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

tests/ClipCacheTest.cpp

 /*
  * Copyright 2012 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"
 // This is a GR test
@@ skipping 88 matching lines @@
     REPORTER_ASSERT(reporter, isIntersectionOfRects);
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // verify that the top state of the stack matches the passed in state
 static void check_state(skiatest::Reporter* reporter,
                         const GrClipMaskCache& cache,
                         const SkClipStack& clip,
                         GrTexture* mask,
                         const SkIRect& bound) {
-    SkClipStack cacheClip;
     REPORTER_ASSERT(reporter, clip.getTopmostGenID() == cache.getLastClipGenID());
 
     REPORTER_ASSERT(reporter, mask == cache.getLastMask());
 
     SkIRect cacheBound;
     cache.getLastBound(&cacheBound);
     REPORTER_ASSERT(reporter, bound == cacheBound);
 }
 
+static void check_empty_state(skiatest::Reporter* reporter,
+                              const GrClipMaskCache& cache) {
+    REPORTER_ASSERT(reporter, SkClipStack::kInvalidGenID == cache.getLastClipGenID());
+    REPORTER_ASSERT(reporter, NULL == cache.getLastMask());
+
+    SkIRect emptyBound;
+    emptyBound.setEmpty();
+
+    SkIRect cacheBound;
+    cache.getLastBound(&cacheBound);
+    REPORTER_ASSERT(reporter, emptyBound == cacheBound);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // basic test of the cache's base functionality:
 //  push, pop, set, canReuse & getters
 static void test_cache(skiatest::Reporter* reporter, GrContext* context) {
 
     if (false) { // avoid bit rot, suppress warning
         createTexture(context);
     }
     GrClipMaskCache cache;
 
     cache.setContext(context);
 
-    SkClipStack emptyClip;
-    emptyClip.reset();
-
-    SkIRect emptyBound;
-    emptyBound.setEmpty();
-
     // check initial state
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
 
     // set the current state
     SkIRect bound1;
     bound1.set(0, 0, 100, 100);
 
     SkClipStack clip1(bound1);
 
     GrTextureDesc desc;
     desc.fFlags = kRenderTarget_GrTextureFlagBit;
     desc.fWidth = X_SIZE;
     desc.fHeight = Y_SIZE;
     desc.fConfig = kSkia8888_GrPixelConfig;
 
     cache.acquireMask(clip1.getTopmostGenID(), desc, bound1);
 
     GrTexture* texture1 = cache.getLastMask();
     REPORTER_ASSERT(reporter, texture1);
     if (NULL == texture1) {
         return;
     }
 
     // check that the set took
     check_state(reporter, cache, clip1, texture1, bound1);
     REPORTER_ASSERT(reporter, texture1->getRefCnt());
 
     // push the state
     cache.push();
 
     // verify that the pushed state is initially empty
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
     REPORTER_ASSERT(reporter, texture1->getRefCnt());
 
     // modify the new state
     SkIRect bound2;
     bound2.set(-10, -10, 10, 10);
 
     SkClipStack clip2(bound2);
 
     cache.acquireMask(clip2.getTopmostGenID(), desc, bound2);
 
@@ skipping 16 matching lines @@
     cache.pop();
 
     // verify that the old state is restored
     check_state(reporter, cache, clip1, texture1, bound1);
     REPORTER_ASSERT(reporter, texture1->getRefCnt());
 
     // manually clear the state
     cache.reset();
 
     // verify it is now empty
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
 
     // pop again - so there is no state
     cache.pop();
 
 #if !defined(SK_DEBUG)
     // verify that the getters don't crash
     // only do in release since it generates asserts in debug
-    check_state(reporter, cache, emptyClip, NULL, emptyBound);
+    check_empty_state(reporter, cache);
 #endif
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 static void TestClipCache(skiatest::Reporter* reporter, GrContextFactory* factory) {
     for (int type = 0; type < GrContextFactory::kLastGLContextType; ++type) {
         GrContextFactory::GLContextType glType = static_cast<GrContextFactory::GLContextType>(type);
         if (!GrContextFactory::IsRenderingGLContext(glType)) {
             continue;
         }
         GrContext* context = factory->get(glType);
         if (NULL == context) {
             continue;
         }
 
         test_cache(reporter, context);
         test_clip_bounds(reporter, context);
     }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 #include "TestClassDef.h"
 DEFINE_GPUTESTCLASS("ClipCache", ClipCacheTestClass, TestClipCache)
 
 #endif