refactor bitmapshader to use a controller

src/core/SkBitmapController.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBitmap.h"
+#include "SkBitmapController.h"
+#include "SkMatrix.h"
+
+static bool valid_for_drawing(const SkBitmap& bm) {
+    if (0 == bm.width() || 0 == bm.height()) {
+        return false;   // nothing to draw
+    }
+    if (NULL == bm.pixelRef()) {
+        return false;   // no pixels to read
+    }
+    if (bm.getTexture()) {
+        // we can handle texture (ugh) since lockPixels will perform a read-back
+        return true;
+    }
+    if (kIndex_8_SkColorType == bm.colorType()) {
+        SkAutoLockPixels alp(bm); // but we need to call it before getColorTable() is safe.
+        if (!bm.getColorTable()) {
+            return false;
+        }
+    }
+    return true;
+}
+
+bool SkBitmapController::requestBitmap(const SkBitmap& inBM, const SkMatrix& inv,
+                                       SkFilterQuality inQuality, SkBitmap* outBM, SkMatrix* outInv,
+                                       SkFilterQuality* outQuality) {
+    if (!valid_for_drawing(inBM)) {
+        return false;
+    }
+    return this->onRequestBitmap(inBM, inv, inQuality, outBM, outInv, outQuality);
+}
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+#include "SkBitmapCache.h"
+#include "SkBitmapScaler.h"
+#include "SkMipMap.h"
+#include "SkResourceCache.h"
+
+class SkDefaultBitmapControllerState {
+public:
+    SkDefaultBitmapControllerState(const SkBitmap& src, const SkMatrix& inv, SkFilterQuality qual)
+        : fOrigBitmap(src), fInvMatrix(inv), fFilterLevel(qual)
+    {}
+
+    const SkBitmap& fOrigBitmap;
+    SkMatrix        fInvMatrix;
+    SkFilterQuality fFilterLevel;
+    
+    SkBitmap                     fScaledBitmap;
+    SkAutoTUnref<const SkMipMap> fCurrMip;
+    
+    bool processHQRequest();
+    bool processMediumRequest();
+};
+
+// Check to see that the size of the bitmap that would be produced by
+// scaling by the given inverted matrix is less than the maximum allowed.
+static inline bool cache_size_okay(const SkBitmap& bm, const SkMatrix& invMat) {
+    size_t maximumAllocation = SkResourceCache::GetEffectiveSingleAllocationByteLimit();
+    if (0 == maximumAllocation) {
+        return true;
+    }
+    // float matrixScaleFactor = 1.0 / (invMat.scaleX * invMat.scaleY);
+    // return ((origBitmapSize * matrixScaleFactor) < maximumAllocationSize);
+    // Skip the division step:
+    const size_t size = bm.info().getSafeSize(bm.info().minRowBytes());
+    return size < (maximumAllocation * invMat.getScaleX() * invMat.getScaleY());
+}
+
+/*
+ *  High quality is implemented by performing up-right scale-only filtering and then
+ *  using bilerp for any remaining transformations.
+ */
+bool SkDefaultBitmapControllerState::processHQRequest() {
+    SkASSERT(kHigh_SkFilterQuality == fFilterLevel);
+    
+    // Our default return state is to downgrade the request to Medium, w/ or w/o setting fBitmap
+    // to a valid bitmap. If we succeed, we will set this to Low instead.
+    fFilterLevel = kMedium_SkFilterQuality;
+    
+    if (kN32_SkColorType != fOrigBitmap.colorType() || !cache_size_okay(fOrigBitmap, fInvMatrix) ||
+        fInvMatrix.hasPerspective())
+    {
+        return false; // can't handle the reqeust
+    }
+    
+    SkScalar invScaleX = fInvMatrix.getScaleX();
+    SkScalar invScaleY = fInvMatrix.getScaleY();
+    if (fInvMatrix.getType() & SkMatrix::kAffine_Mask) {
+        SkSize scale;
+        if (!fInvMatrix.decomposeScale(&scale)) {
+            return false;
+        }
+        invScaleX = scale.width();
+        invScaleY = scale.height();
+    }
+    if (SkScalarNearlyEqual(invScaleX, 1) && SkScalarNearlyEqual(invScaleY, 1)) {
+        return false; // no need for HQ
+    }
+    
+    SkScalar trueDestWidth  = fOrigBitmap.width() / invScaleX;
+    SkScalar trueDestHeight = fOrigBitmap.height() / invScaleY;
+    SkScalar roundedDestWidth = SkScalarRoundToScalar(trueDestWidth);
+    SkScalar roundedDestHeight = SkScalarRoundToScalar(trueDestHeight);
+    
+    if (!SkBitmapCache::Find(fOrigBitmap, roundedDestWidth, roundedDestHeight, &fScaledBitmap)) {
+        if (!SkBitmapScaler::Resize(&fScaledBitmap,
+                                    fOrigBitmap,
+                                    SkBitmapScaler::RESIZE_BEST,
+                                    roundedDestWidth,
+                                    roundedDestHeight,
+                                    SkResourceCache::GetAllocator())) {
+            return false; // we failed to create fScaledBitmap
+        }
+        
+        SkASSERT(fScaledBitmap.getPixels());
+        fScaledBitmap.setImmutable();
+        SkBitmapCache::Add(fOrigBitmap, roundedDestWidth, roundedDestHeight, fScaledBitmap);
+    }
+    
+    SkASSERT(fScaledBitmap.getPixels());
+    
+    fInvMatrix.postScale(roundedDestWidth / fOrigBitmap.width(),
+                         roundedDestHeight / fOrigBitmap.height());
+    fFilterLevel = kLow_SkFilterQuality;
+    return true;
+}
+
+/*
+ *  Modulo internal errors, this should always succeed *if* the matrix is downscaling
+ *  (in this case, we have the inverse, so it succeeds if fInvMatrix is upscaling)
+ */
+bool SkDefaultBitmapControllerState::processMediumRequest() {
+    SkASSERT(kMedium_SkFilterQuality == fFilterLevel);
+    
+    // Our default return state is to downgrade the request to Low, w/ or w/o setting fBitmap
+    // to a valid bitmap.
+    fFilterLevel = kLow_SkFilterQuality;
+    
+    SkSize invScaleSize;
+    if (!fInvMatrix.decomposeScale(&invScaleSize, NULL)) {
+        return false;
+    }
+    SkScalar invScale = SkScalarSqrt(invScaleSize.width() * invScaleSize.height());
+    
+    if (invScale > SK_Scalar1) {
+        fCurrMip.reset(SkMipMapCache::FindAndRef(fOrigBitmap));
+        if (NULL == fCurrMip.get()) {
+            fCurrMip.reset(SkMipMapCache::AddAndRef(fOrigBitmap));
+            if (NULL == fCurrMip.get()) {
+                return false;
+            }
+        }
+        // diagnostic for a crasher...
+        if (NULL == fCurrMip->data()) {
+            sk_throw();
+        }
+        
+        SkScalar levelScale = SkScalarInvert(invScale);
+        SkMipMap::Level level;
+        if (fCurrMip->extractLevel(levelScale, &level)) {
+            SkScalar invScaleFixup = level.fScale;
+            fInvMatrix.postScale(invScaleFixup, invScaleFixup);
+            
+            const SkImageInfo info = fOrigBitmap.info().makeWH(level.fWidth, level.fHeight);
+            // todo: if we could wrap the fCurrMip in a pixelref, then we could just install
+            //       that here, and not need to explicitly track it ourselves.
+            fScaledBitmap.installPixels(info, level.fPixels, level.fRowBytes);

