Revert of Improve usage of window rectangles

src/gpu/GrClipStackClip.cpp

 /*
  * 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 "GrClipStackClip.h"
 
 #include "GrAppliedClip.h"
@@ skipping 269 matching lines @@
                             bool hasUserStencilSettings, GrAppliedClip* out) const {
     if (!fStack || fStack->isWideOpen()) {
         return true;
     }
 
     SkRect devBounds = SkRect::MakeIWH(drawContext->width(), drawContext->height());
     if (!devBounds.intersect(out->clippedDrawBounds())) {
         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)) {
         SkIRect scissorSpaceIBounds(reducedClip.ibounds());
         scissorSpaceIBounds.offset(-fOrigin);
         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
     //   isect convex_poly
     //   isect convex_poly
     // when drawing rounded div borders. This could probably be tuned based on a
     // configuration's relative costs of switching RTs to generate a mask vs
     // longer shaders.
     if (reducedClip.elements().count() <= kMaxAnalyticElements) {
         // When there are multiple samples we want to do per-sample clipping, not compute a
@@ skipping 34 matching lines @@
             rtSpaceMaskBounds.offset(-fOrigin);
             out->addCoverageFP(create_fp_for_mask(result.get(), rtSpaceMaskBounds));
             return true;
         }
         // if alpha clip mask creation fails fall through to the non-AA code paths
     }
 
     // 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);
         stencilAttachment->setLastClip(reducedClip.elementsGenID(), reducedClip.ibounds(),
                                        fOrigin);
     }
     out->addStencilClip();
     return true;
 }
 
@@ skipping 106 matching lines @@
     sk_sp<GrTexture> result(texProvider->createApproxTexture(desc));
     if (!result) {
         return nullptr;
     }
     result->resourcePriv().setUniqueKey(key);
 
     helper.toTexture(result.get());
 
     return result;
 }