QGIS学习之-显示SVG图片

这个功能其实很简单，但是看到网上很多人不知道怎么做，故记录下帮助需要的朋友。

其实看源码就知道怎么做了。

如果自己重新QGraphicsItem 可以将图片加入图层，但是有很多问题，比如地图坐标等等，其实QGIS已经帮我们实现了，它就是QgsAnnotationItem

所以我们要实现显示SVG图片 又不想自己去管理缩放，坐标等等 就从QgsAnnotationItem继承并重新paint就好了.

头文件定义如下：

#ifndef SVGANNOTATIONITEM_H

#define SVGANNOTATIONITEM_H

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include 

#include "SCVectorLayer.h"

#include "SCMapCanvas.h"

#include "qgstextannotationitem.h"

#include 

#include "MeasureTool.h"

#include 

class  QSvgRenderer;

class SvgAnnotationImageItem: public QgsAnnotationItem

{

  public:

    SvgAnnotationImageItem( QgsMapCanvas* canvas );

    ~SvgAnnotationImageItem();

    void writeXML( QDomDocument& doc ) const override;

     void readXML( const QDomDocument& doc, const QDomElement& itemElem ) override;

    void paint( QPainter* painter ) override;

    void setFilePath( const QString& file );

    QString filePath() const { return mFilePath; }

  private:

    QSvgRenderer *mSvgRenderer;

    QString mFilePath;

};

#endif // SVGANNOTATIONITEM_H

源文件如下:

#include "SvgAnnotationItem.h"

#include "qgsproject.h"

#include 

#include 

SvgAnnotationImageItem::SvgAnnotationImageItem( QgsMapCanvas* canvas ): QgsAnnotationItem( canvas )

{

    mSvgRenderer = new QSvgRenderer();

}

SvgAnnotationImageItem::~SvgAnnotationImageItem()

{

    mSvgRenderer->deleteLater();

}

void SvgAnnotationImageItem::writeXML( QDomDocument& doc ) const

{

  QDomElement documentElem = doc.documentElement();

  if ( documentElem.isNull() )

  {

    return;

  }

  QDomElement svgAnnotationElem = doc.createElement( "SVGAnnotationItem" );

  svgAnnotationElem.setAttribute( "file", QgsProject::instance()->writePath( mFilePath ) );

  _writeXML( doc, svgAnnotationElem );

  documentElem.appendChild( svgAnnotationElem );

}

void SvgAnnotationImageItem::readXML( const QDomDocument& doc, const QDomElement& itemElem )

{

  QString filePath = QgsProject::instance()->readPath( itemElem.attribute( "file" ) );

  setFilePath( filePath );

  QDomElement annotationElem = itemElem.firstChildElement( "AnnotationItem" );

  if ( !annotationElem.isNull() )

  {

    _readXML( doc, annotationElem );

  }

}

void SvgAnnotationImageItem::paint( QPainter* painter )

{

  if ( !painter )

  {

    return;

  }

  //keep width/height ratio of svg

  QRect viewBox = mSvgRenderer->viewBox();

  if ( viewBox.isValid() )

  {

    double widthRatio = mFrameSize.width() / viewBox.width();

    double heightRatio = mFrameSize.height() / viewBox.height();

    double renderWidth = 0;

    double renderHeight = 0;

    if ( widthRatio <= heightRatio )

    {

      renderWidth = mFrameSize.width();

      renderHeight = viewBox.height() * mFrameSize.width() / viewBox.width();

    }

    else

    {

      renderHeight = mFrameSize.height();

      renderWidth = viewBox.width() * mFrameSize.height() / viewBox.height();

    }

    mSvgRenderer->render( painter, QRectF( mOffsetFromReferencePoint.x(), mOffsetFromReferencePoint.y(), renderWidth,

                                          renderHeight ) );

  }

  if ( isSelected() )

  {

    drawSelectionBoxes( painter );

  }

}

void SvgAnnotationImageItem::setFilePath( const QString& file )

{

  mFilePath = file;

  mSvgRenderer->load( mFilePath );

}

使用方法:

   SvgAnnotationImageItem *item = new SvgAnnotationImageItem(mapCanvas);

   item->setFrameSize(QSizeF(64, 64));

   item->setFrameBorderWidth(0);

   item->setMapPosition(QgsPoint(200, 300));

   item->setFilePath("F:\\3.svg");
 


so easy