text: 
  /*
   * 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 "GrClipMaskManager.h"
  #include "GrAAConvexPathRenderer.h"
  #include "GrAAHairLinePathRenderer.h"
  #include "GrAARectRenderer.h"
  #include "GrDrawTargetCaps.h"
  #include "GrGpu.h"
  #include "GrPaint.h"
  #include "GrPathRenderer.h"
  #include "GrRenderTarget.h"
  #include "GrStencilBuffer.h"
  #include "GrSWMaskHelper.h"
  #include "effects/GrTextureDomain.h"
  #include "effects/GrConvexPolyEffect.h"
  #include "effects/GrRRectEffect.h"
  #include "SkRasterClip.h"
  #include "SkStrokeRec.h"
  #include "SkTLazy.h"
  
  #define GR_AA_CLIP 1
  
  typedef SkClipStack::Element Element;
  
  using namespace GrReducedClip;
  
  ////////////////////////////////////////////////////////////////////////////////
  namespace {
  // set up the draw state to enable the aa clipping mask. Besides setting up the
  // stage matrix this also alters the vertex layout
  void setup_drawstate_aaclip(GrGpu* gpu,
                              GrTexture* result,
                              const SkIRect &devBound) {
      GrDrawState* drawState = gpu->drawState();
      SkASSERT(drawState);
  
      SkMatrix mat;
      // We want to use device coords to compute the texture coordinates. We set our matrix to be
      // equal to the view matrix followed by an offset to the devBound, and then a scaling matrix to
      // normalized coords. We apply this matrix to the vertex positions rather than local coords.
      mat.setIDiv(result->width(), result->height());
      mat.preTranslate(SkIntToScalar(-devBound.fLeft),
                       SkIntToScalar(-devBound.fTop));
      mat.preConcat(drawState->getViewMatrix());
  
      SkIRect domainTexels = SkIRect::MakeWH(devBound.width(), devBound.height());
      // This could be a long-lived effect that is cached with the alpha-mask.
      drawState->addCoverageEffect(
          GrTextureDomainEffect::Create(result,
                                        mat,
                                        GrTextureDomain::MakeTexelDomain(result, domainTexels),
                                        GrTextureDomain::kDecal_Mode,
                                        GrTextureParams::kNone_FilterMode,
                                        kPosition_GrCoordSet))->unref();
  }
  
  bool path_needs_SW_renderer(GrContext* context,
                              GrGpu* gpu,
                              const SkPath& origPath,
                              const SkStrokeRec& stroke,
                              bool doAA) {
      // the gpu alpha mask will draw the inverse paths as non-inverse to a temp buffer
      SkTCopyOnFirstWrite<SkPath> path(origPath);
      if (path->isInverseFillType()) {
          path.writable()->toggleInverseFillType();
      }
      // last (false) parameter disallows use of the SW path renderer
      GrPathRendererChain::DrawType type = doAA ?
                                           GrPathRendererChain::kColorAntiAlias_DrawType :
                                           GrPathRendererChain::kColor_DrawType;
  
      return NULL == context->getPathRenderer(*path, stroke, gpu, false, type);
  }
  
  }
  
  /*
   * This method traverses the clip stack to see if the GrSoftwarePathRenderer
   * will be used on any element. If so, it returns true to indicate that the
   * entire clip should be rendered in SW and then uploaded en masse to the gpu.
   */
  bool GrClipMaskManager::useSWOnlyPath(const ElementList& elements) {
  
      // TODO: generalize this function so that when
      // a clip gets complex enough it can just be done in SW regardless
      // of whether it would invoke the GrSoftwarePathRenderer.
      SkStrokeRec stroke(SkStrokeRec::kFill_InitStyle);
  
      for (ElementList::Iter iter(elements.headIter()); iter.get(); iter.next()) {
          const Element* element = iter.get();
          // rects can always be drawn directly w/o using the software path
          // Skip rrects once we're drawing them directly.
          if (Element::kRect_Type != element->getType()) {
              SkPath path;
              element->asPath(&path);
              if (path_needs_SW_renderer(this->getContext(), fGpu, path, stroke, element->isAA())) {
                  return true;
              }
          }
      }
      return false;
  }
  
  bool GrClipMaskManager::installClipEffects(const ElementList& elements,
                                             GrDrawState::AutoRestoreEffects* are,
                                             const SkVector& clipToRTOffset,
                                             const SkRect* drawBounds) {
  
      GrDrawState* drawState = fGpu->drawState();
      SkRect boundsInClipSpace;
      if (NULL != drawBounds) {
          boundsInClipSpace = *drawBounds;
          boundsInClipSpace.offset(-clipToRTOffset.fX, -clipToRTOffset.fY);
      }
  
      are->set(drawState);
      GrRenderTarget* rt = drawState->getRenderTarget();
      ElementList::Iter iter(elements);
  
      bool setARE = false;
      bool failed = false;
  
      while (NULL != iter.get()) {
          SkRegion::Op op = iter.get()->getOp();
          bool invert;
          bool skip = false;
          switch (op) {
              case SkRegion::kReplace_Op:
                  SkASSERT(iter.get() == elements.head());
                  // Fallthrough, handled same as intersect.
              case SkRegion::kIntersect_Op:
                  invert = false;
                  if (NULL != drawBounds && iter.get()->contains(boundsInClipSpace)) {
                      skip = true;
                  }
                  break;
              case SkRegion::kDifference_Op:
                  invert = true;
                  // We don't currently have a cheap test for whether a rect is fully outside an
                  // element's primitive, so don't attempt to set skip.
                  break;
              default:
                  failed = true;
                  break;
          }
          if (failed) {
              break;
          }
  
