs[kFront_Face], (GrStencilFunc) fFuncs[kBack_Face]);
-    }
-    bool computeDoesWrite() const {
-        return DoesWrite((GrStencilOp)fPassOps[kFront_Face], (GrStencilOp)fPassOps[kBack_Face],
-                         (GrStencilOp)fFailOps[kFront_Face], (GrStencilOp)fFailOps[kBack_Face],
-                         (GrStencilFunc)fFuncs[kFront_Face], (GrStencilFunc)fFuncs[kBack_Face],
-                         fWriteMasks[kFront_Face],           fWriteMasks[kBack_Face]);
-    }
-
-    enum GrStencilFlags {
-        kIsDisabled_StencilFlag      = 0x1,
-        kNotDisabled_StencilFlag     = 0x2,
-        kDoesWrite_StencilFlag       = 0x4,
-        kDoesNotWrite_StencilFlag    = 0x8,
-    };
-
-    uint8_t fPassOps[2];     // op to perform when faces pass (GrStencilOp)
-    uint8_t fFailOps[2];     // op to perform when faces fail (GrStencilOp)
-    uint8_t fFuncs[2];       // test function for faces (GrStencilFunc)
-    uint8_t fPad0;
-    uint8_t fPad1;
-    uint16_t fFuncMasks[2];  // mask for face tests
-    uint16_t fFuncRefs[2];   // reference values for face tests
-    uint16_t fWriteMasks[2]; // stencil write masks
-    mutable uint32_t fFlags;
-
+    uint32_t   fFlags;
+    Face       fFront;
+    Face       fBack;
 };
 
-// We rely on this being packed and aligned (memcmp'ed and memcpy'ed)
-GR_STATIC_ASSERT(sizeof(GrStencilSettings) % 4 == 0);
-GR_STATIC_ASSERT(sizeof(GrStencilSettings) ==
-                 4*sizeof(uint8_t) + // ops
-                 2*sizeof(uint8_t) + // funcs
-                 2*sizeof(uint8_t) + // pads
-                 2*sizeof(uint16_t) + // func masks
-                 2*sizeof(uint16_t) + // ref values
-                 2*sizeof(uint16_t) + // write masks
-                 sizeof(uint32_t)); // flags
-
 #endif