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* Copyright 2011 The Android Open Source Project
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkDrawLooper_DEFINED
#define SkDrawLooper_DEFINED
#include "SkBlurTypes.h"
#include "SkFlattenable.h"
#include "SkPoint.h"
#include "SkColor.h"
class SkCanvas;
class SkPaint;
struct SkRect;
class SkString;
/** \class SkDrawLooper
Subclasses of SkDrawLooper can be attached to a SkPaint. Where they are,
and something is drawn to a canvas with that paint, the looper subclass will
be called, allowing it to modify the canvas and/or paint for that draw call.
More than that, via the next() method, the looper can modify the draw to be
invoked multiple times (hence the name loop-er), allow it to perform effects
like shadows or frame/fills, that require more than one pass.
class SK_API SkDrawLooper : public SkFlattenable {
* Holds state during a draw. Users call next() until it returns false.
* Subclasses of SkDrawLooper should create a subclass of this object to
* hold state specific to their subclass.
class SK_API Context : ::SkNoncopyable {
Context() {}
virtual ~Context() {}
* Called in a loop on objects returned by SkDrawLooper::createContext().
* Each time true is returned, the object is drawn (possibly with a modified
* canvas and/or paint). When false is finally returned, drawing for the object
* stops.
* On each call, the paint will be in its original state, but the
* canvas will be as it was following the previous call to next() or
* createContext().
* The implementation must ensure that, when next() finally returns
* false, the canvas has been restored to the state it was
* initially, before createContext() was first called.
virtual bool next(SkCanvas* canvas, SkPaint* paint) = 0;
* Called right before something is being drawn. Returns a Context
* whose next() method should be called until it returns false.
* The caller has to ensure that the storage pointer provides enough
* memory for the Context. The required size can be queried by calling
* contextSize(). It is also the caller's responsibility to destroy the
* object after use.
virtual Context* createContext(SkCanvas*, void* storage) const = 0;
* Returns the number of bytes needed to store subclasses of Context (belonging to the
* corresponding SkDrawLooper subclass).
virtual size_t contextSize() const = 0;
* The fast bounds functions are used to enable the paint to be culled early
* in the drawing pipeline. If a subclass can support this feature it must
* return true for the canComputeFastBounds() function. If that function
* returns false then computeFastBounds behavior is undefined otherwise it
* is expected to have the following behavior. Given the parent paint and
* the parent's bounding rect the subclass must fill in and return the
* storage rect, where the storage rect is with the union of the src rect
* and the looper's bounding rect.
virtual bool canComputeFastBounds(const SkPaint& paint) const;
virtual void computeFastBounds(const SkPaint& paint,
const SkRect& src, SkRect* dst) const;
struct BlurShadowRec {
SkScalar fSigma;
SkVector fOffset;
SkColor fColor;
SkBlurStyle fStyle;
SkBlurQuality fQuality;
* If this looper can be interpreted as having two layers, such that
* 1. The first layer (bottom most) just has a blur and translate
* 2. The second layer has no modifications to either paint or canvas
* 3. No other layers.
* then return true, and if not null, fill out the BlurShadowRec).
* If any of the above are not met, return false and ignore the BlurShadowRec parameter.
virtual bool asABlurShadow(BlurShadowRec*) const;
SkDrawLooper() {}
SkDrawLooper(SkReadBuffer& buffer) : INHERITED(buffer) {}
typedef SkFlattenable INHERITED;