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# starwidget.cpp Example File

openvg/star/starwidget.cpp

     /****************************************************************************
     **
     ** Copyright (C) 2015 The Qt Company Ltd.
     ** Contact: http://www.qt.io/licensing/
     **
     ** This file is part of the QtOpenGL module of the Qt Toolkit.
     **
     ** $QT_BEGIN_LICENSE:BSD$
     ** You may use this file under the terms of the BSD license as follows:
     **
     ** "Redistribution and use in source and binary forms, with or without
     ** modification, are permitted provided that the following conditions are
     ** met:
     **   * Redistributions of source code must retain the above copyright
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     **     notice, this list of conditions and the following disclaimer in
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     **     contributors may be used to endorse or promote products derived
     **     from this software without specific prior written permission.
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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();
     }