move blurimagefilter.cpp back into effects

Bug: skia:
Change-Id: I5711a9a8fcd135344e75cb4b505bd06044414c85
Reviewed-on: https://skia-review.googlesource.com/137581
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Mike Reed <reed@google.com>

1 files changed, 698 insertions, 0 deletions

diff --git a/src/effects/imagefilters/SkBlurImageFilter.cpp b/src/effects/imagefilters/SkBlurImageFilter.cpp
new file mode 100644
index 0000000000..818644818c
--- /dev/null
+++ b/src/effects/imagefilters/SkBlurImageFilter.cpp
@@ -0,0 +1,698 @@
+/*
+ * Copyright 2011 The Android Open Source Project
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBlurImageFilter.h"
+
+#include <algorithm>
+
+#include "SkArenaAlloc.h"
+#include "SkAutoPixmapStorage.h"
+#include "SkBitmap.h"
+#include "SkColorData.h"
+#include "SkColorSpaceXformer.h"
+#include "SkImageFilterPriv.h"
+#include "SkTFitsIn.h"
+#include "SkGpuBlurUtils.h"
+#include "SkNx.h"
+#include "SkOpts.h"
+#include "SkReadBuffer.h"
+#include "SkSpecialImage.h"
+#include "SkWriteBuffer.h"
+
+#if SK_SUPPORT_GPU
+#include "GrContext.h"
+#include "GrTextureProxy.h"
+#include "SkGr.h"
+#endif
+
+static constexpr double kPi = 3.14159265358979323846264338327950288;
+
+class SkBlurImageFilterImpl final : public SkImageFilter {
+public:
+    SkBlurImageFilterImpl(SkScalar sigmaX,
+                          SkScalar sigmaY,
+                          sk_sp<SkImageFilter> input,
+                          const CropRect* cropRect,
+                          SkBlurImageFilter::TileMode tileMode);
+
+    SkRect computeFastBounds(const SkRect&) const override;
+
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkBlurImageFilterImpl)
+
+protected:
+    void flatten(SkWriteBuffer&) const override;
+    sk_sp<SkSpecialImage> onFilterImage(SkSpecialImage* source, const Context&,
+                                        SkIPoint* offset) const override;
+    sk_sp<SkImageFilter> onMakeColorSpace(SkColorSpaceXformer*) const override;
+    SkIRect onFilterNodeBounds(const SkIRect& src, const SkMatrix& ctm,
+                               MapDirection, const SkIRect* inputRect) const override;
+
+private:
+    typedef SkImageFilter INHERITED;
+    friend class SkImageFilter;
+
+#if SK_SUPPORT_GPU
+    sk_sp<SkSpecialImage> gpuFilter(
+            SkSpecialImage *source, SkVector sigma, const sk_sp<SkSpecialImage> &input,
+            SkIRect inputBounds, SkIRect dstBounds, SkIPoint inputOffset,
+            const OutputProperties& outProps, SkIPoint* offset) const;
+#endif
+
+    SkSize                      fSigma;
+    SkBlurImageFilter::TileMode fTileMode;
+};
+
+SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkImageFilter)
+    SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkBlurImageFilterImpl)
+SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END
+
+///////////////////////////////////////////////////////////////////////////////
+
+sk_sp<SkImageFilter> SkBlurImageFilter::Make(SkScalar sigmaX, SkScalar sigmaY,
+                                             sk_sp<SkImageFilter> input,
+                                             const SkImageFilter::CropRect* cropRect,
+                                             TileMode tileMode) {
+    if (sigmaX < SK_ScalarNearlyZero && sigmaY < SK_ScalarNearlyZero && !cropRect) {
+        return input;
+    }
+    return sk_sp<SkImageFilter>(
+          new SkBlurImageFilterImpl(sigmaX, sigmaY, input, cropRect, tileMode));
+}
+
+// This rather arbitrary-looking value results in a maximum box blur kernel size
+// of 1000 pixels on the raster path, which matches the WebKit and Firefox
+// implementations. Since the GPU path does not compute a box blur, putting
+// the limit on sigma ensures consistent behaviour between the GPU and
+// raster paths.
