关于C#：QGraphicsLineItem :: paint()工件

QGraphicsLineItem::paint() artifacts

我有自己的类，该类继承自QGraphicsLineItem，并覆盖了paint()方法以绘制带有箭头的粗线：

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void MyGraphicsItem::paint( QPainter* aPainter,
const QStyleOptionGraphicsItem* aOption,
QWidget* aWidget /*= nullptr*/ )
{
Q_UNUSED( aOption );
Q_UNUSED( aWidget );

QLineF cLine = line();

aPainter->setPen( QPen( Qt::black, 6, Qt::SolidLine ) );
aPainter->drawLine( cLine );

qreal lineAngle = cLine.angle();

const qreal radius = 2.0;
QLineF head1 = cLine;
head1.setAngle(lineAngle+32);
head1.setLength( 12 );
QLineF head2 = cLine;
head2.setAngle(lineAngle-32);
head2.setLength( 12 );

aPainter->drawLine( head1 );
aPainter->drawLine( head2 );

aPainter->setPen( QPen( Qt::yellow, 2, Qt::SolidLine ) );

aPainter->drawLine( cLine );

aPainter->drawLine( head1 );
aPainter->drawLine( head2 );
}

当我在场景中绘制项目时，这似乎会导致渲染失真。据我所知，因为我已经在QPen上设置了厚度，这使我相信必须以某种方式在矩形的外部进行绘制？

是什么导致我的渲染问题，我该如何解决？

enter

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// This code lives in the QGraphicsScene constructor, doesn't have to be there though since QGraphicsScene::setBackgroundBrush is public.
int gridSizeX = 25;
int gridSizeY = 20;
QImage singleGrid( gridSizeX, gridSizeY, QImage::Format_RGB32 );
singleGrid.fill( Qt::white );
{
QPainter painter( &singleGrid );

// Lighter background
painter.setPen( QPen( QColor( 240, 240, 240 ) ));

qreal midx = gridSizeX / 2;
qreal midy = gridSizeY / 2;
painter.drawLine( 0, midy, gridSizeX, midy );
painter.drawLine( midx, 0, midx, gridSizeY );

// Darker foregound
painter.setPen( QPen( QColor( 180, 180, 180 ) ));
painter.drawRect( 0, 0, gridSizeX, gridSizeY );

painter.end();
}
QBrush brushBackground( singleGrid );
setBackgroundBrush( brushBackground );

然后，场景在所有位置重复此笔刷，从而产生相同的网格背景效果，甚至在缩放/缩放时也可以按预期工作。：)。

当重写paint()函数时，还需要重写类中的QGraphicsItem :: boundingRect()来定义自定义图形项的外部边界。如果在边界之外绘制，则最终会出现渲染瑕疵。现在，您依赖QGraphicsLineItem的boundingRect()的实现，它当然不知道您对paint()函数的实现。有关详细信息，请参见http://doc.qt.digia.com/main-snapshot/qgraphicsitem.html#boundingRect。