[scroggo, 2015/06/02 13:24:53]

Should we check the return value? (Even just to assert?)

[reed1, 2015/06/02 14:07:46]

Done.

+            return true;
+        } else {
+            // failed to extract, so release the mipmap
+            fCurrMip.reset(NULL);
+        }
+    }
+    return false;
+}
+
+bool SkDefaultBitmapController::onRequestBitmap(const SkBitmap& inBM, const SkMatrix& inInverse,
+                                                SkFilterQuality inQuality, SkBitmap* outBM,
+                                                SkMatrix* outInverse, SkFilterQuality* outQuality) {
+    SkDefaultBitmapControllerState state(inBM, inInverse, inQuality);
+
+    if (!state.processHQRequest() && !state.processHQRequest()) {

[scroggo, 2015/06/02 13:24:54]

Two questions:
- if inQuality is not kHigh, won't the (first) call to processHQRequest assert?
- is the second call supposed to be processMediumRequest?

[reed1, 2015/06/02 14:07:46]

Done.

+        state.fScaledBitmap = inBM;
+    }
+    SkASSERT(state.fFilterLevel <= kLow_SkFilterQuality);
+    *outBM = state.fScaledBitmap;
+    *outInverse = inInverse;
+    *outQuality = state.fFilterLevel;
+    return true;
+}
+