Move GrReducedClip to its own files.

R=robertphillips@google.com
Review URL: https://codereview.appspot.com/6891045

git-svn-id: http://skia.googlecode.com/svn/trunk@6686 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 328 insertions, 0 deletions

diff --git a/src/gpu/GrReducedClip.cpp b/src/gpu/GrReducedClip.cpp
new file mode 100644
index 0000000000..8ee28ddfb1
--- /dev/null
+++ b/src/gpu/GrReducedClip.cpp
@@ -0,0 +1,328 @@
+
+/*
+ * 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"
+
+typedef SkClipStack::Element Element;
+////////////////////////////////////////////////////////////////////////////////
+
+namespace GrReducedClip {
+
+/*
+There are plenty of optimizations that could be added here. For example we could consider
+checking for cases where an inverse path can be changed to a regular fill with a different op.
+(e.g. [kIntersect, inverse path] -> [kDifference, path]). Maybe flips could be folded into
+earlier operations. Or would inserting flips and reversing earlier ops ever be a win? Perhaps
+for the case where the bounds are kInsideOut_BoundsType. We could restrict earlier operations
+based on later intersect operations, and perhaps remove intersect-rects. We could optionally
+take a rect in case the caller knows a bound on what is to be drawn through this clip.
+*/
+void GrReduceClipStack(const SkClipStack& stack,
+                       const SkRect& queryBounds,
+                       ElementList* result,
+                       InitialState* initialState) {
+    result->reset();
+
+    if (stack.isWideOpen()) {
+        *initialState = kAllIn_InitialState;
+        return;
+    }
+
+    SkClipStack::BoundsType stackBoundsType;
+    SkRect stackBounds;
+    bool iior;
+    stack.getBounds(&stackBounds, &stackBoundsType, &iior);
+
+    if (iior) {
+        SkASSERT(SkClipStack::kNormal_BoundsType == stackBoundsType);
+        SkRect isectRect;
+        if (stackBounds.contains(queryBounds)) {
+            *initialState = kAllIn_InitialState;
+        } else if (isectRect.intersect(stackBounds, queryBounds)) {
+            // 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));
+        } else {
+            *initialState = kAllOut_InitialState;
+        }
+        return;
+    } else {
+        if (SkClipStack::kNormal_BoundsType == stackBoundsType) {
+            if (!SkRect::Intersects(stackBounds, queryBounds)) {
+                *initialState = kAllOut_InitialState;
+                return;
+            }
+        } else {
+            if (stackBounds.contains(queryBounds)) {
+                *initialState = kAllOut_InitialState;
+                return;
+            }
+        }
+    }
+
+    // walk backwards until we get to:
+    //  a) the beginning
+    //  b) an operation that is known to make the bounds all inside/outside
+    //  c) a replace operation
+
+    static const InitialState kUnknown_InitialState = static_cast<InitialState>(-1);
+    *initialState = kUnknown_InitialState;
+
+    // During our backwards walk, track whether we've seen ops that either grow or shrink the clip.
+    // TODO: track these per saved clip so that we can consider them on the forward pass.
+    bool embiggens = false;
+    bool emsmallens = false;
+
+    SkClipStack::Iter iter(stack, SkClipStack::Iter::kTop_IterStart);
+    while ((kUnknown_InitialState == *initialState)) {
+        const Element* element = iter.prev();
+        if (NULL == element) {
+            *initialState = kAllIn_InitialState;
+            break;
+        }
+        if (SkClipStack::kEmptyGenID == element->getGenID()) {
+            *initialState = kAllOut_InitialState;
+            break;
+        }
+        if (SkClipStack::kWideOpenGenID == element->getGenID()) {
+            *initialState = kAllIn_InitialState;
+            break;
+        }
+
+        bool skippable = false;
+        bool isFlip = false; // does this op just flip the in/out state of every point in the bounds
+
+        switch (element->getOp()) {
+            case SkRegion::kDifference_Op:
+                // check if the shape subtracted either contains the entire bounds (and makes
+                // the clip empty) or is outside the bounds and therefore can be skipped.
+                if (element->isInverseFilled()) {
+                    if (element->contains(queryBounds)) {
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    }
+                } else {
+                    if (element->contains(queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        skippable = true;
+                    }
+                }
+                if (!skippable) {
+                    emsmallens = true;
+                }
+                break;
+            case SkRegion::kIntersect_Op:
+                // check if the shape intersected contains the entire bounds and therefore can
+                // be skipped or it is outside the entire bounds and therefore makes the clip
+                // empty.
+                if (element->isInverseFilled()) {
+                    if (element->contains(queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        skippable = true;
+                    }
+                } else {
+                    if (element->contains(queryBounds)) {
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    }
+                }
+                if (!skippable) {
+                    emsmallens = true;
+                }
+                break;
+            case SkRegion::kUnion_Op:
+                // If the union-ed shape contains the entire bounds then after this element
+                // the bounds is entirely inside the clip. If the union-ed shape is outside the
+                // bounds then this op can be skipped.
+                if (element->isInverseFilled()) {
+                    if (element->contains(queryBounds)) {
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        *initialState = kAllIn_InitialState;
+                        skippable = true;
+                    }
+                } else {
+                    if (element->contains(queryBounds)) {
+                        *initialState = kAllIn_InitialState;
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        skippable = true;
+                    }
+                }
+                if (!skippable) {
+                    embiggens = true;
+                }
+                break;
+            case SkRegion::kXOR_Op:
+                // If the bounds is entirely inside the shape being xor-ed then the effect is
+                // to flip the inside/outside state of every point in the bounds. We may be
+                // able to take advantage of this in the forward pass. If the xor-ed shape
+                // doesn't intersect the bounds then it can be skipped.
+                if (element->isInverseFilled()) {
+                    if (element->contains(queryBounds)) {
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        isFlip = true;
+                    }
+                } else {
+                    if (element->contains(queryBounds)) {
+                        isFlip = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        skippable = true;
+                    }
+                }
+                if (!skippable) {
+                    emsmallens = embiggens = true;
+                }
+                break;
+            case SkRegion::kReverseDifference_Op:
+                // When the bounds is entirely within the rev-diff shape then this behaves like xor
+                // and reverses every point inside the bounds. If the shape is completely outside
+                // the bounds then we know after this element is applied that the bounds will be
+                // all outside the current clip.B
+                if (element->isInverseFilled()) {
+                    if (element->contains(queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        isFlip = true;
+                    }
+                } else {
+                    if (element->contains(queryBounds)) {
+                        isFlip = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    }
+                }
+                if (!skippable) {
+                    emsmallens = embiggens = true;
+                }
+                break;
+            case SkRegion::kReplace_Op:
+                // Replace will always terminate our walk. We will either begin the forward walk
+                // at the replace op or detect here than the shape is either completely inside
+                // or completely outside the bounds. In this latter case it can be skipped by
+                // setting the correct value for initialState.
+                if (element->isInverseFilled()) {
+                    if (element->contains(queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        *initialState = kAllIn_InitialState;
+                        skippable = true;
+                    }
+                } else {
+                    if (element->contains(queryBounds)) {
+                        *initialState = kAllIn_InitialState;
+                        skippable = true;
+                    } else if (!SkRect::Intersects(element->getBounds(), queryBounds)) {
+                        *initialState = kAllOut_InitialState;
+                        skippable = true;
+                    }
+                }
+                if (!skippable) {
+                    *initialState = kAllOut_InitialState;
+                    embiggens = emsmallens = true;
+                }
+                break;
+            default:
+                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));
+            } else {
+                result->addToHead(*element);
+            }
+        }
+    }
+
+    if ((kAllOut_InitialState == *initialState && !embiggens) ||
+        (kAllIn_InitialState == *initialState && !emsmallens)) {
+        result->reset();
+    } else {
+        int clipsToSkip = 0;
+        Element* element = result->headIter().get();
+        while (NULL != element) {
+            bool skippable = false;
+            switch (element->getOp()) {
+                case SkRegion::kDifference_Op:
+                    // subtracting from the empty set yields the empty set.
+                    skippable = kAllOut_InitialState == *initialState;
+                    break;
+                case SkRegion::kIntersect_Op:
+                    // intersecting with the empty set yields the empty set
+                    skippable = kAllOut_InitialState == *initialState;
+                    break;
+                case SkRegion::kUnion_Op:
+                    if (kAllIn_InitialState == *initialState) {
+                        // unioning the infinite plane with anything is a no-op.
+                        skippable = true;
+                    } else {
+                        // unioning the empty set with a shape is the shape.
+                        element->setOp(SkRegion::kReplace_Op);
+                    }
+                    break;
+                case SkRegion::kXOR_Op:
+                    if (kAllOut_InitialState == *initialState) {
+                        // xor could be changed to diff in the kAllIn case, not sure it's a win.
+                        element->setOp(SkRegion::kReplace_Op);
+                    }
+                    break;
+                case SkRegion::kReverseDifference_Op:
+                    if (kAllIn_InitialState == *initialState) {
+                        // subtracting the whole plane will yield the empty set.
+                        skippable = true;
+                        *initialState = kAllOut_InitialState;
+                    } else {
+                        // this picks up flips inserted in the backwards pass.
+                        skippable = element->isInverseFilled() ?
+                            !SkRect::Intersects(element->getBounds(), queryBounds) :
+                            element->contains(queryBounds);
+                        if (skippable) {
+                            *initialState = kAllIn_InitialState;
+                        } else {
+                            element->setOp(SkRegion::kReplace_Op);
+                        }
+                    }
+                    break;
+                case SkRegion::kReplace_Op:
+                    SkASSERT(!clipsToSkip); // replace should always be the first op
+                    skippable = false; // we would have skipped it in the backwards walk if we
+                                       // could've.
+                    break;
+                default:
+                    SkDEBUGFAIL("Unexpected op.");
+                    break;
+            }
+            if (!skippable) {
+                break;
+            } else {
+                result->popHead();
+                element = result->headIter().get();
+            }
+        }
+    }
+}
+} // namespace GrReducedClip