+#define MAX_SIGMA SkIntToScalar(532)
+
+static SkVector map_sigma(const SkSize& localSigma, const SkMatrix& ctm) {
+    SkVector sigma = SkVector::Make(localSigma.width(), localSigma.height());
+    ctm.mapVectors(&sigma, 1);
+    sigma.fX = SkMinScalar(SkScalarAbs(sigma.fX), MAX_SIGMA);
+    sigma.fY = SkMinScalar(SkScalarAbs(sigma.fY), MAX_SIGMA);
+    return sigma;
+}
+
+SkBlurImageFilterImpl::SkBlurImageFilterImpl(SkScalar sigmaX,
+                                             SkScalar sigmaY,
+                                             sk_sp<SkImageFilter> input,
+                                             const CropRect* cropRect,
+                                             SkBlurImageFilter::TileMode tileMode)
+        : INHERITED(&input, 1, cropRect), fSigma{sigmaX, sigmaY}, fTileMode(tileMode) {}
+
+sk_sp<SkFlattenable> SkBlurImageFilterImpl::CreateProc(SkReadBuffer& buffer) {
+    SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 1);
+    SkScalar sigmaX = buffer.readScalar();
+    SkScalar sigmaY = buffer.readScalar();
+    SkBlurImageFilter::TileMode tileMode;
+    if (buffer.isVersionLT(SkReadBuffer::kTileModeInBlurImageFilter_Version)) {
+        tileMode = SkBlurImageFilter::kClampToBlack_TileMode;
+    } else {
+        tileMode = buffer.read32LE(SkBlurImageFilter::kLast_TileMode);
+    }
+
+    static_assert(SkBlurImageFilter::kLast_TileMode == 2, "CreateProc");
+
+    return SkBlurImageFilter::Make(
+          sigmaX, sigmaY, common.getInput(0), &common.cropRect(), tileMode);
+}
+
+void SkBlurImageFilterImpl::flatten(SkWriteBuffer& buffer) const {
+    this->INHERITED::flatten(buffer);
+    buffer.writeScalar(fSigma.fWidth);
+    buffer.writeScalar(fSigma.fHeight);
+
+    static_assert(SkBlurImageFilter::kLast_TileMode == 2, "flatten");
+    SkASSERT(fTileMode <= SkBlurImageFilter::kLast_TileMode);
+
+    buffer.writeInt(static_cast<int>(fTileMode));
+}
+
+#if SK_SUPPORT_GPU
+static GrTextureDomain::Mode to_texture_domain_mode(SkBlurImageFilter::TileMode tileMode) {
+    switch (tileMode) {
+      case SkBlurImageFilter::TileMode::kClamp_TileMode:
+        return GrTextureDomain::kClamp_Mode;
+      case SkBlurImageFilter::TileMode::kClampToBlack_TileMode:
+        return GrTextureDomain::kDecal_Mode;
+      case SkBlurImageFilter::TileMode::kRepeat_TileMode:
+        return GrTextureDomain::kRepeat_Mode;
+      default:
+        SK_ABORT("Unsupported tile mode.");
+        return GrTextureDomain::kDecal_Mode;
+    }
+}
+#endif
+
+// This is defined by the SVG spec:
+// https://drafts.fxtf.org/filter-effects/#feGaussianBlurElement
+static int calculate_window(double sigma) {
+    // NB 136 is the largest sigma that will not cause a buffer full of 255 mask values to overflow
+    // using the Gauss filter. It also limits the size of buffers used hold intermediate values.
