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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * DownscalingSurfaceFilter is a SurfaceFilter implementation for use with
+ * SurfacePipe which performs Lanczos downscaling.
+ *
+ * It's in this header file, separated from the other SurfaceFilters, because
+ * some preprocessor magic is necessary to ensure that there aren't compilation
+ * issues on platforms where Skia is unavailable.
+ */
+
+#ifndef mozilla_image_DownscalingFilter_h
+#define mozilla_image_DownscalingFilter_h
+
+#include <algorithm>
+#include <ctime>
+#include <stdint.h>
+
+#include "mozilla/Maybe.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/gfx/2D.h"
+
+#include "mozilla/gfx/ConvolutionFilter.h"
+
+#include "SurfacePipe.h"
+
+namespace mozilla {
+namespace image {
+
+//////////////////////////////////////////////////////////////////////////////
+// DownscalingFilter
+//////////////////////////////////////////////////////////////////////////////
+
+template <typename Next>
+class DownscalingFilter;
+
+/**
+ * A configuration struct for DownscalingConfig.
+ */
+struct DownscalingConfig {
+ template <typename Next>
+ using Filter = DownscalingFilter<Next>;
+ gfx::IntSize mInputSize; /// The size of the input image. We'll downscale
+ /// from this size to the input size of the next
+ /// SurfaceFilter in the chain.
+ gfx::SurfaceFormat mFormat; /// The pixel format - BGRA or BGRX. (BGRX has
+ /// slightly better performance.)
+};
+
+/**
+ * DownscalingFilter performs Lanczos downscaling, taking image input data at
+ * one size and outputting it rescaled to a different size.
+ *
+ * The 'Next' template parameter specifies the next filter in the chain.
+ */
+template <typename Next>
+class DownscalingFilter final : public SurfaceFilter {
+ public:
+ DownscalingFilter()
+ : mWindowCapacity(0),
+ mRowsInWindow(0),
+ mInputRow(0),
+ mOutputRow(0),
+ mHasAlpha(true) {}
+
+ ~DownscalingFilter() { ReleaseWindow(); }
+
+ template <typename... Rest>
+ nsresult Configure(const DownscalingConfig& aConfig, const Rest&... aRest) {
+ nsresult rv = mNext.Configure(aRest...);
+ if (NS_FAILED(rv)) {
+ return rv;
+ }
+
+ if (mNext.InputSize() == aConfig.mInputSize) {
+ NS_WARNING("Created a downscaler, but not downscaling?");
+ return NS_ERROR_INVALID_ARG;
+ }
+ if (mNext.InputSize().width > aConfig.mInputSize.width) {
+ NS_WARNING("Created a downscaler, but width is larger");
+ return NS_ERROR_INVALID_ARG;
+ }
+ if (mNext.InputSize().height > aConfig.mInputSize.height) {
+ NS_WARNING("Created a downscaler, but height is larger");
+ return NS_ERROR_INVALID_ARG;
+ }
+ if (aConfig.mInputSize.width <= 0 || aConfig.mInputSize.height <= 0) {
+ NS_WARNING("Invalid input size for DownscalingFilter");
+ return NS_ERROR_INVALID_ARG;
+ }
+
+ mInputSize = aConfig.mInputSize;
+ gfx::IntSize outputSize = mNext.InputSize();
+ mScale =
+ gfx::MatrixScalesDouble(double(mInputSize.width) / outputSize.width,
+ double(mInputSize.height) / outputSize.height);
+ mHasAlpha = aConfig.mFormat == gfx::SurfaceFormat::OS_RGBA;
+
+ ReleaseWindow();
+
+ auto resizeMethod = gfx::ConvolutionFilter::ResizeMethod::LANCZOS3;
+ if (!mXFilter.ComputeResizeFilter(resizeMethod, mInputSize.width,
+ outputSize.width) ||
+ !mYFilter.ComputeResizeFilter(resizeMethod, mInputSize.height,
+ outputSize.height)) {
+ NS_WARNING("Failed to compute filters for image downscaling");
+ return NS_ERROR_OUT_OF_MEMORY;
+ }
+
+ // Allocate the buffer, which contains scanlines of the input image.
