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

src/gpu/GrReducedClip.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 "GrReducedClip.h"
 
@@ skipping 52 matching lines @@
             }
             if (NULL != requiresAA) {
                *requiresAA = false;
             }
         } else if (isectRect.intersect(stackBounds, scalarQueryBounds)) {
             if (NULL != tighterBounds) {
                 isectRect.roundOut(tighterBounds);
                 SkRect scalarTighterBounds = SkRect::MakeFromIRect(*tighterBounds);
                 if (scalarTighterBounds == isectRect) {
                     // the round-out didn't add any area outside the clip rect.
-                    *requiresAA = false;
+                    if (NULL != requiresAA) {
+                        *requiresAA = false;
+                    }
                     *initialState = kAllIn_InitialState;
                     return;
                 }
                 *initialState = kAllOut_InitialState;
                 // iior should only be true if aa/non-aa status matches among all elements.
                 SkClipStack::Iter iter(stack, SkClipStack::Iter::kTop_IterStart);
                 bool doAA = iter.prev()->isAA();
-                SkNEW_INSERT_AT_LLIST_HEAD(result, Element, (isectRect, SkRegion::kReplace_Op, doAA));
+                // The clip established by the element list might be cached based on the last
+                // generation id. Without walking the stack, we do not knoow what was the generation
+                // id that lead to this state. Make a conservative guess.
+                SkNEW_INSERT_AT_LLIST_HEAD(result, Element, (isectRect, SkRegion::kReplace_Op, doAA,

[bsalomon, 2013/10/30 14:25:59]

Rather than assigning a genID to the manufactured element maybe this function
could just take an int32_t* genID param that gets updated?

Then we wouldn't need a public Element constructor that takes a genID. That
seems a like an avenue for someone to introduce future bugs.

[Kimmo Kinnunen, 2013/11/01 12:12:20]

Done.

+                                                             stack.getTopmostGenID()));
+
                 if (NULL != requiresAA) {
                     *requiresAA = doAA;
                 }
             }
         } else {
             *initialState = kAllOut_InitialState;
              if (NULL != requiresAA) {
                 *requiresAA = false;
              }
         }
@@ skipping 25 matching lines @@
                 *tighterBounds = queryBounds;
             }
         }
     }
 
     SkRect scalarBounds = SkRect::MakeFromIRect(*bounds);
 
     // Now that we have determined the bounds to use and filtered out the trivial cases, call the
     // helper that actually walks the stack.
     reduced_stack_walker(stack, scalarBounds, result, initialState, requiresAA);
+
+    // The list that was computed in this function may be cached based on the gen id of the last
+    // element.
+    SkASSERT(0 == result->count() || SkClipStack::kInvalidGenID  != result->tail()->getGenID());
 }
 
 void reduced_stack_walker(const SkClipStack& stack,
                           const SkRect& queryBounds,
                           ElementList* result,
                           InitialState* initialState,
                           bool* requiresAA) {
 
     // walk backwards until we get to:
     //  a) the beginning
@@ skipping 174 matching lines @@
                 SkDEBUGFAIL("Unexpected op.");
                 break;
         }
         if (!skippable) {
             // if it is a flip, change it to a bounds-filling rect
             if (isFlip) {
                 SkASSERT(SkRegion::kXOR_Op == element->getOp() ||
                          SkRegion::kReverseDifference_Op == element->getOp());
                 SkNEW_INSERT_AT_LLIST_HEAD(result,
                                            Element,
-                                           (queryBounds, SkRegion::kReverseDifference_Op, false));
+                                           (queryBounds, SkRegion::kReverseDifference_Op, false, element->getGenID()));
             } else {
                 Element* newElement = result->addToHead(*element);
                 if (newElement->isAA()) {
                     ++numAAElements;
                 }
                 // Intersecting an inverse shape is the same as differencing the non-inverse shape.
                 // Replacing with an inverse shape is the same as setting initialState=kAllIn and
                 // differencing the non-inverse shape.
                 bool isReplace = SkRegion::kReplace_Op == newElement->getOp();
                 if (newElement->isInverseFilled() &&
@@ skipping 80 matching lines @@
                 result->popHead();
                 element = result->headIter().get();
             }
         }
     }
     if (NULL != requiresAA) {
         *requiresAA = numAAElements > 0;
     }
 }
 } // namespace GrReducedClip