src/core/SkRecord.h - skia - Git at Google

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */

 #ifndef SkRecord_DEFINED
 #define SkRecord_DEFINED

 #include "SkArenaAlloc.h"
 #include "SkRecords.h"
 #include "SkTLogic.h"
 #include "SkTemplates.h"

 // SkRecord represents a sequence of SkCanvas calls, saved for future use.
 // These future uses may include: replay, optimization, serialization, or combinations of those.
 //
 // Though an enterprising user may find calling alloc(), append(), visit(), and mutate() enough to
 // work with SkRecord, you probably want to look at SkRecorder which presents an SkCanvas interface
 // for creating an SkRecord, and SkRecordDraw which plays an SkRecord back into another SkCanvas.
 //
 // SkRecord often looks like it's compatible with any type T, but really it's compatible with any
 // type T which has a static const SkRecords::Type kType.  That is to say, SkRecord is compatible
 // only with SkRecords::* structs defined in SkRecords.h.  Your compiler will helpfully yell if you
 // get this wrong.

 class SkRecord : public SkRefCnt {
 public:
     SkRecord() = default;
     ~SkRecord();

     // Returns the number of canvas commands in this SkRecord.
     int count() const { return fCount; }

     // Visit the i-th canvas command with a functor matching this interface:
     //   template <typename T>
     //   R operator()(const T& record) { ... }
     // This operator() must be defined for at least all SkRecords::*.
     template <typename F>
     auto visit(int i, F&& f) const -> decltype(f(SkRecords::NoOp())) {
         return fRecords[i].visit(f);
     }

     // Mutate the i-th canvas command with a functor matching this interface:
     //   template <typename T>
     //   R operator()(T* record) { ... }
     // This operator() must be defined for at least all SkRecords::*.
     template <typename F>
     auto mutate(int i, F&& f) -> decltype(f((SkRecords::NoOp*)nullptr)) {
         return fRecords[i].mutate(f);
     }

     // Allocate contiguous space for count Ts, to be freed when the SkRecord is destroyed.
     // Here T can be any class, not just those from SkRecords.  Throws on failure.
     template <typename T>
     T* alloc(size_t count = 1) {
         struct RawBytes {
             alignas(T) char data[sizeof(T)];
         };
         fApproxBytesAllocated += count * sizeof(T) + alignof(T);
         return (T*)fAlloc.makeArrayDefault<RawBytes>(count);
     }

     // Add a new command of type T to the end of this SkRecord.
     // You are expected to placement new an object of type T onto this pointer.
     template <typename T>
     T* append() {
         if (fCount == fReserved) {
             this->grow();
         }
         return fRecords[fCount++].set(this->allocCommand<T>());
     }

     // Replace the i-th command with a new command of type T.
     // You are expected to placement new an object of type T onto this pointer.
     // References to the original command are invalidated.
     template <typename T>
     T* replace(int i) {
         SkASSERT(i < this->count());

         Destroyer destroyer;
         this->mutate(i, destroyer);

         return fRecords[i].set(this->allocCommand<T>());
     }

     // Replace the i-th command with a new command of type T.
     // You are expected to placement new an object of type T onto this pointer.
     // You must show proof that you've already adopted the existing command.
     template <typename T, typename Existing>
     T* replace(int i, const SkRecords::Adopted<Existing>& proofOfAdoption) {
         SkASSERT(i < this->count());

         SkASSERT(Existing::kType == fRecords[i].type());
         SkASSERT(proofOfAdoption == fRecords[i].ptr());

         return fRecords[i].set(this->allocCommand<T>());
     }

     // Does not return the bytes in any pointers embedded in the Records; callers
     // need to iterate with a visitor to measure those they care for.
     size_t bytesUsed() const;

     // Rearrange and resize this record to eliminate any NoOps.
     // May change count() and the indices of ops, but preserves their order.
     void defrag();

 private:
     // An SkRecord is structured as an array of pointers into a big chunk of memory where
     // records representing each canvas draw call are stored:
     //
     // fRecords:  [*][*][*]...
     //             |  |  |
     //             |  |  |
     //             |  |  +---------------------------------------+
     //             |  +-----------------+                        |
     //             |                    |                        |
     //             v                    v                        v
     //   fAlloc:  [SkRecords::DrawRect][SkRecords::DrawPosTextH][SkRecords::DrawRect]...
     //
     // We store the types of each of the pointers alongside the pointer.
     // The cost to append a T to this structure is 8 + sizeof(T) bytes.