          if (!skip) {
              GrEffectEdgeType edgeType;
              if (GR_AA_CLIP && iter.get()->isAA()) {
                  if (rt->isMultisampled()) {
                      // Coverage based AA clips don't place nicely with MSAA.
                      failed = true;
                      break;
                  }
                  edgeType = invert ? kInverseFillAA_GrEffectEdgeType : kFillAA_GrEffectEdgeType;
              } else {
                  edgeType = invert ? kInverseFillBW_GrEffectEdgeType : kFillBW_GrEffectEdgeType;
              }
              SkAutoTUnref<GrEffect> effect;
              switch (iter.get()->getType()) {
                  case SkClipStack::Element::kPath_Type:
                      effect.reset(GrConvexPolyEffect::Create(edgeType, iter.get()->getPath(),
                          &clipToRTOffset));
                      break;
                  case SkClipStack::Element::kRRect_Type: {
                      SkRRect rrect = iter.get()->getRRect();
                      rrect.offset(clipToRTOffset.fX, clipToRTOffset.fY);
                      effect.reset(GrRRectEffect::Create(edgeType, rrect));
                      break;
                  }
                  case SkClipStack::Element::kRect_Type: {
                      SkRect rect = iter.get()->getRect();
                      rect.offset(clipToRTOffset.fX, clipToRTOffset.fY);
                      effect.reset(GrConvexPolyEffect::Create(edgeType, rect));
                      break;
                  }
                  default:
                      break;
              }
              if (effect) {
                  if (!setARE) {
                      are->set(fGpu->drawState());
                      setARE = true;
                  }
                  fGpu->drawState()->addCoverageEffect(effect);
              } else {
                  failed = true;
                  break;
              }
          }
          iter.next();
      }
  
      if (failed) {
          are->set(NULL);
      }
  
      return !failed;
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  // sort out what kind of clip mask needs to be created: alpha, stencil,
  // scissor, or entirely software
  bool GrClipMaskManager::setupClipping(const GrClipData* clipDataIn,
                                        GrDrawState::AutoRestoreEffects* are,
                                        const SkRect* devBounds) {
      fCurrClipMaskType = kNone_ClipMaskType;
  
      ElementList elements(16);
      int32_t genID;
      InitialState initialState;
      SkIRect clipSpaceIBounds;
      bool requiresAA;
  
      GrDrawState* drawState = fGpu->drawState();
  
      const GrRenderTarget* rt = drawState->getRenderTarget();
      // GrDrawTarget should have filtered this for us
      SkASSERT(NULL != rt);
  
      bool ignoreClip = !drawState->isClipState() || clipDataIn->fClipStack->isWideOpen();
  
      if (!ignoreClip) {
          SkIRect clipSpaceRTIBounds = SkIRect::MakeWH(rt->width(), rt->height());
          clipSpaceRTIBounds.offset(clipDataIn->fOrigin);
          ReduceClipStack(*clipDataIn->fClipStack,
                          clipSpaceRTIBounds,
                          &elements,
                          &genID,
                          &initialState,
                          &clipSpaceIBounds,
                          &requiresAA);
          if (elements.isEmpty()) {
              if (kAllIn_InitialState == initialState) {
                  ignoreClip = clipSpaceIBounds == clipSpaceRTIBounds;
              } else {
                  return false;
              }
          }
      }
  
      if (ignoreClip) {
          fGpu->disableScissor();
          this->setGpuStencil();
          return true;
      }
  
      // An element count of 4 was chosen because of the common pattern in Blink of:
      //   isect RR
      //   diff  RR
      //   isect convex_poly
      //   isect convex_poly
      // when drawing rounded div borders. This could probably be tuned based on a
      // configuration's relative costs of switching RTs to generate a mask vs
      // longer shaders.
      if (elements.count() <= 4) {
          SkVector clipToRTOffset = { SkIntToScalar(-clipDataIn->fOrigin.fX),
                                      SkIntToScalar(-clipDataIn->fOrigin.fY) };
          if (elements.isEmpty() ||
              (requiresAA && this->installClipEffects(elements, are, clipToRTOffset, devBounds))) {
              SkIRect scissorSpaceIBounds(clipSpaceIBounds);
              scissorSpaceIBounds.offset(-clipDataIn->fOrigin);
              if (NULL == devBounds ||
                  !SkRect::Make(scissorSpaceIBounds).contains(*devBounds)) {
                  fGpu->enableScissor(scissorSpaceIBounds);
              } else {
                  fGpu->disableScissor();
              }
              this->setGpuStencil();
              return true;
          }
      }
  
  #if GR_AA_CLIP
      // If MSAA is enabled we can do everything in the stencil buffer.
      if (0 == rt->numSamples() && requiresAA) {
          GrTexture* result = NULL;
  
          if (this->useSWOnlyPath(elements)) {
              // The clip geometry is complex enough that it will be more efficient to create it
              // entirely in software
              result = this->createSoftwareClipMask(genID,
                                                    initialState,
                                                    elements,
                                                    clipSpaceIBounds);
          } else {
              result = this->createAlphaClipMask(genID,
                                                 initialState,
                                                 elements,
                                                 clipSpaceIBounds);
          }
  
          if (NULL != result) {
              // The mask's top left coord should be pinned to the rounded-out top left corner of
              // clipSpace bounds. We determine the mask's position WRT to the render target here.
              SkIRect rtSpaceMaskBounds = clipSpaceIBounds;
              rtSpaceMaskBounds.offset(-clipDataIn->fOrigin);
              are->set(fGpu->drawState());
              setup_drawstate_aaclip(fGpu, result, rtSpaceMaskBounds);
              fGpu->disableScissor();
              this->setGpuStencil();
              return true;
          }
          // if alpha clip mask creation fails fall through to the non-AA code paths
      }
  #endif // GR_AA_CLIP
  
