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Bug 778045. Add helpful comment to ImageContainer explaining its modes. r=bas

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This commit is contained in:
Robert O'Callahan 2012-08-03 15:23:27 +12:00
parent cc1037deb4
commit 676bce6e67
1 changed files with 17 additions and 0 deletions
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17
gfx/layers/ImageLayers.h
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@ -301,6 +301,23 @@ struct RemoteImageData {
* (because layers can only be used on the main thread) and we want to
* be able to set the current Image from any thread, to facilitate
* video playback without involving the main thread, for example.
*
* An ImageContainer can operate in one of three modes:
* 1) Normal. Triggered by constructing the ImageContainer with
* DISABLE_ASYNC or when compositing is happening on the main thread.
* SetCurrentImage changes ImageContainer state but nothing is sent to the
* compositor until the next layer transaction.
* 2) Asynchronous. Initiated by constructing the ImageContainer with
* ENABLE_ASYNC when compositing is happening on the main thread.
* SetCurrentImage sends a message through the ImageBridge to the compositor
* thread to update the image, without going through the main thread or
* a layer transaction.
* 3) Remote. Initiated by calling SetRemoteImageData on the ImageContainer
* before any other activity.
* The ImageContainer uses a shared memory block containing a cross-process mutex
* to communicate with the compositor thread. SetCurrentImage synchronously
* updates the shared state to point to the new image and the old image
* is immediately released (not true in Normal or Asynchronous modes).
*/
class THEBES_API ImageContainer {
NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ImageContainer)