Line data    Source code

       1             : /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
       2             :  * This Source Code Form is subject to the terms of the Mozilla Public
       3             :  * License, v. 2.0. If a copy of the MPL was not distributed with this
       4             :  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
       5             : 
       6             : #include "ImageComposite.h"
       7             : 
       8             : namespace mozilla {
       9             : 
      10             : using namespace gfx;
      11             : 
      12             : namespace layers {
      13             : 
      14             : /* static */ const float ImageComposite::BIAS_TIME_MS = 1.0f;
      15             : 
      16           0 : ImageComposite::ImageComposite()
      17             :   : mLastFrameID(-1)
      18             :   , mLastProducerID(-1)
      19           0 :   , mBias(BIAS_NONE)
      20           0 : {}
      21             : 
      22           0 : ImageComposite::~ImageComposite()
      23             : {
      24           0 : }
      25             : 
      26             : /* static */ TimeStamp
      27           0 : ImageComposite::GetBiasedTime(const TimeStamp& aInput, ImageComposite::Bias aBias)
      28             : {
      29           0 :   switch (aBias) {
      30             :   case ImageComposite::BIAS_NEGATIVE:
      31           0 :     return aInput - TimeDuration::FromMilliseconds(BIAS_TIME_MS);
      32             :   case ImageComposite::BIAS_POSITIVE:
      33           0 :     return aInput + TimeDuration::FromMilliseconds(BIAS_TIME_MS);
      34             :   default:
      35           0 :     return aInput;
      36             :   }
      37             : }
      38             : 
      39             : /* static */ ImageComposite::Bias
      40           0 : ImageComposite::UpdateBias(const TimeStamp& aCompositionTime,
      41             :                            const TimeStamp& aCompositedImageTime,
      42             :                            const TimeStamp& aNextImageTime, // may be null
      43             :                            ImageComposite::Bias aBias)
      44             : {
      45           0 :   if (aCompositedImageTime.IsNull()) {
      46           0 :     return ImageComposite::BIAS_NONE;
      47             :   }
      48           0 :   TimeDuration threshold = TimeDuration::FromMilliseconds(1.0);
      49           0 :   if (aCompositionTime - aCompositedImageTime < threshold &&
      50           0 :       aCompositionTime - aCompositedImageTime > -threshold) {
      51             :     // The chosen frame's time is very close to the composition time (probably
      52             :     // just before the current composition time, but due to previously set
      53             :     // negative bias, it could be just after the current composition time too).
      54             :     // If the inter-frame time is almost exactly equal to (a multiple of)
      55             :     // the inter-composition time, then we're in a dangerous situation because
      56             :     // jitter might cause frames to fall one side or the other of the
      57             :     // composition times, causing many frames to be skipped or duplicated.
      58             :     // Try to prevent that by adding a negative bias to the frame times during
      59             :     // the next composite; that should ensure the next frame's time is treated
      60             :     // as falling just before a composite time.
      61           0 :     return ImageComposite::BIAS_NEGATIVE;
      62             :   }
      63           0 :   if (!aNextImageTime.IsNull() &&
      64           0 :       aNextImageTime - aCompositionTime < threshold &&
      65           0 :       aNextImageTime - aCompositionTime > -threshold) {
      66             :     // The next frame's time is very close to our composition time (probably
      67             :     // just after the current composition time, but due to previously set
      68             :     // positive bias, it could be just before the current composition time too).
      69             :     // We're in a dangerous situation because jitter might cause frames to
      70             :     // fall one side or the other of the composition times, causing many frames
      71             :     // to be skipped or duplicated.
      72             :     // Try to prevent that by adding a negative bias to the frame times during
      73             :     // the next composite; that should ensure the next frame's time is treated
      74             :     // as falling just before a composite time.
      75           0 :     return ImageComposite::BIAS_POSITIVE;
      76             :   }
      77           0 :   return ImageComposite::BIAS_NONE;
      78             : }
      79             : 
      80             : int
      81           0 : ImageComposite::ChooseImageIndex() const
      82             : {
      83           0 :   if (mImages.IsEmpty()) {
      84           0 :     return -1;
      85             :   }
      86           0 :   TimeStamp now = GetCompositionTime();
      87             : 
      88           0 :   if (now.IsNull()) {
      89             :     // Not in a composition, so just return the last image we composited
      90             :     // (if it's one of the current images).
      91           0 :     for (uint32_t i = 0; i < mImages.Length(); ++i) {
      92           0 :       if (mImages[i].mFrameID == mLastFrameID &&
      93           0 :           mImages[i].mProducerID == mLastProducerID) {
      94           0 :         return i;
      95             :       }
      96             :     }
      97           0 :     return -1;
      98             :   }
      99             : 
     100           0 :   uint32_t result = 0;
     101           0 :   while (result + 1 < mImages.Length() &&
     102           0 :       GetBiasedTime(mImages[result + 1].mTimeStamp, mBias) <= now) {
     103           0 :     ++result;
     104             :   }
     105           0 :   return result;
     106             : }
     107             : 
     108           0 : const ImageComposite::TimedImage* ImageComposite::ChooseImage() const
     109             : {
     110           0 :   int index = ChooseImageIndex();
     111           0 :   return index >= 0 ? &mImages[index] : nullptr;
     112             : }
     113             : 
     114           0 : ImageComposite::TimedImage* ImageComposite::ChooseImage()
     115             : {
     116           0 :   int index = ChooseImageIndex();
     117           0 :   return index >= 0 ? &mImages[index] : nullptr;
     118             : }
     119             : 
     120             : } // namespace layers
     121             : } // namespace mozilla