src/effects/SkBitmapCache.cpp

/*
    Copyright 2010 Google Inc.

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
 */

#include "SkBitmapCache.h"

struct SkBitmapCache::Entry {
    Entry*      fPrev;
    Entry*      fNext;

    void*       fBuffer;
    size_t      fSize;
    SkBitmap    fBitmap;

    Entry(const void* buffer, size_t size, const SkBitmap& bm)
            : fPrev(NULL),
              fNext(NULL),
              fBitmap(bm) {
        fBuffer = sk_malloc_throw(size);
        fSize = size;
        memcpy(fBuffer, buffer, size);
    }

    ~Entry() { sk_free(fBuffer); }

    bool equals(const void* buffer, size_t size) const {
        return (fSize == size) && !memcmp(fBuffer, buffer, size);
    }
};

SkBitmapCache::SkBitmapCache(int max) : fMaxEntries(max) {
    fEntryCount = 0;
    fHead = fTail = NULL;

    this->validate();
}

SkBitmapCache::~SkBitmapCache() {
    this->validate();

    Entry* entry = fHead;
    while (entry) {
        Entry* next = entry->fNext;
        delete entry;
        entry = next;
    }
}

SkBitmapCache::Entry* SkBitmapCache::detach(Entry* entry) const {
    if (entry->fPrev) {
        SkASSERT(fHead != entry);
        entry->fPrev->fNext = entry->fNext;
    } else {
        SkASSERT(fHead == entry);
        fHead = entry->fNext;
    }
    if (entry->fNext) {
        SkASSERT(fTail != entry);
        entry->fNext->fPrev = entry->fPrev;
    } else {
        SkASSERT(fTail == entry);
        fTail = entry->fPrev;
    }
    return entry;
}

void SkBitmapCache::attachToHead(Entry* entry) const {
    entry->fPrev = NULL;
    entry->fNext = fHead;
    if (fHead) {
        fHead->fPrev = entry;
    } else {
        fTail = entry;
    }
    fHead = entry;
}

bool SkBitmapCache::find(const void* buffer, size_t size, SkBitmap* bm) const {
    AutoValidate av(this);

    Entry* entry = fHead;
    while (entry) {
        if (entry->equals(buffer, size)) {
            if (bm) {
                *bm = entry->fBitmap;
            }
            // move to the head of our list, so we purge it last
            this->detach(entry);
            this->attachToHead(entry);
            return true;
        }
        entry = entry->fNext;
    }
    return false;
}

void SkBitmapCache::add(const void* buffer, size_t len, const SkBitmap& bm) {
    AutoValidate av(this);

    if (fEntryCount == fMaxEntries) {
        SkASSERT(fTail);
        delete this->detach(fTail);
        fEntryCount -= 1;
    }

    Entry* entry = new Entry(buffer, len, bm);
    this->attachToHead(entry);
    fEntryCount += 1;
}

///////////////////////////////////////////////////////////////////////////////

#ifdef SK_DEBUG

void SkBitmapCache::validate() const {
    SkASSERT(fEntryCount >= 0 && fEntryCount <= fMaxEntries);

    if (fEntryCount > 0) {
        SkASSERT(NULL == fHead->fPrev);
        SkASSERT(NULL == fTail->fNext);

        if (fEntryCount == 1) {
            SkASSERT(fHead == fTail);
        } else {
            SkASSERT(fHead != fTail);
        }

        Entry* entry = fHead;
        int count = 0;
        while (entry) {
            count += 1;
            entry = entry->fNext;
        }
        SkASSERT(count == fEntryCount);

        entry = fTail;
        while (entry) {
            count -= 1;
            entry = entry->fPrev;
        }
        SkASSERT(0 == count);
    } else {
        SkASSERT(NULL == fHead);
        SkASSERT(NULL == fTail);
    }
}

#endif