Copyright © 2013-2014 Collabora, Ltd. Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice (including the next paragraph) shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. The main feature of this interface is accurate presentation timing feedback to ensure smooth video playback while maintaining audio/video synchronization. Some features use the concept of a presentation clock, which is defined in presentation.clock_id event. Request 'feedback' can be regarded as an additional wl_surface method. It is part of the double-buffered surface state update mechanism, where other requests first set up the state and then wl_surface.commit atomically applies the state into use. In other words, wl_surface.commit submits a content update. When the final realized presentation time is available, e.g. after a framebuffer flip completes, the requested presentation_feedback.presented events are sent. The final presentation time can differ from the compositor's predicted display update time and the update's target time, especially when the compositor misses its target vertical blanking period. These fatal protocol errors may be emitted in response to illegal presentation requests. Informs the server that the client will not be using this protocol object anymore. This does not affect any existing objects created by this interface. Request presentation feedback for the current content submission on the given surface. This creates a new presentation_feedback object, which will deliver the feedback information once. If multiple presentation_feedback objects are created for the same submission, they will all deliver the same information. For details on what information is returned, see presentation_feedback interface. This event tells the client in which clock domain the compositor interprets the timestamps used by the presentation extension. This clock is called the presentation clock. The compositor sends this event when the client binds to the presentation interface. The presentation clock does not change during the lifetime of the client connection. The clock identifier is platform dependent. Clients must be able to query the current clock value directly, not by asking the compositor. On Linux/glibc, the identifier value is one of the clockid_t values accepted by clock_gettime(). clock_gettime() is defined by POSIX.1-2001. Compositors should prefer a clock which does not jump and is not slewed e.g. by NTP. The absolute value of the clock is irrelevant. Precision of one millisecond or better is recommended. Timestamps in this clock domain are expressed as tv_sec_hi, tv_sec_lo, tv_nsec triples, each component being an unsigned 32-bit value. Whole seconds are in tv_sec which is a 64-bit value combined from tv_sec_hi and tv_sec_lo, and the additional fractional part in tv_nsec as nanoseconds. Hence, for valid timestamps tv_nsec must be in [0, 999999999]. Note that clock_id applies only to the presentation clock, and implies nothing about e.g. the timestamps used in the Wayland core protocol input events. A presentation_feedback object returns an indication that a wl_surface content update has become visible to the user. One object corresponds to one content update submission (wl_surface.commit). There are two possible outcomes: the content update is presented to the user, and a presentation timestamp delivered; or, the user did not see the content update because it was superseded or its surface destroyed, and the content update is discarded. Once a presentation_feedback object has delivered an 'presented' or 'discarded' event it is automatically destroyed. As presentation can be synchronized to only one output at a time, this event tells which output it was. This event is only sent prior to the presented event. As clients may bind to the same global wl_output multiple times, this event is sent for each bound instance that matches the synchronized output. If a client has not bound to the right wl_output global at all, this event is not sent. These flags provide information about how the presentation of the related content update was done. The intent is to help clients assess the reliability of the feedback and the visual quality with respect to possible tearing and timings. The flags are: VSYNC: The presentation was synchronized to the "vertical retrace" by the display hardware such that tearing does not happen. Relying on user space scheduling is not acceptable for this flag. If presentation is done by a copy to the active frontbuffer, then it must guarantee that tearing cannot happen. HW_CLOCK: The display hardware provided measurements that the hardware driver converted into a presentation timestamp. Sampling a clock in user space is not acceptable for this flag. HW_COMPLETION: The display hardware signalled that it started using the new image content. The opposite of this is e.g. a timer being used to guess when the display hardware has switched to the new image content. ZERO_COPY: The presentation of this update was done zero-copy. This means the buffer from the client was given to display hardware as is, without copying it. Compositing with OpenGL counts as copying, even if textured directly from the client buffer. Possible zero-copy cases include direct scanout of a fullscreen surface and a surface on a hardware overlay. The associated content update was displayed to the user at the indicated time (tv_sec_hi/lo, tv_nsec). For the interpretation of the timestamp, see presentation.clock_id event. The timestamp corresponds to the time when the content update turned into light the first time on the surface's main output. Compositors may approximate this from the framebuffer flip completion events from the system, and the latency of the physical display path if known. This event is preceded by all related sync_output events telling which output's refresh cycle the feedback corresponds to, i.e. the main output for the surface. Compositors are recommended to choose the output containing the largest part of the wl_surface, or keeping the output they previously chose. Having a stable presentation output association helps clients predict future output refreshes (vblank). Argument 'refresh' gives the compositor's prediction of how many nanoseconds after tv_sec, tv_nsec the very next output refresh may occur. This is to further aid clients in predicting future refreshes, i.e., estimating the timestamps targeting the next few vblanks. If such prediction cannot usefully be done, the argument is zero. The 64-bit value combined from seq_hi and seq_lo is the value of the output's vertical retrace counter when the content update was first scanned out to the display. This value must be compatible with the definition of MSC in GLX_OML_sync_control specification. Note, that if the display path has a non-zero latency, the time instant specified by this counter may differ from the timestamp's. If the output does not have a constant refresh rate, explicit video mode switches excluded, then the refresh argument must be zero. If the output does not have a concept of vertical retrace or a refresh cycle, or the output device is self-refreshing without a way to query the refresh count, then the arguments seq_hi and seq_lo must be zero. The content update was never displayed to the user.