+    // Explanation of maximums:
+    //   sum0 = window * 255
+    //   sum1 = window * sum0 -> window * window * 255
+    //   sum2 = window * sum1 -> window * window * window * 255 -> window^3 * 255
+    //
+    //   The value window^3 * 255 must fit in a uint32_t. So,
+    //      window^3 < 2^32. window = 255.
+    //
+    //   window = floor(sigma * 3 * sqrt(2 * kPi) / 4 + 0.5)
+    //   For window <= 255, the largest value for sigma is 136.
+    sigma = SkTPin(sigma, 0.0, 136.0);
+    auto possibleWindow = static_cast<int>(floor(sigma * 3 * sqrt(2 * kPi) / 4 + 0.5));
+    return std::max(1, possibleWindow);
+}
+
+// Calculating the border is tricky. The border is the distance in pixels between the first dst
+// pixel and the first src pixel (or the last src pixel and the last dst pixel).
+// I will go through the odd case which is simpler, and then through the even case. Given a
+// stack of filters seven wide for the odd case of three passes.
+//
+//        S
+//     aaaAaaa
+//     bbbBbbb
+//     cccCccc
+//        D
+//
+// The furthest changed pixel is when the filters are in the following configuration.
+//
+//                 S
+//           aaaAaaa
+//        bbbBbbb
+//     cccCccc
+//        D
+//
+//  The A pixel is calculated using the value S, the B uses A, and the C uses B, and
+// finally D is C. So, with a window size of seven the border is nine. In the odd case, the
+// border is 3*((window - 1)/2).
+//
+// For even cases the filter stack is more complicated. The spec specifies two passes
+// of even filters and a final pass of odd filters. A stack for a width of six looks like
+// this.
+//
+//       S
+//    aaaAaa
+//     bbBbbb
+//    cccCccc
+//       D
+//
+// The furthest pixel looks like this.
+//
+//               S
+//          aaaAaa
+//        bbBbbb
+//    cccCccc
+//       D
+//
+// For a window of six, the border value is eight. In the even case the border is 3 *
+// (window/2) - 1.
+static int calculate_border(int window) {
+    return (window & 1) == 1 ? 3 * ((window - 1) / 2) : 3 * (window / 2) - 1;
+}
+
+static int calculate_buffer(int window) {
+    int bufferSize = window - 1;
+    return (window & 1) == 1 ? 3 * bufferSize : 3 * bufferSize + 1;
+}
+
+// blur_one_direction implements the common three pass box filter approximation of Gaussian blur,
+// but combines all three passes into a single pass. This approach is facilitated by three circular
+// buffers the width of the window which track values for trailing edges of each of the three
+// passes. This allows the algorithm to use more precision in the calculation because the values
+// are not rounded each pass. And this implementation also avoids a trap that's easy to fall
+// into resulting in blending in too many zeroes near the edge.
+//
+//  In general, a window sum has the form:
+//     sum_n+1 = sum_n + leading_edge - trailing_edge.
+//  If instead we do the subtraction at the end of the previous iteration, we can just
+// calculate the sums instead of having to do the subtractions too.
+//
+//      In previous iteration:
+//      sum_n+1 = sum_n - trailing_edge.
+//
+//      In this iteration:
+//      sum_n+1 = sum_n + leading_edge.
+//
+//  Now we can stack all three sums and do them at once. Sum0 gets its leading edge from the
+// actual data. Sum1's leading edge is just Sum0, and Sum2's leading edge is Sum1. So, doing the
+// three passes at the same time has the form:
+//
+//    sum0_n+1 = sum0_n + leading edge
+//    sum1_n+1 = sum1_n + sum0_n+1
+//    sum2_n+1 = sum2_n + sum1_n+1
+//
+//    sum2_n+1 / window^3 is the new value of the destination pixel.
+//
+//    Reduce the sums by the trailing edges which were stored in the circular buffers,
+// for the next go around. This is the case for odd sized windows, even windows the the third
+// circular buffer is one larger then the first two circular buffers.
