本文详细介绍了如何在QGIS+qt环境下进行地图要素的缩放功能二次开发，从源码分析到代码调整，再到功能调用，最后展示了缩放效果。
目录
1 前言
上一篇文章《QGIS+qt 二次开发 移动要素》中提到了如何实现要素移动的功能，本文来说一下要素的缩放功能怎么实现。
2 缩放要素
打开QGIS，先导入一张shp图层文件：
观察到要素工具栏里有缩放要素按钮，按下激活要素缩放功能。
然后和移动要素一样，鼠标点击图层中的要素，再移动鼠标，会有缩放调整效果的展示，如下：
有了之前移动要素的实现经验，我们还是先来看一下源码，在qgsmaptoolmovefeature.cpp的目录下，很快就能看见一个叫qgsmaptoolscalefeature.cpp的文件，打开看一下。
qgsmaptoolscalefeature.cpp
/***************************************************************************
qgsmaptoolscalefeature.cpp - map tool for scaling features by mouse drag
---------------------
Date : December 2020
Copyright : (C) 2020 by roya0045
Contact : ping me on github
***************************************************************************
* *
* This program is free software; you can redistribute it and/or modify *
* it under the terms of the GNU General Public License as published by *
* the Free Software Foundation; either version 2 of the License, or *
* (at your option) any later version. *
* *
***************************************************************************/
#include <QSettings>
#include <QEvent>
#include <QHBoxLayout>
#include <QKeyEvent>
#include <QLabel>
#include <limits>
#include <cmath>
#include "qgsadvanceddigitizingdockwidget.h"
#include "qgsmaptoolscalefeature.h"
#include "qgsfeatureiterator.h"
#include "qgsgeometry.h"
#include "qgslogger.h"
#include "qgsmapcanvas.h"
#include "qgsrubberband.h"
#include "qgsvectorlayer.h"
#include "qgstolerance.h"
#include "qgisapp.h"
#include "qgsspinbox.h"
#include "qgsdoublespinbox.h"
#include "qgssnapindicator.h"
#include "qgsmapmouseevent.h"
QgsScaleMagnetWidget::QgsScaleMagnetWidget( const QString &label, QWidget *parent )
: QWidget( parent )
{
mLayout = new QHBoxLayout( this );
mLayout->setContentsMargins( 0, 0, 0, 0 );
//mLayout->setAlignment( Qt::AlignLeft );
setLayout( mLayout );
if ( !label.isEmpty() )
{
QLabel *lbl = new QLabel( label, this );
lbl->setAlignment( Qt::AlignRight | Qt::AlignCenter );
mLayout->addWidget( lbl );
}
mScaleSpinBox = new QgsDoubleSpinBox( this );
mScaleSpinBox->setSingleStep( 0.5 );
mScaleSpinBox->setMinimum( 0 );
mScaleSpinBox->setValue( 1 );
mScaleSpinBox->setShowClearButton( false );
mScaleSpinBox->setSizePolicy( QSizePolicy::MinimumExpanding, QSizePolicy::Preferred );
mLayout->addWidget( mScaleSpinBox );
// connect signals
mScaleSpinBox->installEventFilter( this );
connect( mScaleSpinBox, static_cast < void ( QgsDoubleSpinBox::* )( double ) > ( &QgsDoubleSpinBox::valueChanged ), this, &QgsScaleMagnetWidget::scaleSpinBoxValueChanged );
// config focus
setFocusProxy( mScaleSpinBox );
}
void QgsScaleMagnetWidget::setScale( double scale )
{
mScaleSpinBox->setValue( scale );
}
double QgsScaleMagnetWidget::scale() const
{
return mScaleSpinBox->value();
}
bool QgsScaleMagnetWidget::eventFilter( QObject *obj, QEvent *ev )
{
if ( obj == mScaleSpinBox && ev->type() == QEvent::KeyPress )
{
QKeyEvent *event = static_cast<QKeyEvent *>( ev );
if ( event->key() == Qt::Key_Escape )
{
emit scaleEditingCanceled();
return true;
}
if ( event->key() == Qt::Key_Enter || event->key() == Qt::Key_Return )
{
emit scaleEditingFinished( scale() );
return true;
}
}
return false;
}
void QgsScaleMagnetWidget::scaleSpinBoxValueChanged( double scale )
{
emit scaleChanged( scale );
}
//
// QgsMapToolScaleFeature
//
QgsMapToolScaleFeature::QgsMapToolScaleFeature( QgsMapCanvas *canvas )
: QgsMapToolAdvancedDigitizing( canvas, QgisApp::instance()->cadDockWidget() )
, mSnapIndicator( std::make_unique< QgsSnapIndicator>( canvas ) )
{
mToolName = tr( "Scale feature" );
}
QgsMapToolScaleFeature::~QgsMapToolScaleFeature()
{
deleteScalingWidget();
mAnchorPoint.reset();
deleteRubberband();
mSnapIndicator->setMatch( QgsPointLocator::Match() );
}
void QgsMapToolScaleFeature::cadCanvasMoveEvent( QgsMapMouseEvent *e )
{
mSnapIndicator->setMatch( e->mapPointMatch() );
if ( mBaseDistance == 0 )
{
return;
}
if ( mScalingActive )
{
const double distance = mFeatureCenterMapCoords.distance( e->mapPoint() );
const double scale = distance / mBaseDistance; // min 0 or no limit?