      // Either a hard (stencil buffer) clip was explicitly requested or an anti-aliased clip couldn't
      // be created. In either case, free up the texture in the anti-aliased mask cache.
      // TODO: this may require more investigation. Ganesh performs a lot of utility draws (e.g.,
      // clears, InOrderDrawBuffer playbacks) that hit the stencil buffer path. These may be
      // "incorrectly" clearing the AA cache.
      fAACache.reset();
  
      // use the stencil clip if we can't represent the clip as a rectangle.
      SkIPoint clipSpaceToStencilSpaceOffset = -clipDataIn->fOrigin;
      this->createStencilClipMask(genID,
                                  initialState,
                                  elements,
                                  clipSpaceIBounds,
                                  clipSpaceToStencilSpaceOffset);
  
      // This must occur after createStencilClipMask. That function may change the scissor. Also, it
      // only guarantees that the stencil mask is correct within the bounds it was passed, so we must
      // use both stencil and scissor test to the bounds for the final draw.
      SkIRect scissorSpaceIBounds(clipSpaceIBounds);
      scissorSpaceIBounds.offset(clipSpaceToStencilSpaceOffset);
      fGpu->enableScissor(scissorSpaceIBounds);
      this->setGpuStencil();
      return true;
  }
  
  #define VISUALIZE_COMPLEX_CLIP 0
  
  #if VISUALIZE_COMPLEX_CLIP
      #include "SkRandom.h"
      SkRandom gRandom;
      #define SET_RANDOM_COLOR drawState->setColor(0xff000000 | gRandom.nextU());
  #else
      #define SET_RANDOM_COLOR
  #endif
  
  namespace {
  
  ////////////////////////////////////////////////////////////////////////////////
  // set up the OpenGL blend function to perform the specified
  // boolean operation for alpha clip mask creation
  void setup_boolean_blendcoeffs(GrDrawState* drawState, SkRegion::Op op) {
  
      switch (op) {
          case SkRegion::kReplace_Op:
              drawState->setBlendFunc(kOne_GrBlendCoeff, kZero_GrBlendCoeff);
              break;
          case SkRegion::kIntersect_Op:
              drawState->setBlendFunc(kDC_GrBlendCoeff, kZero_GrBlendCoeff);
              break;
          case SkRegion::kUnion_Op:
              drawState->setBlendFunc(kOne_GrBlendCoeff, kISC_GrBlendCoeff);
              break;
          case SkRegion::kXOR_Op:
              drawState->setBlendFunc(kIDC_GrBlendCoeff, kISC_GrBlendCoeff);
              break;
          case SkRegion::kDifference_Op:
              drawState->setBlendFunc(kZero_GrBlendCoeff, kISC_GrBlendCoeff);
              break;
          case SkRegion::kReverseDifference_Op:
              drawState->setBlendFunc(kIDC_GrBlendCoeff, kZero_GrBlendCoeff);
              break;
          default:
              SkASSERT(false);
              break;
      }
  }
  
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  bool GrClipMaskManager::drawElement(GrTexture* target,
                                      const SkClipStack::Element* element,
                                      GrPathRenderer* pr) {
      GrDrawState* drawState = fGpu->drawState();
  
      drawState->setRenderTarget(target->asRenderTarget());
  
      // TODO: Draw rrects directly here.
      switch (element->getType()) {
          case Element::kEmpty_Type:
              SkDEBUGFAIL("Should never get here with an empty element.");
              break;
          case Element::kRect_Type:
              // TODO: Do rects directly to the accumulator using a aa-rect GrEffect that covers the
              // entire mask bounds and writes 0 outside the rect.
              if (element->isAA()) {
                  getContext()->getAARectRenderer()->fillAARect(fGpu,
                                                                fGpu,
                                                                element->getRect(),
                                                                SkMatrix::I(),
                                                                element->getRect());
              } else {
                  fGpu->drawSimpleRect(element->getRect());
              }
              return true;
          default: {
              SkPath path;
              element->asPath(&path);
              if (path.isInverseFillType()) {
                  path.toggleInverseFillType();
              }
              SkStrokeRec stroke(SkStrokeRec::kFill_InitStyle);
              if (NULL == pr) {
                  GrPathRendererChain::DrawType type;
                  type = element->isAA() ? GrPathRendererChain::kColorAntiAlias_DrawType :
                                           GrPathRendererChain::kColor_DrawType;
                  pr = this->getContext()->getPathRenderer(path, stroke, fGpu, false, type);
              }
              if (NULL == pr) {
                  return false;
              }
              pr->drawPath(path, stroke, fGpu, element->isAA());
              break;
          }
      }
      return true;
  }
  
  bool GrClipMaskManager::canStencilAndDrawElement(GrTexture* target,
                                                   const SkClipStack::Element* element,
                                                   GrPathRenderer** pr) {
      GrDrawState* drawState = fGpu->drawState();
      drawState->setRenderTarget(target->asRenderTarget());
  
      if (Element::kRect_Type == element->getType()) {
          return true;
      } else {
          // We shouldn't get here with an empty clip element.
          SkASSERT(Element::kEmpty_Type != element->getType());
          SkPath path;
          element->asPath(&path);
          if (path.isInverseFillType()) {
              path.toggleInverseFillType();
          }
          SkStrokeRec stroke(SkStrokeRec::kFill_InitStyle);
          GrPathRendererChain::DrawType type = element->isAA() ?
              GrPathRendererChain::kStencilAndColorAntiAlias_DrawType :
              GrPathRendererChain::kStencilAndColor_DrawType;
          *pr = this->getContext()->getPathRenderer(path, stroke, fGpu, false, type);
          return NULL != *pr;
      }
  }
  
  void GrClipMaskManager::mergeMask(GrTexture* dstMask,
                                    GrTexture* srcMask,
                                    SkRegion::Op op,
                                    const SkIRect& dstBound,
                                    const SkIRect& srcBound) {
      GrDrawState::AutoViewMatrixRestore avmr;
      GrDrawState* drawState = fGpu->drawState();
      SkAssertResult(avmr.setIdentity(drawState));
      GrDrawState::AutoRestoreEffects are(drawState);
  
      drawState->setRenderTarget(dstMask->asRenderTarget());
  
      setup_boolean_blendcoeffs(drawState, op);
  