+//
+//    sum2_n+2 = sum2_n+1 - buffer2[i];
+//    buffer2[i] = sum1;
+//    sum1_n+2 = sum1_n+1 - buffer1[i];
+//    buffer1[i] = sum0;
+//    sum0_n+2 = sum0_n+1 - buffer0[i];
+//    buffer0[i] = leading edge
+//
+//   This is all encapsulated in the processValue function below.
+//
+using Pass0And1 = Sk4u[2];
+// The would be dLeft parameter is assumed to be 0.
+static void blur_one_direction(Sk4u* buffer, int window,
+                               int srcLeft, int srcRight, int dstRight,
+                               const uint32_t* src, int srcXStride, int srcYStride, int srcH,
+                                     uint32_t* dst, int dstXStride, int dstYStride) {
+
+    // The circular buffers are one less than the window.
+    auto pass0Count = window - 1,
+         pass1Count = window - 1,
+         pass2Count = (window & 1) == 1 ? window - 1 : window;
+
+    Pass0And1* buffer01Start = (Pass0And1*)buffer;
+    Sk4u*      buffer2Start  = buffer + pass0Count + pass1Count;
+    Pass0And1* buffer01End   = (Pass0And1*)buffer2Start;
+    Sk4u*      buffer2End    = buffer2Start + pass2Count;
+
+    // If the window is odd then the divisor is just window ^ 3 otherwise,
+    // it is window * window * (window + 1) = window ^ 3 + window ^ 2;
+    auto window2 = window * window;
+    auto window3 = window2 * window;
+    auto divisor = (window & 1) == 1 ? window3 : window3 + window2;
+
+    // NB the sums in the blur code use the following technique to avoid
+    // adding 1/2 to round the divide.
+    //
+    //   Sum/d + 1/2 == (Sum + h) / d
+    //   Sum + d(1/2) ==  Sum + h
+    //     h == (1/2)d
+    //
+    // But the d/2 it self should be rounded.
+    //    h == d/2 + 1/2 == (d + 1) / 2
+    //
+    // weight = 1 / d * 2 ^ 32
+    auto weight = static_cast<uint32_t>(round(1.0 / divisor * (1ull << 32)));
+    auto half = static_cast<uint32_t>((divisor + 1) / 2);
+
+    auto border = calculate_border(window);
+
+    // Calculate the start and end of the source pixels with respect to the destination start.
+    auto srcStart = srcLeft - border,
+         srcEnd   = srcRight - border,
+         dstEnd   = dstRight;
+
+    for (auto y = 0; y < srcH; y++) {
+        auto buffer01Cursor = buffer01Start;
+        auto buffer2Cursor  = buffer2Start;
+
+        Sk4u sum0{0u};
+        Sk4u sum1{0u};
+        Sk4u sum2{half};
+
+        sk_bzero(buffer01Start, (buffer2End - (Sk4u *) (buffer01Start)) * sizeof(*buffer2Start));
+
+        // Given an expanded input pixel, move the window ahead using the leadingEdge value.
+        auto processValue = [&](const Sk4u& leadingEdge) -> Sk4u {
+            sum0 += leadingEdge;
+            sum1 += sum0;
+            sum2 += sum1;
+
+            Sk4u value = sum2.mulHi(weight);
+
+            sum2 -= *buffer2Cursor;
+            *buffer2Cursor = sum1;
+            buffer2Cursor = (buffer2Cursor + 1) < buffer2End ? buffer2Cursor + 1 : buffer2Start;
+
+            sum1 -= (*buffer01Cursor)[1];
+            (*buffer01Cursor)[1] = sum0;
+            sum0 -= (*buffer01Cursor)[0];
+            (*buffer01Cursor)[0] = leadingEdge;
+            buffer01Cursor =
+                    (buffer01Cursor + 1) < buffer01End ? buffer01Cursor + 1 : buffer01Start;
+
+            return value;
+        };
+
+        auto srcIdx = srcStart;
+        auto dstIdx = 0;
+        const uint32_t* srcCursor = src;
+              uint32_t* dstCursor = dst;
+
+        // The destination pixels are not effected by the src pixels,
+        // change to zero as per the spec.
