Drive cursor animation with a timer

Using only wl_surface_frame callbacks to update the cursor does so much
more often than needed. In addition, at least GNOME and Weston fire the
callback for the cursor surface immediately, which ends up updating the
cursor at over 3000 Hz here.

Use wl_cursor_frame_and_duration to drive a single shot timer. This
function is also guaranteed to return 0 for single frame cursors, so we
can avoid starting the timer at all.

We wait for both the surface frame callback and the timer to fire before
updating the cursor for the next frame of animation. This reduces our
update rate to the frame rate of the cursor or the rate requested by the
compositor, whichever is lower.

Change-Id: I10277460ebe9b547ebaf7f73424b9ef17614107f
Reviewed-by: Johan Helsing <johan.helsing@qt.io>

2 files changed, 36 insertions, 3 deletions

diff --git a/src/client/qwaylandinputdevice.cpp b/src/client/qwaylandinputdevice.cpp
index 3b26dc427..3f0d61d6a 100644
--- a/src/client/qwaylandinputdevice.cpp
+++ b/src/client/qwaylandinputdevice.cpp
@@ -143,6 +143,12 @@ QWaylandWindow *QWaylandInputDevice::Keyboard::focusWindow() const
 QWaylandInputDevice::Pointer::Pointer(QWaylandInputDevice *seat)
     : mParent(seat)
 {
+#if QT_CONFIG(cursor)
+    mCursor.frameTimer.setSingleShot(true);
+    mCursor.frameTimer.callOnTimeout([&]() {
+        cursorTimerCallback();
+    });
+#endif
 }
 
 QWaylandInputDevice::Pointer::~Pointer()
@@ -224,7 +230,7 @@ public:
         if (animated) {
             m_frameCallback.reset(new WlCallback(frame(), [this](uint32_t time){
                Q_UNUSED(time);
-               m_pointer->updateCursor();
+               m_pointer->cursorFrameCallback();
             }));
         }
         commit();
@@ -328,7 +334,8 @@ void QWaylandInputDevice::Pointer::updateCursor()
     uint time = seat()->mCursor.animationTimer.elapsed();
 
     if (struct ::wl_cursor *waylandCursor = mCursor.theme->cursor(shape)) {
-        int frame = wl_cursor_frame(waylandCursor, time);
+        uint duration = 0;
+        int frame = wl_cursor_frame_and_duration(waylandCursor, time, &duration);
         ::wl_cursor_image *image = waylandCursor->images[frame];
 
         struct wl_buffer *buffer = wl_cursor_image_get_buffer(image);
@@ -339,7 +346,12 @@ void QWaylandInputDevice::Pointer::updateCursor()
         int bufferScale = mCursor.themeBufferScale;
         QPoint hotspot = QPoint(image->hotspot_x, image->hotspot_y) / bufferScale;
         QSize size = QSize(image->width, image->height) / bufferScale;
-        bool animated = waylandCursor->image_count > 1 && image->delay > 0;
+        bool animated = duration > 0;
+        if (animated) {
+            mCursor.gotFrameCallback = false;
+            mCursor.gotTimerCallback = false;
+            mCursor.frameTimer.start(duration);
+        }
         getOrCreateCursorSurface()->update(buffer, hotspot, size, bufferScale, animated);
         return;
     }
@@ -354,6 +366,22 @@ CursorSurface *QWaylandInputDevice::Pointer::getOrCreateCursorSurface()
     return mCursor.surface.get();
 }
 
+void QWaylandInputDevice::Pointer::cursorTimerCallback()
+{
+    mCursor.gotTimerCallback = true;
+    if (mCursor.gotFrameCallback) {
+        updateCursor();
+    }
+}
+
+void QWaylandInputDevice::Pointer::cursorFrameCallback()
+{
+    mCursor.gotFrameCallback = true;
+    if (mCursor.gotTimerCallback) {
+        updateCursor();
+    }
+}
+
 #endif // QT_CONFIG(cursor)
 
 QWaylandInputDevice::Touch::Touch(QWaylandInputDevice *p)
diff --git a/src/client/qwaylandinputdevice_p.h b/src/client/qwaylandinputdevice_p.h
index 60d6f2c17..a567c57b4 100644
--- a/src/client/qwaylandinputdevice_p.h
+++ b/src/client/qwaylandinputdevice_p.h
@@ -286,6 +286,8 @@ public:
     int idealCursorScale() const;
     void updateCursorTheme();
     void updateCursor();
+    void cursorTimerCallback();
+    void cursorFrameCallback();
     CursorSurface *getOrCreateCursorSurface();
 #endif
     QWaylandInputDevice *seat() const { return mParent; }
@@ -325,6 +327,9 @@ public:
         QWaylandCursorTheme *theme = nullptr;
         int themeBufferScale = 0;
         QScopedPointer<CursorSurface> surface;
+        QTimer frameTimer;
+        bool gotFrameCallback = false;
+        bool gotTimerCallback = false;
     } mCursor;
 #endif
     QPointF mSurfacePos;