Qt Reference Documentation

starwidget.cpp Example File

openvg/star/starwidget.cpp
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 #include "starwidget.h"

 StarWidget::StarWidget(QWidget *parent)
     : QWidget(parent)
     , path(VG_INVALID_HANDLE)
     , pen(Qt::red, 4.0, Qt::SolidLine, Qt::RoundCap, Qt::RoundJoin)
     , brush(Qt::yellow)
 {
     setMinimumSize(220, 250);
     setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::MinimumExpanding);
 }

 static VGubyte const starSegments[] = {
     VG_MOVE_TO_ABS,
     VG_LINE_TO_REL,
     VG_LINE_TO_REL,
     VG_LINE_TO_REL,
     VG_LINE_TO_REL,
     VG_CLOSE_PATH
 };
 static VGfloat const starCoords[] = {
     110, 35,
     50, 160,
     -130, -100,
     160, 0,
     -130, 100
 };

 void StarWidget::paintEvent(QPaintEvent *)
 {
     QPainter painter;
     painter.begin(this);

     // Make sure that we are using the OpenVG paint engine.
     if (painter.paintEngine()->type() != QPaintEngine::OpenVG) {
 #ifdef Q_WS_QWS
         qWarning("Not using OpenVG: use the '-display' option to specify an OpenVG driver");
 #else
         qWarning("Not using OpenVG: specify '-graphicssystem OpenVG'");
 #endif
         return;
     }

     // Select a pen and a brush for drawing the star.
     painter.setPen(pen);
     painter.setBrush(brush);

     // We want the star border to be anti-aliased.
     painter.setRenderHints(QPainter::Antialiasing);

     // Flush the state changes to the OpenVG implementation
     // and prepare to perform raw OpenVG calls.
     painter.beginNativePainting();

     // Cache the path if we haven't already or if the path has
     // become invalid because the window's context has changed.
     if (path == VG_INVALID_HANDLE || !vgGetPathCapabilities(path)) {
         path = vgCreatePath(VG_PATH_FORMAT_STANDARD,
                             VG_PATH_DATATYPE_F,
                             1.0f, // scale
                             0.0f, // bias
                             6,    // segmentCapacityHint
                             10,   // coordCapacityHint
                             VG_PATH_CAPABILITY_ALL);
         vgAppendPathData(path, sizeof(starSegments), starSegments, starCoords);
     }

     // Draw the star directly using the OpenVG API.
     vgDrawPath(path, VG_FILL_PATH | VG_STROKE_PATH);

     // Restore normal QPainter operations.
     painter.endNativePainting();

     painter.end();
 }
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