[backends/drm] Double Tap to enable output

If the output is off a double tap (touch) can re-enable it. The two
taps have to happen in the double click interval (we don't have
something better and it kind of matches) and have to be by only one
touch point. If there are multiple touch points it's not considered
as a double tap. A todo is to restrict the possible distance of the
two taps to one thumb.

Tested-By: Marco Martin

backends/drm/drm_backend.cpp

@@ -93,6 +93,54 @@ bool DpmsInputEventFilter::keyEvent(QKeyEvent *event)
     return true;
 }
 
+bool DpmsInputEventFilter::touchDown(quint32 id, const QPointF &pos, quint32 time)
+{
+    Q_UNUSED(pos)
+    Q_UNUSED(time)
+    if (m_touchPoints.isEmpty()) {
+        if (!m_doubleTapTimer.isValid()) {
+            // this is the first tap
+            m_doubleTapTimer.start();
+        } else {
+            if (m_doubleTapTimer.elapsed() < qApp->doubleClickInterval()) {
+                m_secondTap = true;
+            } else {
+                // took too long. Let's consider it a new click
+                m_doubleTapTimer.restart();
+            }
+        }
+    } else {
+        // not a double tap
+        m_doubleTapTimer.invalidate();
+        m_secondTap = false;
+    }
+    m_touchPoints << id;
+    return true;
+}
+
+bool DpmsInputEventFilter::touchUp(quint32 id, quint32 time)
+{
+    Q_UNUSED(time)
+    m_touchPoints.removeAll(id);
+    if (m_touchPoints.isEmpty() && m_doubleTapTimer.isValid() && m_secondTap) {
+        if (m_doubleTapTimer.elapsed() < qApp->doubleClickInterval()) {
+            notify();
+        }
+        m_doubleTapTimer.invalidate();
+        m_secondTap = false;
+    }
+    return true;
+}
+
+bool DpmsInputEventFilter::touchMotion(quint32 id, const QPointF &pos, quint32 time)
+{
+    Q_UNUSED(id)
+    Q_UNUSED(pos)
+    Q_UNUSED(time)
+    // ignore the event
+    return true;
+}
+
 void DpmsInputEventFilter::notify()
 {
     // queued to not modify the list of event filters while filtering

backends/drm/drm_backend.h

@@ -22,6 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #include "abstract_backend.h"
 #include "input.h"
 
+#include <QElapsedTimer>
 #include <QImage>
 #include <QPointer>
 #include <QSize>
@@ -261,10 +262,16 @@ public:
     bool pointerEvent(QMouseEvent *event, quint32 nativeButton) override;
     bool wheelEvent(QWheelEvent *event) override;
     bool keyEvent(QKeyEvent *event) override;
+    bool touchDown(quint32 id, const QPointF &pos, quint32 time) override;
+    bool touchMotion(quint32 id, const QPointF &pos, quint32 time) override;
+    bool touchUp(quint32 id, quint32 time) override;
 
 private:
     void notify();
     DrmBackend *m_backend;
+    QElapsedTimer m_doubleTapTimer;
+    QVector<qint32> m_touchPoints;
+    bool m_secondTap = false;
 };
 
 }