Create a single command buffer for GrInOrderDrawBuffer

src/gpu/GrTRecorder.h

+/*
+ * 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 GrTRecorder_DEFINED
+#define GrTRecorder_DEFINED
+
+#include "SkTemplates.h"
+#include "SkTypes.h"
+
+template<typename TBase, typename TAlign> class GrTRecorder;
+template<typename TItem> struct GrTRecorderAllocWrapper;
+
+/**
+ * Records a list of items with a common base type, optional associated data, and
+ * permanent memory addresses.
+ *
+ * This class preallocates its own chunks of memory for hosting objects, so new items can
+ * be created without excessive calls to malloc().
+ *
+ * To create a new item and append it to the back of the list, use the following macros:
+ *
+ *     GrNEW_APPEND_TO_RECORDER(recorder, SubclassName, (args))
+ *     GrNEW_APPEND_WITH_DATA_TO_RECORDER(recorder, SubclassName, (args), sizeOfData)
+ *
+ * @param TBase   Common base type of items in the list. If TBase is not a class with a
+ *                virtual destructor, the client is responsible for invoking any necessary
+ *                destructors.
+ *
+ *                For now, any subclass used in the list must have the same start address
+ *                as TBase (or in other words, the types must be convertible via
+ *                reinterpret_cast<>). Classes with multiple inheritance (or any subclass
+ *                on an obscure compiler) may not be compatible. This is runtime asserted
+ *                in debug builds.
+ *
+ * @param TAlign  A type whose size is the desired memory alignment for object allocations.
+ *                This should be the largest known alignment requirement for all objects
+ *                that may be stored in the list.
+ */
+template<typename TBase, typename TAlign> class GrTRecorder : SkNoncopyable {
+public:
+    class Iter;
+
+    /**
+     * Create a recorder.
+     *
+     * @param initialSizeInBytes  The amount of memory reserved by the recorder initially,
+                                  and after calls to reset().
+     */
+    GrTRecorder(int initialSizeInBytes)
+        : fHeadBlock(LengthOf(initialSizeInBytes)),
+          fTailBlock(&fHeadBlock),
+          fLastItem(NULL) {}
+
+    ~GrTRecorder() { this->reset(); }
+
+    bool empty() { return !fLastItem; }
+
+    TBase& back() {
+        SkASSERT(!this->empty());
+        return *fLastItem;
+    }
+
+    /**
+     * Destruct all items in the list and reset to empty.
+     */
+    void reset();
+
+    /**
+     * Retrieve the extra data associated with an item that was allocated using
+     * GrNEW_APPEND_WITH_DATA_TO_RECORDER().
+     *
+     * @param item  The item whose data to retrieve. The pointer must be of the same type
+     *              that was allocated initally; it can't be a pointer to a base class.
+     *
+     * @return The item's associated data.
+     */
+    template<typename TItem> static const void* GetDataForItem(const TItem* item) {
+        const TAlign* ptr = reinterpret_cast<const TAlign*>(item);
+        return &ptr[length_of<TItem>::kValue];
+    }
+    template<typename TItem> static void* GetDataForItem(TItem* item) {
+        TAlign* ptr = reinterpret_cast<TAlign*>(item);
+        return &ptr[length_of<TItem>::kValue];
+    }
+
+private:
+    template<typename TItem> struct length_of {
+        enum { kValue = (sizeof(TItem) + sizeof(TAlign) - 1) / sizeof(TAlign) };
+    };
+    static int LengthOf(int bytes) { return (bytes + sizeof(TAlign) - 1) / sizeof(TAlign); }
+
+    struct ItemHeader {
+        int fTotalLength;
+    };
+    enum { kHeaderLength = length_of<ItemHeader>::kValue };
+
+    template<typename TItem> TItem* alloc_back(int dataLength);
+
+    struct MemBlock {
+        MemBlock(int length) : fLength(length), fBack(0), fBuffer(fLength) {}

[bsalomon, 2014/10/11 11:32:49]

I didn't pay that much attention to MemBlock before.. Now I've got a question:
Why use a separate allocation for Memblock and it's storage rather than one
allocation where the first part is a memblock struct?

[Chris Dalton, 2014/10/13 18:27:46]

It was just a quick code complexity vs perf impact decision. I've changed it to
only do one malloc now and I quite like it.