+        // https://drafts.fxtf.org/filter-effects/#FilterPrimitivesOverviewIntro
+        while (dstIdx < srcIdx) {
+            *dstCursor = 0;
+            dstCursor += dstXStride;
+            SK_PREFETCH(dstCursor);
+            dstIdx++;
+        }
+
+        // The edge of the source is before the edge of the destination. Calculate the sums for
+        // the pixels before the start of the destination.
+        while (dstIdx > srcIdx) {
+            Sk4u leadingEdge = srcIdx < srcEnd ? SkNx_cast<uint32_t>(Sk4b::Load(srcCursor)) : 0;
+            (void) processValue(leadingEdge);
+            srcCursor += srcXStride;
+            srcIdx++;
+        }
+
+        // The dstIdx and srcIdx are in sync now; the code just uses the dstIdx for both now.
+        // Consume the source generating pixels to dst.
+        auto loopEnd = std::min(dstEnd, srcEnd);
+        while (dstIdx < loopEnd) {
+            Sk4u leadingEdge = SkNx_cast<uint32_t>(Sk4b::Load(srcCursor));
+            SkNx_cast<uint8_t>(processValue(leadingEdge)).store(dstCursor);
+            srcCursor += srcXStride;
+            dstCursor += dstXStride;
+            SK_PREFETCH(dstCursor);
+            dstIdx++;
+        }
+
+        // The leading edge is beyond the end of the source. Assume that the pixels
+        // are now 0x0000 until the end of the destination.
+        loopEnd = dstEnd;
+        while (dstIdx < loopEnd) {
+            SkNx_cast<uint8_t>(processValue(0u)).store(dstCursor);
+            dstCursor += dstXStride;
+            SK_PREFETCH(dstCursor);
+            dstIdx++;
+        }
+
+        src += srcYStride;
+        dst += dstYStride;
+    }
+}
+
+static sk_sp<SkSpecialImage> copy_image_with_bounds(
+        SkSpecialImage *source, const sk_sp<SkSpecialImage> &input,
+        SkIRect srcBounds, SkIRect dstBounds) {
+    SkBitmap inputBM;
+    if (!input->getROPixels(&inputBM)) {
+        return nullptr;
+    }
+
+    if (inputBM.colorType() != kN32_SkColorType) {
+        return nullptr;
+    }
+
+    SkBitmap src;
+    inputBM.extractSubset(&src, srcBounds);
+
+    // Make everything relative to the destination bounds.
+    srcBounds.offset(-dstBounds.x(), -dstBounds.y());
+    dstBounds.offset(-dstBounds.x(), -dstBounds.y());
+
+    auto srcW = srcBounds.width(),
+         dstW = dstBounds.width(),
+         dstH = dstBounds.height();
+
+    SkImageInfo dstInfo = SkImageInfo::Make(dstW, dstH, inputBM.colorType(), inputBM.alphaType());
+
+    SkBitmap dst;
+    if (!dst.tryAllocPixels(dstInfo)) {
+        return nullptr;
+    }
+
+    // There is no blurring to do, but we still need to copy the source while accounting for the
+    // dstBounds. Remember that the src was intersected with the dst.
