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-rw-r--r--image/FrameTimeout.h114
1 files changed, 114 insertions, 0 deletions
diff --git a/image/FrameTimeout.h b/image/FrameTimeout.h
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+/* -*- 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_FrameTimeout_h
+#define mozilla_image_FrameTimeout_h
+
+#include <stdint.h>
+#include "mozilla/Assertions.h"
+
+namespace mozilla {
+namespace image {
+
+/**
+ * FrameTimeout wraps a frame timeout value (measured in milliseconds) after
+ * first normalizing it. This normalization is necessary because some tools
+ * generate incorrect frame timeout values which we nevertheless have to
+ * support. For this reason, code that deals with frame timeouts should always
+ * use a FrameTimeout value rather than the raw value from the image header.
+ */
+struct FrameTimeout {
+ /**
+ * @return a FrameTimeout of zero. This should be used only for math
+ * involving FrameTimeout values. You can't obtain a zero FrameTimeout from
+ * FromRawMilliseconds().
+ */
+ static FrameTimeout Zero() { return FrameTimeout(0); }
+
+ /// @return an infinite FrameTimeout.
+ static FrameTimeout Forever() { return FrameTimeout(-1); }
+
+ /// @return a FrameTimeout obtained by normalizing a raw timeout value.
+ static FrameTimeout FromRawMilliseconds(int32_t aRawMilliseconds) {
+ // Normalize all infinite timeouts to the same value.
+ if (aRawMilliseconds < 0) {
+ return FrameTimeout::Forever();
+ }
+
+ // Very small timeout values are problematic for two reasons: we don't want
+ // to burn energy redrawing animated images extremely fast, and broken tools
+ // generate these values when they actually want a "default" value, so such
+ // images won't play back right without normalization. For some context,
+ // see bug 890743, bug 125137, bug 139677, and bug 207059. The historical
+ // behavior of IE and Opera was:
+ // IE 6/Win:
+ // 10 - 50ms is normalized to 100ms.
+ // >50ms is used unnormalized.
+ // Opera 7 final/Win:
+ // 10ms is normalized to 100ms.
+ // >10ms is used unnormalized.
+ if (aRawMilliseconds >= 0 && aRawMilliseconds <= 10) {
+ return FrameTimeout(100);
+ }
+
+ // The provided timeout value is OK as-is.
+ return FrameTimeout(aRawMilliseconds);
+ }
+
+ bool operator==(const FrameTimeout& aOther) const {
+ return mTimeout == aOther.mTimeout;
+ }
+
+ bool operator!=(const FrameTimeout& aOther) const {
+ return !(*this == aOther);
+ }
+
+ FrameTimeout operator+(const FrameTimeout& aOther) {
+ if (*this == Forever() || aOther == Forever()) {
+ return Forever();
+ }
+
+ return FrameTimeout(mTimeout + aOther.mTimeout);
+ }
+
+ FrameTimeout& operator+=(const FrameTimeout& aOther) {
+ *this = *this + aOther;
+ return *this;
+ }
+
+ /**
+ * @return this FrameTimeout's value in milliseconds. Illegal to call on a
+ * an infinite FrameTimeout value.
+ */
+ uint32_t AsMilliseconds() const {
+ if (*this == Forever()) {
+ MOZ_ASSERT_UNREACHABLE(
+ "Calling AsMilliseconds() on an infinite FrameTimeout");
+ return 100; // Fail to something sane.
+ }
+
+ return uint32_t(mTimeout);
+ }
+
+ /**
+ * @return this FrameTimeout value encoded so that non-negative values
+ * represent a timeout in milliseconds, and -1 represents an infinite
+ * timeout.
+ *
+ * XXX(seth): This is a backwards compatibility hack that should be removed.
+ */
+ int32_t AsEncodedValueDeprecated() const { return mTimeout; }
+
+ private:
+ explicit FrameTimeout(int32_t aTimeout) : mTimeout(aTimeout) {}
+
+ int32_t mTimeout;
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif // mozilla_image_FrameTimeout_h