Bug 1209715 - Add operator overloads for combining DrawResults. r=tn

image/DrawResult.h

@@ -0,0 +1,89 @@
+/* -*- 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_DrawResult_h
+#define mozilla_image_DrawResult_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/Likely.h"
+
+namespace mozilla {
+namespace image {
+
+/**
+ * An enumeration representing the result of a drawing operation.
+ *
+ * Most users of DrawResult will only be interested in whether the value is
+ * SUCCESS or not. The other values are primarily useful for debugging and error
+ * handling.
+ *
+ * SUCCESS: We successfully drew a completely decoded frame of the requested
+ * size. Drawing again with FLAG_SYNC_DECODE would not change the result.
+ *
+ * INCOMPLETE: We successfully drew a frame that was partially decoded. (Note
+ * that successfully drawing a partially decoded frame may not actually draw any
+ * pixels!) Drawing again with FLAG_SYNC_DECODE would improve the result.
+ *
+ * WRONG_SIZE: We successfully drew a wrongly-sized frame that had to be scaled.
+ * This is only returned if drawing again with FLAG_SYNC_DECODE would improve
+ * the result; if the size requested was larger than the intrinsic size of the
+ * image, for example, we would generally have to scale whether FLAG_SYNC_DECODE
+ * was specified or not, and therefore we would not return WRONG_SIZE.
+ *
+ * NOT_READY: We failed to draw because no decoded version of the image was
+ * available. Drawing again with FLAG_SYNC_DECODE would improve the result.
+ * (Though FLAG_SYNC_DECODE will not necessarily work until after the image's
+ * load event!)
+ *
+ * TEMPORARY_ERROR: We failed to draw due to a temporary error. Drawing may
+ * succeed at a later time.
+ *
+ * BAD_IMAGE: We failed to draw because the image has an error. This is a
+ * permanent condition.
+ *
+ * BAD_ARGS: We failed to draw because bad arguments were passed to draw().
+ */
+enum class DrawResult : uint8_t
+{
+  SUCCESS,
+  INCOMPLETE,
+  WRONG_SIZE,
+  NOT_READY,
+  TEMPORARY_ERROR,
+  BAD_IMAGE,
+  BAD_ARGS
+};
+
+/**
+ * You can combine DrawResults with &. By analogy to bitwise-&, the result is
+ * DrawResult::SUCCESS only if both operands are DrawResult::SUCCESS. Otherwise,
+ * a failing DrawResult is returned; we favor the left operand's failure when
+ * deciding which failure to return, with the exception that we always prefer
+ * any other kind of failure over DrawResult::BAD_IMAGE, since other failures
+ * are recoverable and we want to know if any recoverable failures occurred.
+ */
+inline DrawResult
+operator&(const DrawResult aLeft, const DrawResult aRight)
+{
+  if (MOZ_LIKELY(aLeft == DrawResult::SUCCESS)) {
+    return aRight;
+  }
+  if (aLeft == DrawResult::BAD_IMAGE && aRight != DrawResult::SUCCESS) {
+    return aRight;
+  }
+  return aLeft;
+}
+
+inline DrawResult&
+operator&=(DrawResult& aLeft, const DrawResult aRight)
+{
+  aLeft = aLeft & aRight;
+  return aLeft;
+}
+
+} // namespace image
+} // namespace mozilla
+
+#endif // mozilla_image_DrawResult_h

image/imgIContainer.idl

@@ -7,6 +7,7 @@
 #include "nsISupports.idl"
 
 %{C++
+#include "DrawResult.h"
 #include "gfxContext.h"
 #include "gfxMatrix.h"
 #include "gfxRect.h"
@@ -39,50 +40,6 @@ namespace image {
 class ImageRegion;
 struct Orientation;
 
-/**
- * An enumeration representing the result of a drawing operation.
- *
- * Most users of DrawResult will only be interested in whether the value is
- * SUCCESS or not. The other values are primarily useful for debugging and error
- * handling.
- *
- * SUCCESS: We successfully drew a completely decoded frame of the requested
- * size. Drawing again with FLAG_SYNC_DECODE would not change the result.
- *
- * INCOMPLETE: We successfully drew a frame that was partially decoded. (Note
- * that successfully drawing a partially decoded frame may not actually draw any
- * pixels!) Drawing again with FLAG_SYNC_DECODE would improve the result.
- *
- * WRONG_SIZE: We successfully drew a wrongly-sized frame that had to be scaled.
- * This is only returned if drawing again with FLAG_SYNC_DECODE would improve
- * the result; if the size requested was larger than the intrinsic size of the
- * image, for example, we would generally have to scale whether FLAG_SYNC_DECODE
- * was specified or not, and therefore we would not return WRONG_SIZE.
- *
- * NOT_READY: We failed to draw because no decoded version of the image was
- * available. Drawing again with FLAG_SYNC_DECODE would improve the result.
- * (Though FLAG_SYNC_DECODE will not necessarily work until after the image's
- * load event!)
- *
- * TEMPORARY_ERROR: We failed to draw due to a temporary error. Drawing may
- * succeed at a later time.
- *
- * BAD_IMAGE: We failed to draw because the image has an error. This is a
- * permanent condition.
- *
- * BAD_ARGS: We failed to draw because bad arguments were passed to draw().
- */
-enum class DrawResult : uint8_t
-{
-  SUCCESS,
-  INCOMPLETE,
-  WRONG_SIZE,
-  NOT_READY,
-  TEMPORARY_ERROR,
-  BAD_IMAGE,
-  BAD_ARGS
-};
-
 }
 }
 

image/moz.build

@@ -36,6 +36,7 @@ XPIDL_SOURCES += [
 XPIDL_MODULE = 'imglib2'
 
 EXPORTS += [
+    'DrawResult.h',
     'ImageCacheKey.h',
     'ImageLogging.h',
     'ImageOps.h',