+    int y = 0;
+    size_t dstWBytes = dstW * sizeof(uint32_t);
+    for (;y < srcBounds.top(); y++) {
+        sk_bzero(dst.getAddr32(0, y), dstWBytes);
+    }
+
+    for (;y < srcBounds.bottom(); y++) {
+        int x = 0;
+        uint32_t* dstPtr = dst.getAddr32(0, y);
+        for (;x < srcBounds.left(); x++) {
+            *dstPtr++ = 0;
+        }
+
+        memcpy(dstPtr, src.getAddr32(x - srcBounds.left(), y - srcBounds.top()),
+               srcW * sizeof(uint32_t));
+
+        dstPtr += srcW;
+        x += srcW;
+
+        for (;x < dstBounds.right(); x++) {
+            *dstPtr++ = 0;
+        }
+    }
+
+    for (;y < dstBounds.bottom(); y++) {
+        sk_bzero(dst.getAddr32(0, y), dstWBytes);
+    }
+
+    return SkSpecialImage::MakeFromRaster(SkIRect::MakeWH(dstBounds.width(),
+                                                          dstBounds.height()),
+                                          dst, &source->props());
+}
+
+// TODO: Implement CPU backend for different fTileMode.
+static sk_sp<SkSpecialImage> cpu_blur(
+        SkVector sigma,
+        SkSpecialImage *source, const sk_sp<SkSpecialImage> &input,
+        SkIRect srcBounds, SkIRect dstBounds) {
+    auto windowW = calculate_window(sigma.x()),
+         windowH = calculate_window(sigma.y());
+
+    if (windowW <= 1 && windowH <= 1) {
+        return copy_image_with_bounds(source, input, srcBounds, dstBounds);
+    }
+
+    SkBitmap inputBM;
+
+    if (!input->getROPixels(&inputBM)) {
+        return nullptr;
+    }
+
+    if (inputBM.colorType() != kN32_SkColorType) {
+        return nullptr;
+    }
+
+    SkBitmap src;
+    inputBM.extractSubset(&src, srcBounds);
+
+    // Make everything relative to the destination bounds.
+    srcBounds.offset(-dstBounds.x(), -dstBounds.y());
+    dstBounds.offset(-dstBounds.x(), -dstBounds.y());
+
+    auto srcW = srcBounds.width(),
+         srcH = srcBounds.height(),
+         dstW = dstBounds.width(),
+         dstH = dstBounds.height();
+
+    SkImageInfo dstInfo = SkImageInfo::Make(dstW, dstH, inputBM.colorType(), inputBM.alphaType());
+
+    SkBitmap dst;
+    if (!dst.tryAllocPixels(dstInfo)) {
+        return nullptr;
+    }
+
+    auto bufferSizeW = calculate_buffer(windowW),
+         bufferSizeH = calculate_buffer(windowH);
+
+    // The amount 1024 is enough for buffers up to 10 sigma. The tmp bitmap will be
+    // allocated on the heap.
+    SkSTArenaAlloc<1024> alloc;
+    Sk4u* buffer = alloc.makeArrayDefault<Sk4u>(std::max(bufferSizeW, bufferSizeH));
+
+    // Basic Plan: The three cases to handle
+    // * Horizontal and Vertical - blur horizontally while copying values from the source to
+    //     the destination. Then, do an in-place vertical blur.
+    // * Horizontal only - blur horizontally copying values from the source to the destination.
+    // * Vertical only - blur vertically copying values from the source to the destination.
+
+    // Default to vertical only blur case. If a horizontal blur is needed, then these values
+    // will be adjusted while doing the horizontal blur.
+    auto intermediateSrc = static_cast<uint32_t *>(src.getPixels());
+    auto intermediateRowBytesAsPixels = src.rowBytesAsPixels();
+    auto intermediateWidth = srcW;
+
+    // Because the border is calculated before the fork of the GPU/CPU path. The border is
+    // the maximum of the two rendering methods. In the case where sigma is zero, then the
+    // src and dst left values are the same. If sigma is small resulting in a window size of
+    // 1, then border calculations add some pixels which will always be zero. Inset the
+    // destination by those zero pixels. This case is very rare.
+    auto intermediateDst = dst.getAddr32(srcBounds.left(), 0);
+
+    // The following code is executed very rarely, I have never seen it in a real web
+    // page. If sigma is small but not zero then shared GPU/CPU border calculation
+    // code adds extra pixels for the border. Just clear everything to clear those pixels.
