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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* 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 */
* Downscaler is a high-quality, streaming image downscaler based upon Skia's
* scaling implementation.
#ifndef mozilla_image_Downscaler_h
#define mozilla_image_Downscaler_h
#include "mozilla/Maybe.h"
#include "mozilla/UniquePtr.h"
#include "gfxPoint.h"
#include "nsRect.h"
#include "mozilla/gfx/ConvolutionFilter.h"
#include "mozilla/gfx/Matrix.h"
namespace mozilla {
namespace image {
* DownscalerInvalidRect wraps two invalidation rects: one in terms of the
* original image size, and one in terms of the target size.
struct DownscalerInvalidRect {
nsIntRect mOriginalSizeRect;
nsIntRect mTargetSizeRect;
* Downscaler is a high-quality, streaming image downscaler based upon Skia's
* scaling implementation.
* Decoders can construct a Downscaler once they know their target size, then
* call BeginFrame() for each frame they decode. They should write a decoded row
* into the buffer returned by RowBuffer(), and then call CommitRow() to signal
* that they have finished.
* Because invalidations need to be computed in terms of the scaled version of
* the image, Downscaler also tracks them. Decoders can call HasInvalidation()
* and TakeInvalidRect() instead of tracking invalidations themselves.
class Downscaler {
/// Constructs a new Downscaler which to scale to size @aTargetSize.
explicit Downscaler(const nsIntSize& aTargetSize);
const nsIntSize& OriginalSize() const { return mOriginalSize; }
const nsIntSize& TargetSize() const { return mTargetSize; }
const nsIntSize FrameSize() const {
return nsIntSize(mFrameRect.Width(), mFrameRect.Height());
const gfx::MatrixScalesDouble& Scale() const { return mScale; }
* Begins a new frame and reinitializes the Downscaler.
* @param aOriginalSize The original size of this frame, before scaling.
* @param aFrameRect The region of the original image which has data.
* Every pixel outside @aFrameRect is considered blank and
* has zero alpha.
* @param aOutputBuffer The buffer to which the Downscaler should write its
* output; this is the same buffer where the Decoder
* would write its output when not downscaling during
* decode.
* @param aHasAlpha Whether or not this frame has an alpha channel.
* Performance is a little better if it doesn't have one.
* @param aFlipVertically If true, output rows will be written to the output
* buffer in reverse order vertically, which matches
* the way they are stored in some image formats.
nsresult BeginFrame(const nsIntSize& aOriginalSize,
const Maybe<nsIntRect>& aFrameRect,
uint8_t* aOutputBuffer, bool aHasAlpha,
bool aFlipVertically = false);
bool IsFrameComplete() const {
return mCurrentInLine >= mOriginalSize.height;
/// Retrieves the buffer into which the Decoder should write each row.
uint8_t* RowBuffer() {
return mRowBuffer.get() + mFrameRect.X() * sizeof(uint32_t);
/// Clears the current row buffer.
void ClearRow() { ClearRestOfRow(0); }
/// Clears the current row buffer starting at @aStartingAtCol.
void ClearRestOfRow(uint32_t aStartingAtCol);
/// Signals that the decoder has finished writing a row into the row buffer.
void CommitRow();
/// Returns true if there is a non-empty invalid rect available.
bool HasInvalidation() const;
/// Takes the Downscaler's current invalid rect and resets it.
DownscalerInvalidRect TakeInvalidRect();
* Resets the Downscaler's position in the image, for a new progressive pass
* over the same frame. Because the same data structures can be reused, this
* is more efficient than calling BeginFrame.
void ResetForNextProgressivePass();
void DownscaleInputLine();
void ReleaseWindow();
void SkipToRow(int32_t aRow);
nsIntSize mOriginalSize;
nsIntSize mTargetSize;
nsIntRect mFrameRect;
gfx::MatrixScalesDouble mScale;
uint8_t* mOutputBuffer;
UniquePtr<uint8_t[]> mRowBuffer;
UniquePtr<uint8_t*[]> mWindow;
gfx::ConvolutionFilter mXFilter;
gfx::ConvolutionFilter mYFilter;
int32_t mWindowCapacity;
int32_t mLinesInBuffer;
int32_t mPrevInvalidatedLine;
int32_t mCurrentOutLine;
int32_t mCurrentInLine;
bool mHasAlpha : 1;
bool mFlipVertically : 1;
} // namespace image
} // namespace mozilla
#endif // mozilla_image_Downscaler_h