      SkMatrix sampleM;
      sampleM.setIDiv(srcMask->width(), srcMask->height());
  
      drawState->addColorEffect(
          GrTextureDomainEffect::Create(srcMask,
                                        sampleM,
                                        GrTextureDomain::MakeTexelDomain(srcMask, srcBound),
                                        GrTextureDomain::kDecal_Mode,
                                        GrTextureParams::kNone_FilterMode))->unref();
      fGpu->drawSimpleRect(SkRect::Make(dstBound));
  }
  
  // get a texture to act as a temporary buffer for AA clip boolean operations
  // TODO: given the expense of createTexture we may want to just cache this too
  void GrClipMaskManager::getTemp(int width, int height, GrAutoScratchTexture* temp) {
      if (NULL != temp->texture()) {
          // we've already allocated the temp texture
          return;
      }
  
      GrTextureDesc desc;
      desc.fFlags = kRenderTarget_GrTextureFlagBit|kNoStencil_GrTextureFlagBit;
      desc.fWidth = width;
      desc.fHeight = height;
      desc.fConfig = kAlpha_8_GrPixelConfig;
  
      temp->set(this->getContext(), desc);
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  // Return the texture currently in the cache if it exists. Otherwise, return NULL
  GrTexture* GrClipMaskManager::getCachedMaskTexture(int32_t elementsGenID,
                                                     const SkIRect& clipSpaceIBounds) {
      bool cached = fAACache.canReuse(elementsGenID, clipSpaceIBounds);
      if (!cached) {
          return NULL;
      }
  
      return fAACache.getLastMask();
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  // Allocate a texture in the texture cache. This function returns the texture
  // allocated (or NULL on error).
  GrTexture* GrClipMaskManager::allocMaskTexture(int32_t elementsGenID,
                                                 const SkIRect& clipSpaceIBounds,
                                                 bool willUpload) {
      // Since we are setting up the cache we should free up the
      // currently cached mask so it can be reused.
      fAACache.reset();
  
      GrTextureDesc desc;
      desc.fFlags = willUpload ? kNone_GrTextureFlags : kRenderTarget_GrTextureFlagBit;
      desc.fWidth = clipSpaceIBounds.width();
      desc.fHeight = clipSpaceIBounds.height();
      desc.fConfig = kRGBA_8888_GrPixelConfig;
      if (willUpload || this->getContext()->isConfigRenderable(kAlpha_8_GrPixelConfig, false)) {
          // We would always like A8 but it isn't supported on all platforms
          desc.fConfig = kAlpha_8_GrPixelConfig;
      }
  
      fAACache.acquireMask(elementsGenID, desc, clipSpaceIBounds);
      return fAACache.getLastMask();
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  // Create a 8-bit clip mask in alpha
  GrTexture* GrClipMaskManager::createAlphaClipMask(int32_t elementsGenID,
                                                    InitialState initialState,
                                                    const ElementList& elements,
                                                    const SkIRect& clipSpaceIBounds) {
      SkASSERT(kNone_ClipMaskType == fCurrClipMaskType);
  
      // First, check for cached texture
      GrTexture* result = this->getCachedMaskTexture(elementsGenID, clipSpaceIBounds);
      if (NULL != result) {
          fCurrClipMaskType = kAlpha_ClipMaskType;
          return result;
      }
  
      // There's no texture in the cache. Let's try to allocate it then.
      result = this->allocMaskTexture(elementsGenID, clipSpaceIBounds, false);
      if (NULL == result) {
          fAACache.reset();
          return NULL;
      }
  
      // The top-left of the mask corresponds to the top-left corner of the bounds.
      SkVector clipToMaskOffset = {
          SkIntToScalar(-clipSpaceIBounds.fLeft),
          SkIntToScalar(-clipSpaceIBounds.fTop)
      };
      // The texture may be larger than necessary, this rect represents the part of the texture
      // we populate with a rasterization of the clip.
      SkIRect maskSpaceIBounds = SkIRect::MakeWH(clipSpaceIBounds.width(), clipSpaceIBounds.height());
  
      // Set the matrix so that rendered clip elements are transformed to mask space from clip space.
      SkMatrix translate;
      translate.setTranslate(clipToMaskOffset);
      GrDrawTarget::AutoGeometryAndStatePush agasp(fGpu, GrDrawTarget::kReset_ASRInit, &translate);
  
      GrDrawState* drawState = fGpu->drawState();
  
      // We're drawing a coverage mask and want coverage to be run through the blend function.
      drawState->enableState(GrDrawState::kCoverageDrawing_StateBit);
  
      // The scratch texture that we are drawing into can be substantially larger than the mask. Only
      // clear the part that we care about.
      fGpu->clear(&maskSpaceIBounds,
                  kAllIn_InitialState == initialState ? 0xffffffff : 0x00000000,
                  true,
                  result->asRenderTarget());
  
