一、有关渲染的类
QgsVectorLayerRenderer类：（渲染矢量图层要素）
{
drawRendererV2( QgsFeatureIterator& fit ) 渲染要素遍历器中的单个要素
setGeometryCachePointer( QgsGeometryCache* cache ) 建立缓存，存储要渲染的几何对象
render()
stopRendererV2( QgsSingleSymbolRendererV2* selRenderer ) 结束渲染
}
QgsFeatureRendererV2类：子类（QgsSingleSymbolRendererV2、Qgs25DRenderer、QgsCategorizedSymbolRendererV2、 QgsGraduatedSymbolRendererV2、QgsHeatmapRenderer、QgsInvertedPolygonRenderer、 QgsNullSymbolRenderer、 QgsPointDisplacementRenderer ）
QgsSingleSymbolRendererV2类：
{
startRender( QgsRenderContext& context, const QgsFields& fields )
}
QgsVectorLayer类：矢量图层类功能（图层数据调度、图层要素操作、选择要素操作、图层渲染操作、要素节点操作、添加要素操作、）
QgsVectorLayerFeatureIterator类：图层要素遍历操作（）
{
fetchFeature( QgsFeature& f )//获取feature
fetchNextChangedGeomFeature( QgsFeature& f ) //遍历编辑过的feature
fetchNextChangedAttributeFeature( QgsFeature& f )
fetchNextAddedFeature( QgsFeature& f )
}
QgsVectorLayerEditBuffer类：缓存矢量图层编辑（存储编辑的要素（要素操作、节点操作 ））
QgsSettingsTree类：
QgsMapRendererSequentialJob类：画布操作（创建QImage画布、在画布渲染）
QgsMapRendererJob类：子类（QgsMapRendererCustomPainterJob类、QgsMapRendererQImageJob类、）
QgsMapRendererCustomPainterJob类：（渲染工作的准备）
QgsOgrFeatureIterator类：
{
QgsOgrFeatureIterator( QgsOgrFeatureSource*source, bool ownSource, const
QgsFeatureRequest& request )// 根据图层索引号从数据库获取该图层及信息
nextFeatureFilterExpresson( QgsFeature& f )
fetchFeature( QgsFeature& feature ) //获取下个要素、
fetchFeatureWithId( QgsFeatureId id, QgsFeature& feature ) const
readFeature( OGRFeatureH fet, QgsFeature& feature ) // 将OgrFeatue 转QgisFeature
rewind()// 重置以开始读取下一个要素
getFeatureAttribute( OGRFeatureH ogrFet, QgsFeature & f, int attindex ) //将OgrFeatueAttribute 转QgisFeatureAttribute
}
QgsOgrFeatureSource类：
{
virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest& request ) override//将数据库获取的数据存储到Qgs要素遍历器中
}
QgsOpenVectorLayerDialog类：加载数据对话框
QgisApp类：Qgis窗口的操作（添加矢量栅格图层、设置地图窗口大小、放大缩小、移动、地图编辑操作）
{
askUserForOGRSublayers( QgsVectorLayer *layer ) //
}
QgsVectorDataProvider类：
二、操作流程：
QgsVectorLayerRenderer::render() //图层渲染
{
//从数据库中获取当前视图窗口的要素
QgsFeatureIterator fit = mSource->getFeatures( featureRequest );
}
//////////////////如果编辑要素，获取编辑的要素；否则获取当前视图窗口显示的要素////////////////////
↓
QgsVectorLayerFeatureSource::getFeatures( const QgsFeatureRequest& request ) //获取改变节点的要素列表、添加的要素列表、改变属性的要素列表
{
// return feature iterator that does not own this source
return QgsFeatureIterator( new QgsVectorLayerFeatureIterator( this, false, request ) );
}
QgsVectorLayerFeatureIterator::QgsVectorLayerFeatureIterator( QgsVectorLayerFeatureSource* source, bool ownSource, const QgsFeatureRequest& request )
: QgsAbstractFeatureIteratorFromSource( source, ownSource, request )
, mFetchedFid( false )
, mInterruptionChecker( nullptr )
{
......
if ( mSource->mHasEditBuffer )
是否编辑要素（添加、修改）
{
mChangedFeaturesIterator = mSource->mProviderFeatureSource->getFeatures( mChangedFeaturesRequest );
} else{
mProviderIterator = mSource->mProviderFeatureSource->getFeatures( mProviderRequest );
}
rewindEditBuffer(); //mSource里编辑的要素存到QgsVectorLayerFeatureIterator
}
↓
QgsOgrFeatureSource::getFeatures( const QgsFeatureRequest& request )
{
return QgsFeatureIterator( new QgsOgrFeatureIterator( this, false, request ) );
}
↓
//从数据库获取当前视图窗口的额要素
QgsOgrFeatureIterator::QgsOgrFeatureIterator( QgsOgrFeatureSource* source, bool ownSource, const QgsFeatureRequest& request )
: QgsAbstractFeatureIteratorFromSource( source, ownSource, request )
, mFeatureFetched( false )
, mConn( nullptr )
, ogrLayer( nullptr )
, mSubsetStringSet( false )
, mFetchGeometry( false )
, mExpressonCompiled( false )
, mFilterFids( mRequest.filterFids() )
, mFilterFidsIt( mFilterFids.constBegin() )
{
.......
if ( mSource->mLayerName.isNull() )
{
//根据索引号（图层序列号）获取图层
ogrLayer = OGR_DS_GetLayer( mConn->ds, mSource->mLayerIndex );
int LayerCount =OGR_L_GetFeatureCount(ogrLayer,1);
QgsDebugMsg( QString( "LayerCount = %1 OGR_L_GetRefCount = %2 " ).arg( LayerCount ).arg( OGR_L_GetRefCount(ogrLayer)) );
}
.........