+ mRowBuffer.reset(new (fallible)
+ uint8_t[PaddedWidthInBytes(mInputSize.width)]);
+ if (MOZ_UNLIKELY(!mRowBuffer)) {
+ return NS_ERROR_OUT_OF_MEMORY;
+ }
+
+ // Clear the buffer to avoid writing uninitialized memory to the output.
+ memset(mRowBuffer.get(), 0, PaddedWidthInBytes(mInputSize.width));
+
+ // Allocate the window, which contains horizontally downscaled scanlines.
+ // (We can store scanlines which are already downscaled because our
+ // downscaling filter is separable.)
+ mWindowCapacity = mYFilter.MaxFilter();
+ mWindow.reset(new (fallible) uint8_t*[mWindowCapacity]);
+ if (MOZ_UNLIKELY(!mWindow)) {
+ return NS_ERROR_OUT_OF_MEMORY;
+ }
+
+ // Allocate the "window" of recent rows that we keep in memory as input for
+ // the downscaling code. We intentionally iterate through the entire array
+ // even if an allocation fails, to ensure that all the pointers in it are
+ // either valid or nullptr. That in turn ensures that ReleaseWindow() can
+ // clean up correctly.
+ bool anyAllocationFailed = false;
+ const size_t windowRowSizeInBytes = PaddedWidthInBytes(outputSize.width);
+ for (int32_t i = 0; i < mWindowCapacity; ++i) {
+ mWindow[i] = new (fallible) uint8_t[windowRowSizeInBytes];
+ anyAllocationFailed = anyAllocationFailed || mWindow[i] == nullptr;
+ }
+
+ if (MOZ_UNLIKELY(anyAllocationFailed)) {
+ return NS_ERROR_OUT_OF_MEMORY;
+ }
+
+ ConfigureFilter(mInputSize, sizeof(uint32_t));
+ return NS_OK;
+ }
+
+ Maybe<SurfaceInvalidRect> TakeInvalidRect() override {
+ Maybe<SurfaceInvalidRect> invalidRect = mNext.TakeInvalidRect();
+
+ if (invalidRect) {
+ // Compute the input space invalid rect by scaling.
+ invalidRect->mInputSpaceRect.ScaleRoundOut(mScale.xScale, mScale.yScale);
+ }
+
+ return invalidRect;
+ }
+
+ protected:
+ uint8_t* DoResetToFirstRow() override {
+ mNext.ResetToFirstRow();
+
+ mInputRow = 0;
+ mOutputRow = 0;
+ mRowsInWindow = 0;
+
+ return GetRowPointer();
+ }
+
+ uint8_t* DoAdvanceRowFromBuffer(const uint8_t* aInputRow) override {
+ if (mInputRow >= mInputSize.height) {
+ NS_WARNING("Advancing DownscalingFilter past the end of the input");
+ return nullptr;
+ }
+
+ if (mOutputRow >= mNext.InputSize().height) {
+ NS_WARNING("Advancing DownscalingFilter past the end of the output");
+ return nullptr;
+ }
+
+ int32_t filterOffset = 0;
+ int32_t filterLength = 0;
+ mYFilter.GetFilterOffsetAndLength(mOutputRow, &filterOffset, &filterLength);
+
+ int32_t inputRowToRead = filterOffset + mRowsInWindow;
+ MOZ_ASSERT(mInputRow <= inputRowToRead, "Reading past end of input");
+ if (mInputRow == inputRowToRead) {
+ MOZ_RELEASE_ASSERT(mRowsInWindow < mWindowCapacity,
+ "Need more rows than capacity!");
+ mXFilter.ConvolveHorizontally(aInputRow, mWindow[mRowsInWindow++],
+ mHasAlpha);
+ }
+
+ MOZ_ASSERT(mOutputRow < mNext.InputSize().height,
+ "Writing past end of output");
+
+ while (mRowsInWindow >= filterLength) {
+ DownscaleInputRow();
+
+ if (mOutputRow == mNext.InputSize().height) {
+ break; // We're done.