      // When we use the stencil in the below loop it is important to have this clip installed.
      // The second pass that zeros the stencil buffer renders the rect maskSpaceIBounds so the first
      // pass must not set values outside of this bounds or stencil values outside the rect won't be
      // cleared.
      GrDrawTarget::AutoClipRestore acr(fGpu, maskSpaceIBounds);
      drawState->enableState(GrDrawState::kClip_StateBit);
  
      GrAutoScratchTexture temp;
      // walk through each clip element and perform its set op
      for (ElementList::Iter iter = elements.headIter(); iter.get(); iter.next()) {
          const Element* element = iter.get();
          SkRegion::Op op = element->getOp();
          bool invert = element->isInverseFilled();
  
          if (invert || SkRegion::kIntersect_Op == op || SkRegion::kReverseDifference_Op == op) {
              GrPathRenderer* pr = NULL;
              bool useTemp = !this->canStencilAndDrawElement(result, element, &pr);
              GrTexture* dst;
              // This is the bounds of the clip element in the space of the alpha-mask. The temporary
              // mask buffer can be substantially larger than the actually clip stack element. We
              // touch the minimum number of pixels necessary and use decal mode to combine it with
              // the accumulator.
              SkIRect maskSpaceElementIBounds;
  
              if (useTemp) {
                  if (invert) {
                      maskSpaceElementIBounds = maskSpaceIBounds;
                  } else {
                      SkRect elementBounds = element->getBounds();
                      elementBounds.offset(clipToMaskOffset);
                      elementBounds.roundOut(&maskSpaceElementIBounds);
                  }
  
                  this->getTemp(maskSpaceIBounds.fRight, maskSpaceIBounds.fBottom, &temp);
                  if (NULL == temp.texture()) {
                      fAACache.reset();
                      return NULL;
                  }
                  dst = temp.texture();
                  // clear the temp target and set blend to replace
                  fGpu->clear(&maskSpaceElementIBounds,
                              invert ? 0xffffffff : 0x00000000,
                              true,
                              dst->asRenderTarget());
                  setup_boolean_blendcoeffs(drawState, SkRegion::kReplace_Op);
  
              } else {
                  // draw directly into the result with the stencil set to make the pixels affected
                  // by the clip shape be non-zero.
                  dst = result;
                  GR_STATIC_CONST_SAME_STENCIL(kStencilInElement,
                                               kReplace_StencilOp,
                                               kReplace_StencilOp,
                                               kAlways_StencilFunc,
                                               0xffff,
                                               0xffff,
                                               0xffff);
                  drawState->setStencil(kStencilInElement);
                  setup_boolean_blendcoeffs(drawState, op);
              }
  
              drawState->setAlpha(invert ? 0x00 : 0xff);
  
              if (!this->drawElement(dst, element, pr)) {
                  fAACache.reset();
                  return NULL;
              }
  
              if (useTemp) {
                  // Now draw into the accumulator using the real operation and the temp buffer as a
                  // texture
                  this->mergeMask(result,
                                  temp.texture(),
                                  op,
                                  maskSpaceIBounds,
                                  maskSpaceElementIBounds);
              } else {
                  // Draw to the exterior pixels (those with a zero stencil value).
                  drawState->setAlpha(invert ? 0xff : 0x00);
                  GR_STATIC_CONST_SAME_STENCIL(kDrawOutsideElement,
                                               kZero_StencilOp,
                                               kZero_StencilOp,
                                               kEqual_StencilFunc,
                                               0xffff,
                                               0x0000,
                                               0xffff);
                  drawState->setStencil(kDrawOutsideElement);
                  fGpu->drawSimpleRect(clipSpaceIBounds);
                  drawState->disableStencil();
              }
          } else {
              // all the remaining ops can just be directly draw into the accumulation buffer
              drawState->setAlpha(0xff);
              setup_boolean_blendcoeffs(drawState, op);
              this->drawElement(result, element);
          }
      }
  
      fCurrClipMaskType = kAlpha_ClipMaskType;
      return result;
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  // Create a 1-bit clip mask in the stencil buffer. 'devClipBounds' are in device
  // (as opposed to canvas) coordinates
  bool GrClipMaskManager::createStencilClipMask(int32_t elementsGenID,
                                                InitialState initialState,
                                                const ElementList& elements,
                                                const SkIRect& clipSpaceIBounds,
                                                const SkIPoint& clipSpaceToStencilOffset) {
  
      SkASSERT(kNone_ClipMaskType == fCurrClipMaskType);
  
      GrDrawState* drawState = fGpu->drawState();
      SkASSERT(drawState->isClipState());
  
      GrRenderTarget* rt = drawState->getRenderTarget();
      SkASSERT(NULL != rt);
  
      // TODO: dynamically attach a SB when needed.
      GrStencilBuffer* stencilBuffer = rt->getStencilBuffer();
      if (NULL == stencilBuffer) {
          return false;
      }
  
      if (stencilBuffer->mustRenderClip(elementsGenID, clipSpaceIBounds, clipSpaceToStencilOffset)) {
  
          stencilBuffer->setLastClip(elementsGenID, clipSpaceIBounds, clipSpaceToStencilOffset);
  
          // Set the matrix so that rendered clip elements are transformed from clip to stencil space.
          SkVector translate = {
              SkIntToScalar(clipSpaceToStencilOffset.fX),
              SkIntToScalar(clipSpaceToStencilOffset.fY)
          };
          SkMatrix matrix;
          matrix.setTranslate(translate);
          GrDrawTarget::AutoGeometryAndStatePush agasp(fGpu, GrDrawTarget::kReset_ASRInit, &matrix);
          drawState = fGpu->drawState();
  
          drawState->setRenderTarget(rt);
  
