add scaledimagecache

src/core/SkScaledImageCache.cpp

+#include "SkScaledImageCache.h"
+#include "SkPixelRef.h"
+#include "SkRect.h"
+
+static const size_t DEF_BYTE_LIMIT = 2 * 1024 * 1024;

[ernstm, 2013/07/23 06:36:50]

Two megabyte is quite low. Should we set this to a value that makes the cache
big enough to hold at least one full screen image? Maybe use a platform
dependent value?

[reed1, 2013/07/23 14:50:29]

There is now a define that chrome can set in skia.gyp if its likes, or it can
call the public api in SkGraphics. This is similar to how the current fontcache
is managed.

+
+struct Key {
+    bool init(const SkBitmap& bm, SkScalar scaleX, SkScalar scaleY) {
+        SkPixelRef* pr = bm.pixelRef();
+        if (!pr) {
+            return false;
+        }
+
+        size_t offset = bm.pixelRefOffset();
+        size_t rowBytes = bm.rowBytes();
+        int x = (offset % rowBytes) >> 2;
+        int y = offset / rowBytes;
+
+        fGenID = pr->getGenerationID();
+        fBounds.set(x, y, x + bm.width(), y + bm.height());
+        fScaleX = scaleX;
+        fScaleY = scaleY;
+        return true;
+    }
+
+    bool operator<(const Key& other) {
+        const uint32_t* a = &fGenID;
+        const uint32_t* b = &other.fGenID;
+        for (int i = 0; i < 7; ++i) {
+            if (a[i] < b[i]) {
+                return true;
+            }
+            if (a[i] > b[i]) {
+                return false;
+            }
+        }
+        return false;
+    }
+
+    bool operator==(const Key& other) {
+        const uint32_t* a = &fGenID;
+        const uint32_t* b = &other.fGenID;
+        for (int i = 0; i < 7; ++i) {
+            if (a[i] != b[i]) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    uint32_t    fGenID;
+    SkIRect     fBounds;
+    float       fScaleX;
+    float       fScaleY;
+};
+
+struct SkScaledImageCache::Rec {
+    Rec(const Key& key, const SkBitmap& bm) : fKey(key), fBitmap(bm) {
+        fLockCount = 1;
+    }
+
+    size_t bytesUsed() const {
+        return fBitmap.getSize();
+    }
+
+    Rec*    fNext;
+    Rec*    fPrev;
+
+    int32_t fLockCount;
+    Key     fKey;
+    SkBitmap fBitmap;
+};
+
+SkScaledImageCache::SkScaledImageCache() {
+    fHead = NULL;
+    fTail = NULL;
+    fBytesUsed = 0;
+    fByteLimit = DEF_BYTE_LIMIT;
+    fCount = 0;
+}
+
+SkScaledImageCache::~SkScaledImageCache() {
+    Rec* rec = fHead;
+    while (rec) {
+        Rec* next = rec->fNext;
+        SkDELETE(rec);
+        rec = next;
+    }
+}
+
+SkScaledImageCache::ID* SkScaledImageCache::findAndLock(const SkBitmap& orig,

[humper, 2013/07/23 01:25:44]

Possibly worth a comment here saying that any necessary mutexes will be acquired
(by the static method of nearly the same name) before this function is called.

[reed1, 2013/07/23 14:50:29]

Done.

+                                                        SkScalar scaleX,
+                                                        SkScalar scaleY,
+                                                        SkBitmap* scaled) {
+    Key key;
+    if (!key.init(orig, scaleX, scaleY)) {
+        return NULL;
+    }
+
+    Rec* rec = fHead;
+    while (rec != NULL) {
+        if (rec->fKey == key) {
+            this->moveToHead(rec);  // for our LRU
+            rec->fLockCount += 1;
+            *scaled = rec->fBitmap;
+//            SkDebugf("Found: [%d %d] %d\n", rec->fBitmap.width(), rec->fBitmap.height(), rec->fLockCount);
+            return (ID*)rec;
+        }
+        rec = rec->fNext;
+    }
+    return NULL;
+}
+
+SkScaledImageCache::ID* SkScaledImageCache::addAndLock(const SkBitmap& orig,

[humper, 2013/07/23 01:25:44]

same as above re: comment

[reed1, 2013/07/23 14:50:29]

Done.