+ }
+
+ mYFilter.GetFilterOffsetAndLength(mOutputRow, &filterOffset,
+ &filterLength);
+ }
+
+ mInputRow++;
+
+ return mInputRow < mInputSize.height ? GetRowPointer() : nullptr;
+ }
+
+ uint8_t* DoAdvanceRow() override {
+ return DoAdvanceRowFromBuffer(mRowBuffer.get());
+ }
+
+ private:
+ uint8_t* GetRowPointer() const { return mRowBuffer.get(); }
+
+ static size_t PaddedWidthInBytes(size_t aLogicalWidth) {
+ // Convert from width in BGRA/BGRX pixels to width in bytes, padding
+ // to handle overreads by the SIMD code inside Skia.
+ return gfx::ConvolutionFilter::PadBytesForSIMD(aLogicalWidth *
+ sizeof(uint32_t));
+ }
+
+ void DownscaleInputRow() {
+ MOZ_ASSERT(mOutputRow < mNext.InputSize().height,
+ "Writing past end of output");
+
+ int32_t filterOffset = 0;
+ int32_t filterLength = 0;
+ mYFilter.GetFilterOffsetAndLength(mOutputRow, &filterOffset, &filterLength);
+
+ mNext.template WriteUnsafeComputedRow<uint32_t>([&](uint32_t* aRow,
+ uint32_t aLength) {
+ mYFilter.ConvolveVertically(mWindow.get(),
+ reinterpret_cast<uint8_t*>(aRow), mOutputRow,
+ mXFilter.NumValues(), mHasAlpha);
+ });
+
+ mOutputRow++;
+
+ if (mOutputRow == mNext.InputSize().height) {
+ return; // We're done.
+ }
+
+ int32_t newFilterOffset = 0;
+ int32_t newFilterLength = 0;
+ mYFilter.GetFilterOffsetAndLength(mOutputRow, &newFilterOffset,
+ &newFilterLength);
+
+ int diff = newFilterOffset - filterOffset;
+ MOZ_ASSERT(diff >= 0, "Moving backwards in the filter?");
+
+ // Shift the buffer. We're just moving pointers here, so this is cheap.
+ mRowsInWindow -= diff;
+ mRowsInWindow = std::min(std::max(mRowsInWindow, 0), mWindowCapacity);
+
+ // If we already have enough rows to satisfy the filter, there is no need
+ // to swap as we won't be writing more before the next convolution.
+ if (filterLength > mRowsInWindow) {
+ for (int32_t i = 0; i < mRowsInWindow; ++i) {
+ std::swap(mWindow[i], mWindow[filterLength - mRowsInWindow + i]);
+ }
+ }
+ }
+
+ void ReleaseWindow() {
+ if (!mWindow) {
+ return;
+ }
+
+ for (int32_t i = 0; i < mWindowCapacity; ++i) {
+ delete[] mWindow[i];
+ }
+
+ mWindow = nullptr;
+ mWindowCapacity = 0;
+ }
+
+ Next mNext; /// The next SurfaceFilter in the chain.
+
+ gfx::IntSize mInputSize; /// The size of the input image.
+ gfx::MatrixScalesDouble mScale; /// The scale factors in each dimension.
+ /// Computed from @mInputSize and
+ /// the next filter's input size.
+
+ UniquePtr<uint8_t[]> mRowBuffer; /// The buffer into which input is written.
+ UniquePtr<uint8_t*[]> mWindow; /// The last few rows which were written.
+
+ gfx::ConvolutionFilter mXFilter; /// The Lanczos filter in X.
+ gfx::ConvolutionFilter mYFilter; /// The Lanczos filter in Y.
+
+ int32_t mWindowCapacity; /// How many rows the window contains.
+
+ int32_t mRowsInWindow; /// How many rows we've buffered in the window.
+ int32_t mInputRow; /// The current row we're reading. (0-indexed)
+ int32_t mOutputRow; /// The current row we're writing. (0-indexed)
+
+ bool mHasAlpha; /// If true, the image has transparency.
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif // mozilla_image_DownscalingFilter_h