if ( mScalingWidget )
{
disconnect( mScalingWidget, &QgsScaleMagnetWidget::scaleChanged, this, &QgsMapToolScaleFeature::updateRubberband );
mScalingWidget->setScale( scale );
mScalingWidget->setFocus( Qt::TabFocusReason );
mScalingWidget->editor()->selectAll();
connect( mScalingWidget, &QgsScaleMagnetWidget::scaleChanged, this, &QgsMapToolScaleFeature::updateRubberband );
}
updateRubberband( scale );
}
}
void QgsMapToolScaleFeature::cadCanvasReleaseEvent( QgsMapMouseEvent *e )
{
if ( !mCanvas )
{
return;
}
QgsVectorLayer *vlayer = currentVectorLayer();
if ( !vlayer )
{
deleteScalingWidget();
deleteRubberband();
notifyNotVectorLayer();
mSnapIndicator->setMatch( QgsPointLocator::Match() );
mCadDockWidget->clear();
return;
}
if ( e->button() == Qt::RightButton )
{
cancel();
return;
}
// place anchor point on CTRL + click
if ( e->modifiers() & Qt::ControlModifier )
{
if ( !mAnchorPoint )
{
mAnchorPoint = std::make_unique<QgsVertexMarker>( mCanvas );
mAnchorPoint->setIconType( QgsVertexMarker::ICON_CROSS );
}
mAnchorPoint->setCenter( e->mapPoint() );
mFeatureCenterMapCoords = e->mapPoint();
cadDockWidget()->clear();
return;
}
deleteScalingWidget();
// Initialize scaling if not yet active
if ( !mScalingActive )
{
mScaling = 1;
deleteRubberband();
if ( !vlayer->isEditable() )
{
notifyNotEditableLayer();
return;
}
const QgsPointXY layerCoords = toLayerCoordinates( vlayer, e->mapPoint() );
const double searchRadius = QgsTolerance::vertexSearchRadius( mCanvas->currentLayer(), mCanvas->mapSettings() );
const QgsRectangle selectRect( layerCoords.x() - searchRadius, layerCoords.y() - searchRadius,
layerCoords.x() + searchRadius, layerCoords.y() + searchRadius );
mAutoSetAnchorPoint = false;
if ( !mAnchorPoint )
{
mAnchorPoint = std::make_unique<QgsVertexMarker>( mCanvas );
mAnchorPoint->setIconType( QgsVertexMarker::ICON_CROSS );
mAutoSetAnchorPoint = true;
}
if ( vlayer->selectedFeatureCount() == 0 )
{
QgsFeatureIterator fit = vlayer->getFeatures( QgsFeatureRequest().setNoAttributes().setFilterRect( selectRect ) );
//find the closest feature
const QgsGeometry pointGeometry = QgsGeometry::fromPointXY( layerCoords );
if ( pointGeometry.isNull() )
{
return;
}
double minDistance = std::numeric_limits<double>::max();
QgsFeature cf;
QgsFeature f;
while ( fit.nextFeature( f ) )
{
if ( f.hasGeometry() )
{
const double currentDistance = pointGeometry.distance( f.geometry() );
if ( currentDistance < minDistance )
{
minDistance = currentDistance;
cf = f;
}
}
}
if ( minDistance == std::numeric_limits<double>::max() )
{
emit messageEmitted( tr( "Could not find a nearby feature in the current layer." ) );
if ( mAutoSetAnchorPoint )
mAnchorPoint.reset();
return;
}
mExtent = cf.geometry().boundingBox();
if ( mAutoSetAnchorPoint )
{
mFeatureCenterMapCoords = toMapCoordinates( vlayer, mExtent.center() );
mAnchorPoint->setCenter( mFeatureCenterMapCoords );
}
else
{
mFeatureCenterMapCoords = mAnchorPoint->center();
}
mScaledFeatures.clear();
mScaledFeatures << cf.id(); //todo: take the closest feature, not the first one...