+                                                       SkScalar scaleX,
+                                                       SkScalar scaleY,
+                                                       const SkBitmap& scaled) {
+    Key key;
+    if (!key.init(orig, scaleX, scaleY)) {
+        return NULL;
+    }
+
+    Rec* rec = SkNEW_ARGS(Rec, (key, scaled));
+    this->addToHead(rec);
+    SkASSERT(1 == rec->fLockCount);
+
+//    SkDebugf("Added: [%d %d]\n", rec->fBitmap.width(), rec->fBitmap.height());
+
+    // We may (now) be overbudget, so see if we need to purge something.
+    this->purgeAsNeeded();
+    return (ID*)rec;
+}
+
+void SkScaledImageCache::unlock(SkScaledImageCache::ID* id) {

[humper, 2013/07/23 01:25:44]

ditto above re: comment

[reed1, 2013/07/23 14:50:29]

Done.

+    SkASSERT(id);
+
+#ifdef SK_DEBUG
+    {
+        bool found = false;
+        Rec* rec = fHead;
+        while (rec != NULL) {
+            if ((ID*)rec == id) {
+                found = true;
+                break;
+            }
+            rec = rec->fNext;
+        }
+        SkASSERT(found);
+    }
+#endif
+    Rec* rec = (Rec*)id;
+    SkASSERT(rec->fLockCount > 0);
+    rec->fLockCount -= 1;
+
+//    SkDebugf("Unlock: [%d %d] %d\n", rec->fBitmap.width(), rec->fBitmap.height(), rec->fLockCount);
+
+    // we may have been over-budget, but now have released something, so check
+    // if we should purge.
+    if (0 == rec->fLockCount) {
+        this->purgeAsNeeded();
+    }
+}
+
+void SkScaledImageCache::purgeAsNeeded() {
+    size_t byteLimit = fByteLimit;
+    size_t bytesUsed = fBytesUsed;
+    
+    Rec* rec = fTail;
+    while (rec) {
+        if (bytesUsed < byteLimit) {
+            break;
+        }
+        Rec* prev = rec->fPrev;
+        if (0 == rec->fLockCount) {
+//            SkDebugf("Purge: [%d %d] %d\n", rec->fBitmap.width(), rec->fBitmap.height(), fCount);
+            size_t used = rec->bytesUsed();
+            SkASSERT(used <= bytesUsed);
+            bytesUsed -= used;
+            this->detach(rec);
+            SkDELETE(rec);
+            fCount -= 1;
+        }
+        rec = prev;
+    }
+    fBytesUsed = bytesUsed;
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+void SkScaledImageCache::detach(Rec* rec) {
+    Rec* prev = rec->fPrev;
+    Rec* next = rec->fNext;
+    
+    if (!prev) {
+        SkASSERT(fHead == rec);
+        fHead = next;
+    } else {
+        prev->fNext = next;
+    }
+    
+    if (!next) {
+        fTail = prev;
+    } else {
+        next->fPrev = prev;
+    }
+    
+    rec->fNext = rec->fPrev = NULL;
+}
+
+void SkScaledImageCache::moveToHead(Rec* rec) {
+    if (fHead == rec) {
+        return;
+    }
+
+    SkASSERT(fHead);
+    SkASSERT(fTail);
+
+    this->validate();
+
+    if (3 == fCount)
+        SkDebugf("");

[humper, 2013/07/23 01:25:44]

Obviously the debug statements are intended to be temporary, just wanted to
remind you to remove them at some point :)

[reed1, 2013/07/23 14:50:29]

Done.