+        const int               fLength;
+        int                     fBack;
+        SkAutoTMalloc<TAlign>   fBuffer;
+        SkAutoTDelete<MemBlock> fNext;
+    };
+    MemBlock  fHeadBlock;
+    MemBlock* fTailBlock;
+
+    TBase*    fLastItem;
+
+    template<typename TItem> friend struct GrTRecorderAllocWrapper;
+
+    template <typename UBase, typename UAlign, typename UAlloc>
+    friend void* operator new(size_t, GrTRecorder<UBase, UAlign>&,
+                              const GrTRecorderAllocWrapper<UAlloc>&);
+
+    friend class Iter;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+template<typename TBase, typename TAlign>
+template<typename TItem>
+TItem* GrTRecorder<TBase, TAlign>::alloc_back(int dataLength) {
+    const int totalLength = kHeaderLength + length_of<TItem>::kValue + dataLength;
+
+    if (fTailBlock->fBack + totalLength > fTailBlock->fLength) {
+        SkASSERT(!fTailBlock->fNext.get());
+        MemBlock* next = SkNEW_ARGS(MemBlock, (SkTMax(2 * fTailBlock->fLength, totalLength)));
+        fTailBlock->fNext.reset(next);
+        fTailBlock = next;
+    }
+
+    ItemHeader* header = reinterpret_cast<ItemHeader*>(&fTailBlock->fBuffer[fTailBlock->fBack]);
+    TItem* rawPtr =
+        reinterpret_cast<TItem*>(&fTailBlock->fBuffer[fTailBlock->fBack + kHeaderLength]);
+
+    header->fTotalLength = totalLength;
+    fLastItem = rawPtr;
+    fTailBlock->fBack += totalLength;
+
+    // FIXME: We currently require that the base and subclass share the same start address.
+    // This is not required by the C++ spec, and is likely to not be true in the case of
+    // multiple inheritance or a base class that doesn't have virtual methods (when the
+    // subclass does). It would be ideal to find a more robust solution that comes at no
+    // extra cost to performance or code generality.
+    SkDEBUGCODE(void* baseAddr = fLastItem;
+                void* subclassAddr = rawPtr);
+    SkASSERT(baseAddr == subclassAddr);
+
+    return rawPtr;
+}
+
+template<typename TBase, typename TAlign>
+class GrTRecorder<TBase, TAlign>::Iter {
+public:
+    Iter(GrTRecorder& recorder) : fBlock(&recorder.fHeadBlock), fPosition(0), fItem(NULL) {}
+
+    bool next() {
+        if (fPosition >= fBlock->fBack) {
+            SkASSERT(fPosition == fBlock->fBack);
+            if (!fBlock->fNext.get()) {
+                return false;
+            }
+            SkASSERT(0 != fBlock->fNext->fBack);
+            fBlock = fBlock->fNext.get();
+            fPosition = 0;
+        }
+
+        ItemHeader* header = reinterpret_cast<ItemHeader*>(&fBlock->fBuffer[fPosition]);
+        fItem = reinterpret_cast<TBase*>(&fBlock->fBuffer[fPosition + kHeaderLength]);
+        fPosition += header->fTotalLength;
+        return true;
+    }
+
+    TBase* get() const {
+        SkASSERT(fItem);
+        return fItem;
+    }
+
+    TBase* operator->() const { return this->get(); }
+
+private:
+    MemBlock* fBlock;
+    int       fPosition;
+    TBase*    fItem;
+};
+
+template<typename TBase, typename TAlign>
+void GrTRecorder<TBase, TAlign>::reset() {
+    Iter iter(*this);
+    while (iter.next()) {
+        iter->~TBase();
+    }
+    fHeadBlock.fBack = 0;
+    fHeadBlock.fNext.free();
+    fTailBlock = &fHeadBlock;
+    fLastItem = NULL;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+template<typename TItem> struct GrTRecorderAllocWrapper {
+    GrTRecorderAllocWrapper() : fDataLength(0) {}
+
+    template <typename TBase, typename TAlign>
+    GrTRecorderAllocWrapper(const GrTRecorder<TBase, TAlign>&, int sizeOfData)
+        : fDataLength(GrTRecorder<TBase, TAlign>::LengthOf(sizeOfData)) {}
+
+    const int fDataLength;
+};
+
+template <typename TBase, typename TAlign, typename TItem>
+void* operator new(size_t size, GrTRecorder<TBase, TAlign>& recorder,
+                   const GrTRecorderAllocWrapper<TItem>& wrapper) {
+    SkASSERT(size == sizeof(TItem));
+    return recorder.template alloc_back<TItem>(wrapper.fDataLength);
+}
+
+template <typename TBase, typename TAlign, typename TItem>
+void operator delete(void*, GrTRecorder<TBase, TAlign>&, const GrTRecorderAllocWrapper<TItem>&) {
+    // We only provide an operator delete to work around compiler warnings that can come
+    // up for an unmatched operator new when compiling with exceptions.
+    SK_CRASH();
+}
+
+#define GrNEW_APPEND_TO_RECORDER(recorder, type_name, args) \
+    (new (recorder, GrTRecorderAllocWrapper<type_name>()) type_name args)
+
+#define GrNEW_APPEND_WITH_DATA_TO_RECORDER(recorder, type_name, args, size_of_data) \
+    (new (recorder, GrTRecorderAllocWrapper<type_name>(recorder, size_of_data)) type_name args)
+
+#endif