91 lines
3.1 KiB
C++
91 lines
3.1 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_image_DrawResult_h
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#define mozilla_image_DrawResult_h
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#include <cstdint> // for uint8_t
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#include "mozilla/Attributes.h"
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#include "mozilla/Likely.h"
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namespace mozilla {
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namespace image {
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/**
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* An enumeration representing the result of a drawing operation.
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*
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* Most users of DrawResult will only be interested in whether the value is
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* SUCCESS or not. The other values are primarily useful for debugging and error
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* handling.
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*
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* SUCCESS: We successfully drew a completely decoded frame of the requested
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* size. Drawing again with FLAG_SYNC_DECODE would not change the result.
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*
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* INCOMPLETE: We successfully drew a frame that was partially decoded. (Note
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* that successfully drawing a partially decoded frame may not actually draw any
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* pixels!) Drawing again with FLAG_SYNC_DECODE would improve the result.
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*
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* WRONG_SIZE: We successfully drew a wrongly-sized frame that had to be scaled.
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* This is only returned if drawing again with FLAG_SYNC_DECODE would improve
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* the result; if the size requested was larger than the intrinsic size of the
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* image, for example, we would generally have to scale whether FLAG_SYNC_DECODE
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* was specified or not, and therefore we would not return WRONG_SIZE.
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*
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* NOT_READY: We failed to draw because no decoded version of the image was
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* available. Drawing again with FLAG_SYNC_DECODE would improve the result.
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* (Though FLAG_SYNC_DECODE will not necessarily work until after the image's
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* load event!)
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*
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* TEMPORARY_ERROR: We failed to draw due to a temporary error. Drawing may
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* succeed at a later time.
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*
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* BAD_IMAGE: We failed to draw because the image has an error. This is a
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* permanent condition.
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*
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* BAD_ARGS: We failed to draw because bad arguments were passed to draw().
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*/
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enum class MOZ_MUST_USE_TYPE DrawResult : uint8_t
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{
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SUCCESS,
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INCOMPLETE,
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WRONG_SIZE,
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NOT_READY,
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TEMPORARY_ERROR,
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BAD_IMAGE,
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BAD_ARGS
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};
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/**
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* You can combine DrawResults with &. By analogy to bitwise-&, the result is
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* DrawResult::SUCCESS only if both operands are DrawResult::SUCCESS. Otherwise,
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* a failing DrawResult is returned; we favor the left operand's failure when
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* deciding which failure to return, with the exception that we always prefer
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* any other kind of failure over DrawResult::BAD_IMAGE, since other failures
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* are recoverable and we want to know if any recoverable failures occurred.
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*/
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inline DrawResult
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operator&(const DrawResult aLeft, const DrawResult aRight)
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{
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if (MOZ_LIKELY(aLeft == DrawResult::SUCCESS)) {
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return aRight;
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}
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if (aLeft == DrawResult::BAD_IMAGE && aRight != DrawResult::SUCCESS) {
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return aRight;
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}
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return aLeft;
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}
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inline DrawResult&
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operator&=(DrawResult& aLeft, const DrawResult aRight)
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{
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aLeft = aLeft & aRight;
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return aLeft;
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}
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} // namespace image
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} // namespace mozilla
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#endif // mozilla_image_DrawResult_h
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