mOriginalGeometries << cf.geometry();
mRubberBand = createRubberBand( vlayer->geometryType() );
mRubberBand->setToGeometry( cf.geometry(), vlayer );
}
else
{
mScaledFeatures = vlayer->selectedFeatureIds();
mRubberBand = createRubberBand( vlayer->geometryType() );
QgsFeature feat;
QgsFeatureIterator it = vlayer->getSelectedFeatures();
while ( it.nextFeature( feat ) )
{
mRubberBand->addGeometry( feat.geometry(), vlayer, false );
mOriginalGeometries << feat.geometry();
}
mRubberBand->updatePosition();
mRubberBand->update();
}
mScalingActive = true;
mBaseDistance = e->mapPoint().distance( mFeatureCenterMapCoords );
mScaling = 1.0;
createScalingWidget();
mScalingActive = true;
return;
}
applyScaling( mScaling );
}
void QgsMapToolScaleFeature::cancel()
{
deleteScalingWidget();
deleteRubberband();
QgsVectorLayer *vlayer = currentVectorLayer();
if ( vlayer->selectedFeatureCount() == 0 || mAutoSetAnchorPoint )
{
mAnchorPoint.reset();
}
mScalingActive = false;
mSnapIndicator->setMatch( QgsPointLocator::Match() );
mCadDockWidget->clear();
}
void QgsMapToolScaleFeature::updateRubberband( double scale )
{
if ( mScalingActive && mRubberBand )
{
mScaling = scale;
QgsVectorLayer *vlayer = currentVectorLayer();
if ( !vlayer )
return;
const QgsPointXY layerCoords = toLayerCoordinates( vlayer, mFeatureCenterMapCoords );
QTransform t;
t.translate( layerCoords.x(), layerCoords.y() );
t.scale( mScaling, mScaling );
t.translate( -layerCoords.x(), -layerCoords.y() );
mRubberBand->reset( vlayer->geometryType() );
for ( const QgsGeometry &originalGeometry : mOriginalGeometries )
{
QgsGeometry geom = originalGeometry;
geom.transform( t );
mRubberBand->addGeometry( geom, vlayer );
}
}
}
void QgsMapToolScaleFeature::applyScaling( double scale )
{
mScaling = scale;
mScalingActive = false;
QgsVectorLayer *vlayer = currentVectorLayer();
if ( !vlayer )
{
deleteRubberband();
notifyNotVectorLayer();
mSnapIndicator->setMatch( QgsPointLocator::Match() );
mCadDockWidget->clear();
return;
}
//calculations for affine transformation
vlayer->beginEditCommand( tr( "Features Scaled" ) );
const QgsPointXY layerCoords = toLayerCoordinates( vlayer, mFeatureCenterMapCoords );
QTransform t;
t.translate( layerCoords.x(), layerCoords.y() );
t.scale( mScaling, mScaling );
t.translate( -layerCoords.x(), -layerCoords.y() );
QgsFeatureRequest request;
request.setFilterFids( mScaledFeatures ).setNoAttributes();
QgsFeatureIterator fi = vlayer->getFeatures( request );
QgsFeature feat;
while ( fi.nextFeature( feat ) )
{
if ( !feat.hasGeometry() )
continue;
QgsGeometry geom = feat.geometry();
if ( !( geom.transform( t ) == Qgis::GeometryOperationResult::Success ) )
continue;
const QgsFeatureId id = feat.id();
vlayer->changeGeometry( id, geom );
}
deleteScalingWidget();
deleteRubberband();
mSnapIndicator->setMatch( QgsPointLocator::Match() );
mCadDockWidget->clear();
if ( mAutoSetAnchorPoint )
mAnchorPoint.reset();
vlayer->endEditCommand();
vlayer->triggerRepaint();
}
void QgsMapToolScaleFeature::keyReleaseEvent( QKeyEvent *e )
{
if ( mScalingActive && e->key() == Qt::Key_Escape )
{
cancel();
return;
}
QgsMapToolAdvancedDigitizing::keyReleaseEvent( e );
}
void QgsMapToolScaleFeature::activate()
{
QgsVectorLayer *vlayer = currentVectorLayer();
if ( !vlayer )
{
return;
}
if ( !vlayer->isEditable() )
{
return;
}
if ( vlayer->selectedFeatureCount() > 0 )
{
mExtent = vlayer->boundingBoxOfSelected();
