flutter::LayerStateStack Class Reference

#include <layer_state_stack.h>

Classes
class	AutoRestore
class	MutatorContext

Public Member Functions
	LayerStateStack ()
void	clear_delegate ()
DlCanvas *	canvas_delegate ()
void	set_delegate (DlCanvas *canvas)
void	set_preroll_delegate (const SkRect &cull_rect, const SkMatrix &matrix)
void	set_preroll_delegate (const SkRect &cull_rect)
void	set_preroll_delegate (const SkMatrix &matrix)
void	fill (MutatorsStack *mutators)
AutoRestore	applyState (const SkRect &bounds, int can_apply_flags)
SkScalar	outstanding_opacity () const
std::shared_ptr< const DlColorFilter >	outstanding_color_filter () const
std::shared_ptr< const DlImageFilter >	outstanding_image_filter () const
SkRect	outstanding_bounds () const
DlPaint *	fill (DlPaint &paint) const
SkRect	device_cull_rect () const
SkRect	local_cull_rect () const
SkM44	transform_4x4 () const
SkMatrix	transform_3x3 () const
bool	painting_is_nop () const
bool	content_culled (const SkRect &content_bounds) const
MutatorContext	save ()
bool	is_empty () const

Static Public Attributes
static constexpr int	kCallerCanApplyOpacity = 0x1
static constexpr int	kCallerCanApplyColorFilter = 0x2
static constexpr int	kCallerCanApplyImageFilter = 0x4
static constexpr int	kCallerCanApplyAnything

Friends
class	SaveEntry
class	SaveLayerEntry
class	BackdropFilterEntry
class	OpacityEntry
class	ImageFilterEntry
class	ColorFilterEntry
class	TranslateEntry
class	TransformMatrixEntry
class	TransformM44Entry
class	IntegralTransformEntry
class	ClipEntry
class	ClipRectEntry
class	ClipRRectEntry
class	ClipPathEntry
class	DummyDelegate
class	DlCanvasDelegate
class	PrerollDelegate
class	MutatorContext

Detailed Description

The LayerStateStack manages the inherited state passed down between |Layer| objects in a |LayerTree| during |Preroll| and |Paint|.

More specifically, it manages the clip and transform state during recursive rendering and will hold and lazily apply opacity, ImageFilter and ColorFilter attributes to recursive content. This is not a truly general state management mechnanism as it makes assumptions that code will be applying the attributes to rendered content that happens in recursive calls. The automatic save/restore mechanisms only work in a context where C++ auto-destruct calls will engage the restore at the end of a code block and that any applied attributes will only be applied to the content rendered inside that block. These restrictions match the organization of the |LayerTree| methods precisely.

The stack can manage a single state delegate. The delegate will provide tracking of the current transform and clip and will also execute saveLayer calls at the appropriate time if it is a rendering delegate. The delegate can be swapped out on the fly (as is typically done by PlatformViewLayer when recording the state for multiple "overlay" layers that occur between embedded view subtrees. The old delegate will be restored to its original state before it became a delegate and the new delegate will have all of the state recorded by the stack replayed into it to bring it up to speed with the current rendering context.

The delegate can be any one of:

• Preroll delegate: used during Preroll to remember the outstanding state for embedded platform layers
• DlCanvas: used during Paint for rendering output The stack will know which state needs to be conveyed to any of these delegates and when is the best time to convey that state (i.e. lazy saveLayer calls for example).

The rendering state attributes will be automatically applied to the nested content using a |saveLayer| call at the point at which we encounter rendered content (i.e. various nested layers that exist only to apply new state will not trigger the |saveLayer| and the attributes can accumulate until we reach actual content that is rendered.) Some rendered content can avoid the |saveLayer| if it reports to the object that it is able to apply all of the attributes that happen to be outstanding (accumulated from parent state-modifiers). A |ContainerLayer| can also monitor the attribute rendering capabilities of a list of children and can ask the object to apply a protective |saveLayer| or not based on the negotiated capabilities of the entire group.

Any code that is planning to modify the clip, transform, or rendering attributes for its child content must start by calling the |save| method which returns a MutatorContext object. The methods that modify such state only exist on the MutatorContext object so it is difficult to get that wrong, but the caller must make sure that the call happens within a C++ code block that will define the "rendering scope" of those state changes as they will be automatically restored on exit from that block. Note that the layer might make similar state calls directly on the canvas or builder during the Paint cycle (via saveLayer, transform, or clip calls), but should avoid doing so if there is any nested content that needs to track or react to those state calls.