     // A mutator that can be used with replace to destroy canvas commands.
     struct Destroyer {
         template <typename T>
         void operator()(T* record) { record->~T(); }
     };

     template <typename T>
     SK_WHEN(std::is_empty<T>::value, T*) allocCommand() {
         static T singleton = {};
         return &singleton;
     }

     template <typename T>
     SK_WHEN(!std::is_empty<T>::value, T*) allocCommand() { return this->alloc<T>(); }

     void grow();

     // A typed pointer to some bytes in fAlloc.  visit() and mutate() allow polymorphic dispatch.
     struct Record {
         // On 32-bit machines we store type in 4 bytes, followed by a pointer.  Simple.
         // On 64-bit machines we store a pointer with the type slotted into two top (unused) bytes.
         // FWIW, SkRecords::Type is tiny.  It can easily fit in one byte.
         uint64_t fTypeAndPtr;
         static const int kTypeShift = sizeof(void*) == 4 ? 32 : 48;

         // Point this record to its data in fAlloc.  Returns ptr for convenience.
         template <typename T>
         T* set(T* ptr) {
             fTypeAndPtr = ((uint64_t)T::kType) << kTypeShift | (uintptr_t)ptr;
             SkASSERT(this->ptr() == ptr && this->type() == T::kType);
             return ptr;
         }

         SkRecords::Type type() const { return (SkRecords::Type)(fTypeAndPtr >> kTypeShift); }
         void* ptr() const { return (void*)(fTypeAndPtr & ((1ull<<kTypeShift)-1)); }

         // Visit this record with functor F (see public API above).
         template <typename F>
         auto visit(F&& f) const -> decltype(f(SkRecords::NoOp())) {
         #define CASE(T) case SkRecords::T##_Type: return f(*(const SkRecords::T*)this->ptr());
             switch(this->type()) { SK_RECORD_TYPES(CASE) }
         #undef CASE
             SkDEBUGFAIL("Unreachable");
             static const SkRecords::NoOp noop{};
             return f(noop);
         }

         // Mutate this record with functor F (see public API above).
         template <typename F>
         auto mutate(F&& f) -> decltype(f((SkRecords::NoOp*)nullptr)) {
         #define CASE(T) case SkRecords::T##_Type: return f((SkRecords::T*)this->ptr());
             switch(this->type()) { SK_RECORD_TYPES(CASE) }
         #undef CASE
             SkDEBUGFAIL("Unreachable");
             static const SkRecords::NoOp noop{};
             return f(const_cast<SkRecords::NoOp*>(&noop));
         }
     };

     // fRecords needs to be a data structure that can append fixed length data, and need to
     // support efficient random access and forward iteration.  (It doesn't need to be contiguous.)
     int fCount{0},
         fReserved{0};
     SkAutoTMalloc<Record> fRecords;

     // fAlloc needs to be a data structure which can append variable length data in contiguous
     // chunks, returning a stable handle to that data for later retrieval.
     SkArenaAlloc fAlloc{256};
     size_t       fApproxBytesAllocated{0};
 };

 #endif//SkRecord_DEFINED
	/*
	* Copyright 2014 Google Inc.
	*
	* Use of this source code is governed by a BSD-style license that can be
	* found in the LICENSE file.
	*/

	#ifndef SkRecord_DEFINED
	#define SkRecord_DEFINED

	#include "SkArenaAlloc.h"
	#include "SkRecords.h"
	#include "SkTLogic.h"
	#include "SkTemplates.h"

	// SkRecord represents a sequence of SkCanvas calls, saved for future use.
	// These future uses may include: replay, optimization, serialization, or combinations of those.
	//
	// Though an enterprising user may find calling alloc(), append(), visit(), and mutate() enough to
	// work with SkRecord, you probably want to look at SkRecorder which presents an SkCanvas interface
	// for creating an SkRecord, and SkRecordDraw which plays an SkRecord back into another SkCanvas.
	//
	// SkRecord often looks like it's compatible with any type T, but really it's compatible with any
	// type T which has a static const SkRecords::Type kType. That is to say, SkRecord is compatible
	// only with SkRecords::* structs defined in SkRecords.h. Your compiler will helpfully yell if you
	// get this wrong.

	class SkRecord : public SkRefCnt {
	public:
	SkRecord() = default;
	~SkRecord();

	// Returns the number of canvas commands in this SkRecord.
	int count() const { return fCount; }

	// Visit the i-th canvas command with a functor matching this interface:
	// template <typename T>
	// R operator()(const T& record) { ... }
	// This operator() must be defined for at least all SkRecords::*.
	template <typename F>
	auto visit(int i, F&& f) const -> decltype(f(SkRecords::NoOp())) {
	return fRecords[i].visit(f);
	}

	// Mutate the i-th canvas command with a functor matching this interface:
	// template <typename T>
	// R operator()(T* record) { ... }
	// This operator() must be defined for at least all SkRecords::*.
	template <typename F>
	auto mutate(int i, F&& f) -> decltype(f((SkRecords::NoOp*)nullptr)) {
	return fRecords[i].mutate(f);
	}

	// Allocate contiguous space for count Ts, to be freed when the SkRecord is destroyed.
	// Here T can be any class, not just those from SkRecords. Throws on failure.
	template <typename T>
	T* alloc(size_t count = 1) {
	struct RawBytes {
	alignas(T) char data[sizeof(T)];
	};
	fApproxBytesAllocated += count * sizeof(T) + alignof(T);
	return (T*)fAlloc.makeArrayDefault<RawBytes>(count);
	}