mFeatureCenterMapCoords = toMapCoordinates( vlayer, mExtent.center() );
mAnchorPoint = std::make_unique<QgsVertexMarker>( mCanvas );
mAnchorPoint->setIconType( QgsVertexMarker::ICON_CROSS );
mAnchorPoint->setCenter( mFeatureCenterMapCoords );
}
QgsMapToolAdvancedDigitizing::activate();
}
void QgsMapToolScaleFeature::deleteRubberband()
{
delete mRubberBand;
mRubberBand = nullptr;
mOriginalGeometries.clear();
}
void QgsMapToolScaleFeature::deactivate()
{
deleteScalingWidget();
mScalingActive = false;
mAnchorPoint.reset();
deleteRubberband();
mSnapIndicator->setMatch( QgsPointLocator::Match() );
QgsMapToolAdvancedDigitizing::deactivate();
}
void QgsMapToolScaleFeature::createScalingWidget()
{
if ( !mCanvas )
{
return;
}
deleteScalingWidget();
mScalingWidget = new QgsScaleMagnetWidget( QStringLiteral( "Scaling:" ) );
QgisApp::instance()->addUserInputWidget( mScalingWidget );
mScalingWidget->setFocus( Qt::TabFocusReason );
connect( mScalingWidget, &QgsScaleMagnetWidget::scaleChanged, this, &QgsMapToolScaleFeature::updateRubberband );
connect( mScalingWidget, &QgsScaleMagnetWidget::scaleEditingFinished, this, &QgsMapToolScaleFeature::applyScaling );
connect( mScalingWidget, &QgsScaleMagnetWidget::scaleEditingCanceled, this, &QgsMapToolScaleFeature::cancel );
}
void QgsMapToolScaleFeature::deleteScalingWidget()
{
if ( mScalingWidget )
{
disconnect( mScalingWidget, &QgsScaleMagnetWidget::scaleChanged, this, &QgsMapToolScaleFeature::updateRubberband );
disconnect( mScalingWidget, &QgsScaleMagnetWidget::scaleEditingFinished, this, &QgsMapToolScaleFeature::applyScaling );
disconnect( mScalingWidget, &QgsScaleMagnetWidget::scaleEditingCanceled, this, &QgsMapToolScaleFeature::cancel );
mScalingWidget->releaseKeyboard();
mScalingWidget->deleteLater();
}
mScalingWidget = nullptr;
}
和移动要素类似，也是继承了QgsMapToolAdvancedDigitizing，然后在cadCanvasReleaseEvent和cadCanvasMoveEvent中实现缩放效果，流程也类似，创建一个rubberband，然后鼠标点击后进入缩放编辑状态，移动的时候根据鼠标距离中心锚点mAnchorPoint的位置来动态改变要素的尺寸。
这里需要多说一句，和移动要素不同，缩放要素中多了一个锚点定位的功能，具体代码参考cadCanvasReleaseEvent的下面一段，这里通过判断CTRL是否按下来决定锚点是否要进行调整。
// place anchor point on CTRL + click
if ( e->modifiers() & Qt::ControlModifier )
{
if ( !mAnchorPoint )
{
mAnchorPoint = std::make_unique<QgsVertexMarker>( mCanvas );
mAnchorPoint->setIconType( QgsVertexMarker::ICON_CROSS );
}
mAnchorPoint->setCenter( e->mapPoint() );
mFeatureCenterMapCoords = e->mapPoint();
cadDockWidget()->clear();
return;
}3 代码调整
里面同样有一些我们不需要的功能，比如QgsScaleMagnetWidget的实现和调用可以移除，cadDockWidget相关调用也可以移除，QgsSnapIndicator也没用，所以我们移除头文件中变量和函数：
void createScalingWidget();
void deleteScalingWidget();
//! Snapping indicators
std::unique_ptr<QgsSnapIndicator> mSnapIndicator;
//! Shows current scale value and allows numerical editing
QgsScaleMagnetWidget *mScalingWidget = nullptr;同样的，构造函数里要把dockWidget做为参数传入，：
QgsMapToolScaleFeature::QgsMapToolScaleFeature( QgsMapCanvas *canvas, QgsAdvancedDigitizingDockWidget* dock)
: QgsMapToolAdvancedDigitizing( canvas, dock)
{
}4 如何调用
qgsadvanceddigitizingdockwidgetbase.ui，qgsadvanceddigitizingfloaterbase.ui，这两个ui样式文件需要拷贝到工程目录下，因为QgsMapToolAdvancedDigitizing这个类编译的时候需要。
还是以创建的MainWindow实例为例，在头文件中添加变量：
QgsMapToolScaleFeature* m_mapScaleFeature;
QgsAdvancedDigitizingDockWidget *m_pDockWidget;构造函数里添加：
m_mapScaleFeature = new QgsMapToolScaleFeature(m_mapCanvas, m_pDockWidget);调用时设置maptool
m_mapCanvas->setMapTool(m_mapScaleFeature);//将工具添加到m_mapcanvas上5 最后效果
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