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# Objective - The time update is currently done in the wrong part of the schedule. For a single frame the current order of things is update input, update time (First stage), other stages, render stage (frame presentation). So when we update the time it includes the input processing of the current frame and the frame presentation of the previous frame. This is a problem when vsync is on. When input processing takes a longer amount of time for a frame, the vsync wait time gets shorter. So when these are not paired correctly we can potentially have a long input processing time added to the normal vsync wait time in the previous frame. This leads to inaccurate frame time reporting and more variance of the time than actually exists. For more details of why this is an issue see the linked issue below. - Helps with https://github.com/bevyengine/bevy/issues/4669 - Supercedes https://github.com/bevyengine/bevy/pull/4728 and https://github.com/bevyengine/bevy/pull/4735. This PR should be less controversial than those because it doesn't add to the API surface. ## Solution - The most accurate frame time would come from hardware. We currently don't have access to that for multiple reasons, so the next best thing we can do is measure the frame time as close to frame presentation as possible. This PR gets the Instant::now() for the time immediately after frame presentation in the render system and then sends that time to the app world through a channel. - implements suggestion from @aevyrie from here https://github.com/bevyengine/bevy/pull/4728#discussion_r872010606 ## Statistics  --- ## Changelog - Make frame time reporting more accurate. ## Migration Guide `time.delta()` now reports zero for 2 frames on startup instead of 1 frame. |
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