Code that needs to render content can simply inform the parent of their abilities by setting the |PrerollContext::renderable_state_flags| during |Preroll| and then render with those attributes during |Paint| by requesting the outstanding values of those attributes from the state_stack object. Individual leaf layers can ignore this feature as the default behavior during |Preroll| will have their parent |ContainerLayer| assume that they cannot render any outstanding state attributes and will apply the protective saveLayer on their behalf if needed. As such, this object only provides "opt-in" features for leaf layers and no responsibilities otherwise. See |LayerStateStack::fill| See |LayerStateStack::outstanding_opacity| See |LayerStateStack::outstanding_color_filter| See |LayerStateStack::outstanding_image_filter|

State-modifying layers should contain code similar to this pattern in both their |Preroll| and |Paint| methods.

void [LayerType]::[Preroll/Paint](context) { auto mutator = context.state_stack.save(); mutator.translate(origin.x, origin.y); mutator.applyOpacity(content_bounds, opacity_value); mutator.applyColorFilter(content_bounds, color_filter); // or any of the mutator transform, clip or attribute methods

// Children will react to the state applied above during their // Preroll/Paint methods or ContainerLayer will protect them // conservatively by default. [Preroll/Paint]Children(context);

// here the mutator will be auto-destructed and the state accumulated // by it will be restored out of the state_stack and its associated // delegates. }

Definition at line 105 of file layer_state_stack.h.

Constructor & Destructor Documentation

LayerStateStack()

flutter::LayerStateStack::LayerStateStack

(

)

Definition at line 621 of file layer_state_stack.cc.

: delegate_(DummyDelegate::kInstance) {}

Member Function Documentation

applyState()

AutoRestore flutter::LayerStateStack::applyState ( const SkRect &  bounds, int  can_apply_flags  )

inline

Definition at line 243 of file layer_state_stack.h.

                                                                   {
    return AutoRestore(this, bounds, can_apply_flags);
  }

canvas_delegate()

DlCanvas * flutter::LayerStateStack::canvas_delegate ( )

inline

Definition at line 115 of file layer_state_stack.h.

{ return delegate_->canvas(); }

clear_delegate()

void flutter::LayerStateStack::clear_delegate

(

)

Definition at line 623 of file layer_state_stack.cc.

                                     {
  delegate_->decommission();
  delegate_ = DummyDelegate::kInstance;
}

content_culled()

bool flutter::LayerStateStack::content_culled ( const SkRect &  content_bounds ) const

inline

Definition at line 305 of file layer_state_stack.h.

                                                          {
    return delegate_->content_culled(content_bounds);
  }

device_cull_rect()

SkRect flutter::LayerStateStack::device_cull_rect ( ) const

inline

Definition at line 274 of file layer_state_stack.h.

{ return delegate_->device_cull_rect(); }

fill() [1/2]

DlPaint * flutter::LayerStateStack::fill ( DlPaint &  paint ) const

inline

Definition at line 270 of file layer_state_stack.h.

{ return outstanding_.fill(paint); }

fill() [2/2]

void flutter::LayerStateStack::fill

(

MutatorsStack *

mutators

)

Definition at line 668 of file layer_state_stack.cc.

                                                  {
  for (auto& state : state_stack_) {
    state->update_mutators(mutators);
  }
}

is_empty()

bool flutter::LayerStateStack::is_empty ( ) const

inline

Definition at line 317 of file layer_state_stack.h.

{ return state_stack_.empty(); }

local_cull_rect()

SkRect flutter::LayerStateStack::local_cull_rect ( ) const

inline

Definition at line 278 of file layer_state_stack.h.

{ return delegate_->local_cull_rect(); }

outstanding_bounds()

SkRect flutter::LayerStateStack::outstanding_bounds ( ) const

inline

Definition at line 265 of file layer_state_stack.h.

{ return outstanding_.save_layer_bounds; }

outstanding_color_filter()

std::shared_ptr< const DlColorFilter > flutter::LayerStateStack::outstanding_color_filter ( ) const

inline

Definition at line 250 of file layer_state_stack.h.

                                                                      {
    return outstanding_.color_filter;
  }

outstanding_image_filter()

std::shared_ptr< const DlImageFilter > flutter::LayerStateStack::outstanding_image_filter ( ) const

inline

Definition at line 254 of file layer_state_stack.h.

                                                                      {
    return outstanding_.image_filter;
  }

outstanding_opacity()

SkScalar flutter::LayerStateStack::outstanding_opacity ( ) const

inline

Definition at line 248 of file layer_state_stack.h.

{ return outstanding_.opacity; }

painting_is_nop()

bool flutter::LayerStateStack::painting_is_nop ( ) const

inline

Definition at line 299 of file layer_state_stack.h.

{ return outstanding_.opacity <= 0; }

save()

MutatorContext flutter::LayerStateStack::save ( )

inline

Definition at line 313 of file layer_state_stack.h.

{ return MutatorContext(this); }

set_delegate()

void flutter::LayerStateStack::set_delegate

(

DlCanvas *

canvas

)

Definition at line 628 of file layer_state_stack.cc.