+    this->detach(rec);
+
+    fHead->fPrev = rec;
+    rec->fNext = fHead;
+    fHead = rec;
+    
+    this->validate();
+}
+
+void SkScaledImageCache::addToHead(Rec* rec) {
+    this->validate();
+
+    rec->fPrev = NULL;
+    rec->fNext = fHead;
+    if (fHead) {
+        fHead->fPrev = rec;
+    }
+    fHead = rec;
+    if (!fTail) {
+        fTail = rec;
+    }
+    fBytesUsed += rec->bytesUsed();
+    fCount += 1;
+
+    this->validate();
+}
+
+#ifdef SK_DEBUG
+void SkScaledImageCache::validate() const {
+    if (NULL == fHead) {
+        SkASSERT(NULL == fTail);
+        SkASSERT(0 == fBytesUsed);
+        return;
+    }
+
+    if (fHead == fTail) {
+        SkASSERT(NULL == fHead->fPrev);
+        SkASSERT(NULL == fHead->fNext);
+        SkASSERT(fHead->bytesUsed() == fBytesUsed);
+        return;
+    }
+
+    SkASSERT(NULL == fHead->fPrev);
+    SkASSERT(NULL != fHead->fNext);
+    SkASSERT(NULL == fTail->fNext);
+    SkASSERT(NULL != fTail->fPrev);
+
+    size_t used = 0;
+    int count = 0;
+    const Rec* rec = fHead;
+    while (rec) {
+        count += 1;
+        used += rec->bytesUsed();
+        SkASSERT(used <= fBytesUsed);
+        rec = rec->fNext;
+    }
+    SkASSERT(fCount == count);
+
+    rec = fTail;
+    while (rec) {
+        SkASSERT(count > 0);
+        count -= 1;
+        SkASSERT(used >= rec->bytesUsed());
+        used -= rec->bytesUsed();
+        rec = rec->fPrev;
+    }
+    
+    SkASSERT(0 == count);
+    SkASSERT(0 == used);
+}
+#endif
+
+///////////////////////////////////////////////////////////////////////////////
+
+#include "SkThread.h"
+
+static SkMutex gMutex;
+
+static SkScaledImageCache* get_cache() {
+    static SkScaledImageCache* gCache;

[humper, 2013/07/23 01:25:44]

I know the standard says that this will be initialized to 0, but it seems like
good practice to explicitly = NULL here anyhow.  Is there a Skia coding
convention that says not to?

[reed1, 2013/07/23 14:50:29]

I don't know if anything is written in the doc, but the skia and chrome use the
implicit null in many places.

+    if (!gCache) {
+        gCache = SkNEW(SkScaledImageCache);
+    }
+    return gCache;
+}
+
+SkScaledImageCache::ID* SkScaledImageCache::FindAndLock(const SkBitmap& orig,
+                                                        SkScalar scaleX,
+                                                        SkScalar scaleY,
+                                                        SkBitmap* scaled) {
+    SkAutoMutexAcquire am(gMutex);
+    return get_cache()->findAndLock(orig, scaleX, scaleY, scaled);
+}
+
+SkScaledImageCache::ID* SkScaledImageCache::AddAndLock(const SkBitmap& orig,
+                                                       SkScalar scaleX,
+                                                       SkScalar scaleY,
+                                                       const SkBitmap& scaled) {
+    SkAutoMutexAcquire am(gMutex);
+    return get_cache()->addAndLock(orig, scaleX, scaleY, scaled);
+}
+
+void SkScaledImageCache::Unlock(SkScaledImageCache::ID* id) {
+    SkAutoMutexAcquire am(gMutex);
+    return get_cache()->unlock(id);
+}
+
+size_t SkScaledImageCache::GetByteLimit() {
+    SkAutoMutexAcquire am(gMutex);
+    return get_cache()->fByteLimit;
+}
+
+size_t SkScaledImageCache::SetByteLimit(size_t newLimit) {
+    SkAutoMutexAcquire am(gMutex);
+    SkScaledImageCache* cache = get_cache();
+    size_t prevLimit = cache->fByteLimit;
+    cache->fByteLimit = newLimit;
+    cache->purgeAsNeeded();
+    return prevLimit;
+}
+
+size_t SkScaledImageCache::GetBytesUsed() {
+    SkAutoMutexAcquire am(gMutex);
+    return get_cache()->fBytesUsed;
+}
+