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QLevelOfDetail Class

(Qt3DRender::QLevelOfDetail)

The QLevelOfDetail class provides a way of controlling the complexity of rendered entities based on their size on the screen. More...

Header: #include <QLevelOfDetail>
qmake: QT += 3drender
Since: Qt 5.9
Instantiated By: LevelOfDetail
Inherits: Qt3DCore::QComponent
Inherited By:

Qt3DRender::QLevelOfDetailSwitch

This class was introduced in Qt 5.9.

Public Types

enum ThresholdType { DistanceToCameraThreshold, ProjectedScreenPixelSizeThreshold }

Properties

Public Functions

QLevelOfDetail(Qt3DCore::QNode *parent = nullptr)
Qt3DRender::QCamera *camera() const
int currentIndex() const
Qt3DRender::QLevelOfDetail::ThresholdType thresholdType() const
QVector<qreal> thresholds() const
Qt3DRender::QLevelOfDetailBoundingSphere volumeOverride() const

Public Slots

void setCamera(Qt3DRender::QCamera *camera)
void setCurrentIndex(int currentIndex)
void setThresholdType(Qt3DRender::QLevelOfDetail::ThresholdType thresholdType)
void setThresholds(const QVector<qreal> &thresholds)
void setVolumeOverride(const Qt3DRender::QLevelOfDetailBoundingSphere &volumeOverride)

Signals

void cameraChanged(Qt3DRender::QCamera *camera)
void currentIndexChanged(int currentIndex)
void thresholdTypeChanged(Qt3DRender::QLevelOfDetail::ThresholdType thresholdType)
void thresholdsChanged(const QVector<qreal> &thresholds)
void volumeOverrideChanged(const Qt3DRender::QLevelOfDetailBoundingSphere &volumeOverride)

Detailed Description

QLevelOfDetail can be used to control the representation of an entity based on distance from the observer or size on the screen.

In order to improve rendering performance, objects that are very small can be rendered using far fewer details, in geometry or texture.

The component is controlled by specifying thresholds of values which are interpreted as either distances from the camera or screen size.

As the point of view changes, the currentIndex property will change to reflect matching value in the range array.

The currentIndex property can then be used, for example, to enable or disable entities, change material, etc.

The LevelOfDetail component is not shareable between multiple entities.

 #include <Qt3DCore/QEntity>
 #include <Qt3DRender/QGeometryRenderer>
 #include <Qt3DRender/QLevelOfDetail>

// Scene
Qt3DCore::QEntity *rootEntity = new Qt3DCore::Qt3DCore::QEntity;

Qt3DCore::QEntity *renderableEntity = new Qt3DCore::QEntity(rootEntity);
Qt3DRender::QGeometryRenderer *geometryRenderer = new Qt3DCore::QGeometryRenderer(renderableEntity);
renderableEntity->addComponent(geometryRenderer);
Qt3DRender::QLevelOfDetail* lod = new Qt3Render::QLevelOfDetail(renderableEntity);
QVector<qreal> thresholds = {20, 35, 50, 65};
lod->setThresholds(thresholds);
lod->setCamera(mainCamera);
renderableEntity->addComponent(lod);

// connect to QLevelOfDetail::currentIndexChanged to toggle rendering
...

Member Type Documentation

enum QLevelOfDetail::ThresholdType

Specifies how the values in the thresholds are interpreted

ConstantValueDescription
Qt3DRender::QLevelOfDetail::DistanceToCameraThreshold0Distance from the entity to the selected camera
Qt3DRender::QLevelOfDetail::ProjectedScreenPixelSizeThreshold1Size of the entity when projected on the screen as seen from the selected camera, expressed in number of pixels on the side of the bounding square in screen space.

Property Documentation

camera : Qt3DRender::QCamera*

Holds the id of the camera that is used to compute the actual distance or the screen size.

Access functions:

Qt3DRender::QCamera *camera() const
void setCamera(Qt3DRender::QCamera *camera)

Notifier signal:

void cameraChanged(Qt3DRender::QCamera *camera)

currentIndex : int

The index in the range array which matches the current distance to the camera or screen size.

Access functions:

int currentIndex() const
void setCurrentIndex(int currentIndex)

Notifier signal:

void currentIndexChanged(int currentIndex)

thresholdType : ThresholdType

Specifies how range values are interpreted.

Access functions:

Qt3DRender::QLevelOfDetail::ThresholdType thresholdType() const
void setThresholdType(Qt3DRender::QLevelOfDetail::ThresholdType thresholdType)

Notifier signal:

void thresholdTypeChanged(Qt3DRender::QLevelOfDetail::ThresholdType thresholdType)

See also Qt3DRender::QLevelOfDetail::ThresholdType.

thresholds : QVector<qreal>

Array of range values as float point numbers. The value for the most detailed representation should be specified first.

If Qt3DRender::QLevelOfDetail::thresholdType is set to Qt3DRender::QLevelOfDetail::DistanceToCameraThreshold, values should be specified in ascending order, in camera space coordinates

If Qt3DRender::QLevelOfDetail::thresholdType is set to Qt3DRender::QLevelOfDetail::ProjectedScreenPixelSizeThreshold, values should be specified in descending order, in screen space pixels.

Access functions:

QVector<qreal> thresholds() const
void setThresholds(const QVector<qreal> &thresholds)

Notifier signal:

void thresholdsChanged(const QVector<qreal> &thresholds)

See also Qt3DRender::QLevelOfDetail::ThresholdType.

volumeOverride : Qt3DRender::QLevelOfDetailBoundingSphere

The default is a sphere of radius 1 and centered at the local origin of the entity. This proxy volume is used to compute the distance to the camera or the size of the screen projection.

If this value to nullptr, the bounding volume of the entity is used. Care must be taken that this bounding volume never becomes invalid.

Access functions:

Qt3DRender::QLevelOfDetailBoundingSphere volumeOverride() const
void setVolumeOverride(const Qt3DRender::QLevelOfDetailBoundingSphere &volumeOverride)

Notifier signal:

void volumeOverrideChanged(const Qt3DRender::QLevelOfDetailBoundingSphere &volumeOverride)

See also Qt3DRender::QLevelOfDetailBoundingSphere.

Member Function Documentation

QLevelOfDetail::QLevelOfDetail(Qt3DCore::QNode *parent = nullptr)

Constructs a new QLevelOfDetail with the specified parent.

[slot] void QLevelOfDetail::setCamera(Qt3DRender::QCamera *camera)

Sets the camera relative to which distance and size are computed.

Note: Setter function for property camera.

See also camera().

[slot] void QLevelOfDetail::setCurrentIndex(int currentIndex)

Sets the currentIndex.

Note: This should not normally be set by the user.

However, if the component is disabled, then changing the current index is a simple way of switching between multiple representations.

Note: Setter function for property currentIndex.

See also currentIndex().

[slot] void QLevelOfDetail::setThresholdType(Qt3DRender::QLevelOfDetail::ThresholdType thresholdType)

Sets the way thresholds values are interpreted with parameter thresholdType

Note: Setter function for property thresholdType.

See also thresholdType() and Qt3DRender::QLevelOfDetail::ThresholdType.

[slot] void QLevelOfDetail::setThresholds(const QVector<qreal> &thresholds)

Sets the range values in thresholds.

Note: Setter function for property thresholds.

See also thresholds() and Qt3DRender::QLevelOfDetail::thresholdType.

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