Implement a Wayland Vsync source using frame callbacks

app/streaming/video/ffmpeg-renderers/pacer/waylandvsyncsource.cpp

@@ -0,0 +1,77 @@
+#include "waylandvsyncsource.h"
+
+#include <SDL_syswm.h>
+
+const struct wl_callback_listener WaylandVsyncSource::s_FrameListener = {
+    .done = WaylandVsyncSource::frameDone,
+};
+
+WaylandVsyncSource::WaylandVsyncSource(Pacer* pacer)
+    : m_Pacer(pacer),
+      m_Display(nullptr),
+      m_Surface(nullptr),
+      m_Callback(nullptr),
+      m_LastFrameTime(0)
+{
+
+}
+
+WaylandVsyncSource::~WaylandVsyncSource()
+{
+    if (m_Callback != nullptr) {
+        wl_callback_destroy(m_Callback);
+        wl_display_roundtrip(m_Display);
+    }
+}
+
+bool WaylandVsyncSource::initialize(SDL_Window* window, int displayFps)
+{
+    SDL_SysWMinfo info;
+
+    SDL_VERSION(&info.version);
+
+    if (!SDL_GetWindowWMInfo(window, &info)) {
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                     "SDL_GetWindowWMInfo() failed: %s",
+                     SDL_GetError());
+        return false;
+    }
+
+    // Pacer shoud not create us for non-Wayland windows
+    SDL_assert(info.subsystem == SDL_SYSWM_WAYLAND);
+
+    m_DisplayFps = displayFps;
+    m_Display = info.info.wl.display;
+    m_Surface = info.info.wl.surface;
+
+    // Enqueue our first frame callback
+    m_Callback = wl_surface_frame(m_Surface);
+    wl_callback_add_listener(m_Callback, &s_FrameListener, this);
+    wl_surface_commit(m_Surface);
+
+    return true;
+}
+
+void WaylandVsyncSource::frameDone(void* data, struct wl_callback* oldCb, uint32_t time)
+{
+    auto me = (WaylandVsyncSource*)data;
+
+    // Free this callback
+    SDL_assert(oldCb == me->m_Callback);
+    wl_callback_destroy(oldCb);
+
+    // Register for another callback before invoking Pacer to ensure we don't miss
+    // a frame callback if Pacer takes too long.
+    me->m_Callback = wl_surface_frame(me->m_Surface);
+    wl_callback_add_listener(me->m_Callback, &s_FrameListener, data);
+    wl_surface_commit(me->m_Surface);
+    wl_display_flush(me->m_Display);
+
+    if (me->m_LastFrameTime != 0) {
+        // Assuming that the time until the next V-Sync will usually be equal to the
+        // time from last callback to this one but cap it at 2x the expected frame period.
+        me->m_Pacer->vsyncCallback(SDL_min(time - me->m_LastFrameTime, 2000 / me->m_DisplayFps));
+    }
+
+    me->m_LastFrameTime = time;
+}