image/ImgDrawResult.h

   1 /* -*- Mode: C++; tab-width: 2; 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 #ifndef mozilla_image_ImgDrawResult_h
   7 #define mozilla_image_ImgDrawResult_h
   8
   9 #include <cstdint>  // for uint8_t
  10 #include "mozilla/Attributes.h"
  11 #include "mozilla/Likely.h"
  12
  13 namespace mozilla {
  14 namespace image {
  15
  16 /**
  17  * An enumeration representing the result of a drawing operation.
  18  *
  19  * Most users of ImgDrawResult will only be interested in whether the value is
  20  * SUCCESS or not. The other values are primarily useful for debugging and error
  21  * handling.
  22  *
  23  * SUCCESS: We successfully drew a completely decoded frame of the requested
  24  * size. Drawing again with FLAG_SYNC_DECODE would not change the result.
  25  *
  26  * SUCCESS_NOT_COMPLETE: The image was drawn successfully and completely, but
  27  * it hasn't notified about the sync-decode yet. This can only happen when
  28  * layout pokes at the internal image state beforehand via the result of
  29  * StartDecodingWithResult. This should probably go away eventually, somehow,
  30  * see bug 1471583.
  31  *
  32  * INCOMPLETE: We successfully drew a frame that was partially decoded. (Note
  33  * that successfully drawing a partially decoded frame may not actually draw any
  34  * pixels!) Drawing again with FLAG_SYNC_DECODE would improve the result.
  35  *
  36  * WRONG_SIZE: We successfully drew a wrongly-sized frame that had to be scaled.
  37  * This is only returned if drawing again with FLAG_SYNC_DECODE would improve
  38  * the result; if the size requested was larger than the intrinsic size of the
  39  * image, for example, we would generally have to scale whether FLAG_SYNC_DECODE
  40  * was specified or not, and therefore we would not return WRONG_SIZE.
  41  *
  42  * NOT_READY: We failed to draw because no decoded version of the image was
  43  * available. Drawing again with FLAG_SYNC_DECODE would improve the result.
  44  * (Though FLAG_SYNC_DECODE will not necessarily work until after the image's
  45  * load event!)
  46  *
  47  * TEMPORARY_ERROR: We failed to draw due to a temporary error. Drawing may
  48  * succeed at a later time.
  49  *
  50  * BAD_IMAGE: We failed to draw because the image has an error. This is a
  51  * permanent condition.
  52  *
  53  * BAD_ARGS: We failed to draw because bad arguments were passed to draw().
  54  *
  55  * NOT_SUPPORTED: The requested operation is not supported, but the image is
  56  *                otherwise valid.
  57  */
  58 enum class [[nodiscard]] ImgDrawResult : uint8_t{
  59     SUCCESS,      SUCCESS_NOT_COMPLETE, INCOMPLETE, WRONG_SIZE,
  60     NOT_READY,    TEMPORARY_ERROR,      BAD_IMAGE,  BAD_ARGS,
  61     NOT_SUPPORTED};
  62
  63 /**
  64  * You can combine ImgDrawResults with &. By analogy to bitwise-&, the result is
  65  * ImgDrawResult::SUCCESS only if both operands are ImgDrawResult::SUCCESS.
  66  * Otherwise, a failing ImgDrawResult is returned; we favor the left operand's
  67  * failure when deciding which failure to return, with the exception that we
  68  * always prefer any other kind of failure over ImgDrawResult::BAD_IMAGE, since
  69  * other failures are recoverable and we want to know if any recoverable
  70  * failures occurred.
  71  */
  72 inline ImgDrawResult operator&(const ImgDrawResult aLeft,
  73                                const ImgDrawResult aRight) {
  74   if (MOZ_LIKELY(aLeft == ImgDrawResult::SUCCESS)) {
  75     return aRight;
  76   }
  77
  78   if (aLeft == ImgDrawResult::NOT_SUPPORTED ||
  79       aRight == ImgDrawResult::NOT_SUPPORTED) {
  80     return ImgDrawResult::NOT_SUPPORTED;
  81   }
  82
  83   if ((aLeft == ImgDrawResult::BAD_IMAGE ||
  84        aLeft == ImgDrawResult::SUCCESS_NOT_COMPLETE) &&
  85       aRight != ImgDrawResult::SUCCESS &&
  86       aRight != ImgDrawResult::SUCCESS_NOT_COMPLETE) {
  87     return aRight;
  88   }
  89   return aLeft;
  90 }
  91
  92 inline ImgDrawResult& operator&=(ImgDrawResult& aLeft,
  93                                  const ImgDrawResult aRight) {
  94   aLeft = aLeft & aRight;
  95   return aLeft;
  96 }
  97
  98 /**
  99  * A struct used during painting to provide input flags to determine how
 100  * imagelib draw calls should behave and an output ImgDrawResult to return
 101  * information about the result of any imagelib draw calls that may have
 102  * occurred.
 103  */
 104 struct imgDrawingParams {
 105   explicit imgDrawingParams(uint32_t aImageFlags = 0)
 106       : imageFlags(aImageFlags), result(ImgDrawResult::SUCCESS) {}
 107
 108   const uint32_t imageFlags;  // imgIContainer::FLAG_* image flags to pass to
 109                               // image lib draw calls.
 110   ImgDrawResult result;       // To return results from image lib painting.
 111 };
 112
 113 }  // namespace image
 114 }  // namespace mozilla
 115
 116 #endif  // mozilla_image_ImgDrawResult_h