+    // This solution is overkill, but very simple.
+    if (windowW == 1 || windowH == 1) {
+        dst.eraseColor(0);
+    }
+
+    if (windowW > 1) {
+        // Make int64 to avoid overflow in multiplication below.
+        int64_t shift = srcBounds.top() - dstBounds.top();
+
+        // For the horizontal blur, starts part way down in anticipation of the vertical blur.
+        // For a vertical sigma of zero shift should be zero. But, for small sigma,
+        // shift may be > 0 but the vertical window could be 1.
+        intermediateSrc = static_cast<uint32_t *>(dst.getPixels())
+                          + (shift > 0 ? shift * dst.rowBytesAsPixels() : 0);
+        intermediateRowBytesAsPixels = dst.rowBytesAsPixels();
+        intermediateWidth = dstW;
+        intermediateDst = static_cast<uint32_t *>(dst.getPixels());
+
+        blur_one_direction(
+                buffer, windowW,
+                srcBounds.left(), srcBounds.right(), dstBounds.right(),
+                static_cast<uint32_t *>(src.getPixels()), 1, src.rowBytesAsPixels(), srcH,
+                intermediateSrc, 1, intermediateRowBytesAsPixels);
+    }
+
+    if (windowH > 1) {
+        blur_one_direction(
+                buffer, windowH,
+                srcBounds.top(), srcBounds.bottom(), dstBounds.bottom(),
+                intermediateSrc, intermediateRowBytesAsPixels, 1, intermediateWidth,
+                intermediateDst, dst.rowBytesAsPixels(), 1);
+    }
+
+    return SkSpecialImage::MakeFromRaster(SkIRect::MakeWH(dstBounds.width(),
+                                                          dstBounds.height()),
+                                          dst, &source->props());
+}
+
+sk_sp<SkSpecialImage> SkBlurImageFilterImpl::onFilterImage(SkSpecialImage* source,
+                                                           const Context& ctx,
+                                                           SkIPoint* offset) const {
+    SkIPoint inputOffset = SkIPoint::Make(0, 0);
+
+    sk_sp<SkSpecialImage> input(this->filterInput(0, source, ctx, &inputOffset));
+    if (!input) {
+        return nullptr;
+    }
+
+    SkIRect inputBounds = SkIRect::MakeXYWH(inputOffset.fX, inputOffset.fY,
+                                            input->width(), input->height());
+
+    // Calculate the destination bounds.
+    SkIRect dstBounds;
+    if (!this->applyCropRect(this->mapContext(ctx), inputBounds, &dstBounds)) {
+        return nullptr;
+    }
+    if (!inputBounds.intersect(dstBounds)) {
+        return nullptr;
+    }
+
+    // Save the offset in preparation to make all rectangles relative to the inputOffset.
+    SkIPoint resultOffset = SkIPoint::Make(dstBounds.fLeft, dstBounds.fTop);
+
+    // Make all bounds relative to the inputOffset.
+    inputBounds.offset(-inputOffset);
+    dstBounds.offset(-inputOffset);
+
+    const SkVector sigma = map_sigma(fSigma, ctx.ctm());
+    if (sigma.x() < 0 || sigma.y() < 0) {
+        return nullptr;
+    }
+
+    sk_sp<SkSpecialImage> result;
+#if SK_SUPPORT_GPU
+    if (source->isTextureBacked()) {
+        // Ensure the input is in the destination's gamut. This saves us from having to do the
+        // xform during the filter itself.
+        input = ImageToColorSpace(input.get(), ctx.outputProperties());
+
+        result = this->gpuFilter(source, sigma, input, inputBounds, dstBounds, inputOffset,
+                                 ctx.outputProperties(), &resultOffset);
+    } else
+#endif
+    {
+        result = cpu_blur(sigma, source, input, inputBounds, dstBounds);
+    }
+
+    // Return the resultOffset if the blur succeeded.
