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Tablet example: update only the drawn areas of the canvas 

This makes an enormous difference in responsiveness on the iPad Pro:
it actually feels like real-time drawing with hardly any lag.

Change-Id: I17c3b948e818d4ee46b4d24934c929ab9b386e69
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
bb10
Shawn Rutledge 2017-09-14 15:12:56 +02:00
parent c248a1fa57
commit 0d51767b5d
2 changed files with 7 additions and 2 deletions
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7
examples/widgets/widgets/tablet/tabletcanvas.cpp
View File

@ -119,12 +119,12 @@ void TabletCanvas::tabletEvent(QTabletEvent *event)
case QEvent::TabletRelease:
if (m_deviceDown && event->buttons() == Qt::NoButton)
m_deviceDown = false;
update();
break;
default:
break;
}
event->accept();
update();
}
//! [3]
@ -154,6 +154,7 @@ void TabletCanvas::paintEvent(QPaintEvent *)
//! [5]
void TabletCanvas::paintPixmap(QPainter &painter, QTabletEvent *event)
{
static qreal maxPenRadius = pressureToWidth(1.0);
painter.setRenderHint(QPainter::Antialiasing);
switch (event->device()) {
@ -169,6 +170,7 @@ void TabletCanvas::paintPixmap(QPainter &painter, QTabletEvent *event)
painter.setBrush(grad);
qreal radius = grad.radius();
painter.drawEllipse(event->posF(), radius, radius);
update(QRect(event->pos() - QPoint(radius, radius), QSize(radius * 2, radius * 2)));
}
break;
case QTabletEvent::RotationStylus:
@ -188,6 +190,7 @@ void TabletCanvas::paintPixmap(QPainter &painter, QTabletEvent *event)
poly << event->posF() - brushAdjust;
poly << event->posF() + brushAdjust;
painter.drawConvexPolygon(poly);
update(poly.boundingRect().toRect());
}
break;
//! [6]
@ -217,6 +220,8 @@ void TabletCanvas::paintPixmap(QPainter &painter, QTabletEvent *event)
case QTabletEvent::Stylus:
painter.setPen(m_pen);
painter.drawLine(lastPoint.pos, event->posF());
update(QRect(lastPoint.pos.toPoint(), event->pos()).normalized()
.adjusted(-maxPenRadius, -maxPenRadius, maxPenRadius, maxPenRadius));
break;
}
}

2
examples/widgets/widgets/tablet/tabletcanvas.h
View File

@ -103,7 +103,7 @@ private:
void initPixmap();
void paintPixmap(QPainter &painter, QTabletEvent *event);
Qt::BrushStyle brushPattern(qreal value);
qreal pressureToWidth(qreal pressure);
static qreal pressureToWidth(qreal pressure);
void updateBrush(const QTabletEvent *event);
void updateCursor(const QTabletEvent *event);