image/DecoderFlags.h
author Henri Sivonen <hsivonen@hsivonen.fi>
Fri, 06 Jul 2018 10:44:43 +0300
changeset 489140 4ef0f163fdeb9afeddd87b37bfd987298c038542
parent 430942 c856f513264340a2d6c2b70f71f345b5e4c8d6c0
child 495278 1b1e25b0b345cf3774ae7d186dc082430420e056
permissions -rw-r--r--
Bug 1402247 - Use encoding_rs for XPCOM string encoding conversions. r=Nika,erahm,froydnj. Correctness improvements: * UTF errors are handled safely per spec instead of dangerously truncating strings. * There are fewer converter implementations. Performance improvements: * The old code did exact buffer length math, which meant doing UTF math twice on each input string (once for length calculation and another time for conversion). Exact length math is more complicated when handling errors properly, which the old code didn't do. The new code does UTF math on the string content only once (when converting) but risks allocating more than once. There are heuristics in place to lower the probability of reallocation in cases where the double math avoidance isn't enough of a saving to absorb an allocation and memcpy. * Previously, in UTF-16 <-> UTF-8 conversions, an ASCII prefix was optimized but a single non-ASCII code point pessimized the rest of the string. The new code tries to get back on the fast ASCII path. * UTF-16 to Latin1 conversion guarantees less about handling of out-of-range input to eliminate an operation from the inner loop on x86/x86_64. * When assigning to a pre-existing string, the new code tries to reuse the old buffer instead of first releasing the old buffer and then allocating a new one. * When reallocating from the new code, the memcpy covers only the data that is part of the logical length of the old string instead of memcpying the whole capacity. (For old callers old excess memcpy behavior is preserved due to bogus callers. See bug 1472113.) * UTF-8 strings in XPConnect that are in the Latin1 range are passed to SpiderMonkey as Latin1. New features: * Conversion between UTF-8 and Latin1 is added in order to enable faster future interop between Rust code (or otherwise UTF-8-using code) and text node and SpiderMonkey code that uses Latin1. MozReview-Commit-ID: JaJuExfILM9

/* -*- 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 http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_image_DecoderFlags_h
#define mozilla_image_DecoderFlags_h

#include "mozilla/TypedEnumBits.h"

namespace mozilla {
namespace image {

/**
 * Flags that influence decoder behavior. Note that these flags *don't*
 * influence the logical content of the surfaces that the decoder generates, so
 * they're not in a factor in SurfaceCache lookups and the like. These flags
 * instead either influence which surfaces are generated at all or the tune the
 * decoder's behavior for a particular scenario.
 */
enum class DecoderFlags : uint8_t
{
  FIRST_FRAME_ONLY               = 1 << 0,
  IS_REDECODE                    = 1 << 1,
  IMAGE_IS_TRANSIENT             = 1 << 2,
  ASYNC_NOTIFY                   = 1 << 3,

  /**
   * By default, a surface is considered substitutable. That means callers are
   * willing to accept a less than ideal match to display. If a caller requires
   * a specific size and won't accept alternatives, then this flag should be
   * set.
   */
  CANNOT_SUBSTITUTE              = 1 << 4
};
MOZ_MAKE_ENUM_CLASS_BITWISE_OPERATORS(DecoderFlags)

/**
 * @return the default set of decode flags.
 */
inline DecoderFlags
DefaultDecoderFlags()
{
  return DecoderFlags();
}

} // namespace image
} // namespace mozilla

#endif // mozilla_image_DecoderFlags_h