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https://github.com/mpv-player/mpv
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f4e89dde36
This is actually a very nice simplification that should have been thought of years ago (sue me). In a nutshell, the story with the wayland code is that the frame callback and swap buffer behavior doesn't fit very well with mpv's rendering loop. It's been refactored/changed quite a few times over the years and works well enough but things could be better. The current iteration works with an external swapchain to check if we have frame callback before deciding whether or not to render. This logic was implemented in both egl and vulkan. This does have its warts however. There's some hidden state detection logic which works but is kind of ugly. Since wayland doesn't allow clients to know if they are actually visible (questionable but whatever), you can just reasonably assume that if a bunch of callbacks are missed in a row, you're probably not visible. That's fine, but it is indeed less than ideal since the threshold is basically entirely arbitrary and mpv does do a few wasteful renders before it decides that the window is actually hidden. The biggest urk in the vo_wayland_wait_frame is the use of wl_display_roundtrip. Wayland developers would probably be offended by the way mpv abuses that function, but essentially it was a way to have semi-blocking behavior needed for display-resample to work. Since the swap interval must be 0 on wayland (otherwise it will block the entire player's rendering loop), we need some other way to wait on vsync. The idea here was to dispatch and poll a bunch of wayland events, wait (with a timeout) until we get frame callback, and then wait for the compositor to process it. That pretty much perfectly waits on vsync and lets us keep all the good timings and all that jazz that we want for mpv. The problem is that wl_display_roundtrip is conceptually a bad function. It can internally call wl_display_dispatch which in certain instances, empty event queue, will block forever. Now strictly speaking, this probably will never, ever happen (once I was able to to trigger it by hardcoding an error into a compositor), but ideally vo_wayland_wait_frame should never infinitely block and stall the player. Unfortunately, removing that function always lead to problems with timings and unsteady vsync intervals so it survived many refactors. Until now, of course. In wayland, the ideal is to never do wasteful rendering (i.e. don't render if the window isn't visible). Instead of wrestling around with hidden states and possible missed vblanks, let's rearrange the wayland rendering logic so we only ever draw a frame when the frame callback is returned to use (within a reasonable timeout to avoid blocking forever). This slight rearrangement of the wait allows for several simplifications to be made. Namely, wl_display_roundtrip stops being needed. Instead, we can rely entirely on totally nonblocking calls (dispatch_pending, flush, and so on). We still need to poll the fd here to actually get the frame callback event from the compositor, but there's no longer any reason to do extra waiting. As soon as we get the callback, we immediately draw. This works quite well and has stable vsync (display-resample and audio). Additionally, all of the logic about hidden states is no longer needed. If vo_wayland_wait_frame times out, it's okay to assume immediately that the window is not visible and skip rendering. Unfortunately, there's one limitation on this new approach. It will only work correctly if the compositor implements presentation time. That means a reduced version of the old way still has to be carried around in vo_wayland_wait_frame. So if the compositor has no presentation time, then we are forced to use wl_display_roundtrip and juggle some funny assumptions about whether or not the window is hidden or not. Plasma is the only real notable compositor without presentation time at this stage so perhaps this "legacy" mechanism could be removed in the future. |
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| .. | ||
| cocoa | ||
| d3d11 | ||
| gpu | ||
| hwdec | ||
| mac | ||
| opengl | ||
| placebo | ||
| vulkan | ||
| win32 | ||
| android_common.c | ||
| android_common.h | ||
| aspect.c | ||
| aspect.h | ||
| bitmap_packer.c | ||
| bitmap_packer.h | ||
| cocoa_cb_common.swift | ||
| cocoa_common.h | ||
| cocoa_common.m | ||
| dither.c | ||
| dither.h | ||
| dr_helper.c | ||
| dr_helper.h | ||
| drm_atomic.c | ||
| drm_atomic.h | ||
| drm_common.c | ||
| drm_common.h | ||
| drm_prime.c | ||
| drm_prime.h | ||
| filter_kernels.c | ||
| filter_kernels.h | ||
| libmpv_sw.c | ||
| libmpv.h | ||
| vo_caca.c | ||
| vo_direct3d.c | ||
| vo_drm.c | ||
| vo_gpu.c | ||
| vo_image.c | ||
| vo_lavc.c | ||
| vo_libmpv.c | ||
| vo_mediacodec_embed.c | ||
| vo_null.c | ||
| vo_rpi.c | ||
| vo_sdl.c | ||
| vo_sixel.c | ||
| vo_tct.c | ||
| vo_vaapi.c | ||
| vo_vdpau.c | ||
| vo_wlshm.c | ||
| vo_x11.c | ||
| vo_xv.c | ||
| vo.c | ||
| vo.h | ||
| w32_common.c | ||
| w32_common.h | ||
| wayland_common.c | ||
| wayland_common.h | ||
| win_state.c | ||
| win_state.h | ||
| x11_common.c | ||
| x11_common.h | ||