                                                   {
  if (delegate_) {
    if (canvas == delegate_->canvas()) {
      return;
    }
    clear_delegate();
  }
  if (canvas) {
    delegate_ = std::make_shared<DlCanvasDelegate>(canvas);
    reapply_all();
  }
}

set_preroll_delegate() [1/3]

void flutter::LayerStateStack::set_preroll_delegate

(

const SkMatrix &

matrix

)

Definition at line 644 of file layer_state_stack.cc.

                                                                 {
  set_preroll_delegate(kGiantRect, matrix);
}

set_preroll_delegate() [2/3]

void flutter::LayerStateStack::set_preroll_delegate

(

const SkRect &

cull_rect

)

Definition at line 641 of file layer_state_stack.cc.

                                                                  {
  set_preroll_delegate(cull_rect, SkMatrix::I());
}

set_preroll_delegate() [3/3]

void flutter::LayerStateStack::set_preroll_delegate	(	const SkRect &	cull_rect,
		const SkMatrix &	matrix
	)

Definition at line 647 of file layer_state_stack.cc.

                                                                   {
  clear_delegate();
  delegate_ = std::make_shared<PrerollDelegate>(cull_rect, matrix);
  reapply_all();
}

transform_3x3()

SkMatrix flutter::LayerStateStack::transform_3x3 ( ) const

inline

Definition at line 293 of file layer_state_stack.h.

{ return delegate_->matrix_3x3(); }

transform_4x4()

SkM44 flutter::LayerStateStack::transform_4x4 ( ) const

inline

Definition at line 285 of file layer_state_stack.h.

{ return delegate_->matrix_4x4(); }

Friends And Related Function Documentation

BackdropFilterEntry

friend class BackdropFilterEntry

friend

Definition at line 409 of file layer_state_stack.h.

ClipEntry

friend class ClipEntry

friend

Definition at line 417 of file layer_state_stack.h.

ClipPathEntry

friend class ClipPathEntry

friend

Definition at line 420 of file layer_state_stack.h.

ClipRectEntry

friend class ClipRectEntry

friend

Definition at line 418 of file layer_state_stack.h.

ClipRRectEntry

friend class ClipRRectEntry

friend

Definition at line 419 of file layer_state_stack.h.

ColorFilterEntry

friend class ColorFilterEntry

friend

Definition at line 412 of file layer_state_stack.h.

DlCanvasDelegate

friend class DlCanvasDelegate

friend

Definition at line 463 of file layer_state_stack.h.

DummyDelegate

friend class DummyDelegate

friend

Definition at line 462 of file layer_state_stack.h.

ImageFilterEntry

friend class ImageFilterEntry

friend

Definition at line 411 of file layer_state_stack.h.

IntegralTransformEntry

friend class IntegralTransformEntry

friend

Definition at line 416 of file layer_state_stack.h.

MutatorContext

friend class MutatorContext

friend

Definition at line 467 of file layer_state_stack.h.

OpacityEntry

friend class OpacityEntry

friend

Definition at line 410 of file layer_state_stack.h.

PrerollDelegate

friend class PrerollDelegate

friend

Definition at line 464 of file layer_state_stack.h.

SaveEntry

friend class SaveEntry

friend

Definition at line 407 of file layer_state_stack.h.

SaveLayerEntry

SaveLayerEntry

friend

Definition at line 408 of file layer_state_stack.h.

TransformM44Entry

friend class TransformM44Entry

friend

Definition at line 415 of file layer_state_stack.h.

TransformMatrixEntry

friend class TransformMatrixEntry

friend

Definition at line 414 of file layer_state_stack.h.

TranslateEntry

friend class TranslateEntry

friend

Definition at line 413 of file layer_state_stack.h.

Member Data Documentation

kCallerCanApplyAnything

constexpr int flutter::LayerStateStack::kCallerCanApplyAnything

staticconstexpr

Initial value:

=
      (kCallerCanApplyOpacity | kCallerCanApplyColorFilter |
       kCallerCanApplyImageFilter)

Definition at line 228 of file layer_state_stack.h.

kCallerCanApplyColorFilter

constexpr int flutter::LayerStateStack::kCallerCanApplyColorFilter = 0x2

staticconstexpr

Definition at line 226 of file layer_state_stack.h.

kCallerCanApplyImageFilter

constexpr int flutter::LayerStateStack::kCallerCanApplyImageFilter = 0x4

staticconstexpr

Definition at line 227 of file layer_state_stack.h.

kCallerCanApplyOpacity

constexpr int flutter::LayerStateStack::kCallerCanApplyOpacity = 0x1

staticconstexpr

Definition at line 225 of file layer_state_stack.h.

---

The documentation for this class was generated from the following files:

• flow/layers/layer_state_stack.h
• flow/layers/layer_state_stack.cc