	// Add a new command of type T to the end of this SkRecord.
	// You are expected to placement new an object of type T onto this pointer.
	template <typename T>
	T* append() {
	if (fCount == fReserved) {
	this->grow();
	}
	return fRecords[fCount++].set(this->allocCommand<T>());
	}

	// Replace the i-th command with a new command of type T.
	// You are expected to placement new an object of type T onto this pointer.
	// References to the original command are invalidated.
	template <typename T>
	T* replace(int i) {
	SkASSERT(i < this->count());

	Destroyer destroyer;
	this->mutate(i, destroyer);

	return fRecords[i].set(this->allocCommand<T>());
	}

	// Replace the i-th command with a new command of type T.
	// You are expected to placement new an object of type T onto this pointer.
	// You must show proof that you've already adopted the existing command.
	template <typename T, typename Existing>
	T* replace(int i, const SkRecords::Adopted<Existing>& proofOfAdoption) {
	SkASSERT(i < this->count());

	SkASSERT(Existing::kType == fRecords[i].type());
	SkASSERT(proofOfAdoption == fRecords[i].ptr());

	return fRecords[i].set(this->allocCommand<T>());
	}

	// Does not return the bytes in any pointers embedded in the Records; callers
	// need to iterate with a visitor to measure those they care for.
	size_t bytesUsed() const;

	// Rearrange and resize this record to eliminate any NoOps.
	// May change count() and the indices of ops, but preserves their order.
	void defrag();

	private:
	// An SkRecord is structured as an array of pointers into a big chunk of memory where
	// records representing each canvas draw call are stored:
	//
	// fRecords: [][][*]...
	// \| \| \|
	// \| \| \|
	// \| \| +---------------------------------------+
	// \| +-----------------+ \|
	// \| \| \|
	// v v v
	// fAlloc: [SkRecords::DrawRect][SkRecords::DrawPosTextH][SkRecords::DrawRect]...
	//
	// We store the types of each of the pointers alongside the pointer.
	// The cost to append a T to this structure is 8 + sizeof(T) bytes.

	// A mutator that can be used with replace to destroy canvas commands.
	struct Destroyer {
	template <typename T>
	void operator()(T* record) { record->~T(); }
	};

	template <typename T>
	SK_WHEN(std::is_empty<T>::value, T*) allocCommand() {
	static T singleton = {};
	return &singleton;
	}

	template <typename T>
	SK_WHEN(!std::is_empty<T>::value, T*) allocCommand() { return this->alloc<T>(); }

	void grow();

	// A typed pointer to some bytes in fAlloc. visit() and mutate() allow polymorphic dispatch.
	struct Record {
	// On 32-bit machines we store type in 4 bytes, followed by a pointer. Simple.
	// On 64-bit machines we store a pointer with the type slotted into two top (unused) bytes.
	// FWIW, SkRecords::Type is tiny. It can easily fit in one byte.
	uint64_t fTypeAndPtr;
	static const int kTypeShift = sizeof(void*) == 4 ? 32 : 48;

	// Point this record to its data in fAlloc. Returns ptr for convenience.
	template <typename T>
	T* set(T* ptr) {
	fTypeAndPtr = ((uint64_t)T::kType) << kTypeShift \| (uintptr_t)ptr;
	SkASSERT(this->ptr() == ptr && this->type() == T::kType);
	return ptr;
	}

	SkRecords::Type type() const { return (SkRecords::Type)(fTypeAndPtr >> kTypeShift); }
	void* ptr() const { return (void*)(fTypeAndPtr & ((1ull<<kTypeShift)-1)); }

	// Visit this record with functor F (see public API above).
	template <typename F>
	auto visit(F&& f) const -> decltype(f(SkRecords::NoOp())) {
	#define CASE(T) case SkRecords::T##_Type: return f((const SkRecords::T)this->ptr());
	switch(this->type()) { SK_RECORD_TYPES(CASE) }
	#undef CASE
	SkDEBUGFAIL("Unreachable");
	static const SkRecords::NoOp noop{};
	return f(noop);
	}

	// Mutate this record with functor F (see public API above).
	template <typename F>
	auto mutate(F&& f) -> decltype(f((SkRecords::NoOp*)nullptr)) {
	#define CASE(T) case SkRecords::T##_Type: return f((SkRecords::T*)this->ptr());
	switch(this->type()) { SK_RECORD_TYPES(CASE) }
	#undef CASE
	SkDEBUGFAIL("Unreachable");
	static const SkRecords::NoOp noop{};
	return f(const_cast<SkRecords::NoOp*>(&noop));
	}
	};

	// fRecords needs to be a data structure that can append fixed length data, and need to
	// support efficient random access and forward iteration. (It doesn't need to be contiguous.)
	int fCount{0},
	fReserved{0};
	SkAutoTMalloc<Record> fRecords;

	// fAlloc needs to be a data structure which can append variable length data in contiguous
	// chunks, returning a stable handle to that data for later retrieval.
	SkArenaAlloc fAlloc{256};
	size_t fApproxBytesAllocated{0};
	};

	#endif//SkRecord_DEFINED