          // We set the current clip to the bounds so that our recursive draws are scissored to them.
          SkIRect stencilSpaceIBounds(clipSpaceIBounds);
          stencilSpaceIBounds.offset(clipSpaceToStencilOffset);
          GrDrawTarget::AutoClipRestore acr(fGpu, stencilSpaceIBounds);
          drawState->enableState(GrDrawState::kClip_StateBit);
  
  #if !VISUALIZE_COMPLEX_CLIP
          drawState->enableState(GrDrawState::kNoColorWrites_StateBit);
  #endif
  
          int clipBit = stencilBuffer->bits();
          SkASSERT((clipBit <= 16) && "Ganesh only handles 16b or smaller stencil buffers");
          clipBit = (1 << (clipBit-1));
  
          fGpu->clearStencilClip(stencilSpaceIBounds, kAllIn_InitialState == initialState);
  
          // walk through each clip element and perform its set op
          // with the existing clip.
          for (ElementList::Iter iter(elements.headIter()); NULL != iter.get(); iter.next()) {
              const Element* element = iter.get();
              bool fillInverted = false;
              // enabled at bottom of loop
              drawState->disableState(GrGpu::kModifyStencilClip_StateBit);
              // if the target is MSAA then we want MSAA enabled when the clip is soft
              if (rt->isMultisampled()) {
                  drawState->setState(GrDrawState::kHWAntialias_StateBit, element->isAA());
              }
  
              // This will be used to determine whether the clip shape can be rendered into the
              // stencil with arbitrary stencil settings.
              GrPathRenderer::StencilSupport stencilSupport;
  
              SkStrokeRec stroke(SkStrokeRec::kFill_InitStyle);
  
              SkRegion::Op op = element->getOp();
  
              GrPathRenderer* pr = NULL;
              SkPath clipPath;
              if (Element::kRect_Type == element->getType()) {
                  stencilSupport = GrPathRenderer::kNoRestriction_StencilSupport;
                  fillInverted = false;
              } else {
                  element->asPath(&clipPath);
                  fillInverted = clipPath.isInverseFillType();
                  if (fillInverted) {
                      clipPath.toggleInverseFillType();
                  }
                  pr = this->getContext()->getPathRenderer(clipPath,
                                                           stroke,
                                                           fGpu,
                                                           false,
                                                           GrPathRendererChain::kStencilOnly_DrawType,
                                                           &stencilSupport);
                  if (NULL == pr) {
                      return false;
                  }
              }
  
              int passes;
              GrStencilSettings stencilSettings[GrStencilSettings::kMaxStencilClipPasses];
  
              bool canRenderDirectToStencil =
                  GrPathRenderer::kNoRestriction_StencilSupport == stencilSupport;
              bool canDrawDirectToClip; // Given the renderer, the element,
                                        // fill rule, and set operation can
                                        // we render the element directly to
                                        // stencil bit used for clipping.
              canDrawDirectToClip = GrStencilSettings::GetClipPasses(op,
                                                                     canRenderDirectToStencil,
                                                                     clipBit,
                                                                     fillInverted,
                                                                     &passes,
                                                                     stencilSettings);
  
              // draw the element to the client stencil bits if necessary
              if (!canDrawDirectToClip) {
                  GR_STATIC_CONST_SAME_STENCIL(gDrawToStencil,
                                               kIncClamp_StencilOp,
                                               kIncClamp_StencilOp,
                                               kAlways_StencilFunc,
                                               0xffff,
                                               0x0000,
                                               0xffff);
                  SET_RANDOM_COLOR
                  if (Element::kRect_Type == element->getType()) {
                      *drawState->stencil() = gDrawToStencil;
                      fGpu->drawSimpleRect(element->getRect());
                  } else {
                      if (!clipPath.isEmpty()) {
                          if (canRenderDirectToStencil) {
                              *drawState->stencil() = gDrawToStencil;
                              pr->drawPath(clipPath, stroke, fGpu, false);
                          } else {
                              pr->stencilPath(clipPath, stroke, fGpu);
                          }
                      }
                  }
              }
  
              // now we modify the clip bit by rendering either the clip
              // element directly or a bounding rect of the entire clip.
              drawState->enableState(GrGpu::kModifyStencilClip_StateBit);
              for (int p = 0; p < passes; ++p) {
                  *drawState->stencil() = stencilSettings[p];
                  if (canDrawDirectToClip) {
                      if (Element::kRect_Type == element->getType()) {
                          SET_RANDOM_COLOR
                          fGpu->drawSimpleRect(element->getRect());
                      } else {
                          SET_RANDOM_COLOR
                          pr->drawPath(clipPath, stroke, fGpu, false);
                      }
                  } else {
                      SET_RANDOM_COLOR
                      // The view matrix is setup to do clip space -> stencil space translation, so
                      // draw rect in clip space.
                      fGpu->drawSimpleRect(SkRect::Make(clipSpaceIBounds));
                  }
              }
          }
      }
      // set this last because recursive draws may overwrite it back to kNone.
      SkASSERT(kNone_ClipMaskType == fCurrClipMaskType);
      fCurrClipMaskType = kStencil_ClipMaskType;
      return true;
  }
  
  
  // mapping of clip-respecting stencil funcs to normal stencil funcs
  // mapping depends on whether stencil-clipping is in effect.
  static const GrStencilFunc
      gSpecialToBasicStencilFunc[2][kClipStencilFuncCount] = {
      {// Stencil-Clipping is DISABLED,  we are effectively always inside the clip
          // In the Clip Funcs
          kAlways_StencilFunc,          // kAlwaysIfInClip_StencilFunc
          kEqual_StencilFunc,           // kEqualIfInClip_StencilFunc
          kLess_StencilFunc,            // kLessIfInClip_StencilFunc
          kLEqual_StencilFunc,          // kLEqualIfInClip_StencilFunc
          // Special in the clip func that forces user's ref to be 0.
          kNotEqual_StencilFunc,        // kNonZeroIfInClip_StencilFunc
                                        // make ref 0 and do normal nequal.
      },
      {// Stencil-Clipping is ENABLED
          // In the Clip Funcs
          kEqual_StencilFunc,           // kAlwaysIfInClip_StencilFunc
                                        // eq stencil clip bit, mask
                                        // out user bits.
  