+    if (result != nullptr) {
+        *offset = resultOffset;
+    }
+    return result;
+}
+
+#if SK_SUPPORT_GPU
+sk_sp<SkSpecialImage> SkBlurImageFilterImpl::gpuFilter(
+        SkSpecialImage *source, SkVector sigma, const sk_sp<SkSpecialImage> &input,
+        SkIRect inputBounds, SkIRect dstBounds, SkIPoint inputOffset,
+        const OutputProperties& outProps, SkIPoint* offset) const
+{
+    if (0 == sigma.x() && 0 == sigma.y()) {
+        offset->fX = inputBounds.x() + inputOffset.fX;
+        offset->fY = inputBounds.y() + inputOffset.fY;
+        return input->makeSubset(inputBounds);
+    }
+
+    GrContext* context = source->getContext();
+
+    sk_sp<GrTextureProxy> inputTexture(input->asTextureProxyRef(context));
+    if (!inputTexture) {
+        return nullptr;
+    }
+
+    // Typically, we would create the RTC with the output's color space (from ctx), but we
+    // always blur in the PixelConfig of the *input*. Those might not be compatible (if they
+    // have different transfer functions). We've already guaranteed that those color spaces
+    // have the same gamut, so in this case, we do everything in the input's color space.
+    // ...
+    // Unless the output is legacy. In that case, the input could be almost anything (if we're
+    // using SkColorSpaceXformCanvas), but we can't make a corresponding RTC. We don't care to,
+    // either, we want to do our blending (and blurring) without any color correction, so pass
+    // nullptr here, causing us to operate entirely in the input's color space, with no decoding.
+    // Then, when we create the output image later, we tag it with the input's color space, so
+    // it will be tagged correctly, regardless of how we created the intermediate RTCs.
+    sk_sp<GrRenderTargetContext> renderTargetContext(SkGpuBlurUtils::GaussianBlur(
+                            context,
+                            std::move(inputTexture),
+                            outProps.colorSpace() ? sk_ref_sp(input->getColorSpace()) : nullptr,
+                            dstBounds,
+                            inputBounds,
+                            sigma.x(),
+                            sigma.y(),
+                            to_texture_domain_mode(fTileMode),
+                            input->alphaType()));
+    if (!renderTargetContext) {
+        return nullptr;
+    }
+
+    return SkSpecialImage::MakeDeferredFromGpu(
+            context,
+            SkIRect::MakeWH(dstBounds.width(), dstBounds.height()),
+            kNeedNewImageUniqueID_SpecialImage,
+            renderTargetContext->asTextureProxyRef(),
+            sk_ref_sp(input->getColorSpace()),
+            &source->props());
+}
+#endif
+
+sk_sp<SkImageFilter> SkBlurImageFilterImpl::onMakeColorSpace(SkColorSpaceXformer* xformer)
+const {
+    SkASSERT(1 == this->countInputs());
+
+    auto input = xformer->apply(this->getInput(0));
+    if (this->getInput(0) != input.get()) {
+        return SkBlurImageFilter::Make(fSigma.width(), fSigma.height(), std::move(input),
+                                       this->getCropRectIfSet(), fTileMode);
+    }
+    return this->refMe();
+}
+
+SkRect SkBlurImageFilterImpl::computeFastBounds(const SkRect& src) const {
+    SkRect bounds = this->getInput(0) ? this->getInput(0)->computeFastBounds(src) : src;
+    bounds.outset(fSigma.width() * 3, fSigma.height() * 3);
+    return bounds;
+}
+
+SkIRect SkBlurImageFilterImpl::onFilterNodeBounds(const SkIRect& src, const SkMatrix& ctm,
+                                                  MapDirection, const SkIRect* inputRect) const {
+    SkVector sigma = map_sigma(fSigma, ctm);
+    return src.makeOutset(SkScalarCeilToInt(sigma.x() * 3), SkScalarCeilToInt(sigma.y() * 3));
+}