Revert of Improve usage of window rectangles

src/gpu/GrClipStackClip.cpp

Index: src/gpu/GrClipStackClip.cpp
diff --git a/src/gpu/GrClipStackClip.cpp b/src/gpu/GrClipStackClip.cpp
index ff5c860f68325c2808dbb876fce80fc5b372656b..003b4a5d439bb63782dd1370ea6bc7a0f94b4172 100644
--- a/src/gpu/GrClipStackClip.cpp
+++ b/src/gpu/GrClipStackClip.cpp
@@ -287,14 +287,11 @@
         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,
-                                    rt->renderTargetPriv().maxWindowRectangles());
+    const GrReducedClip reducedClip(*fStack, clipSpaceDevBounds);
 
     if (reducedClip.hasIBounds() &&
         !GrClip::IsInsideClip(reducedClip.ibounds(), clipSpaceDevBounds)) {
@@ -303,16 +300,28 @@
         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
@@ -368,15 +377,12 @@
     // 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(rt);
+        context->resourceProvider()->attachStencilAttachment(drawContext->accessRenderTarget());
     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);