          kEqual_StencilFunc,           // kEqualIfInClip_StencilFunc
                                        // add stencil bit to mask and ref
  
          kLess_StencilFunc,            // kLessIfInClip_StencilFunc
          kLEqual_StencilFunc,          // kLEqualIfInClip_StencilFunc
                                        // for both of these we can add
                                        // the clip bit to the mask and
                                        // ref and compare as normal
          // Special in the clip func that forces user's ref to be 0.
          kLess_StencilFunc,            // kNonZeroIfInClip_StencilFunc
                                        // make ref have only the clip bit set
                                        // and make comparison be less
                                        // 10..0 < 1..user_bits..
      }
  };
  
  namespace {
  // Sets the settings to clip against the stencil buffer clip while ignoring the
  // client bits.
  const GrStencilSettings& basic_apply_stencil_clip_settings() {
      // stencil settings to use when clip is in stencil
      GR_STATIC_CONST_SAME_STENCIL_STRUCT(gSettings,
          kKeep_StencilOp,
          kKeep_StencilOp,
          kAlwaysIfInClip_StencilFunc,
          0x0000,
          0x0000,
          0x0000);
      return *GR_CONST_STENCIL_SETTINGS_PTR_FROM_STRUCT_PTR(&gSettings);
  }
  }
  
  void GrClipMaskManager::setGpuStencil() {
      // We make two copies of the StencilSettings here (except in the early
      // exit scenario. One copy from draw state to the stack var. Then another
      // from the stack var to the gpu. We could make this class hold a ptr to
      // GrGpu's fStencilSettings and eliminate the stack copy here.
  
      const GrDrawState& drawState = fGpu->getDrawState();
  
      // use stencil for clipping if clipping is enabled and the clip
      // has been written into the stencil.
      GrClipMaskManager::StencilClipMode clipMode;
      if (this->isClipInStencil() && drawState.isClipState()) {
          clipMode = GrClipMaskManager::kRespectClip_StencilClipMode;
          // We can't be modifying the clip and respecting it at the same time.
          SkASSERT(!drawState.isStateFlagEnabled(
                      GrGpu::kModifyStencilClip_StateBit));
      } else if (drawState.isStateFlagEnabled(
                      GrGpu::kModifyStencilClip_StateBit)) {
          clipMode = GrClipMaskManager::kModifyClip_StencilClipMode;
      } else {
          clipMode = GrClipMaskManager::kIgnoreClip_StencilClipMode;
      }
  
      GrStencilSettings settings;
      // The GrGpu client may not be using the stencil buffer but we may need to
      // enable it in order to respect a stencil clip.
      if (drawState.getStencil().isDisabled()) {
          if (GrClipMaskManager::kRespectClip_StencilClipMode == clipMode) {
              settings = basic_apply_stencil_clip_settings();
          } else {
              fGpu->disableStencil();
              return;
          }
      } else {
          settings = drawState.getStencil();
      }
  
      // TODO: dynamically attach a stencil buffer
      int stencilBits = 0;
      GrStencilBuffer* stencilBuffer =
          drawState.getRenderTarget()->getStencilBuffer();
      if (NULL != stencilBuffer) {
          stencilBits = stencilBuffer->bits();
      }
  
      SkASSERT(fGpu->caps()->stencilWrapOpsSupport() || !settings.usesWrapOp());
      SkASSERT(fGpu->caps()->twoSidedStencilSupport() || !settings.isTwoSided());
      this->adjustStencilParams(&settings, clipMode, stencilBits);
      fGpu->setStencilSettings(settings);
  }
  
  void GrClipMaskManager::adjustStencilParams(GrStencilSettings* settings,
                                              StencilClipMode mode,
                                              int stencilBitCnt) {
      SkASSERT(stencilBitCnt > 0);
  
      if (kModifyClip_StencilClipMode == mode) {
          // We assume that this clip manager itself is drawing to the GrGpu and
          // has already setup the correct values.
          return;
      }
  
      unsigned int clipBit = (1 << (stencilBitCnt - 1));
      unsigned int userBits = clipBit - 1;
  
      GrStencilSettings::Face face = GrStencilSettings::kFront_Face;
      bool twoSided = fGpu->caps()->twoSidedStencilSupport();
  
      bool finished = false;
      while (!finished) {
          GrStencilFunc func = settings->func(face);
          uint16_t writeMask = settings->writeMask(face);
          uint16_t funcMask = settings->funcMask(face);
          uint16_t funcRef = settings->funcRef(face);
  
