Fix SkClipStack bug with inverse-filled difference elements

tests/ClipStackTest.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Test.h"
 #if SK_SUPPORT_GPU
     #include "GrReducedClip.h"
@@ skipping 776 matching lines @@
 
     {
         SkClipStack stack;
         SkPath path = nonIntersectingCircle;
         path.toggleInverseFillType();
         stack.clipDevPath(path, SkRegion::kIntersect_Op, false);
         REPORTER_ASSERT(reporter, true == stack.quickContains(testRect));
     }
 }
 
+static void set_region_to_stack(const SkClipStack& stack, const SkIRect& bounds, SkRegion* region) {
+    region->setRect(bounds);
+    SkClipStack::Iter iter(stack, SkClipStack::Iter::kBottom_IterStart);
+    while (const SkClipStack::Element *element = iter.next()) {
+        SkRegion elemRegion;
+        SkRegion boundsRgn(bounds);
+        SkPath path;
+
+        switch (element->getType()) {
+            case SkClipStack::Element::kEmpty_Type:
+                elemRegion.setEmpty();
+                break;
+            default:
+                element->asPath(&path);
+                elemRegion.setPath(path, boundsRgn);
+                break;
+        }
+        region->op(elemRegion, element->getOp());
+    }
+}
+
+static void test_invfill_diff_bug(skiatest::Reporter* reporter) {
+    SkClipStack stack;
+    stack.clipDevRect({10, 10, 20, 20}, SkRegion::kIntersect_Op, false);
+
+    SkPath path;
+    path.addRect({30, 10, 40, 20});
+    path.setFillType(SkPath::kInverseWinding_FillType);
+    stack.clipDevPath(path, SkRegion::kDifference_Op, false);
+
+    REPORTER_ASSERT(reporter, SkClipStack::kEmptyGenID == stack.getTopmostGenID());
+
+    SkRect stackBounds;
+    SkClipStack::BoundsType stackBoundsType;
+    stack.getBounds(&stackBounds, &stackBoundsType);
+
+    REPORTER_ASSERT(reporter, stackBounds.isEmpty());
+    REPORTER_ASSERT(reporter, SkClipStack::kNormal_BoundsType == stackBoundsType);
+
+    SkRegion region;
+    set_region_to_stack(stack, {0, 0, 50, 30}, &region);
+
+    REPORTER_ASSERT(reporter, region.isEmpty());
+}
+
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 #if SK_SUPPORT_GPU
 // Functions that add a shape to the clip stack. The shape is computed from a rectangle.
 // AA is always disabled since the clip stack reducer can cause changes in aa rasterization of the
 // stack. A fractional edge repeated in different elements may be rasterized fewer times using the
 // reduced stack.
 typedef void (*AddElementFunc) (const SkRect& rect,
                                 bool invert,
                                 SkRegion::Op op,
@@ skipping 45 matching lines @@
         case SkClipStack::Element::kPath_Type:
             stack->clipDevPath(element.getPath(), element.getOp(), element.isAA());
             break;
         case SkClipStack::Element::kEmpty_Type:
             SkDEBUGFAIL("Why did the reducer produce an explicit empty.");
             stack->clipEmpty();
             break;
     }
 }
 
-static void add_elem_to_region(const SkClipStack::Element& element,
-                               const SkIRect& bounds,
-                               SkRegion* region) {
-    SkRegion elemRegion;
-    SkRegion boundsRgn(bounds);
-    SkPath path;
-
-    switch (element.getType()) {
-        case SkClipStack::Element::kEmpty_Type:
-            elemRegion.setEmpty();
-            break;
-        default:
-            element.asPath(&path);
-            elemRegion.setPath(path, boundsRgn);
-            break;
-    }
-    region->op(elemRegion, element.getOp());
-}
-
 static void test_reduced_clip_stack(skiatest::Reporter* reporter) {
     // We construct random clip stacks, reduce them, and then rasterize both versions to verify that
     // they are equal.
 
     // All the clip elements will be contained within these bounds.
     static const SkRect kBounds = SkRect::MakeWH(100, 100);
 
     enum {
         kNumTests = 200,
         kMinElemsPerTest = 1,
@@ skipping 93 matching lines @@
         for (ElementList::Iter iter = reducedClips.headIter(); iter.get(); iter.next()) {
             add_elem_to_stack(*iter.get(), &reducedStack);
         }
 
         // GrReducedClipStack assumes that the final result is clipped to the returned bounds
         reducedStack.clipDevRect(tighterBounds, SkRegion::kIntersect_Op);
         stack.clipDevRect(tighterBounds, SkRegion::kIntersect_Op);
 
         // convert both the original stack and reduced stack to SkRegions and see if they're equal
         SkRegion region;
+        set_region_to_stack(stack, inflatedIBounds, &region);
+
         SkRegion reducedRegion;
+        set_region_to_stack(reducedStack, inflatedIBounds, &reducedRegion);
 
-        region.setRect(inflatedIBounds);
-        const SkClipStack::Element* element;
-        SkClipStack::Iter iter(stack, SkClipStack::Iter::kBottom_IterStart);
-        while ((element = iter.next())) {
-            add_elem_to_region(*element, inflatedIBounds, &region);
-        }
-
-        reducedRegion.setRect(inflatedIBounds);
-        iter.reset(reducedStack, SkClipStack::Iter::kBottom_IterStart);
-        while ((element = iter.next())) {
-            add_elem_to_region(*element, inflatedIBounds, &reducedRegion);
-        }
         SkString testCase;
         testCase.printf("Iteration %d", i);
         REPORTER_ASSERT_MESSAGE(reporter, region == reducedRegion, testCase.c_str());
     }
 }
 
 #ifdef SK_BUILD_FOR_WIN
     #define SUPPRESS_VISIBILITY_WARNING
 #else
     #define SUPPRESS_VISIBILITY_WARNING __attribute__((visibility("hidden")))
@@ skipping 179 matching lines @@
     test_iterators(reporter);
     test_bounds(reporter, SkClipStack::Element::kRect_Type);
     test_bounds(reporter, SkClipStack::Element::kRRect_Type);
     test_bounds(reporter, SkClipStack::Element::kPath_Type);
     test_isWideOpen(reporter);
     test_rect_merging(reporter);
     test_rect_replace(reporter);
     test_rect_inverse_fill(reporter);
     test_path_replace(reporter);
     test_quickContains(reporter);
+    test_invfill_diff_bug(reporter);
 #if SK_SUPPORT_GPU
     test_reduced_clip_stack(reporter);
     test_reduced_clip_stack_genid(reporter);
     test_reduced_clip_stack_no_aa_crash(reporter);
 #endif
 }