Move the Vsync logic from VTRenderer into a VsyncSource

2026-06-17 14:11:33 +00:00 · 2018-08-15 22:02:15 -07:00
parent f929cffce7
commit e68a15c825
7 changed files with 216 additions and 132 deletions
@@ -0,0 +1,133 @@
+#include "pacer.h"
+
+#ifdef Q_OS_DARWIN
+#include "displaylinkvsyncsource.h"
+#endif
+
+#define FRAME_HISTORY_ENTRIES 8
+
+Pacer::Pacer(IVsyncRenderer* renderer) :
+    m_FrameQueueLock(0),
+    m_VsyncSource(nullptr),
+    m_VsyncRenderer(renderer),
+    m_MaxVideoFps(0),
+    m_DisplayFps(0)
+{
+
+}
+
+Pacer::~Pacer()
+{
+    // Stop V-sync callbacks
+    delete m_VsyncSource;
+
+    drain();
+}
+
+// Called in an arbitrary thread by the IVsyncSource on V-sync
+// or an event synchronized with V-sync
+void Pacer::vsyncCallback()
+{
+    // Make sure initialize() has been called
+    SDL_assert(m_MaxVideoFps != 0);
+
+    SDL_AtomicLock(&m_FrameQueueLock);
+
+    // If the queue length history entries are large, be strict
+    // about dropping excess frames.
+    int frameDropTarget = 1;
+
+    // If we may get more frames per second than we can display, use
+    // frame history to drop frames only if consistently above the
+    // one queued frame mark.
+    if (m_MaxVideoFps >= m_DisplayFps) {
+        for (int i = 0; i < m_FrameQueueHistory.count(); i++) {
+            if (m_FrameQueueHistory[i] <= 1) {
+                // Be lenient as long as the queue length
+                // resolves before the end of frame history
+                frameDropTarget = 3;
+                break;
+            }
+        }
+
+        if (m_FrameQueueHistory.count() == FRAME_HISTORY_ENTRIES) {
+            m_FrameQueueHistory.dequeue();
+        }
+
+        m_FrameQueueHistory.enqueue(m_FrameQueue.count());
+    }
+
+    // Catch up if we're several frames ahead
+    while (m_FrameQueue.count() > frameDropTarget) {
+        AVFrame* frame = m_FrameQueue.dequeue();
+        av_frame_free(&frame);
+    }
+
+    if (m_FrameQueue.isEmpty()) {
+        SDL_AtomicUnlock(&m_FrameQueueLock);
+
+        // Nothing to render at this time
+        return;
+    }
+
+    // Grab the first frame
+    AVFrame* frame = m_FrameQueue.dequeue();
+    SDL_AtomicUnlock(&m_FrameQueueLock);
+
+    // Render it
+    m_VsyncRenderer->renderFrameAtVsync(frame);
+
+    // Free the frame
+    av_frame_free(&frame);
+}
+
+bool Pacer::initialize(SDL_Window* window, int maxVideoFps)
+{
+    m_MaxVideoFps = maxVideoFps;
+
+    int displayIndex = SDL_GetWindowDisplayIndex(window);
+    if (displayIndex < 0) {
+        SDL_LogError(SDL_LOG_CATEGORY_APPLICATION,
+                     "Failed to get current display: %s",
+                     SDL_GetError());
+
+        // Assume display 0 if it fails
+        displayIndex = 0;
+    }
+
+    SDL_DisplayMode mode;
+    if (SDL_GetCurrentDisplayMode(displayIndex, &mode) == 0) {
+        // May be zero if undefined
+        m_DisplayFps = mode.refresh_rate;
+    }
+
+    SDL_LogInfo(SDL_LOG_CATEGORY_APPLICATION,
+                "Frame pacing: target %d Hz with %d FPS stream",
+                m_DisplayFps, m_MaxVideoFps);
+
+#ifdef Q_OS_DARWIN
+    m_VsyncSource = new DisplayLinkVsyncSource(this);
+#else
+    SDL_assert(false);
+#endif
+
+    return m_VsyncSource->initialize(window);
+}
+
+void Pacer::submitFrame(AVFrame* frame)
+{
+    // Make sure initialize() has been called
+    SDL_assert(m_MaxVideoFps != 0);
+
+    SDL_AtomicLock(&m_FrameQueueLock);
+    m_FrameQueue.enqueue(frame);
+    SDL_AtomicUnlock(&m_FrameQueueLock);
+}
+
+void Pacer::drain()
+{
+    while (!m_FrameQueue.isEmpty()) {
+        AVFrame* frame = m_FrameQueue.dequeue();
+        av_frame_free(&frame);
+    }
+}