          SkASSERT((unsigned) func < kStencilFuncCount);
  
          writeMask &= userBits;
  
          if (func >= kBasicStencilFuncCount) {
              int respectClip = kRespectClip_StencilClipMode == mode;
              if (respectClip) {
                  // The GrGpu class should have checked this
                  SkASSERT(this->isClipInStencil());
                  switch (func) {
                      case kAlwaysIfInClip_StencilFunc:
                          funcMask = clipBit;
                          funcRef = clipBit;
                          break;
                      case kEqualIfInClip_StencilFunc:
                      case kLessIfInClip_StencilFunc:
                      case kLEqualIfInClip_StencilFunc:
                          funcMask = (funcMask & userBits) | clipBit;
                          funcRef  = (funcRef  & userBits) | clipBit;
                          break;
                      case kNonZeroIfInClip_StencilFunc:
                          funcMask = (funcMask & userBits) | clipBit;
                          funcRef = clipBit;
                          break;
                      default:
                          SkFAIL("Unknown stencil func");
                  }
              } else {
                  funcMask &= userBits;
                  funcRef &= userBits;
              }
              const GrStencilFunc* table =
                  gSpecialToBasicStencilFunc[respectClip];
              func = table[func - kBasicStencilFuncCount];
              SkASSERT(func >= 0 && func < kBasicStencilFuncCount);
          } else {
              funcMask &= userBits;
              funcRef &= userBits;
          }
  
          settings->setFunc(face, func);
          settings->setWriteMask(face, writeMask);
          settings->setFuncMask(face, funcMask);
          settings->setFuncRef(face, funcRef);
  
          if (GrStencilSettings::kFront_Face == face) {
              face = GrStencilSettings::kBack_Face;
              finished = !twoSided;
          } else {
              finished = true;
          }
      }
      if (!twoSided) {
          settings->copyFrontSettingsToBack();
      }
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  GrTexture* GrClipMaskManager::createSoftwareClipMask(int32_t elementsGenID,
                                                       GrReducedClip::InitialState initialState,
                                                       const GrReducedClip::ElementList& elements,
                                                       const SkIRect& clipSpaceIBounds) {
      SkASSERT(kNone_ClipMaskType == fCurrClipMaskType);
  
      GrTexture* result = this->getCachedMaskTexture(elementsGenID, clipSpaceIBounds);
      if (NULL != result) {
          return result;
      }
  
      // The mask texture may be larger than necessary. We round out the clip space bounds and pin
      // the top left corner of the resulting rect to the top left of the texture.
      SkIRect maskSpaceIBounds = SkIRect::MakeWH(clipSpaceIBounds.width(), clipSpaceIBounds.height());
  
      GrSWMaskHelper helper(this->getContext());
  
      SkMatrix matrix;
      matrix.setTranslate(SkIntToScalar(-clipSpaceIBounds.fLeft),
                          SkIntToScalar(-clipSpaceIBounds.fTop));
      helper.init(maskSpaceIBounds, &matrix, false);
  
      helper.clear(kAllIn_InitialState == initialState ? 0xFF : 0x00);
  
      SkStrokeRec stroke(SkStrokeRec::kFill_InitStyle);
  
      for (ElementList::Iter iter(elements.headIter()) ; NULL != iter.get(); iter.next()) {
  
          const Element* element = iter.get();
          SkRegion::Op op = element->getOp();
  
          if (SkRegion::kIntersect_Op == op || SkRegion::kReverseDifference_Op == op) {
              // Intersect and reverse difference require modifying pixels outside of the geometry
              // that is being "drawn". In both cases we erase all the pixels outside of the geometry
              // but leave the pixels inside the geometry alone. For reverse difference we invert all
              // the pixels before clearing the ones outside the geometry.
              if (SkRegion::kReverseDifference_Op == op) {
                  SkRect temp = SkRect::Make(clipSpaceIBounds);
                  // invert the entire scene
                  helper.draw(temp, SkRegion::kXOR_Op, false, 0xFF);
              }
  
              SkPath clipPath;
              element->asPath(&clipPath);
              clipPath.toggleInverseFillType();
              helper.draw(clipPath, stroke, SkRegion::kReplace_Op, element->isAA(), 0x00);
  
              continue;
          }
  
          // The other ops (union, xor, diff) only affect pixels inside
          // the geometry so they can just be drawn normally
          if (Element::kRect_Type == element->getType()) {
              helper.draw(element->getRect(), op, element->isAA(), 0xFF);
          } else {
              SkPath path;
              element->asPath(&path);
              helper.draw(path, stroke, op, element->isAA(), 0xFF);
          }
      }
  
      // Allocate clip mask texture
      result = this->allocMaskTexture(elementsGenID, clipSpaceIBounds, true);
      if (NULL == result) {
          fAACache.reset();
          return NULL;
      }
      helper.toTexture(result);
  
      fCurrClipMaskType = kAlpha_ClipMaskType;
      return result;
  }
  
  ////////////////////////////////////////////////////////////////////////////////
  void GrClipMaskManager::purgeResources() {
      fAACache.purgeResources();
  }
  
  void GrClipMaskManager::setGpu(GrGpu* gpu) {
      fGpu = gpu;
      fAACache.setContext(gpu->getContext());
  }
  
  void GrClipMaskManager::adjustPathStencilParams(GrStencilSettings* settings) {
      const GrDrawState& drawState = fGpu->getDrawState();
      GrClipMaskManager::StencilClipMode clipMode;
      if (this->isClipInStencil() && drawState.isClipState()) {
          clipMode = GrClipMaskManager::kRespectClip_StencilClipMode;
          // We can't be modifying the clip and respecting it at the same time.
          SkASSERT(!drawState.isStateFlagEnabled(
                      GrGpu::kModifyStencilClip_StateBit));
      } else if (drawState.isStateFlagEnabled(
                      GrGpu::kModifyStencilClip_StateBit)) {
          clipMode = GrClipMaskManager::kModifyClip_StencilClipMode;
      } else {
          clipMode = GrClipMaskManager::kIgnoreClip_StencilClipMode;
      }
  
      // TODO: dynamically attach a stencil buffer
      int stencilBits = 0;
      GrStencilBuffer* stencilBuffer =
          drawState.getRenderTarget()->getStencilBuffer();
      if (NULL != stencilBuffer) {
          stencilBits = stencilBuffer->bits();
          this->adjustStencilParams(settings, clipMode, stencilBits);
      }
  }
  