//获取试图窗口范围内的要素
if ( !mRequest.filterRect().isNull() )
{
const QgsRectangle& rect = mRequest.filterRect();
OGR_L_SetSpatialFilterRect( ogrLayer, rect.xMinimum(), rect.yMinimum(), rect.xMaximum(), rect.yMaximum() );
}
else
{
OGR_L_SetSpatialFilter( ogrLayer, nullptr );
}
.......获取属性...
}
//////////////////////////////////////遍历要素渲染到当前视图窗口///////////
QgsVectorLayerRenderer::render() //图层渲染
{
//从数据库中获取当前视图窗口的要素
QgsFeatureIterator fit = mSource->getFeatures( featureRequest );
.......
//渲染要素
if (( mRendererV2->capabilities() & QgsFeatureRendererV2::SymbolLevels ) && mRendererV2->usingSymbolLevels() )
drawRendererV2Levels( fit );
else
drawRendererV2( fit );
}
QgsVectorLayerRenderer::drawRendererV2( QgsFeatureIterator& fit )
{
while ( fit.nextFeature( fet ) )
{
渲染 fet要素
}
}
↓
inline bool QgsFeatureIterator::nextFeature( QgsFeature& f )
{
return mIter ? mIter->nextFeature( f ) : false;
}
bool QgsAbstractFeatureIterator::nextFeature( QgsFeature& f )
{
.........
dataOk = fetchFeature( f );
break;
}
}
if ( dataOk )
mFetchedCount++;
return dataOk;
}
bool QgsVectorLayerFeatureIterator::fetchFeature( QgsFeature& f )
{
f.setValid( false );
if ( mClosed )
return false;
if ( mRequest.filterType() == QgsFeatureRequest::FilterFid )
{
if ( mFetchedFid )
return false;
bool res = nextFeatureFid( f );
mFetchedFid = true;
return res;
}
//遍历改变的要素
if ( !mRequest.filterRect().isNull() )
{
if ( fetchNextChangedGeomFeature( f ) )
return true;
// no more changed geometries
}
//遍历改变要素属性
if ( mRequest.filterType() == QgsFeatureRequest::FilterExpresson )
{
if ( fetchNextChangedAttributeFeature( f ) )
return true;
// no more changed features
}
//遍历添加的要素
while ( fetchNextAddedFeature( f ) )
{
return true;
}
//先清空ogrlayer,重新从数据库中加载当前视图窗口数据
if ( mProviderIterator.isClosed() )
{
mChangedFeaturesIterator.close();
mProviderIterator = mSource->mProviderFeatureSource->getFeatures( mProviderRequest );
mProviderIterator.setInterruptionChecker( mInterruptionChecker )
}
//遍历ogrlayer中没有被编辑的要素 mProviderIterator.nextFeature( f )
// → QgsOgrFeatureIterator::fetchFeature( QgsFeature& feature ) （在下面详细介绍
）
while ( mProviderIterator.nextFeature( f ) )
{
//判断修改的featureID列表是否包括f.id()
if ( mFetchConsidered.contains( f.id() ) )
continue;
// TODO[MD]: just one resize of attributes
f.setFields( mSource->mFields );
// update attributes
if ( mSource->mHasEditBuffer )
updateChangedAttributes( f );
if ( mHasVirtualAttributes )
addVirtualAttributes( f );
if ( mRequest.filterType() == QgsFeatureRequest::FilterExpresson && mProviderRequest.filterType() != QgsFeatureRequest::FilterExpresson )
{ //filtering by expresson, and couldn't do it on the provider side
mRequest.expressonContext()->setFeature( f );
if ( !mRequest.filterExpresson()->evaluate( mRequest.expressonContext() ).toBool() )
{
//feature did not match filter
continue;
}
}
// update geometry
// TODO[MK]: FilterRect check after updating the geometry
if ( !( mRequest.flags() & QgsFeatureRequest::NoGeometry ) )
updateFeatureGeometry( f );
return true;
}
close();
return false;
}
三、附加：
bool QgsOgrFeatureIterator::fetchFeature( QgsFeature& feature )
{
feature.setValid( false );
if ( mClosed || !ogrLayer )
return false;
if ( mRequest.filterType() == QgsFeatureRequest::FilterFid )
{
bool result = fetchFeatureWithId( mRequest.filterFid(), feature );
close(); // the feature has been read or was not found: we have finished here
return result;
}
else if ( mRequest.filterType() == QgsFeatureRequest::FilterFids )
{
while ( mFilterFidsIt != mFilterFids.constEnd() )
{
QgsFeatureId nextId = *mFilterFidsIt;
mFilterFidsIt++;
if ( fetchFeatureWithId( nextId, feature ) )
return true;
}
close();
return false;
}
OGRFeatureH fet;
//遍历ogrLayer
while (( fet = OGR_L_GetNextFeature( ogrLayer ) ) )
{
//将ogrfeature 转 qgisFeature
if ( !readFeature( fet, feature ) )
continue;
else
OGR_F_Destroy( fet );
if ( !mRequest.filterRect().isNull() && !feature.constGeometry() )
continue;
QgsDebugMsg( QString( "ogrLayer -- featureID = %1 " ).arg( feature.id() ) );
// we have a feature, end this cycle
feature.setValid( true );
return true;
} // while
close();
return false;
}
网友评论