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renderarea.cpp Example File
painting/transformations/renderarea.cpp

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 #include <QtGui>

 #include "renderarea.h"

 RenderArea::RenderArea(QWidget *parent)
     : QWidget(parent)
 {
     QFont newFont = font();
     newFont.setPixelSize(12);
     setFont(newFont);

     QFontMetrics fontMetrics(newFont);
     xBoundingRect = fontMetrics.boundingRect(tr("x"));
     yBoundingRect = fontMetrics.boundingRect(tr("y"));
 }

 void RenderArea::setOperations(const QList<Operation> &operations)
 {
     this->operations = operations;
     update();
 }

 void RenderArea::setShape(const QPainterPath &shape)
 {
     this->shape = shape;
     update();
 }

 QSize RenderArea::minimumSizeHint() const
 {
     return QSize(182, 182);
 }

 QSize RenderArea::sizeHint() const
 {
     return QSize(232, 232);
 }

 void RenderArea::paintEvent(QPaintEvent *event)
 {
     QPainter painter(this);
     painter.setRenderHint(QPainter::Antialiasing);
     painter.fillRect(event->rect(), QBrush(Qt::white));

     painter.translate(66, 66);

     painter.save();
     transformPainter(painter);
     drawShape(painter);
     painter.restore();

     drawOutline(painter);

     transformPainter(painter);
     drawCoordinates(painter);
 }

 void RenderArea::drawCoordinates(QPainter &painter)
 {
     painter.setPen(Qt::red);

     painter.drawLine(0, 0, 50, 0);
     painter.drawLine(48, -2, 50, 0);
     painter.drawLine(48, 2, 50, 0);
     painter.drawText(60 - xBoundingRect.width() / 2,
                      0 + xBoundingRect.height() / 2, tr("x"));

     painter.drawLine(0, 0, 0, 50);
     painter.drawLine(-2, 48, 0, 50);
     painter.drawLine(2, 48, 0, 50);
     painter.drawText(0 - yBoundingRect.width() / 2,
                      60 + yBoundingRect.height() / 2, tr("y"));
 }

 void RenderArea::drawOutline(QPainter &painter)
 {
     painter.setPen(Qt::darkGreen);
     painter.setPen(Qt::DashLine);
     painter.setBrush(Qt::NoBrush);
     painter.drawRect(0, 0, 100, 100);
 }

 void RenderArea::drawShape(QPainter &painter)
 {
     painter.fillPath(shape, Qt::blue);
 }

 void RenderArea::transformPainter(QPainter &painter)
 {
     for (int i = 0; i < operations.size(); ++i) {
         switch (operations[i]) {
         case Translate:
             painter.translate(50, 50);
             break;
         case Scale:
             painter.scale(0.75, 0.75);
             break;
         case Rotate:
             painter.rotate(60);
             break;
         case NoTransformation:
         default:
             ;
         }
     }
 }