Define clear regions in terms of GrFixedClip

src/gpu/GrClipStackClip.cpp

Index: src/gpu/GrClipStackClip.cpp
diff --git a/src/gpu/GrClipStackClip.cpp b/src/gpu/GrClipStackClip.cpp
index 695eda981fa379456995dd0ae1f2e22c678b38e0..77c4ecc02376834f2b165568fccd1ddd3264f7dc 100644
--- a/src/gpu/GrClipStackClip.cpp
+++ b/src/gpu/GrClipStackClip.cpp
@@ -468,10 +468,12 @@ sk_sp<GrTexture> GrClipStackClip::CreateAlphaClipMask(GrContext* context,
     // The texture may be larger than necessary, this rect represents the part of the texture
     // we populate with a rasterization of the clip.
     SkIRect maskSpaceIBounds = SkIRect::MakeWH(reducedClip.width(), reducedClip.height());
+    GrFixedClip clip(maskSpaceIBounds);
 
     // The scratch texture that we are drawing into can be substantially larger than the mask. Only
     // clear the part that we care about.
-    dc->clear(&maskSpaceIBounds, InitialState::kAllIn == reducedClip.initialState() ? -1 : 0, true);
+    GrColor initialCoverage = InitialState::kAllIn == reducedClip.initialState() ? -1 : 0;
+    dc->drawContextPriv().clear(clip, initialCoverage, true);
 
     // Set the matrix so that rendered clip elements are transformed to mask space from clip
     // space.
@@ -488,8 +490,6 @@ sk_sp<GrTexture> GrClipStackClip::CreateAlphaClipMask(GrContext* context,
         SkRegion::Op op = element->getOp();
         bool invert = element->isInverseFilled();
         if (invert || SkRegion::kIntersect_Op == op || SkRegion::kReverseDifference_Op == op) {
-            GrFixedClip clip(maskSpaceIBounds);
-
             // draw directly into the result with the stencil set to make the pixels affected
             // by the clip shape be non-zero.
             static constexpr GrUserStencilSettings kStencilInElement(
@@ -539,8 +539,33 @@ sk_sp<GrTexture> GrClipStackClip::CreateAlphaClipMask(GrContext* context,
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-// Create a 1-bit clip mask in the stencil buffer. 'devClipBounds' are in device
-// (as opposed to canvas) coordinates
+// Create a 1-bit clip mask in the stencil buffer.
+
+class StencilFixedClip final : public GrFixedClip {
+public:
+    StencilFixedClip(const SkIRect& scissorRect) : INHERITED(scissorRect), fUseClipBit(false) {}
+    void useClipBit(bool use) { fUseClipBit = use; }
+
+private:
+    bool quickContains(const SkRect& rect) const override {
+        return fUseClipBit ? false : INHERITED::quickContains(rect);
+    }
+    bool apply(GrContext* context, GrDrawContext* drawContext, bool useHWAA,
+               bool hasUserStencilSettings, GrAppliedClip* out) const override {
+        if (!INHERITED::apply(context, drawContext, useHWAA, hasUserStencilSettings, out)) {
+            return false;
+        }
+        if (fUseClipBit) {
+            out->addStencilClip();
+        }
+        return true;
+    }
+
+    bool fUseClipBit;
+
+    typedef GrFixedClip INHERITED;
+};
+
 bool GrClipStackClip::CreateStencilClipMask(GrContext* context,
                                             GrDrawContext* drawContext,
                                             const GrReducedClip& reducedClip,
@@ -569,10 +594,10 @@ bool GrClipStackClip::CreateStencilClipMask(GrContext* context,
         // We set the current clip to the bounds so that our recursive draws are scissored to them.
         SkIRect stencilSpaceIBounds(reducedClip.ibounds());
         stencilSpaceIBounds.offset(clipSpaceToStencilOffset);
-        GrFixedClip clip(stencilSpaceIBounds);
+        StencilFixedClip clip(stencilSpaceIBounds);
 
-        bool insideClip = InitialState::kAllIn == reducedClip.initialState();
-        drawContext->drawContextPriv().clearStencilClip(stencilSpaceIBounds, insideClip);
+        bool initialState = InitialState::kAllIn == reducedClip.initialState();
+        drawContext->drawContextPriv().clearStencilClip(clip, initialState);
 
         // walk through each clip element and perform its set op
         // with the existing clip.
@@ -582,7 +607,7 @@ bool GrClipStackClip::CreateStencilClipMask(GrContext* context,
 
             bool fillInverted = false;
             // enabled at bottom of loop
-            clip.disableStencilClip();
+            clip.useClipBit(false);
 
             // This will be used to determine whether the clip shape can be rendered into the
             // stencil with arbitrary stencil settings.
@@ -677,8 +702,9 @@ bool GrClipStackClip::CreateStencilClipMask(GrContext* context,
                 }
             }
 
-            // Just enable stencil clip. The passes choose whether or not they will actually use it.
-            clip.enableStencilClip();
+            // This doesn't mean the current pass will be clipped by the stencil buffer. That is
+            // decided by GrUserStencilSettings. This just tells it there is data in the clip bit.
+            clip.useClipBit(true);
 
             // now we modify the clip bit by rendering either the clip
             // element directly or a bounding rect of the entire clip.