image/Downscaler.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  *
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /**
   8  * Downscaler is a high-quality, streaming image downscaler based upon Skia's
   9  * scaling implementation.
  10  */
  11
  12 #ifndef mozilla_image_Downscaler_h
  13 #define mozilla_image_Downscaler_h
  14
  15 #include "mozilla/Maybe.h"
  16 #include "mozilla/UniquePtr.h"
  17 #include "gfxPoint.h"
  18 #include "nsRect.h"
  19 #include "mozilla/gfx/ConvolutionFilter.h"
  20
  21 namespace mozilla {
  22 namespace image {
  23
  24 /**
  25  * DownscalerInvalidRect wraps two invalidation rects: one in terms of the
  26  * original image size, and one in terms of the target size.
  27  */
  28 struct DownscalerInvalidRect {
  29   nsIntRect mOriginalSizeRect;
  30   nsIntRect mTargetSizeRect;
  31 };
  32
  33 /**
  34  * Downscaler is a high-quality, streaming image downscaler based upon Skia's
  35  * scaling implementation.
  36  *
  37  * Decoders can construct a Downscaler once they know their target size, then
  38  * call BeginFrame() for each frame they decode. They should write a decoded row
  39  * into the buffer returned by RowBuffer(), and then call CommitRow() to signal
  40  * that they have finished.
  41  *
  42
  43  * Because invalidations need to be computed in terms of the scaled version of
  44  * the image, Downscaler also tracks them. Decoders can call HasInvalidation()
  45  * and TakeInvalidRect() instead of tracking invalidations themselves.
  46  */
  47 class Downscaler {
  48  public:
  49   /// Constructs a new Downscaler which to scale to size @aTargetSize.
  50   explicit Downscaler(const nsIntSize& aTargetSize);
  51   ~Downscaler();
  52
  53   const nsIntSize& OriginalSize() const { return mOriginalSize; }
  54   const nsIntSize& TargetSize() const { return mTargetSize; }
  55   const nsIntSize FrameSize() const {
  56     return nsIntSize(mFrameRect.Width(), mFrameRect.Height());
  57   }
  58   const gfxSize& Scale() const { return mScale; }
  59
  60   /**
  61    * Begins a new frame and reinitializes the Downscaler.
  62    *
  63    * @param aOriginalSize The original size of this frame, before scaling.
  64    * @param aFrameRect The region of  the original image which has data.
  65    *                   Every pixel outside @aFrameRect is considered blank and
  66    *                   has zero alpha.
  67    * @param aOutputBuffer The buffer to which the Downscaler should write its
  68    *                      output; this is the same buffer where the Decoder
  69    *                      would write its output when not downscaling during
  70    *                      decode.
  71    * @param aHasAlpha Whether or not this frame has an alpha channel.
  72    *                  Performance is a little better if it doesn't have one.
  73    * @param aFlipVertically If true, output rows will be written to the output
  74    *                        buffer in reverse order vertically, which matches
  75    *                        the way they are stored in some image formats.
  76    */
  77   nsresult BeginFrame(const nsIntSize& aOriginalSize,
  78                       const Maybe<nsIntRect>& aFrameRect,
  79                       uint8_t* aOutputBuffer, bool aHasAlpha,
  80                       bool aFlipVertically = false);
  81
  82   bool IsFrameComplete() const {
  83     return mCurrentInLine >= mOriginalSize.height;
  84   }
  85
  86   /// Retrieves the buffer into which the Decoder should write each row.
  87   uint8_t* RowBuffer() {
  88     return mRowBuffer.get() + mFrameRect.X() * sizeof(uint32_t);
  89   }
  90
  91   /// Clears the current row buffer.
  92   void ClearRow() { ClearRestOfRow(0); }
  93
  94   /// Clears the current row buffer starting at @aStartingAtCol.
  95   void ClearRestOfRow(uint32_t aStartingAtCol);
  96
  97   /// Signals that the decoder has finished writing a row into the row buffer.
  98   void CommitRow();
  99
 100   /// Returns true if there is a non-empty invalid rect available.
 101   bool HasInvalidation() const;
 102
 103   /// Takes the Downscaler's current invalid rect and resets it.
 104   DownscalerInvalidRect TakeInvalidRect();
 105
 106   /**
 107    * Resets the Downscaler's position in the image, for a new progressive pass
 108    * over the same frame. Because the same data structures can be reused, this
 109    * is more efficient than calling BeginFrame.
 110    */
 111   void ResetForNextProgressivePass();
 112
 113  private:
 114   void DownscaleInputLine();
 115   void ReleaseWindow();
 116   void SkipToRow(int32_t aRow);
 117
 118   nsIntSize mOriginalSize;
 119   nsIntSize mTargetSize;
 120   nsIntRect mFrameRect;
 121   gfxSize mScale;
 122
 123   uint8_t* mOutputBuffer;
 124
 125   UniquePtr<uint8_t[]> mRowBuffer;
 126   UniquePtr<uint8_t*[]> mWindow;
 127
 128   gfx::ConvolutionFilter mXFilter;
 129   gfx::ConvolutionFilter mYFilter;
 130
 131   int32_t mWindowCapacity;
 132
 133   int32_t mLinesInBuffer;
 134   int32_t mPrevInvalidatedLine;
 135   int32_t mCurrentOutLine;
 136   int32_t mCurrentInLine;
 137
 138   bool mHasAlpha : 1;
 139   bool mFlipVertically : 1;
 140 };
 141
 142 }  // namespace image
 143 }  // namespace mozilla
 144
 145 #endif  // mozilla_image_Downscaler_h