Avoid re-rendering stencil clip for every draw with reducable clip stack

tests/ClipStackTest.cpp

Index: tests/ClipStackTest.cpp
diff --git a/tests/ClipStackTest.cpp b/tests/ClipStackTest.cpp
index 04b48b678364ee0f2bd44f532868c32a48e56cfd..03ef72ea8c559975289f2add381b669bde392cea 100644
--- a/tests/ClipStackTest.cpp
+++ b/tests/ClipStackTest.cpp
@@ -271,6 +271,7 @@ static void test_bounds(skiatest::Reporter* reporter, bool useRects) {
             }
 
             REPORTER_ASSERT(reporter, !stack.isWideOpen());
+            REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID != stack.getTopmostGenID());
 
             stack.getConservativeBounds(0, 0, 100, 100, &devClipBound,
                                         &isIntersectionOfRects);
@@ -293,6 +294,12 @@ static void test_bounds(skiatest::Reporter* reporter, bool useRects) {
 
 // Test out 'isWideOpen' entry point
 static void test_isWideOpen(skiatest::Reporter* reporter) {
+    {
+        // Empty stack is wide open. Wide open stack means that gen id is wide open.
+        SkClipStack stack;
+        REPORTER_ASSERT(reporter, stack.isWideOpen());
+        REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID == stack.getTopmostGenID());
+    }
 
     SkRect rectA, rectB;
 
@@ -304,6 +311,7 @@ static void test_isWideOpen(skiatest::Reporter* reporter) {
         SkClipStack stack;
 
         REPORTER_ASSERT(reporter, stack.isWideOpen());
+        REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID == stack.getTopmostGenID());
     }
 
     // Test out case where the user specifies a union that includes everything
@@ -322,6 +330,7 @@ static void test_isWideOpen(skiatest::Reporter* reporter) {
         stack.clipDevPath(clipB, SkRegion::kUnion_Op, false);
 
         REPORTER_ASSERT(reporter, stack.isWideOpen());
+        REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID == stack.getTopmostGenID());
     }
 
     // Test out union w/ a wide open clip
@@ -331,6 +340,7 @@ static void test_isWideOpen(skiatest::Reporter* reporter) {
         stack.clipDevRect(rectA, SkRegion::kUnion_Op, false);
 
         REPORTER_ASSERT(reporter, stack.isWideOpen());
+        REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID == stack.getTopmostGenID());
     }
 
     // Test out empty difference from a wide open clip
@@ -343,6 +353,7 @@ static void test_isWideOpen(skiatest::Reporter* reporter) {
         stack.clipDevRect(emptyRect, SkRegion::kDifference_Op, false);
 
         REPORTER_ASSERT(reporter, stack.isWideOpen());
+        REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID == stack.getTopmostGenID());
     }
 
     // Test out return to wide open
@@ -354,10 +365,12 @@ static void test_isWideOpen(skiatest::Reporter* reporter) {
         stack.clipDevRect(rectA, SkRegion::kReplace_Op, false);
 
         REPORTER_ASSERT(reporter, !stack.isWideOpen());
+        REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID != stack.getTopmostGenID());
 
         stack.restore();
 
         REPORTER_ASSERT(reporter, stack.isWideOpen());
+        REPORTER_ASSERT(reporter, SkClipStack::kWideOpenGenID == stack.getTopmostGenID());
     }
 }
 
@@ -950,6 +963,9 @@ static void test_reduced_clip_stack(skiatest::Reporter* reporter) {
                                        &initial,
                                        tightBounds);
 
+        REPORTER_ASSERT(reporter, reducedClips.count() == 0 ||
+                        reducedClips.tail()->getGenID() != SkClipStack::kInvalidGenID);
+
         // Build a new clip stack based on the reduced clip elements
         SkClipStack reducedStack;
         if (GrReducedClip::kAllOut_InitialState == initial) {
@@ -986,6 +1002,48 @@ static void test_reduced_clip_stack(skiatest::Reporter* reporter) {
     }
 }
 
+static void test_reduced_clip_stack_genid(skiatest::Reporter* reporter) {
+    SkClipStack stack;
+    stack.clipDevRect(SkRect::MakeXYWH(0, 0, 100, 100), SkRegion::kReplace_Op, true);
+    stack.clipDevRect(SkRect::MakeXYWH(0, 0, 50.3, 50.3), SkRegion::kReplace_Op, true);
+    SkIRect inflatedIBounds = SkIRect::MakeXYWH(0, 0, 100, 100);
+
+    GrReducedClip::ElementList reducedClips;
+    GrReducedClip::InitialState initial;
+    SkIRect tightBounds;
+
+    GrReducedClip::ReduceClipStack(stack,
+                                   inflatedIBounds,
+                                   &reducedClips,
+                                   &initial,
+                                   &tightBounds);
+
+    REPORTER_ASSERT(reporter, reducedClips.count() == 1);
+    // Clips will be cached based on the generation id. Make sure the gen id is valid.
+    REPORTER_ASSERT(reporter, SkClipStack::kInvalidGenID != reducedClips.head()->getGenID());
+
+}
+
+static void test_reduced_clip_stack_no_aa_crash(skiatest::Reporter* reporter) {
+    SkClipStack stack;
+    stack.clipDevRect(SkIRect::MakeXYWH(0, 0, 100, 100), SkRegion::kReplace_Op);
+    stack.clipDevRect(SkIRect::MakeXYWH(0, 0, 50, 50), SkRegion::kReplace_Op);
+    SkIRect inflatedIBounds = SkIRect::MakeXYWH(0, 0, 100, 100);
+
+    GrReducedClip::ElementList reducedClips;
+    GrReducedClip::InitialState initial;
+    SkIRect tightBounds;
+
+    // At the time, this would crash.
+    GrReducedClip::ReduceClipStack(stack,
+                                   inflatedIBounds,
+                                   &reducedClips,
+                                   &initial,
+                                   &tightBounds);
+
+    REPORTER_ASSERT(reporter, 0 == reducedClips.count());
+}
+
 #endif
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -1034,6 +1092,8 @@ static void TestClipStack(skiatest::Reporter* reporter) {
     test_quickContains(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
 }